diff --git a/contrib/llvm-project/clang/include/clang/Sema/Sema.h b/contrib/llvm-project/clang/include/clang/Sema/Sema.h
index 7bfdaaae45a9..a59a9342341d 100644
--- a/contrib/llvm-project/clang/include/clang/Sema/Sema.h
+++ b/contrib/llvm-project/clang/include/clang/Sema/Sema.h
@@ -1,15117 +1,15124 @@
 //===--- Sema.h - Semantic Analysis & AST Building --------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the Sema class, which performs semantic analysis and
 // builds ASTs.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_SEMA_SEMA_H
 #define LLVM_CLANG_SEMA_SEMA_H
 
 #include "clang/APINotes/APINotesManager.h"
 #include "clang/AST/ASTConcept.h"
 #include "clang/AST/ASTFwd.h"
 #include "clang/AST/Attr.h"
 #include "clang/AST/Availability.h"
 #include "clang/AST/ComparisonCategories.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/DeclarationName.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/ExprConcepts.h"
 #include "clang/AST/ExprObjC.h"
 #include "clang/AST/ExternalASTSource.h"
 #include "clang/AST/LocInfoType.h"
 #include "clang/AST/MangleNumberingContext.h"
 #include "clang/AST/NSAPI.h"
 #include "clang/AST/PrettyPrinter.h"
 #include "clang/AST/StmtCXX.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/AST/TypeOrdering.h"
 #include "clang/Basic/BitmaskEnum.h"
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/Cuda.h"
 #include "clang/Basic/DarwinSDKInfo.h"
 #include "clang/Basic/ExpressionTraits.h"
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/OpenCLOptions.h"
 #include "clang/Basic/PragmaKinds.h"
 #include "clang/Basic/Specifiers.h"
 #include "clang/Basic/TemplateKinds.h"
 #include "clang/Basic/TypeTraits.h"
 #include "clang/Sema/AnalysisBasedWarnings.h"
 #include "clang/Sema/Attr.h"
 #include "clang/Sema/CleanupInfo.h"
 #include "clang/Sema/DeclSpec.h"
 #include "clang/Sema/ExternalSemaSource.h"
 #include "clang/Sema/IdentifierResolver.h"
 #include "clang/Sema/ObjCMethodList.h"
 #include "clang/Sema/Ownership.h"
 #include "clang/Sema/Redeclaration.h"
 #include "clang/Sema/Scope.h"
 #include "clang/Sema/SemaBase.h"
 #include "clang/Sema/SemaConcept.h"
 #include "clang/Sema/SemaDiagnostic.h"
 #include "clang/Sema/TypoCorrection.h"
 #include "clang/Sema/Weak.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/STLForwardCompat.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallBitVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/TinyPtrVector.h"
 #include <deque>
 #include <memory>
 #include <optional>
 #include <string>
 #include <tuple>
 #include <vector>
 
 namespace llvm {
 class APSInt;
 template <typename ValueT, typename ValueInfoT> class DenseSet;
 class SmallBitVector;
 struct InlineAsmIdentifierInfo;
 } // namespace llvm
 
 namespace clang {
 class ADLResult;
 class ASTConsumer;
 class ASTContext;
 class ASTMutationListener;
 class ASTReader;
 class ASTWriter;
 class ArrayType;
 class ParsedAttr;
 class BindingDecl;
 class BlockDecl;
 class CapturedDecl;
 class CXXBasePath;
 class CXXBasePaths;
 class CXXBindTemporaryExpr;
 typedef SmallVector<CXXBaseSpecifier *, 4> CXXCastPath;
 class CXXConstructorDecl;
 class CXXConversionDecl;
 class CXXDeleteExpr;
 class CXXDestructorDecl;
 class CXXFieldCollector;
 class CXXMemberCallExpr;
 class CXXMethodDecl;
 class CXXScopeSpec;
 class CXXTemporary;
 class CXXTryStmt;
 class CallExpr;
 class ClassTemplateDecl;
 class ClassTemplatePartialSpecializationDecl;
 class ClassTemplateSpecializationDecl;
 class VarTemplatePartialSpecializationDecl;
 class CodeCompleteConsumer;
 class CodeCompletionAllocator;
 class CodeCompletionTUInfo;
 class CodeCompletionResult;
 class CoroutineBodyStmt;
 class Decl;
 class DeclAccessPair;
 class DeclContext;
 class DeclRefExpr;
 class DeclaratorDecl;
 class DeducedTemplateArgument;
 class DependentDiagnostic;
 class DesignatedInitExpr;
 class Designation;
 class EnableIfAttr;
 class EnumConstantDecl;
 class Expr;
 class ExtVectorType;
 class FormatAttr;
 class FriendDecl;
 class FunctionDecl;
 class FunctionProtoType;
 class FunctionTemplateDecl;
 class ImplicitConversionSequence;
 typedef MutableArrayRef<ImplicitConversionSequence> ConversionSequenceList;
 class InitListExpr;
 class InitializationKind;
 class InitializationSequence;
 class InitializedEntity;
 class IntegerLiteral;
 class LabelStmt;
 class LambdaExpr;
 class LangOptions;
 class LocalInstantiationScope;
 class LookupResult;
 class MacroInfo;
 typedef ArrayRef<std::pair<IdentifierInfo *, SourceLocation>> ModuleIdPath;
 class ModuleLoader;
 class MultiLevelTemplateArgumentList;
 class NamedDecl;
 class ObjCImplementationDecl;
 class ObjCInterfaceDecl;
 class ObjCMethodDecl;
 class ObjCProtocolDecl;
 struct OverloadCandidate;
 enum class OverloadCandidateParamOrder : char;
 enum OverloadCandidateRewriteKind : unsigned;
 class OverloadCandidateSet;
 class OverloadExpr;
 class ParenListExpr;
 class ParmVarDecl;
 class Preprocessor;
 class PseudoDestructorTypeStorage;
 class PseudoObjectExpr;
 class QualType;
 class SemaAMDGPU;
 class SemaARM;
 class SemaAVR;
 class SemaBPF;
 class SemaCodeCompletion;
 class SemaCUDA;
 class SemaHLSL;
 class SemaHexagon;
 class SemaLoongArch;
 class SemaM68k;
 class SemaMIPS;
 class SemaMSP430;
 class SemaNVPTX;
 class SemaObjC;
 class SemaOpenACC;
 class SemaOpenCL;
 class SemaOpenMP;
 class SemaPPC;
 class SemaPseudoObject;
 class SemaRISCV;
 class SemaSYCL;
 class SemaSwift;
 class SemaSystemZ;
 class SemaWasm;
 class SemaX86;
 class StandardConversionSequence;
 class Stmt;
 class StringLiteral;
 class SwitchStmt;
 class TemplateArgument;
 class TemplateArgumentList;
 class TemplateArgumentLoc;
 class TemplateDecl;
 class TemplateInstantiationCallback;
 class TemplateParameterList;
 class TemplatePartialOrderingContext;
 class TemplateTemplateParmDecl;
 class Token;
 class TypeAliasDecl;
 class TypedefDecl;
 class TypedefNameDecl;
 class TypeLoc;
 class TypoCorrectionConsumer;
 class UnqualifiedId;
 class UnresolvedLookupExpr;
 class UnresolvedMemberExpr;
 class UnresolvedSetImpl;
 class UnresolvedSetIterator;
 class UsingDecl;
 class UsingShadowDecl;
 class ValueDecl;
 class VarDecl;
 class VarTemplateSpecializationDecl;
 class VisibilityAttr;
 class VisibleDeclConsumer;
 class IndirectFieldDecl;
 struct DeductionFailureInfo;
 class TemplateSpecCandidateSet;
 
 namespace sema {
 class AccessedEntity;
 class BlockScopeInfo;
 class Capture;
 class CapturedRegionScopeInfo;
 class CapturingScopeInfo;
 class CompoundScopeInfo;
 class DelayedDiagnostic;
 class DelayedDiagnosticPool;
 class FunctionScopeInfo;
 class LambdaScopeInfo;
 class PossiblyUnreachableDiag;
 class RISCVIntrinsicManager;
 class SemaPPCallbacks;
 class TemplateDeductionInfo;
 } // namespace sema
 
 namespace threadSafety {
 class BeforeSet;
 void threadSafetyCleanup(BeforeSet *Cache);
 } // namespace threadSafety
 
 // FIXME: No way to easily map from TemplateTypeParmTypes to
 // TemplateTypeParmDecls, so we have this horrible PointerUnion.
 typedef std::pair<llvm::PointerUnion<const TemplateTypeParmType *, NamedDecl *>,
                   SourceLocation>
     UnexpandedParameterPack;
 
 /// Describes whether we've seen any nullability information for the given
 /// file.
 struct FileNullability {
   /// The first pointer declarator (of any pointer kind) in the file that does
   /// not have a corresponding nullability annotation.
   SourceLocation PointerLoc;
 
   /// The end location for the first pointer declarator in the file. Used for
   /// placing fix-its.
   SourceLocation PointerEndLoc;
 
   /// Which kind of pointer declarator we saw.
   uint8_t PointerKind;
 
   /// Whether we saw any type nullability annotations in the given file.
   bool SawTypeNullability = false;
 };
 
 /// A mapping from file IDs to a record of whether we've seen nullability
 /// information in that file.
 class FileNullabilityMap {
   /// A mapping from file IDs to the nullability information for each file ID.
   llvm::DenseMap<FileID, FileNullability> Map;
 
   /// A single-element cache based on the file ID.
   struct {
     FileID File;
     FileNullability Nullability;
   } Cache;
 
 public:
   FileNullability &operator[](FileID file) {
     // Check the single-element cache.
     if (file == Cache.File)
       return Cache.Nullability;
 
     // It's not in the single-element cache; flush the cache if we have one.
     if (!Cache.File.isInvalid()) {
       Map[Cache.File] = Cache.Nullability;
     }
 
     // Pull this entry into the cache.
     Cache.File = file;
     Cache.Nullability = Map[file];
     return Cache.Nullability;
   }
 };
 
 /// Tracks expected type during expression parsing, for use in code completion.
 /// The type is tied to a particular token, all functions that update or consume
 /// the type take a start location of the token they are looking at as a
 /// parameter. This avoids updating the type on hot paths in the parser.
 class PreferredTypeBuilder {
 public:
   PreferredTypeBuilder(bool Enabled) : Enabled(Enabled) {}
 
   void enterCondition(Sema &S, SourceLocation Tok);
   void enterReturn(Sema &S, SourceLocation Tok);
   void enterVariableInit(SourceLocation Tok, Decl *D);
   /// Handles e.g. BaseType{ .D = Tok...
   void enterDesignatedInitializer(SourceLocation Tok, QualType BaseType,
                                   const Designation &D);
   /// Computing a type for the function argument may require running
   /// overloading, so we postpone its computation until it is actually needed.
   ///
   /// Clients should be very careful when using this function, as it stores a
   /// function_ref, clients should make sure all calls to get() with the same
   /// location happen while function_ref is alive.
   ///
   /// The callback should also emit signature help as a side-effect, but only
   /// if the completion point has been reached.
   void enterFunctionArgument(SourceLocation Tok,
                              llvm::function_ref<QualType()> ComputeType);
 
   void enterParenExpr(SourceLocation Tok, SourceLocation LParLoc);
   void enterUnary(Sema &S, SourceLocation Tok, tok::TokenKind OpKind,
                   SourceLocation OpLoc);
   void enterBinary(Sema &S, SourceLocation Tok, Expr *LHS, tok::TokenKind Op);
   void enterMemAccess(Sema &S, SourceLocation Tok, Expr *Base);
   void enterSubscript(Sema &S, SourceLocation Tok, Expr *LHS);
   /// Handles all type casts, including C-style cast, C++ casts, etc.
   void enterTypeCast(SourceLocation Tok, QualType CastType);
 
   /// Get the expected type associated with this location, if any.
   ///
   /// If the location is a function argument, determining the expected type
   /// involves considering all function overloads and the arguments so far.
   /// In this case, signature help for these function overloads will be reported
   /// as a side-effect (only if the completion point has been reached).
   QualType get(SourceLocation Tok) const {
     if (!Enabled || Tok != ExpectedLoc)
       return QualType();
     if (!Type.isNull())
       return Type;
     if (ComputeType)
       return ComputeType();
     return QualType();
   }
 
 private:
   bool Enabled;
   /// Start position of a token for which we store expected type.
   SourceLocation ExpectedLoc;
   /// Expected type for a token starting at ExpectedLoc.
   QualType Type;
   /// A function to compute expected type at ExpectedLoc. It is only considered
   /// if Type is null.
   llvm::function_ref<QualType()> ComputeType;
 };
 
 struct SkipBodyInfo {
   SkipBodyInfo() = default;
   bool ShouldSkip = false;
   bool CheckSameAsPrevious = false;
   NamedDecl *Previous = nullptr;
   NamedDecl *New = nullptr;
 };
 
 /// Describes the result of template argument deduction.
 ///
 /// The TemplateDeductionResult enumeration describes the result of
 /// template argument deduction, as returned from
 /// DeduceTemplateArguments(). The separate TemplateDeductionInfo
 /// structure provides additional information about the results of
 /// template argument deduction, e.g., the deduced template argument
 /// list (if successful) or the specific template parameters or
 /// deduced arguments that were involved in the failure.
 enum class TemplateDeductionResult {
   /// Template argument deduction was successful.
   Success = 0,
   /// The declaration was invalid; do nothing.
   Invalid,
   /// Template argument deduction exceeded the maximum template
   /// instantiation depth (which has already been diagnosed).
   InstantiationDepth,
   /// Template argument deduction did not deduce a value
   /// for every template parameter.
   Incomplete,
   /// Template argument deduction did not deduce a value for every
   /// expansion of an expanded template parameter pack.
   IncompletePack,
   /// Template argument deduction produced inconsistent
   /// deduced values for the given template parameter.
   Inconsistent,
   /// Template argument deduction failed due to inconsistent
   /// cv-qualifiers on a template parameter type that would
   /// otherwise be deduced, e.g., we tried to deduce T in "const T"
   /// but were given a non-const "X".
   Underqualified,
   /// Substitution of the deduced template argument values
   /// resulted in an error.
   SubstitutionFailure,
   /// After substituting deduced template arguments, a dependent
   /// parameter type did not match the corresponding argument.
   DeducedMismatch,
   /// After substituting deduced template arguments, an element of
   /// a dependent parameter type did not match the corresponding element
   /// of the corresponding argument (when deducing from an initializer list).
   DeducedMismatchNested,
   /// A non-depnedent component of the parameter did not match the
   /// corresponding component of the argument.
   NonDeducedMismatch,
   /// When performing template argument deduction for a function
   /// template, there were too many call arguments.
   TooManyArguments,
   /// When performing template argument deduction for a function
   /// template, there were too few call arguments.
   TooFewArguments,
   /// The explicitly-specified template arguments were not valid
   /// template arguments for the given template.
   InvalidExplicitArguments,
   /// Checking non-dependent argument conversions failed.
   NonDependentConversionFailure,
   /// The deduced arguments did not satisfy the constraints associated
   /// with the template.
   ConstraintsNotSatisfied,
   /// Deduction failed; that's all we know.
   MiscellaneousDeductionFailure,
   /// CUDA Target attributes do not match.
   CUDATargetMismatch,
   /// Some error which was already diagnosed.
   AlreadyDiagnosed
 };
 
 /// Kinds of C++ special members.
 enum class CXXSpecialMemberKind {
   DefaultConstructor,
   CopyConstructor,
   MoveConstructor,
   CopyAssignment,
   MoveAssignment,
   Destructor,
   Invalid
 };
 
 /// The kind of conversion being performed.
 enum class CheckedConversionKind {
   /// An implicit conversion.
   Implicit,
   /// A C-style cast.
   CStyleCast,
   /// A functional-style cast.
   FunctionalCast,
   /// A cast other than a C-style cast.
   OtherCast,
   /// A conversion for an operand of a builtin overloaded operator.
   ForBuiltinOverloadedOp
 };
 
 enum class TagUseKind {
   Reference,   // Reference to a tag:  'struct foo *X;'
   Declaration, // Fwd decl of a tag:   'struct foo;'
   Definition,  // Definition of a tag: 'struct foo { int X; } Y;'
   Friend       // Friend declaration:  'friend struct foo;'
 };
 
 /// Used with attributes/effects with a boolean condition, e.g. `nonblocking`.
 enum class FunctionEffectMode : uint8_t {
   None,     // effect is not present.
   False,    // effect(false).
   True,     // effect(true).
   Dependent // effect(expr) where expr is dependent.
 };
 
 struct FunctionEffectDiff {
   enum class Kind { Added, Removed, ConditionMismatch };
 
   FunctionEffect::Kind EffectKind;
   Kind DiffKind;
   FunctionEffectWithCondition Old; // invalid when Added.
   FunctionEffectWithCondition New; // invalid when Removed.
 
   StringRef effectName() const {
     if (Old.Effect.kind() != FunctionEffect::Kind::None)
       return Old.Effect.name();
     return New.Effect.name();
   }
 
   /// Describes the result of effects differing between a base class's virtual
   /// method and an overriding method in a subclass.
   enum class OverrideResult {
     NoAction,
     Warn,
     Merge // Merge missing effect from base to derived.
   };
 
   /// Return true if adding or removing the effect as part of a type conversion
   /// should generate a diagnostic.
   bool shouldDiagnoseConversion(QualType SrcType,
                                 const FunctionEffectsRef &SrcFX,
                                 QualType DstType,
                                 const FunctionEffectsRef &DstFX) const;
 
   /// Return true if adding or removing the effect in a redeclaration should
   /// generate a diagnostic.
   bool shouldDiagnoseRedeclaration(const FunctionDecl &OldFunction,
                                    const FunctionEffectsRef &OldFX,
                                    const FunctionDecl &NewFunction,
                                    const FunctionEffectsRef &NewFX) const;
 
   /// Return true if adding or removing the effect in a C++ virtual method
   /// override should generate a diagnostic.
   OverrideResult shouldDiagnoseMethodOverride(
       const CXXMethodDecl &OldMethod, const FunctionEffectsRef &OldFX,
       const CXXMethodDecl &NewMethod, const FunctionEffectsRef &NewFX) const;
 };
 
 struct FunctionEffectDifferences : public SmallVector<FunctionEffectDiff> {
   /// Caller should short-circuit by checking for equality first.
   FunctionEffectDifferences(const FunctionEffectsRef &Old,
                             const FunctionEffectsRef &New);
 };
 
 /// Sema - This implements semantic analysis and AST building for C.
 /// \nosubgrouping
 class Sema final : public SemaBase {
   // Table of Contents
   // -----------------
   // 1. Semantic Analysis (Sema.cpp)
   // 2. C++ Access Control (SemaAccess.cpp)
   // 3. Attributes (SemaAttr.cpp)
   // 4. Availability Attribute Handling (SemaAvailability.cpp)
   // 5. Casts (SemaCast.cpp)
   // 6. Extra Semantic Checking (SemaChecking.cpp)
   // 7. C++ Coroutines (SemaCoroutine.cpp)
   // 8. C++ Scope Specifiers (SemaCXXScopeSpec.cpp)
   // 9. Declarations (SemaDecl.cpp)
   // 10. Declaration Attribute Handling (SemaDeclAttr.cpp)
   // 11. C++ Declarations (SemaDeclCXX.cpp)
   // 12. C++ Exception Specifications (SemaExceptionSpec.cpp)
   // 13. Expressions (SemaExpr.cpp)
   // 14. C++ Expressions (SemaExprCXX.cpp)
   // 15. Member Access Expressions (SemaExprMember.cpp)
   // 16. Initializers (SemaInit.cpp)
   // 17. C++ Lambda Expressions (SemaLambda.cpp)
   // 18. Name Lookup (SemaLookup.cpp)
   // 19. Modules (SemaModule.cpp)
   // 20. C++ Overloading (SemaOverload.cpp)
   // 21. Statements (SemaStmt.cpp)
   // 22. `inline asm` Statement (SemaStmtAsm.cpp)
   // 23. Statement Attribute Handling (SemaStmtAttr.cpp)
   // 24. C++ Templates (SemaTemplate.cpp)
   // 25. C++ Template Argument Deduction (SemaTemplateDeduction.cpp)
   // 26. C++ Template Deduction Guide (SemaTemplateDeductionGuide.cpp)
   // 27. C++ Template Instantiation (SemaTemplateInstantiate.cpp)
   // 28. C++ Template Declaration Instantiation
   //     (SemaTemplateInstantiateDecl.cpp)
   // 29. C++ Variadic Templates (SemaTemplateVariadic.cpp)
   // 30. Constraints and Concepts (SemaConcept.cpp)
   // 31. Types (SemaType.cpp)
   // 32. FixIt Helpers (SemaFixItUtils.cpp)
 
   /// \name Semantic Analysis
   /// Implementations are in Sema.cpp
   ///@{
 
 public:
   Sema(Preprocessor &pp, ASTContext &ctxt, ASTConsumer &consumer,
        TranslationUnitKind TUKind = TU_Complete,
        CodeCompleteConsumer *CompletionConsumer = nullptr);
   ~Sema();
 
   /// Perform initialization that occurs after the parser has been
   /// initialized but before it parses anything.
   void Initialize();
 
   /// This virtual key function only exists to limit the emission of debug info
   /// describing the Sema class. GCC and Clang only emit debug info for a class
   /// with a vtable when the vtable is emitted. Sema is final and not
   /// polymorphic, but the debug info size savings are so significant that it is
   /// worth adding a vtable just to take advantage of this optimization.
   virtual void anchor();
 
   const LangOptions &getLangOpts() const { return LangOpts; }
   OpenCLOptions &getOpenCLOptions() { return OpenCLFeatures; }
   FPOptions &getCurFPFeatures() { return CurFPFeatures; }
 
   DiagnosticsEngine &getDiagnostics() const { return Diags; }
   SourceManager &getSourceManager() const { return SourceMgr; }
   Preprocessor &getPreprocessor() const { return PP; }
   ASTContext &getASTContext() const { return Context; }
   ASTConsumer &getASTConsumer() const { return Consumer; }
   ASTMutationListener *getASTMutationListener() const;
   ExternalSemaSource *getExternalSource() const { return ExternalSource.get(); }
 
   DarwinSDKInfo *getDarwinSDKInfoForAvailabilityChecking(SourceLocation Loc,
                                                          StringRef Platform);
   DarwinSDKInfo *getDarwinSDKInfoForAvailabilityChecking();
 
   /// Registers an external source. If an external source already exists,
   ///  creates a multiplex external source and appends to it.
   ///
   ///\param[in] E - A non-null external sema source.
   ///
   void addExternalSource(ExternalSemaSource *E);
 
   /// Print out statistics about the semantic analysis.
   void PrintStats() const;
 
   /// Warn that the stack is nearly exhausted.
   void warnStackExhausted(SourceLocation Loc);
 
   /// Run some code with "sufficient" stack space. (Currently, at least 256K is
   /// guaranteed). Produces a warning if we're low on stack space and allocates
   /// more in that case. Use this in code that may recurse deeply (for example,
   /// in template instantiation) to avoid stack overflow.
   void runWithSufficientStackSpace(SourceLocation Loc,
                                    llvm::function_ref<void()> Fn);
 
   /// Returns default addr space for method qualifiers.
   LangAS getDefaultCXXMethodAddrSpace() const;
 
   /// Load weak undeclared identifiers from the external source.
   void LoadExternalWeakUndeclaredIdentifiers();
 
   /// Determine if VD, which must be a variable or function, is an external
   /// symbol that nonetheless can't be referenced from outside this translation
   /// unit because its type has no linkage and it's not extern "C".
   bool isExternalWithNoLinkageType(const ValueDecl *VD) const;
 
   /// Obtain a sorted list of functions that are undefined but ODR-used.
   void getUndefinedButUsed(
       SmallVectorImpl<std::pair<NamedDecl *, SourceLocation>> &Undefined);
 
   typedef std::pair<SourceLocation, bool> DeleteExprLoc;
   typedef llvm::SmallVector<DeleteExprLoc, 4> DeleteLocs;
   /// Retrieves list of suspicious delete-expressions that will be checked at
   /// the end of translation unit.
   const llvm::MapVector<FieldDecl *, DeleteLocs> &
   getMismatchingDeleteExpressions() const;
 
   /// Cause the active diagnostic on the DiagosticsEngine to be
   /// emitted. This is closely coupled to the SemaDiagnosticBuilder class and
   /// should not be used elsewhere.
   void EmitCurrentDiagnostic(unsigned DiagID);
 
   void addImplicitTypedef(StringRef Name, QualType T);
 
   /// Whether uncompilable error has occurred. This includes error happens
   /// in deferred diagnostics.
   bool hasUncompilableErrorOccurred() const;
 
   /// Looks through the macro-expansion chain for the given
   /// location, looking for a macro expansion with the given name.
   /// If one is found, returns true and sets the location to that
   /// expansion loc.
   bool findMacroSpelling(SourceLocation &loc, StringRef name);
 
   /// Calls \c Lexer::getLocForEndOfToken()
   SourceLocation getLocForEndOfToken(SourceLocation Loc, unsigned Offset = 0);
 
   /// Retrieve the module loader associated with the preprocessor.
   ModuleLoader &getModuleLoader() const;
 
   /// Invent a new identifier for parameters of abbreviated templates.
   IdentifierInfo *
   InventAbbreviatedTemplateParameterTypeName(const IdentifierInfo *ParamName,
                                              unsigned Index);
 
   void emitAndClearUnusedLocalTypedefWarnings();
 
   // Emit all deferred diagnostics.
   void emitDeferredDiags();
 
   enum TUFragmentKind {
     /// The global module fragment, between 'module;' and a module-declaration.
     Global,
     /// A normal translation unit fragment. For a non-module unit, this is the
     /// entire translation unit. Otherwise, it runs from the module-declaration
     /// to the private-module-fragment (if any) or the end of the TU (if not).
     Normal,
     /// The private module fragment, between 'module :private;' and the end of
     /// the translation unit.
     Private
   };
 
   /// This is called before the very first declaration in the translation unit
   /// is parsed. Note that the ASTContext may have already injected some
   /// declarations.
   void ActOnStartOfTranslationUnit();
   /// ActOnEndOfTranslationUnit - This is called at the very end of the
   /// translation unit when EOF is reached and all but the top-level scope is
   /// popped.
   void ActOnEndOfTranslationUnit();
   void ActOnEndOfTranslationUnitFragment(TUFragmentKind Kind);
 
   /// Determines the active Scope associated with the given declaration
   /// context.
   ///
   /// This routine maps a declaration context to the active Scope object that
   /// represents that declaration context in the parser. It is typically used
   /// from "scope-less" code (e.g., template instantiation, lazy creation of
   /// declarations) that injects a name for name-lookup purposes and, therefore,
   /// must update the Scope.
   ///
   /// \returns The scope corresponding to the given declaraion context, or NULL
   /// if no such scope is open.
   Scope *getScopeForContext(DeclContext *Ctx);
 
   void PushFunctionScope();
   void PushBlockScope(Scope *BlockScope, BlockDecl *Block);
   sema::LambdaScopeInfo *PushLambdaScope();
 
   /// This is used to inform Sema what the current TemplateParameterDepth
   /// is during Parsing.  Currently it is used to pass on the depth
   /// when parsing generic lambda 'auto' parameters.
   void RecordParsingTemplateParameterDepth(unsigned Depth);
 
   void PushCapturedRegionScope(Scope *RegionScope, CapturedDecl *CD,
                                RecordDecl *RD, CapturedRegionKind K,
                                unsigned OpenMPCaptureLevel = 0);
 
   /// Custom deleter to allow FunctionScopeInfos to be kept alive for a short
   /// time after they've been popped.
   class PoppedFunctionScopeDeleter {
     Sema *Self;
 
   public:
     explicit PoppedFunctionScopeDeleter(Sema *Self) : Self(Self) {}
     void operator()(sema::FunctionScopeInfo *Scope) const;
   };
 
   using PoppedFunctionScopePtr =
       std::unique_ptr<sema::FunctionScopeInfo, PoppedFunctionScopeDeleter>;
 
   /// Pop a function (or block or lambda or captured region) scope from the
   /// stack.
   ///
   /// \param WP The warning policy to use for CFG-based warnings, or null if
   ///        such warnings should not be produced.
   /// \param D The declaration corresponding to this function scope, if
   ///        producing CFG-based warnings.
   /// \param BlockType The type of the block expression, if D is a BlockDecl.
   PoppedFunctionScopePtr
   PopFunctionScopeInfo(const sema::AnalysisBasedWarnings::Policy *WP = nullptr,
                        const Decl *D = nullptr,
                        QualType BlockType = QualType());
 
   sema::FunctionScopeInfo *getEnclosingFunction() const;
 
   void setFunctionHasBranchIntoScope();
   void setFunctionHasBranchProtectedScope();
   void setFunctionHasIndirectGoto();
   void setFunctionHasMustTail();
 
   void PushCompoundScope(bool IsStmtExpr);
   void PopCompoundScope();
 
   /// Determine whether any errors occurred within this function/method/
   /// block.
   bool hasAnyUnrecoverableErrorsInThisFunction() const;
 
   /// Retrieve the current block, if any.
   sema::BlockScopeInfo *getCurBlock();
 
   /// Get the innermost lambda enclosing the current location, if any. This
   /// looks through intervening non-lambda scopes such as local functions and
   /// blocks.
   sema::LambdaScopeInfo *getEnclosingLambda() const;
 
   /// Retrieve the current lambda scope info, if any.
   /// \param IgnoreNonLambdaCapturingScope true if should find the top-most
   /// lambda scope info ignoring all inner capturing scopes that are not
   /// lambda scopes.
   sema::LambdaScopeInfo *
   getCurLambda(bool IgnoreNonLambdaCapturingScope = false);
 
   /// Retrieve the current generic lambda info, if any.
   sema::LambdaScopeInfo *getCurGenericLambda();
 
   /// Retrieve the current captured region, if any.
   sema::CapturedRegionScopeInfo *getCurCapturedRegion();
 
   void ActOnComment(SourceRange Comment);
 
   /// Retrieve the parser's current scope.
   ///
   /// This routine must only be used when it is certain that semantic analysis
   /// and the parser are in precisely the same context, which is not the case
   /// when, e.g., we are performing any kind of template instantiation.
   /// Therefore, the only safe places to use this scope are in the parser
   /// itself and in routines directly invoked from the parser and *never* from
   /// template substitution or instantiation.
   Scope *getCurScope() const { return CurScope; }
 
   IdentifierInfo *getSuperIdentifier() const;
 
   DeclContext *getCurLexicalContext() const {
     return OriginalLexicalContext ? OriginalLexicalContext : CurContext;
   }
 
   SemaDiagnosticBuilder targetDiag(SourceLocation Loc, unsigned DiagID,
                                    const FunctionDecl *FD = nullptr);
   SemaDiagnosticBuilder targetDiag(SourceLocation Loc,
                                    const PartialDiagnostic &PD,
                                    const FunctionDecl *FD = nullptr) {
     return targetDiag(Loc, PD.getDiagID(), FD) << PD;
   }
 
   /// Check if the type is allowed to be used for the current target.
   void checkTypeSupport(QualType Ty, SourceLocation Loc,
                         ValueDecl *D = nullptr);
 
   // /// The kind of conversion being performed.
   // enum CheckedConversionKind {
   //   /// An implicit conversion.
   //   CCK_ImplicitConversion,
   //   /// A C-style cast.
   //   CCK_CStyleCast,
   //   /// A functional-style cast.
   //   CCK_FunctionalCast,
   //   /// A cast other than a C-style cast.
   //   CCK_OtherCast,
   //   /// A conversion for an operand of a builtin overloaded operator.
   //   CCK_ForBuiltinOverloadedOp
   // };
 
   /// ImpCastExprToType - If Expr is not of type 'Type', insert an implicit
   /// cast.  If there is already an implicit cast, merge into the existing one.
   /// If isLvalue, the result of the cast is an lvalue.
   ExprResult ImpCastExprToType(
       Expr *E, QualType Type, CastKind CK, ExprValueKind VK = VK_PRValue,
       const CXXCastPath *BasePath = nullptr,
       CheckedConversionKind CCK = CheckedConversionKind::Implicit);
 
   /// ScalarTypeToBooleanCastKind - Returns the cast kind corresponding
   /// to the conversion from scalar type ScalarTy to the Boolean type.
   static CastKind ScalarTypeToBooleanCastKind(QualType ScalarTy);
 
   /// If \p AllowLambda is true, treat lambda as function.
   DeclContext *getFunctionLevelDeclContext(bool AllowLambda = false) const;
 
   /// Returns a pointer to the innermost enclosing function, or nullptr if the
   /// current context is not inside a function. If \p AllowLambda is true,
   /// this can return the call operator of an enclosing lambda, otherwise
   /// lambdas are skipped when looking for an enclosing function.
   FunctionDecl *getCurFunctionDecl(bool AllowLambda = false) const;
 
   /// getCurMethodDecl - If inside of a method body, this returns a pointer to
   /// the method decl for the method being parsed.  If we're currently
   /// in a 'block', this returns the containing context.
   ObjCMethodDecl *getCurMethodDecl();
 
   /// getCurFunctionOrMethodDecl - Return the Decl for the current ObjC method
   /// or C function we're in, otherwise return null.  If we're currently
   /// in a 'block', this returns the containing context.
   NamedDecl *getCurFunctionOrMethodDecl() const;
 
   /// Warn if we're implicitly casting from a _Nullable pointer type to a
   /// _Nonnull one.
   void diagnoseNullableToNonnullConversion(QualType DstType, QualType SrcType,
                                            SourceLocation Loc);
 
   /// Warn when implicitly casting 0 to nullptr.
   void diagnoseZeroToNullptrConversion(CastKind Kind, const Expr *E);
 
   // ----- function effects ---
 
   /// Warn when implicitly changing function effects.
   void diagnoseFunctionEffectConversion(QualType DstType, QualType SrcType,
                                         SourceLocation Loc);
 
   /// Warn and return true if adding an effect to a set would create a conflict.
   bool diagnoseConflictingFunctionEffect(const FunctionEffectsRef &FX,
                                          const FunctionEffectWithCondition &EC,
                                          SourceLocation NewAttrLoc);
 
   // Report a failure to merge function effects between declarations due to a
   // conflict.
   void
   diagnoseFunctionEffectMergeConflicts(const FunctionEffectSet::Conflicts &Errs,
                                        SourceLocation NewLoc,
                                        SourceLocation OldLoc);
 
   /// Try to parse the conditional expression attached to an effect attribute
   /// (e.g. 'nonblocking'). (c.f. Sema::ActOnNoexceptSpec). Return an empty
   /// optional on error.
   std::optional<FunctionEffectMode>
   ActOnEffectExpression(Expr *CondExpr, StringRef AttributeName);
 
   /// makeUnavailableInSystemHeader - There is an error in the current
   /// context.  If we're still in a system header, and we can plausibly
   /// make the relevant declaration unavailable instead of erroring, do
   /// so and return true.
   bool makeUnavailableInSystemHeader(SourceLocation loc,
                                      UnavailableAttr::ImplicitReason reason);
 
   /// Retrieve a suitable printing policy for diagnostics.
   PrintingPolicy getPrintingPolicy() const {
     return getPrintingPolicy(Context, PP);
   }
 
   /// Retrieve a suitable printing policy for diagnostics.
   static PrintingPolicy getPrintingPolicy(const ASTContext &Ctx,
                                           const Preprocessor &PP);
 
   /// Scope actions.
   void ActOnTranslationUnitScope(Scope *S);
 
   /// Determine whether \param D is function like (function or function
   /// template) for parsing.
   bool isDeclaratorFunctionLike(Declarator &D);
 
   /// The maximum alignment, same as in llvm::Value. We duplicate them here
   /// because that allows us not to duplicate the constants in clang code,
   /// which we must to since we can't directly use the llvm constants.
   /// The value is verified against llvm here: lib/CodeGen/CGDecl.cpp
   ///
   /// This is the greatest alignment value supported by load, store, and alloca
   /// instructions, and global values.
   static const unsigned MaxAlignmentExponent = 32;
   static const uint64_t MaximumAlignment = 1ull << MaxAlignmentExponent;
 
   /// Flag indicating whether or not to collect detailed statistics.
   bool CollectStats;
 
   std::unique_ptr<sema::FunctionScopeInfo> CachedFunctionScope;
 
   /// Stack containing information about each of the nested
   /// function, block, and method scopes that are currently active.
   SmallVector<sema::FunctionScopeInfo *, 4> FunctionScopes;
 
   /// The index of the first FunctionScope that corresponds to the current
   /// context.
   unsigned FunctionScopesStart = 0;
 
   /// Track the number of currently active capturing scopes.
   unsigned CapturingFunctionScopes = 0;
 
   llvm::BumpPtrAllocator BumpAlloc;
 
   /// The kind of translation unit we are processing.
   ///
   /// When we're processing a complete translation unit, Sema will perform
   /// end-of-translation-unit semantic tasks (such as creating
   /// initializers for tentative definitions in C) once parsing has
   /// completed. Modules and precompiled headers perform different kinds of
   /// checks.
   const TranslationUnitKind TUKind;
 
   /// Translation Unit Scope - useful to Objective-C actions that need
   /// to lookup file scope declarations in the "ordinary" C decl namespace.
   /// For example, user-defined classes, built-in "id" type, etc.
   Scope *TUScope;
 
   bool WarnedStackExhausted = false;
 
   void incrementMSManglingNumber() const {
     return CurScope->incrementMSManglingNumber();
   }
 
   /// Try to recover by turning the given expression into a
   /// call.  Returns true if recovery was attempted or an error was
   /// emitted; this may also leave the ExprResult invalid.
   bool tryToRecoverWithCall(ExprResult &E, const PartialDiagnostic &PD,
                             bool ForceComplain = false,
                             bool (*IsPlausibleResult)(QualType) = nullptr);
 
   /// Figure out if an expression could be turned into a call.
   ///
   /// Use this when trying to recover from an error where the programmer may
   /// have written just the name of a function instead of actually calling it.
   ///
   /// \param E - The expression to examine.
   /// \param ZeroArgCallReturnTy - If the expression can be turned into a call
   ///  with no arguments, this parameter is set to the type returned by such a
   ///  call; otherwise, it is set to an empty QualType.
   /// \param OverloadSet - If the expression is an overloaded function
   ///  name, this parameter is populated with the decls of the various
   ///  overloads.
   bool tryExprAsCall(Expr &E, QualType &ZeroArgCallReturnTy,
                      UnresolvedSetImpl &NonTemplateOverloads);
 
   typedef OpaquePtr<DeclGroupRef> DeclGroupPtrTy;
   typedef OpaquePtr<TemplateName> TemplateTy;
   typedef OpaquePtr<QualType> TypeTy;
 
   OpenCLOptions OpenCLFeatures;
   FPOptions CurFPFeatures;
 
   const LangOptions &LangOpts;
   Preprocessor &PP;
   ASTContext &Context;
   ASTConsumer &Consumer;
   DiagnosticsEngine &Diags;
   SourceManager &SourceMgr;
   api_notes::APINotesManager APINotes;
 
   /// A RAII object to enter scope of a compound statement.
   class CompoundScopeRAII {
   public:
     CompoundScopeRAII(Sema &S, bool IsStmtExpr = false) : S(S) {
       S.ActOnStartOfCompoundStmt(IsStmtExpr);
     }
 
     ~CompoundScopeRAII() { S.ActOnFinishOfCompoundStmt(); }
 
   private:
     Sema &S;
   };
 
   /// An RAII helper that pops function a function scope on exit.
   struct FunctionScopeRAII {
     Sema &S;
     bool Active;
     FunctionScopeRAII(Sema &S) : S(S), Active(true) {}
     ~FunctionScopeRAII() {
       if (Active)
         S.PopFunctionScopeInfo();
     }
     void disable() { Active = false; }
   };
 
   sema::FunctionScopeInfo *getCurFunction() const {
     return FunctionScopes.empty() ? nullptr : FunctionScopes.back();
   }
 
   /// Worker object for performing CFG-based warnings.
   sema::AnalysisBasedWarnings AnalysisWarnings;
   threadSafety::BeforeSet *ThreadSafetyDeclCache;
 
   /// Callback to the parser to parse templated functions when needed.
   typedef void LateTemplateParserCB(void *P, LateParsedTemplate &LPT);
   typedef void LateTemplateParserCleanupCB(void *P);
   LateTemplateParserCB *LateTemplateParser;
   LateTemplateParserCleanupCB *LateTemplateParserCleanup;
   void *OpaqueParser;
 
   void SetLateTemplateParser(LateTemplateParserCB *LTP,
                              LateTemplateParserCleanupCB *LTPCleanup, void *P) {
     LateTemplateParser = LTP;
     LateTemplateParserCleanup = LTPCleanup;
     OpaqueParser = P;
   }
 
   /// Callback to the parser to parse a type expressed as a string.
   std::function<TypeResult(StringRef, StringRef, SourceLocation)>
       ParseTypeFromStringCallback;
 
   /// VAListTagName - The declaration name corresponding to __va_list_tag.
   /// This is used as part of a hack to omit that class from ADL results.
   DeclarationName VAListTagName;
 
   /// Is the last error level diagnostic immediate. This is used to determined
   /// whether the next info diagnostic should be immediate.
   bool IsLastErrorImmediate = true;
 
   class DelayedDiagnostics;
 
   class DelayedDiagnosticsState {
     sema::DelayedDiagnosticPool *SavedPool = nullptr;
     friend class Sema::DelayedDiagnostics;
   };
   typedef DelayedDiagnosticsState ParsingDeclState;
   typedef DelayedDiagnosticsState ProcessingContextState;
 
   /// A class which encapsulates the logic for delaying diagnostics
   /// during parsing and other processing.
   class DelayedDiagnostics {
     /// The current pool of diagnostics into which delayed
     /// diagnostics should go.
     sema::DelayedDiagnosticPool *CurPool = nullptr;
 
   public:
     DelayedDiagnostics() = default;
 
     /// Adds a delayed diagnostic.
     void add(const sema::DelayedDiagnostic &diag); // in DelayedDiagnostic.h
 
     /// Determines whether diagnostics should be delayed.
     bool shouldDelayDiagnostics() { return CurPool != nullptr; }
 
     /// Returns the current delayed-diagnostics pool.
     sema::DelayedDiagnosticPool *getCurrentPool() const { return CurPool; }
 
     /// Enter a new scope.  Access and deprecation diagnostics will be
     /// collected in this pool.
     DelayedDiagnosticsState push(sema::DelayedDiagnosticPool &pool) {
       DelayedDiagnosticsState state;
       state.SavedPool = CurPool;
       CurPool = &pool;
       return state;
     }
 
     /// Leave a delayed-diagnostic state that was previously pushed.
     /// Do not emit any of the diagnostics.  This is performed as part
     /// of the bookkeeping of popping a pool "properly".
     void popWithoutEmitting(DelayedDiagnosticsState state) {
       CurPool = state.SavedPool;
     }
 
     /// Enter a new scope where access and deprecation diagnostics are
     /// not delayed.
     DelayedDiagnosticsState pushUndelayed() {
       DelayedDiagnosticsState state;
       state.SavedPool = CurPool;
       CurPool = nullptr;
       return state;
     }
 
     /// Undo a previous pushUndelayed().
     void popUndelayed(DelayedDiagnosticsState state) {
       assert(CurPool == nullptr);
       CurPool = state.SavedPool;
     }
   } DelayedDiagnostics;
 
   ParsingDeclState PushParsingDeclaration(sema::DelayedDiagnosticPool &pool) {
     return DelayedDiagnostics.push(pool);
   }
 
   /// Diagnostics that are emitted only if we discover that the given function
   /// must be codegen'ed.  Because handling these correctly adds overhead to
   /// compilation, this is currently only enabled for CUDA compilations.
   SemaDiagnosticBuilder::DeferredDiagnosticsType DeviceDeferredDiags;
 
   /// CurContext - This is the current declaration context of parsing.
   DeclContext *CurContext;
 
   SemaAMDGPU &AMDGPU() {
     assert(AMDGPUPtr);
     return *AMDGPUPtr;
   }
 
   SemaARM &ARM() {
     assert(ARMPtr);
     return *ARMPtr;
   }
 
   SemaAVR &AVR() {
     assert(AVRPtr);
     return *AVRPtr;
   }
 
   SemaBPF &BPF() {
     assert(BPFPtr);
     return *BPFPtr;
   }
 
   SemaCodeCompletion &CodeCompletion() {
     assert(CodeCompletionPtr);
     return *CodeCompletionPtr;
   }
 
   SemaCUDA &CUDA() {
     assert(CUDAPtr);
     return *CUDAPtr;
   }
 
   SemaHLSL &HLSL() {
     assert(HLSLPtr);
     return *HLSLPtr;
   }
 
   SemaHexagon &Hexagon() {
     assert(HexagonPtr);
     return *HexagonPtr;
   }
 
   SemaLoongArch &LoongArch() {
     assert(LoongArchPtr);
     return *LoongArchPtr;
   }
 
   SemaM68k &M68k() {
     assert(M68kPtr);
     return *M68kPtr;
   }
 
   SemaMIPS &MIPS() {
     assert(MIPSPtr);
     return *MIPSPtr;
   }
 
   SemaMSP430 &MSP430() {
     assert(MSP430Ptr);
     return *MSP430Ptr;
   }
 
   SemaNVPTX &NVPTX() {
     assert(NVPTXPtr);
     return *NVPTXPtr;
   }
 
   SemaObjC &ObjC() {
     assert(ObjCPtr);
     return *ObjCPtr;
   }
 
   SemaOpenACC &OpenACC() {
     assert(OpenACCPtr);
     return *OpenACCPtr;
   }
 
   SemaOpenCL &OpenCL() {
     assert(OpenCLPtr);
     return *OpenCLPtr;
   }
 
   SemaOpenMP &OpenMP() {
     assert(OpenMPPtr && "SemaOpenMP is dead");
     return *OpenMPPtr;
   }
 
   SemaPPC &PPC() {
     assert(PPCPtr);
     return *PPCPtr;
   }
 
   SemaPseudoObject &PseudoObject() {
     assert(PseudoObjectPtr);
     return *PseudoObjectPtr;
   }
 
   SemaRISCV &RISCV() {
     assert(RISCVPtr);
     return *RISCVPtr;
   }
 
   SemaSYCL &SYCL() {
     assert(SYCLPtr);
     return *SYCLPtr;
   }
 
   SemaSwift &Swift() {
     assert(SwiftPtr);
     return *SwiftPtr;
   }
 
   SemaSystemZ &SystemZ() {
     assert(SystemZPtr);
     return *SystemZPtr;
   }
 
   SemaWasm &Wasm() {
     assert(WasmPtr);
     return *WasmPtr;
   }
 
   SemaX86 &X86() {
     assert(X86Ptr);
     return *X86Ptr;
   }
 
   /// Source of additional semantic information.
   IntrusiveRefCntPtr<ExternalSemaSource> ExternalSource;
 
 protected:
   friend class Parser;
   friend class InitializationSequence;
   friend class ASTReader;
   friend class ASTDeclReader;
   friend class ASTWriter;
 
 private:
   std::optional<std::unique_ptr<DarwinSDKInfo>> CachedDarwinSDKInfo;
   bool WarnedDarwinSDKInfoMissing = false;
 
   Sema(const Sema &) = delete;
   void operator=(const Sema &) = delete;
 
   /// The handler for the FileChanged preprocessor events.
   ///
   /// Used for diagnostics that implement custom semantic analysis for #include
   /// directives, like -Wpragma-pack.
   sema::SemaPPCallbacks *SemaPPCallbackHandler;
 
   /// The parser's current scope.
   ///
   /// The parser maintains this state here.
   Scope *CurScope;
 
   mutable IdentifierInfo *Ident_super;
 
   std::unique_ptr<SemaAMDGPU> AMDGPUPtr;
   std::unique_ptr<SemaARM> ARMPtr;
   std::unique_ptr<SemaAVR> AVRPtr;
   std::unique_ptr<SemaBPF> BPFPtr;
   std::unique_ptr<SemaCodeCompletion> CodeCompletionPtr;
   std::unique_ptr<SemaCUDA> CUDAPtr;
   std::unique_ptr<SemaHLSL> HLSLPtr;
   std::unique_ptr<SemaHexagon> HexagonPtr;
   std::unique_ptr<SemaLoongArch> LoongArchPtr;
   std::unique_ptr<SemaM68k> M68kPtr;
   std::unique_ptr<SemaMIPS> MIPSPtr;
   std::unique_ptr<SemaMSP430> MSP430Ptr;
   std::unique_ptr<SemaNVPTX> NVPTXPtr;
   std::unique_ptr<SemaObjC> ObjCPtr;
   std::unique_ptr<SemaOpenACC> OpenACCPtr;
   std::unique_ptr<SemaOpenCL> OpenCLPtr;
   std::unique_ptr<SemaOpenMP> OpenMPPtr;
   std::unique_ptr<SemaPPC> PPCPtr;
   std::unique_ptr<SemaPseudoObject> PseudoObjectPtr;
   std::unique_ptr<SemaRISCV> RISCVPtr;
   std::unique_ptr<SemaSYCL> SYCLPtr;
   std::unique_ptr<SemaSwift> SwiftPtr;
   std::unique_ptr<SemaSystemZ> SystemZPtr;
   std::unique_ptr<SemaWasm> WasmPtr;
   std::unique_ptr<SemaX86> X86Ptr;
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Access Control
   /// Implementations are in SemaAccess.cpp
   ///@{
 
 public:
   enum AccessResult {
     AR_accessible,
     AR_inaccessible,
     AR_dependent,
     AR_delayed
   };
 
   /// SetMemberAccessSpecifier - Set the access specifier of a member.
   /// Returns true on error (when the previous member decl access specifier
   /// is different from the new member decl access specifier).
   bool SetMemberAccessSpecifier(NamedDecl *MemberDecl,
                                 NamedDecl *PrevMemberDecl,
                                 AccessSpecifier LexicalAS);
 
   /// Perform access-control checking on a previously-unresolved member
   /// access which has now been resolved to a member.
   AccessResult CheckUnresolvedMemberAccess(UnresolvedMemberExpr *E,
                                            DeclAccessPair FoundDecl);
   AccessResult CheckUnresolvedLookupAccess(UnresolvedLookupExpr *E,
                                            DeclAccessPair FoundDecl);
 
   /// Checks access to an overloaded operator new or delete.
   AccessResult CheckAllocationAccess(SourceLocation OperatorLoc,
                                      SourceRange PlacementRange,
                                      CXXRecordDecl *NamingClass,
                                      DeclAccessPair FoundDecl,
                                      bool Diagnose = true);
 
   /// Checks access to a constructor.
   AccessResult CheckConstructorAccess(SourceLocation Loc, CXXConstructorDecl *D,
                                       DeclAccessPair FoundDecl,
                                       const InitializedEntity &Entity,
                                       bool IsCopyBindingRefToTemp = false);
 
   /// Checks access to a constructor.
   AccessResult CheckConstructorAccess(SourceLocation Loc, CXXConstructorDecl *D,
                                       DeclAccessPair FoundDecl,
                                       const InitializedEntity &Entity,
                                       const PartialDiagnostic &PDiag);
   AccessResult CheckDestructorAccess(SourceLocation Loc,
                                      CXXDestructorDecl *Dtor,
                                      const PartialDiagnostic &PDiag,
                                      QualType objectType = QualType());
 
   /// Checks access to the target of a friend declaration.
   AccessResult CheckFriendAccess(NamedDecl *D);
 
   /// Checks access to a member.
   AccessResult CheckMemberAccess(SourceLocation UseLoc,
                                  CXXRecordDecl *NamingClass,
                                  DeclAccessPair Found);
 
   /// Checks implicit access to a member in a structured binding.
   AccessResult
   CheckStructuredBindingMemberAccess(SourceLocation UseLoc,
                                      CXXRecordDecl *DecomposedClass,
                                      DeclAccessPair Field);
   AccessResult CheckMemberOperatorAccess(SourceLocation Loc, Expr *ObjectExpr,
                                          const SourceRange &,
                                          DeclAccessPair FoundDecl);
 
   /// Checks access to an overloaded member operator, including
   /// conversion operators.
   AccessResult CheckMemberOperatorAccess(SourceLocation Loc, Expr *ObjectExpr,
                                          Expr *ArgExpr,
                                          DeclAccessPair FoundDecl);
   AccessResult CheckMemberOperatorAccess(SourceLocation Loc, Expr *ObjectExpr,
                                          ArrayRef<Expr *> ArgExprs,
                                          DeclAccessPair FoundDecl);
   AccessResult CheckAddressOfMemberAccess(Expr *OvlExpr,
                                           DeclAccessPair FoundDecl);
 
   /// Checks access for a hierarchy conversion.
   ///
   /// \param ForceCheck true if this check should be performed even if access
   ///     control is disabled;  some things rely on this for semantics
   /// \param ForceUnprivileged true if this check should proceed as if the
   ///     context had no special privileges
   AccessResult CheckBaseClassAccess(SourceLocation AccessLoc, QualType Base,
                                     QualType Derived, const CXXBasePath &Path,
                                     unsigned DiagID, bool ForceCheck = false,
                                     bool ForceUnprivileged = false);
 
   /// Checks access to all the declarations in the given result set.
   void CheckLookupAccess(const LookupResult &R);
 
   /// Checks access to Target from the given class. The check will take access
   /// specifiers into account, but no member access expressions and such.
   ///
   /// \param Target the declaration to check if it can be accessed
   /// \param NamingClass the class in which the lookup was started.
   /// \param BaseType type of the left side of member access expression.
   ///        \p BaseType and \p NamingClass are used for C++ access control.
   ///        Depending on the lookup case, they should be set to the following:
   ///        - lhs.target (member access without a qualifier):
   ///          \p BaseType and \p NamingClass are both the type of 'lhs'.
   ///        - lhs.X::target (member access with a qualifier):
   ///          BaseType is the type of 'lhs', NamingClass is 'X'
   ///        - X::target (qualified lookup without member access):
   ///          BaseType is null, NamingClass is 'X'.
   ///        - target (unqualified lookup).
   ///          BaseType is null, NamingClass is the parent class of 'target'.
   /// \return true if the Target is accessible from the Class, false otherwise.
   bool IsSimplyAccessible(NamedDecl *Decl, CXXRecordDecl *NamingClass,
                           QualType BaseType);
 
   /// Is the given member accessible for the purposes of deciding whether to
   /// define a special member function as deleted?
   bool isMemberAccessibleForDeletion(CXXRecordDecl *NamingClass,
                                      DeclAccessPair Found, QualType ObjectType,
                                      SourceLocation Loc,
                                      const PartialDiagnostic &Diag);
   bool isMemberAccessibleForDeletion(CXXRecordDecl *NamingClass,
                                      DeclAccessPair Found,
                                      QualType ObjectType) {
     return isMemberAccessibleForDeletion(NamingClass, Found, ObjectType,
                                          SourceLocation(), PDiag());
   }
 
   void HandleDependentAccessCheck(
       const DependentDiagnostic &DD,
       const MultiLevelTemplateArgumentList &TemplateArgs);
   void HandleDelayedAccessCheck(sema::DelayedDiagnostic &DD, Decl *Ctx);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Attributes
   /// Implementations are in SemaAttr.cpp
   ///@{
 
 public:
   /// Controls member pointer representation format under the MS ABI.
   LangOptions::PragmaMSPointersToMembersKind
       MSPointerToMemberRepresentationMethod;
 
   bool MSStructPragmaOn; // True when \#pragma ms_struct on
 
   /// Source location for newly created implicit MSInheritanceAttrs
   SourceLocation ImplicitMSInheritanceAttrLoc;
 
   /// pragma clang section kind
   enum PragmaClangSectionKind {
     PCSK_Invalid = 0,
     PCSK_BSS = 1,
     PCSK_Data = 2,
     PCSK_Rodata = 3,
     PCSK_Text = 4,
     PCSK_Relro = 5
   };
 
   enum PragmaClangSectionAction { PCSA_Set = 0, PCSA_Clear = 1 };
 
   struct PragmaClangSection {
     std::string SectionName;
     bool Valid = false;
     SourceLocation PragmaLocation;
   };
 
   PragmaClangSection PragmaClangBSSSection;
   PragmaClangSection PragmaClangDataSection;
   PragmaClangSection PragmaClangRodataSection;
   PragmaClangSection PragmaClangRelroSection;
   PragmaClangSection PragmaClangTextSection;
 
   enum PragmaMsStackAction {
     PSK_Reset = 0x0,                   // #pragma ()
     PSK_Set = 0x1,                     // #pragma (value)
     PSK_Push = 0x2,                    // #pragma (push[, id])
     PSK_Pop = 0x4,                     // #pragma (pop[, id])
     PSK_Show = 0x8,                    // #pragma (show) -- only for "pack"!
     PSK_Push_Set = PSK_Push | PSK_Set, // #pragma (push[, id], value)
     PSK_Pop_Set = PSK_Pop | PSK_Set,   // #pragma (pop[, id], value)
   };
 
   struct PragmaPackInfo {
     PragmaMsStackAction Action;
     StringRef SlotLabel;
     Token Alignment;
   };
 
   // #pragma pack and align.
   class AlignPackInfo {
   public:
     // `Native` represents default align mode, which may vary based on the
     // platform.
     enum Mode : unsigned char { Native, Natural, Packed, Mac68k };
 
     // #pragma pack info constructor
     AlignPackInfo(AlignPackInfo::Mode M, unsigned Num, bool IsXL)
         : PackAttr(true), AlignMode(M), PackNumber(Num), XLStack(IsXL) {
       assert(Num == PackNumber && "The pack number has been truncated.");
     }
 
     // #pragma align info constructor
     AlignPackInfo(AlignPackInfo::Mode M, bool IsXL)
         : PackAttr(false), AlignMode(M),
           PackNumber(M == Packed ? 1 : UninitPackVal), XLStack(IsXL) {}
 
     explicit AlignPackInfo(bool IsXL) : AlignPackInfo(Native, IsXL) {}
 
     AlignPackInfo() : AlignPackInfo(Native, false) {}
 
     // When a AlignPackInfo itself cannot be used, this returns an 32-bit
     // integer encoding for it. This should only be passed to
     // AlignPackInfo::getFromRawEncoding, it should not be inspected directly.
     static uint32_t getRawEncoding(const AlignPackInfo &Info) {
       std::uint32_t Encoding{};
       if (Info.IsXLStack())
         Encoding |= IsXLMask;
 
       Encoding |= static_cast<uint32_t>(Info.getAlignMode()) << 1;
 
       if (Info.IsPackAttr())
         Encoding |= PackAttrMask;
 
       Encoding |= static_cast<uint32_t>(Info.getPackNumber()) << 4;
 
       return Encoding;
     }
 
     static AlignPackInfo getFromRawEncoding(unsigned Encoding) {
       bool IsXL = static_cast<bool>(Encoding & IsXLMask);
       AlignPackInfo::Mode M =
           static_cast<AlignPackInfo::Mode>((Encoding & AlignModeMask) >> 1);
       int PackNumber = (Encoding & PackNumMask) >> 4;
 
       if (Encoding & PackAttrMask)
         return AlignPackInfo(M, PackNumber, IsXL);
 
       return AlignPackInfo(M, IsXL);
     }
 
     bool IsPackAttr() const { return PackAttr; }
 
     bool IsAlignAttr() const { return !PackAttr; }
 
     Mode getAlignMode() const { return AlignMode; }
 
     unsigned getPackNumber() const { return PackNumber; }
 
     bool IsPackSet() const {
       // #pragma align, #pragma pack(), and #pragma pack(0) do not set the pack
       // attriute on a decl.
       return PackNumber != UninitPackVal && PackNumber != 0;
     }
 
     bool IsXLStack() const { return XLStack; }
 
     bool operator==(const AlignPackInfo &Info) const {
       return std::tie(AlignMode, PackNumber, PackAttr, XLStack) ==
              std::tie(Info.AlignMode, Info.PackNumber, Info.PackAttr,
                       Info.XLStack);
     }
 
     bool operator!=(const AlignPackInfo &Info) const {
       return !(*this == Info);
     }
 
   private:
     /// \brief True if this is a pragma pack attribute,
     ///         not a pragma align attribute.
     bool PackAttr;
 
     /// \brief The alignment mode that is in effect.
     Mode AlignMode;
 
     /// \brief The pack number of the stack.
     unsigned char PackNumber;
 
     /// \brief True if it is a XL #pragma align/pack stack.
     bool XLStack;
 
     /// \brief Uninitialized pack value.
     static constexpr unsigned char UninitPackVal = -1;
 
     // Masks to encode and decode an AlignPackInfo.
     static constexpr uint32_t IsXLMask{0x0000'0001};
     static constexpr uint32_t AlignModeMask{0x0000'0006};
     static constexpr uint32_t PackAttrMask{0x00000'0008};
     static constexpr uint32_t PackNumMask{0x0000'01F0};
   };
 
   template <typename ValueType> struct PragmaStack {
     struct Slot {
       llvm::StringRef StackSlotLabel;
       ValueType Value;
       SourceLocation PragmaLocation;
       SourceLocation PragmaPushLocation;
       Slot(llvm::StringRef StackSlotLabel, ValueType Value,
            SourceLocation PragmaLocation, SourceLocation PragmaPushLocation)
           : StackSlotLabel(StackSlotLabel), Value(Value),
             PragmaLocation(PragmaLocation),
             PragmaPushLocation(PragmaPushLocation) {}
     };
 
     void Act(SourceLocation PragmaLocation, PragmaMsStackAction Action,
              llvm::StringRef StackSlotLabel, ValueType Value) {
       if (Action == PSK_Reset) {
         CurrentValue = DefaultValue;
         CurrentPragmaLocation = PragmaLocation;
         return;
       }
       if (Action & PSK_Push)
         Stack.emplace_back(StackSlotLabel, CurrentValue, CurrentPragmaLocation,
                            PragmaLocation);
       else if (Action & PSK_Pop) {
         if (!StackSlotLabel.empty()) {
           // If we've got a label, try to find it and jump there.
           auto I = llvm::find_if(llvm::reverse(Stack), [&](const Slot &x) {
             return x.StackSlotLabel == StackSlotLabel;
           });
           // If we found the label so pop from there.
           if (I != Stack.rend()) {
             CurrentValue = I->Value;
             CurrentPragmaLocation = I->PragmaLocation;
             Stack.erase(std::prev(I.base()), Stack.end());
           }
         } else if (!Stack.empty()) {
           // We do not have a label, just pop the last entry.
           CurrentValue = Stack.back().Value;
           CurrentPragmaLocation = Stack.back().PragmaLocation;
           Stack.pop_back();
         }
       }
       if (Action & PSK_Set) {
         CurrentValue = Value;
         CurrentPragmaLocation = PragmaLocation;
       }
     }
 
     // MSVC seems to add artificial slots to #pragma stacks on entering a C++
     // method body to restore the stacks on exit, so it works like this:
     //
     //   struct S {
     //     #pragma <name>(push, InternalPragmaSlot, <current_pragma_value>)
     //     void Method {}
     //     #pragma <name>(pop, InternalPragmaSlot)
     //   };
     //
     // It works even with #pragma vtordisp, although MSVC doesn't support
     //   #pragma vtordisp(push [, id], n)
     // syntax.
     //
     // Push / pop a named sentinel slot.
     void SentinelAction(PragmaMsStackAction Action, StringRef Label) {
       assert((Action == PSK_Push || Action == PSK_Pop) &&
              "Can only push / pop #pragma stack sentinels!");
       Act(CurrentPragmaLocation, Action, Label, CurrentValue);
     }
 
     // Constructors.
     explicit PragmaStack(const ValueType &Default)
         : DefaultValue(Default), CurrentValue(Default) {}
 
     bool hasValue() const { return CurrentValue != DefaultValue; }
 
     SmallVector<Slot, 2> Stack;
     ValueType DefaultValue; // Value used for PSK_Reset action.
     ValueType CurrentValue;
     SourceLocation CurrentPragmaLocation;
   };
   // FIXME: We should serialize / deserialize these if they occur in a PCH (but
   // we shouldn't do so if they're in a module).
 
   /// Whether to insert vtordisps prior to virtual bases in the Microsoft
   /// C++ ABI.  Possible values are 0, 1, and 2, which mean:
   ///
   /// 0: Suppress all vtordisps
   /// 1: Insert vtordisps in the presence of vbase overrides and non-trivial
   ///    structors
   /// 2: Always insert vtordisps to support RTTI on partially constructed
   ///    objects
   PragmaStack<MSVtorDispMode> VtorDispStack;
   PragmaStack<AlignPackInfo> AlignPackStack;
   // The current #pragma align/pack values and locations at each #include.
   struct AlignPackIncludeState {
     AlignPackInfo CurrentValue;
     SourceLocation CurrentPragmaLocation;
     bool HasNonDefaultValue, ShouldWarnOnInclude;
   };
   SmallVector<AlignPackIncludeState, 8> AlignPackIncludeStack;
   // Segment #pragmas.
   PragmaStack<StringLiteral *> DataSegStack;
   PragmaStack<StringLiteral *> BSSSegStack;
   PragmaStack<StringLiteral *> ConstSegStack;
   PragmaStack<StringLiteral *> CodeSegStack;
 
   // #pragma strict_gs_check.
   PragmaStack<bool> StrictGuardStackCheckStack;
 
   // This stack tracks the current state of Sema.CurFPFeatures.
   PragmaStack<FPOptionsOverride> FpPragmaStack;
   FPOptionsOverride CurFPFeatureOverrides() {
     FPOptionsOverride result;
     if (!FpPragmaStack.hasValue()) {
       result = FPOptionsOverride();
     } else {
       result = FpPragmaStack.CurrentValue;
     }
     return result;
   }
 
   enum PragmaSectionKind {
     PSK_DataSeg,
     PSK_BSSSeg,
     PSK_ConstSeg,
     PSK_CodeSeg,
   };
 
   // RAII object to push / pop sentinel slots for all MS #pragma stacks.
   // Actions should be performed only if we enter / exit a C++ method body.
   class PragmaStackSentinelRAII {
   public:
     PragmaStackSentinelRAII(Sema &S, StringRef SlotLabel, bool ShouldAct);
     ~PragmaStackSentinelRAII();
 
   private:
     Sema &S;
     StringRef SlotLabel;
     bool ShouldAct;
   };
 
   /// Last section used with #pragma init_seg.
   StringLiteral *CurInitSeg;
   SourceLocation CurInitSegLoc;
 
   /// Sections used with #pragma alloc_text.
   llvm::StringMap<std::tuple<StringRef, SourceLocation>> FunctionToSectionMap;
 
   /// VisContext - Manages the stack for \#pragma GCC visibility.
   void *VisContext; // Really a "PragmaVisStack*"
 
   /// This an attribute introduced by \#pragma clang attribute.
   struct PragmaAttributeEntry {
     SourceLocation Loc;
     ParsedAttr *Attribute;
     SmallVector<attr::SubjectMatchRule, 4> MatchRules;
     bool IsUsed;
   };
 
   /// A push'd group of PragmaAttributeEntries.
   struct PragmaAttributeGroup {
     /// The location of the push attribute.
     SourceLocation Loc;
     /// The namespace of this push group.
     const IdentifierInfo *Namespace;
     SmallVector<PragmaAttributeEntry, 2> Entries;
   };
 
   SmallVector<PragmaAttributeGroup, 2> PragmaAttributeStack;
 
   /// The declaration that is currently receiving an attribute from the
   /// #pragma attribute stack.
   const Decl *PragmaAttributeCurrentTargetDecl;
 
   /// This represents the last location of a "#pragma clang optimize off"
   /// directive if such a directive has not been closed by an "on" yet. If
   /// optimizations are currently "on", this is set to an invalid location.
   SourceLocation OptimizeOffPragmaLocation;
 
   /// Get the location for the currently active "\#pragma clang optimize
   /// off". If this location is invalid, then the state of the pragma is "on".
   SourceLocation getOptimizeOffPragmaLocation() const {
     return OptimizeOffPragmaLocation;
   }
 
   /// The "on" or "off" argument passed by \#pragma optimize, that denotes
   /// whether the optimizations in the list passed to the pragma should be
   /// turned off or on. This boolean is true by default because command line
   /// options are honored when `#pragma optimize("", on)`.
   /// (i.e. `ModifyFnAttributeMSPragmaOptimze()` does nothing)
   bool MSPragmaOptimizeIsOn = true;
 
   /// Set of no-builtin functions listed by \#pragma function.
   llvm::SmallSetVector<StringRef, 4> MSFunctionNoBuiltins;
 
   /// AddAlignmentAttributesForRecord - Adds any needed alignment attributes to
   /// a the record decl, to handle '\#pragma pack' and '\#pragma options align'.
   void AddAlignmentAttributesForRecord(RecordDecl *RD);
 
   /// AddMsStructLayoutForRecord - Adds ms_struct layout attribute to record.
   void AddMsStructLayoutForRecord(RecordDecl *RD);
 
   /// Add gsl::Pointer attribute to std::container::iterator
   /// \param ND The declaration that introduces the name
   /// std::container::iterator. \param UnderlyingRecord The record named by ND.
   void inferGslPointerAttribute(NamedDecl *ND, CXXRecordDecl *UnderlyingRecord);
 
   /// Add [[gsl::Owner]] and [[gsl::Pointer]] attributes for std:: types.
   void inferGslOwnerPointerAttribute(CXXRecordDecl *Record);
 
   /// Add [[gsl::Pointer]] attributes for std:: types.
   void inferGslPointerAttribute(TypedefNameDecl *TD);
 
   /// Add _Nullable attributes for std:: types.
   void inferNullableClassAttribute(CXXRecordDecl *CRD);
 
   enum PragmaOptionsAlignKind {
     POAK_Native,  // #pragma options align=native
     POAK_Natural, // #pragma options align=natural
     POAK_Packed,  // #pragma options align=packed
     POAK_Power,   // #pragma options align=power
     POAK_Mac68k,  // #pragma options align=mac68k
     POAK_Reset    // #pragma options align=reset
   };
 
   /// ActOnPragmaClangSection - Called on well formed \#pragma clang section
   void ActOnPragmaClangSection(SourceLocation PragmaLoc,
                                PragmaClangSectionAction Action,
                                PragmaClangSectionKind SecKind,
                                StringRef SecName);
 
   /// ActOnPragmaOptionsAlign - Called on well formed \#pragma options align.
   void ActOnPragmaOptionsAlign(PragmaOptionsAlignKind Kind,
                                SourceLocation PragmaLoc);
 
   /// ActOnPragmaPack - Called on well formed \#pragma pack(...).
   void ActOnPragmaPack(SourceLocation PragmaLoc, PragmaMsStackAction Action,
                        StringRef SlotLabel, Expr *Alignment);
 
   /// ConstantFoldAttrArgs - Folds attribute arguments into ConstantExprs
   /// (unless they are value dependent or type dependent). Returns false
   /// and emits a diagnostic if one or more of the arguments could not be
   /// folded into a constant.
   bool ConstantFoldAttrArgs(const AttributeCommonInfo &CI,
                             MutableArrayRef<Expr *> Args);
 
   enum class PragmaAlignPackDiagnoseKind {
     NonDefaultStateAtInclude,
     ChangedStateAtExit
   };
 
   void DiagnoseNonDefaultPragmaAlignPack(PragmaAlignPackDiagnoseKind Kind,
                                          SourceLocation IncludeLoc);
   void DiagnoseUnterminatedPragmaAlignPack();
 
   /// ActOnPragmaMSStruct - Called on well formed \#pragma ms_struct [on|off].
   void ActOnPragmaMSStruct(PragmaMSStructKind Kind);
 
   /// ActOnPragmaMSComment - Called on well formed
   /// \#pragma comment(kind, "arg").
   void ActOnPragmaMSComment(SourceLocation CommentLoc, PragmaMSCommentKind Kind,
                             StringRef Arg);
 
   /// ActOnPragmaDetectMismatch - Call on well-formed \#pragma detect_mismatch
   void ActOnPragmaDetectMismatch(SourceLocation Loc, StringRef Name,
                                  StringRef Value);
 
   /// Are precise floating point semantics currently enabled?
   bool isPreciseFPEnabled() {
     return !CurFPFeatures.getAllowFPReassociate() &&
            !CurFPFeatures.getNoSignedZero() &&
            !CurFPFeatures.getAllowReciprocal() &&
            !CurFPFeatures.getAllowApproxFunc();
   }
 
   void ActOnPragmaFPEvalMethod(SourceLocation Loc,
                                LangOptions::FPEvalMethodKind Value);
 
   /// ActOnPragmaFloatControl - Call on well-formed \#pragma float_control
   void ActOnPragmaFloatControl(SourceLocation Loc, PragmaMsStackAction Action,
                                PragmaFloatControlKind Value);
 
   /// ActOnPragmaMSPointersToMembers - called on well formed \#pragma
   /// pointers_to_members(representation method[, general purpose
   /// representation]).
   void ActOnPragmaMSPointersToMembers(
       LangOptions::PragmaMSPointersToMembersKind Kind,
       SourceLocation PragmaLoc);
 
   /// Called on well formed \#pragma vtordisp().
   void ActOnPragmaMSVtorDisp(PragmaMsStackAction Action,
                              SourceLocation PragmaLoc, MSVtorDispMode Value);
 
   bool UnifySection(StringRef SectionName, int SectionFlags,
                     NamedDecl *TheDecl);
   bool UnifySection(StringRef SectionName, int SectionFlags,
                     SourceLocation PragmaSectionLocation);
 
   /// Called on well formed \#pragma bss_seg/data_seg/const_seg/code_seg.
   void ActOnPragmaMSSeg(SourceLocation PragmaLocation,
                         PragmaMsStackAction Action,
                         llvm::StringRef StackSlotLabel,
                         StringLiteral *SegmentName, llvm::StringRef PragmaName);
 
   /// Called on well formed \#pragma section().
   void ActOnPragmaMSSection(SourceLocation PragmaLocation, int SectionFlags,
                             StringLiteral *SegmentName);
 
   /// Called on well-formed \#pragma init_seg().
   void ActOnPragmaMSInitSeg(SourceLocation PragmaLocation,
                             StringLiteral *SegmentName);
 
   /// Called on well-formed \#pragma alloc_text().
   void ActOnPragmaMSAllocText(
       SourceLocation PragmaLocation, StringRef Section,
       const SmallVector<std::tuple<IdentifierInfo *, SourceLocation>>
           &Functions);
 
   /// ActOnPragmaMSStrictGuardStackCheck - Called on well formed \#pragma
   /// strict_gs_check.
   void ActOnPragmaMSStrictGuardStackCheck(SourceLocation PragmaLocation,
                                           PragmaMsStackAction Action,
                                           bool Value);
 
   /// ActOnPragmaUnused - Called on well-formed '\#pragma unused'.
   void ActOnPragmaUnused(const Token &Identifier, Scope *curScope,
                          SourceLocation PragmaLoc);
 
   void ActOnPragmaAttributeAttribute(ParsedAttr &Attribute,
                                      SourceLocation PragmaLoc,
                                      attr::ParsedSubjectMatchRuleSet Rules);
   void ActOnPragmaAttributeEmptyPush(SourceLocation PragmaLoc,
                                      const IdentifierInfo *Namespace);
 
   /// Called on well-formed '\#pragma clang attribute pop'.
   void ActOnPragmaAttributePop(SourceLocation PragmaLoc,
                                const IdentifierInfo *Namespace);
 
   /// Adds the attributes that have been specified using the
   /// '\#pragma clang attribute push' directives to the given declaration.
   void AddPragmaAttributes(Scope *S, Decl *D);
 
   void PrintPragmaAttributeInstantiationPoint();
 
   void DiagnoseUnterminatedPragmaAttribute();
 
   /// Called on well formed \#pragma clang optimize.
   void ActOnPragmaOptimize(bool On, SourceLocation PragmaLoc);
 
   /// #pragma optimize("[optimization-list]", on | off).
   void ActOnPragmaMSOptimize(SourceLocation Loc, bool IsOn);
 
   /// Call on well formed \#pragma function.
   void
   ActOnPragmaMSFunction(SourceLocation Loc,
                         const llvm::SmallVectorImpl<StringRef> &NoBuiltins);
 
   /// Only called on function definitions; if there is a pragma in scope
   /// with the effect of a range-based optnone, consider marking the function
   /// with attribute optnone.
   void AddRangeBasedOptnone(FunctionDecl *FD);
 
   /// Only called on function definitions; if there is a `#pragma alloc_text`
   /// that decides which code section the function should be in, add
   /// attribute section to the function.
   void AddSectionMSAllocText(FunctionDecl *FD);
 
   /// Adds the 'optnone' attribute to the function declaration if there
   /// are no conflicts; Loc represents the location causing the 'optnone'
   /// attribute to be added (usually because of a pragma).
   void AddOptnoneAttributeIfNoConflicts(FunctionDecl *FD, SourceLocation Loc);
 
   /// Only called on function definitions; if there is a MSVC #pragma optimize
   /// in scope, consider changing the function's attributes based on the
   /// optimization list passed to the pragma.
   void ModifyFnAttributesMSPragmaOptimize(FunctionDecl *FD);
 
   /// Only called on function definitions; if there is a pragma in scope
   /// with the effect of a range-based no_builtin, consider marking the function
   /// with attribute no_builtin.
   void AddImplicitMSFunctionNoBuiltinAttr(FunctionDecl *FD);
 
   /// AddPushedVisibilityAttribute - If '\#pragma GCC visibility' was used,
   /// add an appropriate visibility attribute.
   void AddPushedVisibilityAttribute(Decl *RD);
 
   /// FreeVisContext - Deallocate and null out VisContext.
   void FreeVisContext();
 
   /// ActOnPragmaVisibility - Called on well formed \#pragma GCC visibility... .
   void ActOnPragmaVisibility(const IdentifierInfo *VisType,
                              SourceLocation PragmaLoc);
 
   /// ActOnPragmaFPContract - Called on well formed
   /// \#pragma {STDC,OPENCL} FP_CONTRACT and
   /// \#pragma clang fp contract
   void ActOnPragmaFPContract(SourceLocation Loc, LangOptions::FPModeKind FPC);
 
   /// Called on well formed
   /// \#pragma clang fp reassociate
   /// or
   /// \#pragma clang fp reciprocal
   void ActOnPragmaFPValueChangingOption(SourceLocation Loc, PragmaFPKind Kind,
                                         bool IsEnabled);
 
   /// ActOnPragmaFenvAccess - Called on well formed
   /// \#pragma STDC FENV_ACCESS
   void ActOnPragmaFEnvAccess(SourceLocation Loc, bool IsEnabled);
 
   /// ActOnPragmaCXLimitedRange - Called on well formed
   /// \#pragma STDC CX_LIMITED_RANGE
   void ActOnPragmaCXLimitedRange(SourceLocation Loc,
                                  LangOptions::ComplexRangeKind Range);
 
   /// Called on well formed '\#pragma clang fp' that has option 'exceptions'.
   void ActOnPragmaFPExceptions(SourceLocation Loc,
                                LangOptions::FPExceptionModeKind);
 
   /// Called to set constant rounding mode for floating point operations.
   void ActOnPragmaFEnvRound(SourceLocation Loc, llvm::RoundingMode);
 
   /// Called to set exception behavior for floating point operations.
   void setExceptionMode(SourceLocation Loc, LangOptions::FPExceptionModeKind);
 
   /// PushNamespaceVisibilityAttr - Note that we've entered a
   /// namespace with a visibility attribute.
   void PushNamespaceVisibilityAttr(const VisibilityAttr *Attr,
                                    SourceLocation Loc);
 
   /// PopPragmaVisibility - Pop the top element of the visibility stack; used
   /// for '\#pragma GCC visibility' and visibility attributes on namespaces.
   void PopPragmaVisibility(bool IsNamespaceEnd, SourceLocation EndLoc);
 
   /// Handles semantic checking for features that are common to all attributes,
   /// such as checking whether a parameter was properly specified, or the
   /// correct number of arguments were passed, etc. Returns true if the
   /// attribute has been diagnosed.
   bool checkCommonAttributeFeatures(const Decl *D, const ParsedAttr &A,
                                     bool SkipArgCountCheck = false);
   bool checkCommonAttributeFeatures(const Stmt *S, const ParsedAttr &A,
                                     bool SkipArgCountCheck = false);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Availability Attribute Handling
   /// Implementations are in SemaAvailability.cpp
   ///@{
 
 public:
   /// Issue any -Wunguarded-availability warnings in \c FD
   void DiagnoseUnguardedAvailabilityViolations(Decl *FD);
 
   void handleDelayedAvailabilityCheck(sema::DelayedDiagnostic &DD, Decl *Ctx);
 
   /// Retrieve the current function, if any, that should be analyzed for
   /// potential availability violations.
   sema::FunctionScopeInfo *getCurFunctionAvailabilityContext();
 
   void DiagnoseAvailabilityOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
                                   const ObjCInterfaceDecl *UnknownObjCClass,
                                   bool ObjCPropertyAccess,
                                   bool AvoidPartialAvailabilityChecks = false,
                                   ObjCInterfaceDecl *ClassReceiver = nullptr);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Casts
   /// Implementations are in SemaCast.cpp
   ///@{
 
 public:
   static bool isCast(CheckedConversionKind CCK) {
     return CCK == CheckedConversionKind::CStyleCast ||
            CCK == CheckedConversionKind::FunctionalCast ||
            CCK == CheckedConversionKind::OtherCast;
   }
 
   /// ActOnCXXNamedCast - Parse
   /// {dynamic,static,reinterpret,const,addrspace}_cast's.
   ExprResult ActOnCXXNamedCast(SourceLocation OpLoc, tok::TokenKind Kind,
                                SourceLocation LAngleBracketLoc, Declarator &D,
                                SourceLocation RAngleBracketLoc,
                                SourceLocation LParenLoc, Expr *E,
                                SourceLocation RParenLoc);
 
   ExprResult BuildCXXNamedCast(SourceLocation OpLoc, tok::TokenKind Kind,
                                TypeSourceInfo *Ty, Expr *E,
                                SourceRange AngleBrackets, SourceRange Parens);
 
   ExprResult ActOnBuiltinBitCastExpr(SourceLocation KWLoc, Declarator &Dcl,
                                      ExprResult Operand,
                                      SourceLocation RParenLoc);
 
   ExprResult BuildBuiltinBitCastExpr(SourceLocation KWLoc, TypeSourceInfo *TSI,
                                      Expr *Operand, SourceLocation RParenLoc);
 
   // Checks that reinterpret casts don't have undefined behavior.
   void CheckCompatibleReinterpretCast(QualType SrcType, QualType DestType,
                                       bool IsDereference, SourceRange Range);
 
   // Checks that the vector type should be initialized from a scalar
   // by splatting the value rather than populating a single element.
   // This is the case for AltiVecVector types as well as with
   // AltiVecPixel and AltiVecBool when -faltivec-src-compat=xl is specified.
   bool ShouldSplatAltivecScalarInCast(const VectorType *VecTy);
 
   // Checks if the -faltivec-src-compat=gcc option is specified.
   // If so, AltiVecVector, AltiVecBool and AltiVecPixel types are
   // treated the same way as they are when trying to initialize
   // these vectors on gcc (an error is emitted).
   bool CheckAltivecInitFromScalar(SourceRange R, QualType VecTy,
                                   QualType SrcTy);
 
   ExprResult BuildCStyleCastExpr(SourceLocation LParenLoc, TypeSourceInfo *Ty,
                                  SourceLocation RParenLoc, Expr *Op);
 
   ExprResult BuildCXXFunctionalCastExpr(TypeSourceInfo *TInfo, QualType Type,
                                         SourceLocation LParenLoc,
                                         Expr *CastExpr,
                                         SourceLocation RParenLoc);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Extra Semantic Checking
   /// Implementations are in SemaChecking.cpp
   ///@{
 
 public:
   /// Used to change context to isConstantEvaluated without pushing a heavy
   /// ExpressionEvaluationContextRecord object.
   bool isConstantEvaluatedOverride = false;
 
   bool isConstantEvaluatedContext() const {
     return currentEvaluationContext().isConstantEvaluated() ||
            isConstantEvaluatedOverride;
   }
 
   SourceLocation getLocationOfStringLiteralByte(const StringLiteral *SL,
                                                 unsigned ByteNo) const;
 
   enum FormatArgumentPassingKind {
     FAPK_Fixed,    // values to format are fixed (no C-style variadic arguments)
     FAPK_Variadic, // values to format are passed as variadic arguments
     FAPK_VAList,   // values to format are passed in a va_list
   };
 
   // Used to grab the relevant information from a FormatAttr and a
   // FunctionDeclaration.
   struct FormatStringInfo {
     unsigned FormatIdx;
     unsigned FirstDataArg;
     FormatArgumentPassingKind ArgPassingKind;
   };
 
   /// Given a FunctionDecl's FormatAttr, attempts to populate the
   /// FomatStringInfo parameter with the FormatAttr's correct format_idx and
   /// firstDataArg. Returns true when the format fits the function and the
   /// FormatStringInfo has been populated.
   static bool getFormatStringInfo(const FormatAttr *Format, bool IsCXXMember,
                                   bool IsVariadic, FormatStringInfo *FSI);
 
   // Used by C++ template instantiation.
   ExprResult BuiltinShuffleVector(CallExpr *TheCall);
 
   /// ConvertVectorExpr - Handle __builtin_convertvector
   ExprResult ConvertVectorExpr(Expr *E, TypeSourceInfo *TInfo,
                                SourceLocation BuiltinLoc,
                                SourceLocation RParenLoc);
 
   enum FormatStringType {
     FST_Scanf,
     FST_Printf,
     FST_NSString,
     FST_Strftime,
     FST_Strfmon,
     FST_Kprintf,
     FST_FreeBSDKPrintf,
     FST_OSTrace,
     FST_OSLog,
     FST_Unknown
   };
   static FormatStringType GetFormatStringType(const FormatAttr *Format);
 
   bool FormatStringHasSArg(const StringLiteral *FExpr);
 
   /// Check for comparisons of floating-point values using == and !=. Issue a
   /// warning if the comparison is not likely to do what the programmer
   /// intended.
   void CheckFloatComparison(SourceLocation Loc, Expr *LHS, Expr *RHS,
                             BinaryOperatorKind Opcode);
 
   /// Register a magic integral constant to be used as a type tag.
   void RegisterTypeTagForDatatype(const IdentifierInfo *ArgumentKind,
                                   uint64_t MagicValue, QualType Type,
                                   bool LayoutCompatible, bool MustBeNull);
 
   struct TypeTagData {
     TypeTagData() {}
 
     TypeTagData(QualType Type, bool LayoutCompatible, bool MustBeNull)
         : Type(Type), LayoutCompatible(LayoutCompatible),
           MustBeNull(MustBeNull) {}
 
     QualType Type;
 
     /// If true, \c Type should be compared with other expression's types for
     /// layout-compatibility.
     LLVM_PREFERRED_TYPE(bool)
     unsigned LayoutCompatible : 1;
     LLVM_PREFERRED_TYPE(bool)
     unsigned MustBeNull : 1;
   };
 
   /// A pair of ArgumentKind identifier and magic value.  This uniquely
   /// identifies the magic value.
   typedef std::pair<const IdentifierInfo *, uint64_t> TypeTagMagicValue;
 
   /// Diagnoses the current set of gathered accesses. This typically
   /// happens at full expression level. The set is cleared after emitting the
   /// diagnostics.
   void DiagnoseMisalignedMembers();
 
   /// This function checks if the expression is in the sef of potentially
   /// misaligned members and it is converted to some pointer type T with lower
   /// or equal alignment requirements. If so it removes it. This is used when
   /// we do not want to diagnose such misaligned access (e.g. in conversions to
   /// void*).
   void DiscardMisalignedMemberAddress(const Type *T, Expr *E);
 
   /// This function calls Action when it determines that E designates a
   /// misaligned member due to the packed attribute. This is used to emit
   /// local diagnostics like in reference binding.
   void RefersToMemberWithReducedAlignment(
       Expr *E,
       llvm::function_ref<void(Expr *, RecordDecl *, FieldDecl *, CharUnits)>
           Action);
 
   enum class AtomicArgumentOrder { API, AST };
   ExprResult
   BuildAtomicExpr(SourceRange CallRange, SourceRange ExprRange,
                   SourceLocation RParenLoc, MultiExprArg Args,
                   AtomicExpr::AtomicOp Op,
                   AtomicArgumentOrder ArgOrder = AtomicArgumentOrder::API);
 
   /// Check to see if a given expression could have '.c_str()' called on it.
   bool hasCStrMethod(const Expr *E);
 
   /// Diagnose pointers that are always non-null.
   /// \param E the expression containing the pointer
   /// \param NullKind NPCK_NotNull if E is a cast to bool, otherwise, E is
   /// compared to a null pointer
   /// \param IsEqual True when the comparison is equal to a null pointer
   /// \param Range Extra SourceRange to highlight in the diagnostic
   void DiagnoseAlwaysNonNullPointer(Expr *E,
                                     Expr::NullPointerConstantKind NullType,
                                     bool IsEqual, SourceRange Range);
 
   /// CheckParmsForFunctionDef - Check that the parameters of the given
   /// function are appropriate for the definition of a function. This
   /// takes care of any checks that cannot be performed on the
   /// declaration itself, e.g., that the types of each of the function
   /// parameters are complete.
   bool CheckParmsForFunctionDef(ArrayRef<ParmVarDecl *> Parameters,
                                 bool CheckParameterNames);
 
   /// CheckCastAlign - Implements -Wcast-align, which warns when a
   /// pointer cast increases the alignment requirements.
   void CheckCastAlign(Expr *Op, QualType T, SourceRange TRange);
 
   /// checkUnsafeAssigns - Check whether +1 expr is being assigned
   /// to weak/__unsafe_unretained type.
   bool checkUnsafeAssigns(SourceLocation Loc, QualType LHS, Expr *RHS);
 
   /// checkUnsafeExprAssigns - Check whether +1 expr is being assigned
   /// to weak/__unsafe_unretained expression.
   void checkUnsafeExprAssigns(SourceLocation Loc, Expr *LHS, Expr *RHS);
 
   /// Emit \p DiagID if statement located on \p StmtLoc has a suspicious null
   /// statement as a \p Body, and it is located on the same line.
   ///
   /// This helps prevent bugs due to typos, such as:
   ///     if (condition);
   ///       do_stuff();
   void DiagnoseEmptyStmtBody(SourceLocation StmtLoc, const Stmt *Body,
                              unsigned DiagID);
 
   /// Warn if a for/while loop statement \p S, which is followed by
   /// \p PossibleBody, has a suspicious null statement as a body.
   void DiagnoseEmptyLoopBody(const Stmt *S, const Stmt *PossibleBody);
 
   /// DiagnoseSelfMove - Emits a warning if a value is moved to itself.
   void DiagnoseSelfMove(const Expr *LHSExpr, const Expr *RHSExpr,
                         SourceLocation OpLoc);
 
   // Used for emitting the right warning by DefaultVariadicArgumentPromotion
   enum VariadicCallType {
     VariadicFunction,
     VariadicBlock,
     VariadicMethod,
     VariadicConstructor,
     VariadicDoesNotApply
   };
 
   bool IsLayoutCompatible(QualType T1, QualType T2) const;
   bool IsPointerInterconvertibleBaseOf(const TypeSourceInfo *Base,
                                        const TypeSourceInfo *Derived);
 
   /// CheckFunctionCall - Check a direct function call for various correctness
   /// and safety properties not strictly enforced by the C type system.
   bool CheckFunctionCall(FunctionDecl *FDecl, CallExpr *TheCall,
                          const FunctionProtoType *Proto);
 
   bool BuiltinVectorMath(CallExpr *TheCall, QualType &Res);
   bool BuiltinVectorToScalarMath(CallExpr *TheCall);
 
   /// Handles the checks for format strings, non-POD arguments to vararg
   /// functions, NULL arguments passed to non-NULL parameters, diagnose_if
   /// attributes and AArch64 SME attributes.
   void checkCall(NamedDecl *FDecl, const FunctionProtoType *Proto,
                  const Expr *ThisArg, ArrayRef<const Expr *> Args,
                  bool IsMemberFunction, SourceLocation Loc, SourceRange Range,
                  VariadicCallType CallType);
 
   /// \brief Enforce the bounds of a TCB
   /// CheckTCBEnforcement - Enforces that every function in a named TCB only
   /// directly calls other functions in the same TCB as marked by the
   /// enforce_tcb and enforce_tcb_leaf attributes.
   void CheckTCBEnforcement(const SourceLocation CallExprLoc,
                            const NamedDecl *Callee);
 
   void CheckConstrainedAuto(const AutoType *AutoT, SourceLocation Loc);
 
   /// BuiltinConstantArg - Handle a check if argument ArgNum of CallExpr
   /// TheCall is a constant expression.
   bool BuiltinConstantArg(CallExpr *TheCall, int ArgNum, llvm::APSInt &Result);
 
   /// BuiltinConstantArgRange - Handle a check if argument ArgNum of CallExpr
   /// TheCall is a constant expression in the range [Low, High].
   bool BuiltinConstantArgRange(CallExpr *TheCall, int ArgNum, int Low, int High,
                                bool RangeIsError = true);
 
   /// BuiltinConstantArgMultiple - Handle a check if argument ArgNum of CallExpr
   /// TheCall is a constant expression is a multiple of Num..
   bool BuiltinConstantArgMultiple(CallExpr *TheCall, int ArgNum,
                                   unsigned Multiple);
 
   /// BuiltinConstantArgPower2 - Check if argument ArgNum of TheCall is a
   /// constant expression representing a power of 2.
   bool BuiltinConstantArgPower2(CallExpr *TheCall, int ArgNum);
 
   /// BuiltinConstantArgShiftedByte - Check if argument ArgNum of TheCall is
   /// a constant expression representing an arbitrary byte value shifted left by
   /// a multiple of 8 bits.
   bool BuiltinConstantArgShiftedByte(CallExpr *TheCall, int ArgNum,
                                      unsigned ArgBits);
 
   /// BuiltinConstantArgShiftedByteOr0xFF - Check if argument ArgNum of
   /// TheCall is a constant expression representing either a shifted byte value,
   /// or a value of the form 0x??FF (i.e. a member of the arithmetic progression
   /// 0x00FF, 0x01FF, ..., 0xFFFF). This strange range check is needed for some
   /// Arm MVE intrinsics.
   bool BuiltinConstantArgShiftedByteOrXXFF(CallExpr *TheCall, int ArgNum,
                                            unsigned ArgBits);
 
   /// Checks that a call expression's argument count is at least the desired
   /// number. This is useful when doing custom type-checking on a variadic
   /// function. Returns true on error.
   bool checkArgCountAtLeast(CallExpr *Call, unsigned MinArgCount);
 
   /// Checks that a call expression's argument count is at most the desired
   /// number. This is useful when doing custom type-checking on a variadic
   /// function. Returns true on error.
   bool checkArgCountAtMost(CallExpr *Call, unsigned MaxArgCount);
 
   /// Checks that a call expression's argument count is in the desired range.
   /// This is useful when doing custom type-checking on a variadic function.
   /// Returns true on error.
   bool checkArgCountRange(CallExpr *Call, unsigned MinArgCount,
                           unsigned MaxArgCount);
 
   /// Checks that a call expression's argument count is the desired number.
   /// This is useful when doing custom type-checking.  Returns true on error.
   bool checkArgCount(CallExpr *Call, unsigned DesiredArgCount);
 
   /// Returns true if the argument consists of one contiguous run of 1s with any
   /// number of 0s on either side. The 1s are allowed to wrap from LSB to MSB,
   /// so 0x000FFF0, 0x0000FFFF, 0xFF0000FF, 0x0 are all runs. 0x0F0F0000 is not,
   /// since all 1s are not contiguous.
   bool ValueIsRunOfOnes(CallExpr *TheCall, unsigned ArgNum);
 
   void CheckImplicitConversion(Expr *E, QualType T, SourceLocation CC,
                                bool *ICContext = nullptr,
                                bool IsListInit = false);
 
   bool BuiltinElementwiseTernaryMath(CallExpr *TheCall,
                                      bool CheckForFloatArgs = true);
   bool PrepareBuiltinElementwiseMathOneArgCall(CallExpr *TheCall);
 
 private:
   void CheckArrayAccess(const Expr *BaseExpr, const Expr *IndexExpr,
                         const ArraySubscriptExpr *ASE = nullptr,
                         bool AllowOnePastEnd = true, bool IndexNegated = false);
   void CheckArrayAccess(const Expr *E);
 
   bool CheckPointerCall(NamedDecl *NDecl, CallExpr *TheCall,
                         const FunctionProtoType *Proto);
 
   /// Checks function calls when a FunctionDecl or a NamedDecl is not available,
   /// such as function pointers returned from functions.
   bool CheckOtherCall(CallExpr *TheCall, const FunctionProtoType *Proto);
 
   /// CheckConstructorCall - Check a constructor call for correctness and safety
   /// properties not enforced by the C type system.
   void CheckConstructorCall(FunctionDecl *FDecl, QualType ThisType,
                             ArrayRef<const Expr *> Args,
                             const FunctionProtoType *Proto, SourceLocation Loc);
 
   /// Warn if a pointer or reference argument passed to a function points to an
   /// object that is less aligned than the parameter. This can happen when
   /// creating a typedef with a lower alignment than the original type and then
   /// calling functions defined in terms of the original type.
   void CheckArgAlignment(SourceLocation Loc, NamedDecl *FDecl,
                          StringRef ParamName, QualType ArgTy, QualType ParamTy);
 
   ExprResult CheckOSLogFormatStringArg(Expr *Arg);
 
   ExprResult CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
                                       CallExpr *TheCall);
 
   bool CheckTSBuiltinFunctionCall(const TargetInfo &TI, unsigned BuiltinID,
                                   CallExpr *TheCall);
 
   void checkFortifiedBuiltinMemoryFunction(FunctionDecl *FD, CallExpr *TheCall);
 
   /// Check the arguments to '__builtin_va_start' or '__builtin_ms_va_start'
   /// for validity.  Emit an error and return true on failure; return false
   /// on success.
   bool BuiltinVAStart(unsigned BuiltinID, CallExpr *TheCall);
   bool BuiltinVAStartARMMicrosoft(CallExpr *Call);
 
   /// BuiltinUnorderedCompare - Handle functions like __builtin_isgreater and
   /// friends.  This is declared to take (...), so we have to check everything.
   bool BuiltinUnorderedCompare(CallExpr *TheCall, unsigned BuiltinID);
 
   /// BuiltinSemaBuiltinFPClassification - Handle functions like
   /// __builtin_isnan and friends.  This is declared to take (...), so we have
   /// to check everything.
   bool BuiltinFPClassification(CallExpr *TheCall, unsigned NumArgs,
                                unsigned BuiltinID);
 
   /// Perform semantic analysis for a call to __builtin_complex.
   bool BuiltinComplex(CallExpr *TheCall);
   bool BuiltinOSLogFormat(CallExpr *TheCall);
 
   /// BuiltinPrefetch - Handle __builtin_prefetch.
   /// This is declared to take (const void*, ...) and can take two
   /// optional constant int args.
   bool BuiltinPrefetch(CallExpr *TheCall);
 
   /// Handle __builtin_alloca_with_align. This is declared
   /// as (size_t, size_t) where the second size_t must be a power of 2 greater
   /// than 8.
   bool BuiltinAllocaWithAlign(CallExpr *TheCall);
 
   /// BuiltinArithmeticFence - Handle __arithmetic_fence.
   bool BuiltinArithmeticFence(CallExpr *TheCall);
 
   /// BuiltinAssume - Handle __assume (MS Extension).
   /// __assume does not evaluate its arguments, and should warn if its argument
   /// has side effects.
   bool BuiltinAssume(CallExpr *TheCall);
 
   /// Handle __builtin_assume_aligned. This is declared
   /// as (const void*, size_t, ...) and can take one optional constant int arg.
   bool BuiltinAssumeAligned(CallExpr *TheCall);
 
   /// BuiltinLongjmp - Handle __builtin_longjmp(void *env[5], int val).
   /// This checks that the target supports __builtin_longjmp and
   /// that val is a constant 1.
   bool BuiltinLongjmp(CallExpr *TheCall);
 
   /// BuiltinSetjmp - Handle __builtin_setjmp(void *env[5]).
   /// This checks that the target supports __builtin_setjmp.
   bool BuiltinSetjmp(CallExpr *TheCall);
 
   /// We have a call to a function like __sync_fetch_and_add, which is an
   /// overloaded function based on the pointer type of its first argument.
   /// The main BuildCallExpr routines have already promoted the types of
   /// arguments because all of these calls are prototyped as void(...).
   ///
   /// This function goes through and does final semantic checking for these
   /// builtins, as well as generating any warnings.
   ExprResult BuiltinAtomicOverloaded(ExprResult TheCallResult);
 
   /// BuiltinNontemporalOverloaded - We have a call to
   /// __builtin_nontemporal_store or __builtin_nontemporal_load, which is an
   /// overloaded function based on the pointer type of its last argument.
   ///
   /// This function goes through and does final semantic checking for these
   /// builtins.
   ExprResult BuiltinNontemporalOverloaded(ExprResult TheCallResult);
   ExprResult AtomicOpsOverloaded(ExprResult TheCallResult,
                                  AtomicExpr::AtomicOp Op);
 
   bool BuiltinElementwiseMath(CallExpr *TheCall);
   bool PrepareBuiltinReduceMathOneArgCall(CallExpr *TheCall);
 
   bool BuiltinNonDeterministicValue(CallExpr *TheCall);
 
   // Matrix builtin handling.
   ExprResult BuiltinMatrixTranspose(CallExpr *TheCall, ExprResult CallResult);
   ExprResult BuiltinMatrixColumnMajorLoad(CallExpr *TheCall,
                                           ExprResult CallResult);
   ExprResult BuiltinMatrixColumnMajorStore(CallExpr *TheCall,
                                            ExprResult CallResult);
 
   /// CheckFormatArguments - Check calls to printf and scanf (and similar
   /// functions) for correct use of format strings.
   /// Returns true if a format string has been fully checked.
   bool CheckFormatArguments(const FormatAttr *Format,
                             ArrayRef<const Expr *> Args, bool IsCXXMember,
                             VariadicCallType CallType, SourceLocation Loc,
                             SourceRange Range,
                             llvm::SmallBitVector &CheckedVarArgs);
   bool CheckFormatArguments(ArrayRef<const Expr *> Args,
                             FormatArgumentPassingKind FAPK, unsigned format_idx,
                             unsigned firstDataArg, FormatStringType Type,
                             VariadicCallType CallType, SourceLocation Loc,
                             SourceRange range,
                             llvm::SmallBitVector &CheckedVarArgs);
 
   void CheckInfNaNFunction(const CallExpr *Call, const FunctionDecl *FDecl);
 
   /// Warn when using the wrong abs() function.
   void CheckAbsoluteValueFunction(const CallExpr *Call,
                                   const FunctionDecl *FDecl);
 
   void CheckMaxUnsignedZero(const CallExpr *Call, const FunctionDecl *FDecl);
 
   /// Check for dangerous or invalid arguments to memset().
   ///
   /// This issues warnings on known problematic, dangerous or unspecified
   /// arguments to the standard 'memset', 'memcpy', 'memmove', and 'memcmp'
   /// function calls.
   ///
   /// \param Call The call expression to diagnose.
   void CheckMemaccessArguments(const CallExpr *Call, unsigned BId,
                                IdentifierInfo *FnName);
 
   // Warn if the user has made the 'size' argument to strlcpy or strlcat
   // be the size of the source, instead of the destination.
   void CheckStrlcpycatArguments(const CallExpr *Call, IdentifierInfo *FnName);
 
   // Warn on anti-patterns as the 'size' argument to strncat.
   // The correct size argument should look like following:
   //   strncat(dst, src, sizeof(dst) - strlen(dest) - 1);
   void CheckStrncatArguments(const CallExpr *Call, IdentifierInfo *FnName);
 
   /// Alerts the user that they are attempting to free a non-malloc'd object.
   void CheckFreeArguments(const CallExpr *E);
 
   void CheckReturnValExpr(Expr *RetValExp, QualType lhsType,
                           SourceLocation ReturnLoc, bool isObjCMethod = false,
                           const AttrVec *Attrs = nullptr,
                           const FunctionDecl *FD = nullptr);
 
   /// Diagnoses "dangerous" implicit conversions within the given
   /// expression (which is a full expression).  Implements -Wconversion
   /// and -Wsign-compare.
   ///
   /// \param CC the "context" location of the implicit conversion, i.e.
   ///   the most location of the syntactic entity requiring the implicit
   ///   conversion
   void CheckImplicitConversions(Expr *E, SourceLocation CC = SourceLocation());
 
   /// CheckBoolLikeConversion - Check conversion of given expression to boolean.
   /// Input argument E is a logical expression.
   void CheckBoolLikeConversion(Expr *E, SourceLocation CC);
 
   /// Diagnose when expression is an integer constant expression and its
   /// evaluation results in integer overflow
   void CheckForIntOverflow(const Expr *E);
   void CheckUnsequencedOperations(const Expr *E);
 
   /// Perform semantic checks on a completed expression. This will either
   /// be a full-expression or a default argument expression.
   void CheckCompletedExpr(Expr *E, SourceLocation CheckLoc = SourceLocation(),
                           bool IsConstexpr = false);
 
   void CheckBitFieldInitialization(SourceLocation InitLoc, FieldDecl *Field,
                                    Expr *Init);
 
   /// A map from magic value to type information.
   std::unique_ptr<llvm::DenseMap<TypeTagMagicValue, TypeTagData>>
       TypeTagForDatatypeMagicValues;
 
   /// Peform checks on a call of a function with argument_with_type_tag
   /// or pointer_with_type_tag attributes.
   void CheckArgumentWithTypeTag(const ArgumentWithTypeTagAttr *Attr,
                                 const ArrayRef<const Expr *> ExprArgs,
                                 SourceLocation CallSiteLoc);
 
   /// Check if we are taking the address of a packed field
   /// as this may be a problem if the pointer value is dereferenced.
   void CheckAddressOfPackedMember(Expr *rhs);
 
   /// Helper class that collects misaligned member designations and
   /// their location info for delayed diagnostics.
   struct MisalignedMember {
     Expr *E;
     RecordDecl *RD;
     ValueDecl *MD;
     CharUnits Alignment;
 
     MisalignedMember() : E(), RD(), MD() {}
     MisalignedMember(Expr *E, RecordDecl *RD, ValueDecl *MD,
                      CharUnits Alignment)
         : E(E), RD(RD), MD(MD), Alignment(Alignment) {}
     explicit MisalignedMember(Expr *E)
         : MisalignedMember(E, nullptr, nullptr, CharUnits()) {}
 
     bool operator==(const MisalignedMember &m) { return this->E == m.E; }
   };
   /// Small set of gathered accesses to potentially misaligned members
   /// due to the packed attribute.
   SmallVector<MisalignedMember, 4> MisalignedMembers;
 
   /// Adds an expression to the set of gathered misaligned members.
   void AddPotentialMisalignedMembers(Expr *E, RecordDecl *RD, ValueDecl *MD,
                                      CharUnits Alignment);
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Coroutines
   /// Implementations are in SemaCoroutine.cpp
   ///@{
 
 public:
   /// The C++ "std::coroutine_traits" template, which is defined in
   /// \<coroutine_traits>
   ClassTemplateDecl *StdCoroutineTraitsCache;
 
   bool ActOnCoroutineBodyStart(Scope *S, SourceLocation KwLoc,
                                StringRef Keyword);
   ExprResult ActOnCoawaitExpr(Scope *S, SourceLocation KwLoc, Expr *E);
   ExprResult ActOnCoyieldExpr(Scope *S, SourceLocation KwLoc, Expr *E);
   StmtResult ActOnCoreturnStmt(Scope *S, SourceLocation KwLoc, Expr *E);
 
   ExprResult BuildOperatorCoawaitLookupExpr(Scope *S, SourceLocation Loc);
   ExprResult BuildOperatorCoawaitCall(SourceLocation Loc, Expr *E,
                                       UnresolvedLookupExpr *Lookup);
   ExprResult BuildResolvedCoawaitExpr(SourceLocation KwLoc, Expr *Operand,
                                       Expr *Awaiter, bool IsImplicit = false);
   ExprResult BuildUnresolvedCoawaitExpr(SourceLocation KwLoc, Expr *Operand,
                                         UnresolvedLookupExpr *Lookup);
   ExprResult BuildCoyieldExpr(SourceLocation KwLoc, Expr *E);
   StmtResult BuildCoreturnStmt(SourceLocation KwLoc, Expr *E,
                                bool IsImplicit = false);
   StmtResult BuildCoroutineBodyStmt(CoroutineBodyStmt::CtorArgs);
   bool buildCoroutineParameterMoves(SourceLocation Loc);
   VarDecl *buildCoroutinePromise(SourceLocation Loc);
   void CheckCompletedCoroutineBody(FunctionDecl *FD, Stmt *&Body);
 
   // As a clang extension, enforces that a non-coroutine function must be marked
   // with [[clang::coro_wrapper]] if it returns a type marked with
   // [[clang::coro_return_type]].
   // Expects that FD is not a coroutine.
   void CheckCoroutineWrapper(FunctionDecl *FD);
   /// Lookup 'coroutine_traits' in std namespace and std::experimental
   /// namespace. The namespace found is recorded in Namespace.
   ClassTemplateDecl *lookupCoroutineTraits(SourceLocation KwLoc,
                                            SourceLocation FuncLoc);
   /// Check that the expression co_await promise.final_suspend() shall not be
   /// potentially-throwing.
   bool checkFinalSuspendNoThrow(const Stmt *FinalSuspend);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Scope Specifiers
   /// Implementations are in SemaCXXScopeSpec.cpp
   ///@{
 
 public:
   // Marks SS invalid if it represents an incomplete type.
   bool RequireCompleteDeclContext(CXXScopeSpec &SS, DeclContext *DC);
   // Complete an enum decl, maybe without a scope spec.
   bool RequireCompleteEnumDecl(EnumDecl *D, SourceLocation L,
                                CXXScopeSpec *SS = nullptr);
 
   /// Compute the DeclContext that is associated with the given type.
   ///
   /// \param T the type for which we are attempting to find a DeclContext.
   ///
   /// \returns the declaration context represented by the type T,
   /// or NULL if the declaration context cannot be computed (e.g., because it is
   /// dependent and not the current instantiation).
   DeclContext *computeDeclContext(QualType T);
 
   /// Compute the DeclContext that is associated with the given
   /// scope specifier.
   ///
   /// \param SS the C++ scope specifier as it appears in the source
   ///
   /// \param EnteringContext when true, we will be entering the context of
   /// this scope specifier, so we can retrieve the declaration context of a
   /// class template or class template partial specialization even if it is
   /// not the current instantiation.
   ///
   /// \returns the declaration context represented by the scope specifier @p SS,
   /// or NULL if the declaration context cannot be computed (e.g., because it is
   /// dependent and not the current instantiation).
   DeclContext *computeDeclContext(const CXXScopeSpec &SS,
                                   bool EnteringContext = false);
   bool isDependentScopeSpecifier(const CXXScopeSpec &SS);
 
   /// If the given nested name specifier refers to the current
   /// instantiation, return the declaration that corresponds to that
   /// current instantiation (C++0x [temp.dep.type]p1).
   ///
   /// \param NNS a dependent nested name specifier.
   CXXRecordDecl *getCurrentInstantiationOf(NestedNameSpecifier *NNS);
 
   /// The parser has parsed a global nested-name-specifier '::'.
   ///
   /// \param CCLoc The location of the '::'.
   ///
   /// \param SS The nested-name-specifier, which will be updated in-place
   /// to reflect the parsed nested-name-specifier.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool ActOnCXXGlobalScopeSpecifier(SourceLocation CCLoc, CXXScopeSpec &SS);
 
   /// The parser has parsed a '__super' nested-name-specifier.
   ///
   /// \param SuperLoc The location of the '__super' keyword.
   ///
   /// \param ColonColonLoc The location of the '::'.
   ///
   /// \param SS The nested-name-specifier, which will be updated in-place
   /// to reflect the parsed nested-name-specifier.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool ActOnSuperScopeSpecifier(SourceLocation SuperLoc,
                                 SourceLocation ColonColonLoc, CXXScopeSpec &SS);
 
   /// Determines whether the given declaration is an valid acceptable
   /// result for name lookup of a nested-name-specifier.
   /// \param SD Declaration checked for nested-name-specifier.
   /// \param IsExtension If not null and the declaration is accepted as an
   /// extension, the pointed variable is assigned true.
   bool isAcceptableNestedNameSpecifier(const NamedDecl *SD,
                                        bool *CanCorrect = nullptr);
 
   /// If the given nested-name-specifier begins with a bare identifier
   /// (e.g., Base::), perform name lookup for that identifier as a
   /// nested-name-specifier within the given scope, and return the result of
   /// that name lookup.
   NamedDecl *FindFirstQualifierInScope(Scope *S, NestedNameSpecifier *NNS);
 
   /// Keeps information about an identifier in a nested-name-spec.
   ///
   struct NestedNameSpecInfo {
     /// The type of the object, if we're parsing nested-name-specifier in
     /// a member access expression.
     ParsedType ObjectType;
 
     /// The identifier preceding the '::'.
     IdentifierInfo *Identifier;
 
     /// The location of the identifier.
     SourceLocation IdentifierLoc;
 
     /// The location of the '::'.
     SourceLocation CCLoc;
 
     /// Creates info object for the most typical case.
     NestedNameSpecInfo(IdentifierInfo *II, SourceLocation IdLoc,
                        SourceLocation ColonColonLoc,
                        ParsedType ObjectType = ParsedType())
         : ObjectType(ObjectType), Identifier(II), IdentifierLoc(IdLoc),
           CCLoc(ColonColonLoc) {}
 
     NestedNameSpecInfo(IdentifierInfo *II, SourceLocation IdLoc,
                        SourceLocation ColonColonLoc, QualType ObjectType)
         : ObjectType(ParsedType::make(ObjectType)), Identifier(II),
           IdentifierLoc(IdLoc), CCLoc(ColonColonLoc) {}
   };
 
   /// Build a new nested-name-specifier for "identifier::", as described
   /// by ActOnCXXNestedNameSpecifier.
   ///
   /// \param S Scope in which the nested-name-specifier occurs.
   /// \param IdInfo Parser information about an identifier in the
   ///        nested-name-spec.
   /// \param EnteringContext If true, enter the context specified by the
   ///        nested-name-specifier.
   /// \param SS Optional nested name specifier preceding the identifier.
   /// \param ScopeLookupResult Provides the result of name lookup within the
   ///        scope of the nested-name-specifier that was computed at template
   ///        definition time.
   /// \param ErrorRecoveryLookup Specifies if the method is called to improve
   ///        error recovery and what kind of recovery is performed.
   /// \param IsCorrectedToColon If not null, suggestion of replace '::' -> ':'
   ///        are allowed.  The bool value pointed by this parameter is set to
   ///       'true' if the identifier is treated as if it was followed by ':',
   ///        not '::'.
   /// \param OnlyNamespace If true, only considers namespaces in lookup.
   ///
   /// This routine differs only slightly from ActOnCXXNestedNameSpecifier, in
   /// that it contains an extra parameter \p ScopeLookupResult, which provides
   /// the result of name lookup within the scope of the nested-name-specifier
   /// that was computed at template definition time.
   ///
   /// If ErrorRecoveryLookup is true, then this call is used to improve error
   /// recovery.  This means that it should not emit diagnostics, it should
   /// just return true on failure.  It also means it should only return a valid
   /// scope if it *knows* that the result is correct.  It should not return in a
   /// dependent context, for example. Nor will it extend \p SS with the scope
   /// specifier.
   bool BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
                                    bool EnteringContext, CXXScopeSpec &SS,
                                    NamedDecl *ScopeLookupResult,
                                    bool ErrorRecoveryLookup,
                                    bool *IsCorrectedToColon = nullptr,
                                    bool OnlyNamespace = false);
 
   /// The parser has parsed a nested-name-specifier 'identifier::'.
   ///
   /// \param S The scope in which this nested-name-specifier occurs.
   ///
   /// \param IdInfo Parser information about an identifier in the
   /// nested-name-spec.
   ///
   /// \param EnteringContext Whether we're entering the context nominated by
   /// this nested-name-specifier.
   ///
   /// \param SS The nested-name-specifier, which is both an input
   /// parameter (the nested-name-specifier before this type) and an
   /// output parameter (containing the full nested-name-specifier,
   /// including this new type).
   ///
   /// \param IsCorrectedToColon If not null, suggestions to replace '::' -> ':'
   /// are allowed.  The bool value pointed by this parameter is set to 'true'
   /// if the identifier is treated as if it was followed by ':', not '::'.
   ///
   /// \param OnlyNamespace If true, only considers namespaces in lookup.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool ActOnCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
                                    bool EnteringContext, CXXScopeSpec &SS,
                                    bool *IsCorrectedToColon = nullptr,
                                    bool OnlyNamespace = false);
 
   /// The parser has parsed a nested-name-specifier
   /// 'template[opt] template-name < template-args >::'.
   ///
   /// \param S The scope in which this nested-name-specifier occurs.
   ///
   /// \param SS The nested-name-specifier, which is both an input
   /// parameter (the nested-name-specifier before this type) and an
   /// output parameter (containing the full nested-name-specifier,
   /// including this new type).
   ///
   /// \param TemplateKWLoc the location of the 'template' keyword, if any.
   /// \param TemplateName the template name.
   /// \param TemplateNameLoc The location of the template name.
   /// \param LAngleLoc The location of the opening angle bracket  ('<').
   /// \param TemplateArgs The template arguments.
   /// \param RAngleLoc The location of the closing angle bracket  ('>').
   /// \param CCLoc The location of the '::'.
   ///
   /// \param EnteringContext Whether we're entering the context of the
   /// nested-name-specifier.
   ///
   ///
   /// \returns true if an error occurred, false otherwise.
   bool ActOnCXXNestedNameSpecifier(
       Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
       TemplateTy TemplateName, SourceLocation TemplateNameLoc,
       SourceLocation LAngleLoc, ASTTemplateArgsPtr TemplateArgs,
       SourceLocation RAngleLoc, SourceLocation CCLoc, bool EnteringContext);
 
   bool ActOnCXXNestedNameSpecifierDecltype(CXXScopeSpec &SS, const DeclSpec &DS,
                                            SourceLocation ColonColonLoc);
 
   bool ActOnCXXNestedNameSpecifierIndexedPack(CXXScopeSpec &SS,
                                               const DeclSpec &DS,
                                               SourceLocation ColonColonLoc,
                                               QualType Type);
 
   /// IsInvalidUnlessNestedName - This method is used for error recovery
   /// purposes to determine whether the specified identifier is only valid as
   /// a nested name specifier, for example a namespace name.  It is
   /// conservatively correct to always return false from this method.
   ///
   /// The arguments are the same as those passed to ActOnCXXNestedNameSpecifier.
   bool IsInvalidUnlessNestedName(Scope *S, CXXScopeSpec &SS,
                                  NestedNameSpecInfo &IdInfo,
                                  bool EnteringContext);
 
   /// Given a C++ nested-name-specifier, produce an annotation value
   /// that the parser can use later to reconstruct the given
   /// nested-name-specifier.
   ///
   /// \param SS A nested-name-specifier.
   ///
   /// \returns A pointer containing all of the information in the
   /// nested-name-specifier \p SS.
   void *SaveNestedNameSpecifierAnnotation(CXXScopeSpec &SS);
 
   /// Given an annotation pointer for a nested-name-specifier, restore
   /// the nested-name-specifier structure.
   ///
   /// \param Annotation The annotation pointer, produced by
   /// \c SaveNestedNameSpecifierAnnotation().
   ///
   /// \param AnnotationRange The source range corresponding to the annotation.
   ///
   /// \param SS The nested-name-specifier that will be updated with the contents
   /// of the annotation pointer.
   void RestoreNestedNameSpecifierAnnotation(void *Annotation,
                                             SourceRange AnnotationRange,
                                             CXXScopeSpec &SS);
 
   bool ShouldEnterDeclaratorScope(Scope *S, const CXXScopeSpec &SS);
 
   /// ActOnCXXEnterDeclaratorScope - Called when a C++ scope specifier (global
   /// scope or nested-name-specifier) is parsed, part of a declarator-id.
   /// After this method is called, according to [C++ 3.4.3p3], names should be
   /// looked up in the declarator-id's scope, until the declarator is parsed and
   /// ActOnCXXExitDeclaratorScope is called.
   /// The 'SS' should be a non-empty valid CXXScopeSpec.
   bool ActOnCXXEnterDeclaratorScope(Scope *S, CXXScopeSpec &SS);
 
   /// ActOnCXXExitDeclaratorScope - Called when a declarator that previously
   /// invoked ActOnCXXEnterDeclaratorScope(), is finished. 'SS' is the same
   /// CXXScopeSpec that was passed to ActOnCXXEnterDeclaratorScope as well.
   /// Used to indicate that names should revert to being looked up in the
   /// defining scope.
   void ActOnCXXExitDeclaratorScope(Scope *S, const CXXScopeSpec &SS);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Declarations
   /// Implementations are in SemaDecl.cpp
   ///@{
 
 public:
   IdentifierResolver IdResolver;
 
   /// The index of the first InventedParameterInfo that refers to the current
   /// context.
   unsigned InventedParameterInfosStart = 0;
 
   /// A RAII object to temporarily push a declaration context.
   class ContextRAII {
   private:
     Sema &S;
     DeclContext *SavedContext;
     ProcessingContextState SavedContextState;
     QualType SavedCXXThisTypeOverride;
     unsigned SavedFunctionScopesStart;
     unsigned SavedInventedParameterInfosStart;
 
   public:
     ContextRAII(Sema &S, DeclContext *ContextToPush, bool NewThisContext = true)
         : S(S), SavedContext(S.CurContext),
           SavedContextState(S.DelayedDiagnostics.pushUndelayed()),
           SavedCXXThisTypeOverride(S.CXXThisTypeOverride),
           SavedFunctionScopesStart(S.FunctionScopesStart),
           SavedInventedParameterInfosStart(S.InventedParameterInfosStart) {
       assert(ContextToPush && "pushing null context");
       S.CurContext = ContextToPush;
       if (NewThisContext)
         S.CXXThisTypeOverride = QualType();
       // Any saved FunctionScopes do not refer to this context.
       S.FunctionScopesStart = S.FunctionScopes.size();
       S.InventedParameterInfosStart = S.InventedParameterInfos.size();
     }
 
     void pop() {
       if (!SavedContext)
         return;
       S.CurContext = SavedContext;
       S.DelayedDiagnostics.popUndelayed(SavedContextState);
       S.CXXThisTypeOverride = SavedCXXThisTypeOverride;
       S.FunctionScopesStart = SavedFunctionScopesStart;
       S.InventedParameterInfosStart = SavedInventedParameterInfosStart;
       SavedContext = nullptr;
     }
 
     ~ContextRAII() { pop(); }
   };
 
   void DiagnoseInvalidJumps(Stmt *Body);
 
   /// The function definitions which were renamed as part of typo-correction
   /// to match their respective declarations. We want to keep track of them
   /// to ensure that we don't emit a "redefinition" error if we encounter a
   /// correctly named definition after the renamed definition.
   llvm::SmallPtrSet<const NamedDecl *, 4> TypoCorrectedFunctionDefinitions;
 
   /// A cache of the flags available in enumerations with the flag_bits
   /// attribute.
   mutable llvm::DenseMap<const EnumDecl *, llvm::APInt> FlagBitsCache;
 
   /// WeakUndeclaredIdentifiers - Identifiers contained in \#pragma weak before
   /// declared. Rare. May alias another identifier, declared or undeclared.
   ///
   /// For aliases, the target identifier is used as a key for eventual
   /// processing when the target is declared. For the single-identifier form,
   /// the sole identifier is used as the key. Each entry is a `SetVector`
   /// (ordered by parse order) of aliases (identified by the alias name) in case
   /// of multiple aliases to the same undeclared identifier.
   llvm::MapVector<
       IdentifierInfo *,
       llvm::SetVector<
           WeakInfo, llvm::SmallVector<WeakInfo, 1u>,
           llvm::SmallDenseSet<WeakInfo, 2u, WeakInfo::DenseMapInfoByAliasOnly>>>
       WeakUndeclaredIdentifiers;
 
   /// ExtnameUndeclaredIdentifiers - Identifiers contained in
   /// \#pragma redefine_extname before declared.  Used in Solaris system headers
   /// to define functions that occur in multiple standards to call the version
   /// in the currently selected standard.
   llvm::DenseMap<IdentifierInfo *, AsmLabelAttr *> ExtnameUndeclaredIdentifiers;
 
   /// Set containing all typedefs that are likely unused.
   llvm::SmallSetVector<const TypedefNameDecl *, 4>
       UnusedLocalTypedefNameCandidates;
 
   typedef LazyVector<const DeclaratorDecl *, ExternalSemaSource,
                      &ExternalSemaSource::ReadUnusedFileScopedDecls, 2, 2>
       UnusedFileScopedDeclsType;
 
   /// The set of file scoped decls seen so far that have not been used
   /// and must warn if not used. Only contains the first declaration.
   UnusedFileScopedDeclsType UnusedFileScopedDecls;
 
   typedef LazyVector<VarDecl *, ExternalSemaSource,
                      &ExternalSemaSource::ReadTentativeDefinitions, 2, 2>
       TentativeDefinitionsType;
 
   /// All the tentative definitions encountered in the TU.
   TentativeDefinitionsType TentativeDefinitions;
 
   /// All the external declarations encoutered and used in the TU.
   SmallVector<DeclaratorDecl *, 4> ExternalDeclarations;
 
   /// Generally null except when we temporarily switch decl contexts,
   /// like in \see SemaObjC::ActOnObjCTemporaryExitContainerContext.
   DeclContext *OriginalLexicalContext;
 
   /// Is the module scope we are in a C++ Header Unit?
   bool currentModuleIsHeaderUnit() const {
     return ModuleScopes.empty() ? false
                                 : ModuleScopes.back().Module->isHeaderUnit();
   }
 
   /// Get the module owning an entity.
   Module *getOwningModule(const Decl *Entity) {
     return Entity->getOwningModule();
   }
 
   DeclGroupPtrTy ConvertDeclToDeclGroup(Decl *Ptr, Decl *OwnedType = nullptr);
 
   /// If the identifier refers to a type name within this scope,
   /// return the declaration of that type.
   ///
   /// This routine performs ordinary name lookup of the identifier II
   /// within the given scope, with optional C++ scope specifier SS, to
   /// determine whether the name refers to a type. If so, returns an
   /// opaque pointer (actually a QualType) corresponding to that
   /// type. Otherwise, returns NULL.
   ParsedType getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
                          Scope *S, CXXScopeSpec *SS = nullptr,
                          bool isClassName = false, bool HasTrailingDot = false,
                          ParsedType ObjectType = nullptr,
                          bool IsCtorOrDtorName = false,
                          bool WantNontrivialTypeSourceInfo = false,
                          bool IsClassTemplateDeductionContext = true,
                          ImplicitTypenameContext AllowImplicitTypename =
                              ImplicitTypenameContext::No,
                          IdentifierInfo **CorrectedII = nullptr);
 
   /// isTagName() - This method is called *for error recovery purposes only*
   /// to determine if the specified name is a valid tag name ("struct foo").  If
   /// so, this returns the TST for the tag corresponding to it (TST_enum,
   /// TST_union, TST_struct, TST_interface, TST_class).  This is used to
   /// diagnose cases in C where the user forgot to specify the tag.
   TypeSpecifierType isTagName(IdentifierInfo &II, Scope *S);
 
   /// isMicrosoftMissingTypename - In Microsoft mode, within class scope,
   /// if a CXXScopeSpec's type is equal to the type of one of the base classes
   /// then downgrade the missing typename error to a warning.
   /// This is needed for MSVC compatibility; Example:
   /// @code
   /// template<class T> class A {
   /// public:
   ///   typedef int TYPE;
   /// };
   /// template<class T> class B : public A<T> {
   /// public:
   ///   A<T>::TYPE a; // no typename required because A<T> is a base class.
   /// };
   /// @endcode
   bool isMicrosoftMissingTypename(const CXXScopeSpec *SS, Scope *S);
   void DiagnoseUnknownTypeName(IdentifierInfo *&II, SourceLocation IILoc,
                                Scope *S, CXXScopeSpec *SS,
                                ParsedType &SuggestedType,
                                bool IsTemplateName = false);
 
   /// Attempt to behave like MSVC in situations where lookup of an unqualified
   /// type name has failed in a dependent context. In these situations, we
   /// automatically form a DependentTypeName that will retry lookup in a related
   /// scope during instantiation.
   ParsedType ActOnMSVCUnknownTypeName(const IdentifierInfo &II,
                                       SourceLocation NameLoc,
                                       bool IsTemplateTypeArg);
 
   /// Describes the result of the name lookup and resolution performed
   /// by \c ClassifyName().
   enum NameClassificationKind {
     /// This name is not a type or template in this context, but might be
     /// something else.
     NC_Unknown,
     /// Classification failed; an error has been produced.
     NC_Error,
     /// The name has been typo-corrected to a keyword.
     NC_Keyword,
     /// The name was classified as a type.
     NC_Type,
     /// The name was classified as a specific non-type, non-template
     /// declaration. ActOnNameClassifiedAsNonType should be called to
     /// convert the declaration to an expression.
     NC_NonType,
     /// The name was classified as an ADL-only function name.
     /// ActOnNameClassifiedAsUndeclaredNonType should be called to convert the
     /// result to an expression.
     NC_UndeclaredNonType,
     /// The name denotes a member of a dependent type that could not be
     /// resolved. ActOnNameClassifiedAsDependentNonType should be called to
     /// convert the result to an expression.
     NC_DependentNonType,
     /// The name was classified as an overload set, and an expression
     /// representing that overload set has been formed.
     /// ActOnNameClassifiedAsOverloadSet should be called to form a suitable
     /// expression referencing the overload set.
     NC_OverloadSet,
     /// The name was classified as a template whose specializations are types.
     NC_TypeTemplate,
     /// The name was classified as a variable template name.
     NC_VarTemplate,
     /// The name was classified as a function template name.
     NC_FunctionTemplate,
     /// The name was classified as an ADL-only function template name.
     NC_UndeclaredTemplate,
     /// The name was classified as a concept name.
     NC_Concept,
   };
 
   class NameClassification {
     NameClassificationKind Kind;
     union {
       ExprResult Expr;
       NamedDecl *NonTypeDecl;
       TemplateName Template;
       ParsedType Type;
     };
 
     explicit NameClassification(NameClassificationKind Kind) : Kind(Kind) {}
 
   public:
     NameClassification(ParsedType Type) : Kind(NC_Type), Type(Type) {}
 
     NameClassification(const IdentifierInfo *Keyword) : Kind(NC_Keyword) {}
 
     static NameClassification Error() { return NameClassification(NC_Error); }
 
     static NameClassification Unknown() {
       return NameClassification(NC_Unknown);
     }
 
     static NameClassification OverloadSet(ExprResult E) {
       NameClassification Result(NC_OverloadSet);
       Result.Expr = E;
       return Result;
     }
 
     static NameClassification NonType(NamedDecl *D) {
       NameClassification Result(NC_NonType);
       Result.NonTypeDecl = D;
       return Result;
     }
 
     static NameClassification UndeclaredNonType() {
       return NameClassification(NC_UndeclaredNonType);
     }
 
     static NameClassification DependentNonType() {
       return NameClassification(NC_DependentNonType);
     }
 
     static NameClassification TypeTemplate(TemplateName Name) {
       NameClassification Result(NC_TypeTemplate);
       Result.Template = Name;
       return Result;
     }
 
     static NameClassification VarTemplate(TemplateName Name) {
       NameClassification Result(NC_VarTemplate);
       Result.Template = Name;
       return Result;
     }
 
     static NameClassification FunctionTemplate(TemplateName Name) {
       NameClassification Result(NC_FunctionTemplate);
       Result.Template = Name;
       return Result;
     }
 
     static NameClassification Concept(TemplateName Name) {
       NameClassification Result(NC_Concept);
       Result.Template = Name;
       return Result;
     }
 
     static NameClassification UndeclaredTemplate(TemplateName Name) {
       NameClassification Result(NC_UndeclaredTemplate);
       Result.Template = Name;
       return Result;
     }
 
     NameClassificationKind getKind() const { return Kind; }
 
     ExprResult getExpression() const {
       assert(Kind == NC_OverloadSet);
       return Expr;
     }
 
     ParsedType getType() const {
       assert(Kind == NC_Type);
       return Type;
     }
 
     NamedDecl *getNonTypeDecl() const {
       assert(Kind == NC_NonType);
       return NonTypeDecl;
     }
 
     TemplateName getTemplateName() const {
       assert(Kind == NC_TypeTemplate || Kind == NC_FunctionTemplate ||
              Kind == NC_VarTemplate || Kind == NC_Concept ||
              Kind == NC_UndeclaredTemplate);
       return Template;
     }
 
     TemplateNameKind getTemplateNameKind() const {
       switch (Kind) {
       case NC_TypeTemplate:
         return TNK_Type_template;
       case NC_FunctionTemplate:
         return TNK_Function_template;
       case NC_VarTemplate:
         return TNK_Var_template;
       case NC_Concept:
         return TNK_Concept_template;
       case NC_UndeclaredTemplate:
         return TNK_Undeclared_template;
       default:
         llvm_unreachable("unsupported name classification.");
       }
     }
   };
 
   /// Perform name lookup on the given name, classifying it based on
   /// the results of name lookup and the following token.
   ///
   /// This routine is used by the parser to resolve identifiers and help direct
   /// parsing. When the identifier cannot be found, this routine will attempt
   /// to correct the typo and classify based on the resulting name.
   ///
   /// \param S The scope in which we're performing name lookup.
   ///
   /// \param SS The nested-name-specifier that precedes the name.
   ///
   /// \param Name The identifier. If typo correction finds an alternative name,
   /// this pointer parameter will be updated accordingly.
   ///
   /// \param NameLoc The location of the identifier.
   ///
   /// \param NextToken The token following the identifier. Used to help
   /// disambiguate the name.
   ///
   /// \param CCC The correction callback, if typo correction is desired.
   NameClassification ClassifyName(Scope *S, CXXScopeSpec &SS,
                                   IdentifierInfo *&Name, SourceLocation NameLoc,
                                   const Token &NextToken,
                                   CorrectionCandidateCallback *CCC = nullptr);
 
   /// Act on the result of classifying a name as an undeclared (ADL-only)
   /// non-type declaration.
   ExprResult ActOnNameClassifiedAsUndeclaredNonType(IdentifierInfo *Name,
                                                     SourceLocation NameLoc);
   /// Act on the result of classifying a name as an undeclared member of a
   /// dependent base class.
   ExprResult ActOnNameClassifiedAsDependentNonType(const CXXScopeSpec &SS,
                                                    IdentifierInfo *Name,
                                                    SourceLocation NameLoc,
                                                    bool IsAddressOfOperand);
   /// Act on the result of classifying a name as a specific non-type
   /// declaration.
   ExprResult ActOnNameClassifiedAsNonType(Scope *S, const CXXScopeSpec &SS,
                                           NamedDecl *Found,
                                           SourceLocation NameLoc,
                                           const Token &NextToken);
   /// Act on the result of classifying a name as an overload set.
   ExprResult ActOnNameClassifiedAsOverloadSet(Scope *S, Expr *OverloadSet);
 
   /// Describes the detailed kind of a template name. Used in diagnostics.
   enum class TemplateNameKindForDiagnostics {
     ClassTemplate,
     FunctionTemplate,
     VarTemplate,
     AliasTemplate,
     TemplateTemplateParam,
     Concept,
     DependentTemplate
   };
   TemplateNameKindForDiagnostics
   getTemplateNameKindForDiagnostics(TemplateName Name);
 
   /// Determine whether it's plausible that E was intended to be a
   /// template-name.
   bool mightBeIntendedToBeTemplateName(ExprResult E, bool &Dependent) {
     if (!getLangOpts().CPlusPlus || E.isInvalid())
       return false;
     Dependent = false;
     if (auto *DRE = dyn_cast<DeclRefExpr>(E.get()))
       return !DRE->hasExplicitTemplateArgs();
     if (auto *ME = dyn_cast<MemberExpr>(E.get()))
       return !ME->hasExplicitTemplateArgs();
     Dependent = true;
     if (auto *DSDRE = dyn_cast<DependentScopeDeclRefExpr>(E.get()))
       return !DSDRE->hasExplicitTemplateArgs();
     if (auto *DSME = dyn_cast<CXXDependentScopeMemberExpr>(E.get()))
       return !DSME->hasExplicitTemplateArgs();
     // Any additional cases recognized here should also be handled by
     // diagnoseExprIntendedAsTemplateName.
     return false;
   }
 
   void warnOnReservedIdentifier(const NamedDecl *D);
 
   Decl *ActOnDeclarator(Scope *S, Declarator &D);
 
   NamedDecl *HandleDeclarator(Scope *S, Declarator &D,
                               MultiTemplateParamsArg TemplateParameterLists);
 
   /// Attempt to fold a variable-sized type to a constant-sized type, returning
   /// true if we were successful.
   bool tryToFixVariablyModifiedVarType(TypeSourceInfo *&TInfo, QualType &T,
                                        SourceLocation Loc,
                                        unsigned FailedFoldDiagID);
 
   /// Register the given locally-scoped extern "C" declaration so
   /// that it can be found later for redeclarations. We include any extern "C"
   /// declaration that is not visible in the translation unit here, not just
   /// function-scope declarations.
   void RegisterLocallyScopedExternCDecl(NamedDecl *ND, Scope *S);
 
   /// DiagnoseClassNameShadow - Implement C++ [class.mem]p13:
   ///   If T is the name of a class, then each of the following shall have a
   ///   name different from T:
   ///     - every static data member of class T;
   ///     - every member function of class T
   ///     - every member of class T that is itself a type;
   /// \returns true if the declaration name violates these rules.
   bool DiagnoseClassNameShadow(DeclContext *DC, DeclarationNameInfo Info);
 
   /// Diagnose a declaration whose declarator-id has the given
   /// nested-name-specifier.
   ///
   /// \param SS The nested-name-specifier of the declarator-id.
   ///
   /// \param DC The declaration context to which the nested-name-specifier
   /// resolves.
   ///
   /// \param Name The name of the entity being declared.
   ///
   /// \param Loc The location of the name of the entity being declared.
   ///
   /// \param IsMemberSpecialization Whether we are declaring a member
   /// specialization.
   ///
   /// \param TemplateId The template-id, if any.
   ///
   /// \returns true if we cannot safely recover from this error, false
   /// otherwise.
   bool diagnoseQualifiedDeclaration(CXXScopeSpec &SS, DeclContext *DC,
                                     DeclarationName Name, SourceLocation Loc,
                                     TemplateIdAnnotation *TemplateId,
                                     bool IsMemberSpecialization);
 
   bool checkPointerAuthEnabled(SourceLocation Loc, SourceRange Range);
 
   bool checkConstantPointerAuthKey(Expr *keyExpr, unsigned &key);
 
   /// Diagnose function specifiers on a declaration of an identifier that
   /// does not identify a function.
   void DiagnoseFunctionSpecifiers(const DeclSpec &DS);
 
   /// Return the declaration shadowed by the given typedef \p D, or null
   /// if it doesn't shadow any declaration or shadowing warnings are disabled.
   NamedDecl *getShadowedDeclaration(const TypedefNameDecl *D,
                                     const LookupResult &R);
 
   /// Return the declaration shadowed by the given variable \p D, or null
   /// if it doesn't shadow any declaration or shadowing warnings are disabled.
   NamedDecl *getShadowedDeclaration(const VarDecl *D, const LookupResult &R);
 
   /// Return the declaration shadowed by the given variable \p D, or null
   /// if it doesn't shadow any declaration or shadowing warnings are disabled.
   NamedDecl *getShadowedDeclaration(const BindingDecl *D,
                                     const LookupResult &R);
   /// Diagnose variable or built-in function shadowing.  Implements
   /// -Wshadow.
   ///
   /// This method is called whenever a VarDecl is added to a "useful"
   /// scope.
   ///
   /// \param ShadowedDecl the declaration that is shadowed by the given variable
   /// \param R the lookup of the name
   void CheckShadow(NamedDecl *D, NamedDecl *ShadowedDecl,
                    const LookupResult &R);
 
   /// Check -Wshadow without the advantage of a previous lookup.
   void CheckShadow(Scope *S, VarDecl *D);
 
   /// Warn if 'E', which is an expression that is about to be modified, refers
   /// to a shadowing declaration.
   void CheckShadowingDeclModification(Expr *E, SourceLocation Loc);
 
   /// Diagnose shadowing for variables shadowed in the lambda record \p LambdaRD
   /// when these variables are captured by the lambda.
   void DiagnoseShadowingLambdaDecls(const sema::LambdaScopeInfo *LSI);
 
   void handleTagNumbering(const TagDecl *Tag, Scope *TagScope);
   void setTagNameForLinkagePurposes(TagDecl *TagFromDeclSpec,
                                     TypedefNameDecl *NewTD);
   void CheckTypedefForVariablyModifiedType(Scope *S, TypedefNameDecl *D);
   NamedDecl *ActOnTypedefDeclarator(Scope *S, Declarator &D, DeclContext *DC,
                                     TypeSourceInfo *TInfo,
                                     LookupResult &Previous);
 
   /// ActOnTypedefNameDecl - Perform semantic checking for a declaration which
   /// declares a typedef-name, either using the 'typedef' type specifier or via
   /// a C++0x [dcl.typedef]p2 alias-declaration: 'using T = A;'.
   NamedDecl *ActOnTypedefNameDecl(Scope *S, DeclContext *DC, TypedefNameDecl *D,
                                   LookupResult &Previous, bool &Redeclaration);
   NamedDecl *ActOnVariableDeclarator(
       Scope *S, Declarator &D, DeclContext *DC, TypeSourceInfo *TInfo,
       LookupResult &Previous, MultiTemplateParamsArg TemplateParamLists,
       bool &AddToScope, ArrayRef<BindingDecl *> Bindings = std::nullopt);
 
   /// Perform semantic checking on a newly-created variable
   /// declaration.
   ///
   /// This routine performs all of the type-checking required for a
   /// variable declaration once it has been built. It is used both to
   /// check variables after they have been parsed and their declarators
   /// have been translated into a declaration, and to check variables
   /// that have been instantiated from a template.
   ///
   /// Sets NewVD->isInvalidDecl() if an error was encountered.
   ///
   /// Returns true if the variable declaration is a redeclaration.
   bool CheckVariableDeclaration(VarDecl *NewVD, LookupResult &Previous);
   void CheckVariableDeclarationType(VarDecl *NewVD);
   void CheckCompleteVariableDeclaration(VarDecl *VD);
 
   NamedDecl *ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
                                      TypeSourceInfo *TInfo,
                                      LookupResult &Previous,
                                      MultiTemplateParamsArg TemplateParamLists,
                                      bool &AddToScope);
 
   /// AddOverriddenMethods - See if a method overrides any in the base classes,
   /// and if so, check that it's a valid override and remember it.
   bool AddOverriddenMethods(CXXRecordDecl *DC, CXXMethodDecl *MD);
 
   /// Perform semantic checking of a new function declaration.
   ///
   /// Performs semantic analysis of the new function declaration
   /// NewFD. This routine performs all semantic checking that does not
   /// require the actual declarator involved in the declaration, and is
   /// used both for the declaration of functions as they are parsed
   /// (called via ActOnDeclarator) and for the declaration of functions
   /// that have been instantiated via C++ template instantiation (called
   /// via InstantiateDecl).
   ///
   /// \param IsMemberSpecialization whether this new function declaration is
   /// a member specialization (that replaces any definition provided by the
   /// previous declaration).
   ///
   /// This sets NewFD->isInvalidDecl() to true if there was an error.
   ///
   /// \returns true if the function declaration is a redeclaration.
   bool CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
                                 LookupResult &Previous,
                                 bool IsMemberSpecialization, bool DeclIsDefn);
 
   /// Checks if the new declaration declared in dependent context must be
   /// put in the same redeclaration chain as the specified declaration.
   ///
   /// \param D Declaration that is checked.
   /// \param PrevDecl Previous declaration found with proper lookup method for
   ///                 the same declaration name.
   /// \returns True if D must be added to the redeclaration chain which PrevDecl
   ///          belongs to.
   bool shouldLinkDependentDeclWithPrevious(Decl *D, Decl *OldDecl);
 
   /// Determines if we can perform a correct type check for \p D as a
   /// redeclaration of \p PrevDecl. If not, we can generally still perform a
   /// best-effort check.
   ///
   /// \param NewD The new declaration.
   /// \param OldD The old declaration.
   /// \param NewT The portion of the type of the new declaration to check.
   /// \param OldT The portion of the type of the old declaration to check.
   bool canFullyTypeCheckRedeclaration(ValueDecl *NewD, ValueDecl *OldD,
                                       QualType NewT, QualType OldT);
   void CheckMain(FunctionDecl *FD, const DeclSpec &D);
   void CheckMSVCRTEntryPoint(FunctionDecl *FD);
 
   /// Returns an implicit CodeSegAttr if a __declspec(code_seg) is found on a
   /// containing class. Otherwise it will return implicit SectionAttr if the
   /// function is a definition and there is an active value on CodeSegStack
   /// (from the current #pragma code-seg value).
   ///
   /// \param FD Function being declared.
   /// \param IsDefinition Whether it is a definition or just a declaration.
   /// \returns A CodeSegAttr or SectionAttr to apply to the function or
   ///          nullptr if no attribute should be added.
   Attr *getImplicitCodeSegOrSectionAttrForFunction(const FunctionDecl *FD,
                                                    bool IsDefinition);
 
   /// Common checks for a parameter-declaration that should apply to both
   /// function parameters and non-type template parameters.
   void CheckFunctionOrTemplateParamDeclarator(Scope *S, Declarator &D);
 
   /// ActOnParamDeclarator - Called from Parser::ParseFunctionDeclarator()
   /// to introduce parameters into function prototype scope.
   Decl *ActOnParamDeclarator(Scope *S, Declarator &D,
                              SourceLocation ExplicitThisLoc = {});
 
   /// Synthesizes a variable for a parameter arising from a
   /// typedef.
   ParmVarDecl *BuildParmVarDeclForTypedef(DeclContext *DC, SourceLocation Loc,
                                           QualType T);
   ParmVarDecl *CheckParameter(DeclContext *DC, SourceLocation StartLoc,
                               SourceLocation NameLoc,
                               const IdentifierInfo *Name, QualType T,
                               TypeSourceInfo *TSInfo, StorageClass SC);
 
   // Contexts where using non-trivial C union types can be disallowed. This is
   // passed to err_non_trivial_c_union_in_invalid_context.
   enum NonTrivialCUnionContext {
     // Function parameter.
     NTCUC_FunctionParam,
     // Function return.
     NTCUC_FunctionReturn,
     // Default-initialized object.
     NTCUC_DefaultInitializedObject,
     // Variable with automatic storage duration.
     NTCUC_AutoVar,
     // Initializer expression that might copy from another object.
     NTCUC_CopyInit,
     // Assignment.
     NTCUC_Assignment,
     // Compound literal.
     NTCUC_CompoundLiteral,
     // Block capture.
     NTCUC_BlockCapture,
     // lvalue-to-rvalue conversion of volatile type.
     NTCUC_LValueToRValueVolatile,
   };
 
   /// Emit diagnostics if the initializer or any of its explicit or
   /// implicitly-generated subexpressions require copying or
   /// default-initializing a type that is or contains a C union type that is
   /// non-trivial to copy or default-initialize.
   void checkNonTrivialCUnionInInitializer(const Expr *Init, SourceLocation Loc);
 
   // These flags are passed to checkNonTrivialCUnion.
   enum NonTrivialCUnionKind {
     NTCUK_Init = 0x1,
     NTCUK_Destruct = 0x2,
     NTCUK_Copy = 0x4,
   };
 
   /// Emit diagnostics if a non-trivial C union type or a struct that contains
   /// a non-trivial C union is used in an invalid context.
   void checkNonTrivialCUnion(QualType QT, SourceLocation Loc,
                              NonTrivialCUnionContext UseContext,
                              unsigned NonTrivialKind);
 
   /// AddInitializerToDecl - Adds the initializer Init to the
   /// declaration dcl. If DirectInit is true, this is C++ direct
   /// initialization rather than copy initialization.
   void AddInitializerToDecl(Decl *dcl, Expr *init, bool DirectInit);
   void ActOnUninitializedDecl(Decl *dcl);
 
   /// ActOnInitializerError - Given that there was an error parsing an
   /// initializer for the given declaration, try to at least re-establish
   /// invariants such as whether a variable's type is either dependent or
   /// complete.
   void ActOnInitializerError(Decl *Dcl);
 
   void ActOnCXXForRangeDecl(Decl *D);
   StmtResult ActOnCXXForRangeIdentifier(Scope *S, SourceLocation IdentLoc,
                                         IdentifierInfo *Ident,
                                         ParsedAttributes &Attrs);
 
   /// Check if VD needs to be dllexport/dllimport due to being in a
   /// dllexport/import function.
   void CheckStaticLocalForDllExport(VarDecl *VD);
   void CheckThreadLocalForLargeAlignment(VarDecl *VD);
 
   /// FinalizeDeclaration - called by ParseDeclarationAfterDeclarator to perform
   /// any semantic actions necessary after any initializer has been attached.
   void FinalizeDeclaration(Decl *D);
   DeclGroupPtrTy FinalizeDeclaratorGroup(Scope *S, const DeclSpec &DS,
                                          ArrayRef<Decl *> Group);
 
   /// BuildDeclaratorGroup - convert a list of declarations into a declaration
   /// group, performing any necessary semantic checking.
   DeclGroupPtrTy BuildDeclaratorGroup(MutableArrayRef<Decl *> Group);
 
   /// Should be called on all declarations that might have attached
   /// documentation comments.
   void ActOnDocumentableDecl(Decl *D);
   void ActOnDocumentableDecls(ArrayRef<Decl *> Group);
 
   enum class FnBodyKind {
     /// C++26 [dcl.fct.def.general]p1
     /// function-body:
     ///   ctor-initializer[opt] compound-statement
     ///   function-try-block
     Other,
     ///   = default ;
     Default,
     ///   deleted-function-body
     ///
     /// deleted-function-body:
     ///   = delete ;
     ///   = delete ( unevaluated-string ) ;
     Delete
   };
 
   void ActOnFinishKNRParamDeclarations(Scope *S, Declarator &D,
                                        SourceLocation LocAfterDecls);
   void CheckForFunctionRedefinition(
       FunctionDecl *FD, const FunctionDecl *EffectiveDefinition = nullptr,
       SkipBodyInfo *SkipBody = nullptr);
   Decl *ActOnStartOfFunctionDef(Scope *S, Declarator &D,
                                 MultiTemplateParamsArg TemplateParamLists,
                                 SkipBodyInfo *SkipBody = nullptr,
                                 FnBodyKind BodyKind = FnBodyKind::Other);
   Decl *ActOnStartOfFunctionDef(Scope *S, Decl *D,
                                 SkipBodyInfo *SkipBody = nullptr,
                                 FnBodyKind BodyKind = FnBodyKind::Other);
   void applyFunctionAttributesBeforeParsingBody(Decl *FD);
 
   /// Determine whether we can delay parsing the body of a function or
   /// function template until it is used, assuming we don't care about emitting
   /// code for that function.
   ///
   /// This will be \c false if we may need the body of the function in the
   /// middle of parsing an expression (where it's impractical to switch to
   /// parsing a different function), for instance, if it's constexpr in C++11
   /// or has an 'auto' return type in C++14. These cases are essentially bugs.
   bool canDelayFunctionBody(const Declarator &D);
 
   /// Determine whether we can skip parsing the body of a function
   /// definition, assuming we don't care about analyzing its body or emitting
   /// code for that function.
   ///
   /// This will be \c false only if we may need the body of the function in
   /// order to parse the rest of the program (for instance, if it is
   /// \c constexpr in C++11 or has an 'auto' return type in C++14).
   bool canSkipFunctionBody(Decl *D);
 
   /// Given the set of return statements within a function body,
   /// compute the variables that are subject to the named return value
   /// optimization.
   ///
   /// Each of the variables that is subject to the named return value
   /// optimization will be marked as NRVO variables in the AST, and any
   /// return statement that has a marked NRVO variable as its NRVO candidate can
   /// use the named return value optimization.
   ///
   /// This function applies a very simplistic algorithm for NRVO: if every
   /// return statement in the scope of a variable has the same NRVO candidate,
   /// that candidate is an NRVO variable.
   void computeNRVO(Stmt *Body, sema::FunctionScopeInfo *Scope);
   Decl *ActOnFinishFunctionBody(Decl *Decl, Stmt *Body);
   Decl *ActOnFinishFunctionBody(Decl *Decl, Stmt *Body, bool IsInstantiation);
   Decl *ActOnSkippedFunctionBody(Decl *Decl);
   void ActOnFinishInlineFunctionDef(FunctionDecl *D);
 
   /// ActOnFinishDelayedAttribute - Invoked when we have finished parsing an
   /// attribute for which parsing is delayed.
   void ActOnFinishDelayedAttribute(Scope *S, Decl *D, ParsedAttributes &Attrs);
 
   /// Diagnose any unused parameters in the given sequence of
   /// ParmVarDecl pointers.
   void DiagnoseUnusedParameters(ArrayRef<ParmVarDecl *> Parameters);
 
   /// Diagnose whether the size of parameters or return value of a
   /// function or obj-c method definition is pass-by-value and larger than a
   /// specified threshold.
   void
   DiagnoseSizeOfParametersAndReturnValue(ArrayRef<ParmVarDecl *> Parameters,
                                          QualType ReturnTy, NamedDecl *D);
 
   Decl *ActOnFileScopeAsmDecl(Expr *expr, SourceLocation AsmLoc,
                               SourceLocation RParenLoc);
 
   TopLevelStmtDecl *ActOnStartTopLevelStmtDecl(Scope *S);
   void ActOnFinishTopLevelStmtDecl(TopLevelStmtDecl *D, Stmt *Statement);
 
   void ActOnPopScope(SourceLocation Loc, Scope *S);
 
   /// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
   /// no declarator (e.g. "struct foo;") is parsed.
   Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                    const ParsedAttributesView &DeclAttrs,
                                    RecordDecl *&AnonRecord);
 
   /// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
   /// no declarator (e.g. "struct foo;") is parsed. It also accepts template
   /// parameters to cope with template friend declarations.
   Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                    const ParsedAttributesView &DeclAttrs,
                                    MultiTemplateParamsArg TemplateParams,
                                    bool IsExplicitInstantiation,
                                    RecordDecl *&AnonRecord);
 
   /// BuildAnonymousStructOrUnion - Handle the declaration of an
   /// anonymous structure or union. Anonymous unions are a C++ feature
   /// (C++ [class.union]) and a C11 feature; anonymous structures
   /// are a C11 feature and GNU C++ extension.
   Decl *BuildAnonymousStructOrUnion(Scope *S, DeclSpec &DS, AccessSpecifier AS,
                                     RecordDecl *Record,
                                     const PrintingPolicy &Policy);
 
   /// Called once it is known whether
   /// a tag declaration is an anonymous union or struct.
   void ActOnDefinedDeclarationSpecifier(Decl *D);
 
   /// Emit diagnostic warnings for placeholder members.
   /// We can only do that after the class is fully constructed,
   /// as anonymous union/structs can insert placeholders
   /// in their parent scope (which might be a Record).
   void DiagPlaceholderFieldDeclDefinitions(RecordDecl *Record);
 
   /// BuildMicrosoftCAnonymousStruct - Handle the declaration of an
   /// Microsoft C anonymous structure.
   /// Ref: http://msdn.microsoft.com/en-us/library/z2cx9y4f.aspx
   /// Example:
   ///
   /// struct A { int a; };
   /// struct B { struct A; int b; };
   ///
   /// void foo() {
   ///   B var;
   ///   var.a = 3;
   /// }
   Decl *BuildMicrosoftCAnonymousStruct(Scope *S, DeclSpec &DS,
                                        RecordDecl *Record);
 
   /// Common ways to introduce type names without a tag for use in diagnostics.
   /// Keep in sync with err_tag_reference_non_tag.
   enum NonTagKind {
     NTK_NonStruct,
     NTK_NonClass,
     NTK_NonUnion,
     NTK_NonEnum,
     NTK_Typedef,
     NTK_TypeAlias,
     NTK_Template,
     NTK_TypeAliasTemplate,
     NTK_TemplateTemplateArgument,
   };
 
   /// Given a non-tag type declaration, returns an enum useful for indicating
   /// what kind of non-tag type this is.
   NonTagKind getNonTagTypeDeclKind(const Decl *D, TagTypeKind TTK);
 
   /// Determine whether a tag with a given kind is acceptable
   /// as a redeclaration of the given tag declaration.
   ///
   /// \returns true if the new tag kind is acceptable, false otherwise.
   bool isAcceptableTagRedeclaration(const TagDecl *Previous, TagTypeKind NewTag,
                                     bool isDefinition, SourceLocation NewTagLoc,
                                     const IdentifierInfo *Name);
 
   enum OffsetOfKind {
     // Not parsing a type within __builtin_offsetof.
     OOK_Outside,
     // Parsing a type within __builtin_offsetof.
     OOK_Builtin,
     // Parsing a type within macro "offsetof", defined in __buitin_offsetof
     // To improve our diagnostic message.
     OOK_Macro,
   };
 
   /// This is invoked when we see 'struct foo' or 'struct {'.  In the
   /// former case, Name will be non-null.  In the later case, Name will be null.
   /// TagSpec indicates what kind of tag this is. TUK indicates whether this is
   /// a reference/declaration/definition of a tag.
   ///
   /// \param IsTypeSpecifier \c true if this is a type-specifier (or
   /// trailing-type-specifier) other than one in an alias-declaration.
   ///
   /// \param SkipBody If non-null, will be set to indicate if the caller should
   /// skip the definition of this tag and treat it as if it were a declaration.
   DeclResult ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                       SourceLocation KWLoc, CXXScopeSpec &SS,
                       IdentifierInfo *Name, SourceLocation NameLoc,
                       const ParsedAttributesView &Attr, AccessSpecifier AS,
                       SourceLocation ModulePrivateLoc,
                       MultiTemplateParamsArg TemplateParameterLists,
                       bool &OwnedDecl, bool &IsDependent,
                       SourceLocation ScopedEnumKWLoc,
                       bool ScopedEnumUsesClassTag, TypeResult UnderlyingType,
                       bool IsTypeSpecifier, bool IsTemplateParamOrArg,
                       OffsetOfKind OOK, SkipBodyInfo *SkipBody = nullptr);
 
   /// ActOnField - Each field of a C struct/union is passed into this in order
   /// to create a FieldDecl object for it.
   Decl *ActOnField(Scope *S, Decl *TagD, SourceLocation DeclStart,
                    Declarator &D, Expr *BitfieldWidth);
 
   /// HandleField - Analyze a field of a C struct or a C++ data member.
   FieldDecl *HandleField(Scope *S, RecordDecl *TagD, SourceLocation DeclStart,
                          Declarator &D, Expr *BitfieldWidth,
                          InClassInitStyle InitStyle, AccessSpecifier AS);
 
   /// Build a new FieldDecl and check its well-formedness.
   ///
   /// This routine builds a new FieldDecl given the fields name, type,
   /// record, etc. \p PrevDecl should refer to any previous declaration
   /// with the same name and in the same scope as the field to be
   /// created.
   ///
   /// \returns a new FieldDecl.
   ///
   /// \todo The Declarator argument is a hack. It will be removed once
   FieldDecl *CheckFieldDecl(DeclarationName Name, QualType T,
                             TypeSourceInfo *TInfo, RecordDecl *Record,
                             SourceLocation Loc, bool Mutable,
                             Expr *BitfieldWidth, InClassInitStyle InitStyle,
                             SourceLocation TSSL, AccessSpecifier AS,
                             NamedDecl *PrevDecl, Declarator *D = nullptr);
 
   bool CheckNontrivialField(FieldDecl *FD);
 
   /// ActOnLastBitfield - This routine handles synthesized bitfields rules for
   /// class and class extensions. For every class \@interface and class
   /// extension \@interface, if the last ivar is a bitfield of any type,
   /// then add an implicit `char :0` ivar to the end of that interface.
   void ActOnLastBitfield(SourceLocation DeclStart,
                          SmallVectorImpl<Decl *> &AllIvarDecls);
 
   // This is used for both record definitions and ObjC interface declarations.
   void ActOnFields(Scope *S, SourceLocation RecLoc, Decl *TagDecl,
                    ArrayRef<Decl *> Fields, SourceLocation LBrac,
                    SourceLocation RBrac, const ParsedAttributesView &AttrList);
 
   /// ActOnTagStartDefinition - Invoked when we have entered the
   /// scope of a tag's definition (e.g., for an enumeration, class,
   /// struct, or union).
   void ActOnTagStartDefinition(Scope *S, Decl *TagDecl);
 
   /// Perform ODR-like check for C/ObjC when merging tag types from modules.
   /// Differently from C++, actually parse the body and reject / error out
   /// in case of a structural mismatch.
   bool ActOnDuplicateDefinition(Decl *Prev, SkipBodyInfo &SkipBody);
 
   typedef void *SkippedDefinitionContext;
 
   /// Invoked when we enter a tag definition that we're skipping.
   SkippedDefinitionContext ActOnTagStartSkippedDefinition(Scope *S, Decl *TD);
 
   /// ActOnStartCXXMemberDeclarations - Invoked when we have parsed a
   /// C++ record definition's base-specifiers clause and are starting its
   /// member declarations.
   void ActOnStartCXXMemberDeclarations(Scope *S, Decl *TagDecl,
                                        SourceLocation FinalLoc,
                                        bool IsFinalSpelledSealed,
                                        bool IsAbstract,
                                        SourceLocation LBraceLoc);
 
   /// ActOnTagFinishDefinition - Invoked once we have finished parsing
   /// the definition of a tag (enumeration, class, struct, or union).
   void ActOnTagFinishDefinition(Scope *S, Decl *TagDecl,
                                 SourceRange BraceRange);
 
   void ActOnTagFinishSkippedDefinition(SkippedDefinitionContext Context);
 
   /// ActOnTagDefinitionError - Invoked when there was an unrecoverable
   /// error parsing the definition of a tag.
   void ActOnTagDefinitionError(Scope *S, Decl *TagDecl);
 
   EnumConstantDecl *CheckEnumConstant(EnumDecl *Enum,
                                       EnumConstantDecl *LastEnumConst,
                                       SourceLocation IdLoc, IdentifierInfo *Id,
                                       Expr *val);
 
   /// Check that this is a valid underlying type for an enum declaration.
   bool CheckEnumUnderlyingType(TypeSourceInfo *TI);
 
   /// Check whether this is a valid redeclaration of a previous enumeration.
   /// \return true if the redeclaration was invalid.
   bool CheckEnumRedeclaration(SourceLocation EnumLoc, bool IsScoped,
                               QualType EnumUnderlyingTy, bool IsFixed,
                               const EnumDecl *Prev);
 
   /// Determine whether the body of an anonymous enumeration should be skipped.
   /// \param II The name of the first enumerator.
   SkipBodyInfo shouldSkipAnonEnumBody(Scope *S, IdentifierInfo *II,
                                       SourceLocation IILoc);
 
   Decl *ActOnEnumConstant(Scope *S, Decl *EnumDecl, Decl *LastEnumConstant,
                           SourceLocation IdLoc, IdentifierInfo *Id,
                           const ParsedAttributesView &Attrs,
                           SourceLocation EqualLoc, Expr *Val);
   void ActOnEnumBody(SourceLocation EnumLoc, SourceRange BraceRange,
                      Decl *EnumDecl, ArrayRef<Decl *> Elements, Scope *S,
                      const ParsedAttributesView &Attr);
 
   /// Set the current declaration context until it gets popped.
   void PushDeclContext(Scope *S, DeclContext *DC);
   void PopDeclContext();
 
   /// EnterDeclaratorContext - Used when we must lookup names in the context
   /// of a declarator's nested name specifier.
   void EnterDeclaratorContext(Scope *S, DeclContext *DC);
   void ExitDeclaratorContext(Scope *S);
 
   /// Enter a template parameter scope, after it's been associated with a
   /// particular DeclContext. Causes lookup within the scope to chain through
   /// enclosing contexts in the correct order.
   void EnterTemplatedContext(Scope *S, DeclContext *DC);
 
   /// Push the parameters of D, which must be a function, into scope.
   void ActOnReenterFunctionContext(Scope *S, Decl *D);
   void ActOnExitFunctionContext();
 
   /// Add this decl to the scope shadowed decl chains.
   void PushOnScopeChains(NamedDecl *D, Scope *S, bool AddToContext = true);
 
   /// isDeclInScope - If 'Ctx' is a function/method, isDeclInScope returns true
   /// if 'D' is in Scope 'S', otherwise 'S' is ignored and isDeclInScope returns
   /// true if 'D' belongs to the given declaration context.
   ///
   /// \param AllowInlineNamespace If \c true, allow the declaration to be in the
   ///        enclosing namespace set of the context, rather than contained
   ///        directly within it.
   bool isDeclInScope(NamedDecl *D, DeclContext *Ctx, Scope *S = nullptr,
                      bool AllowInlineNamespace = false) const;
 
   /// Finds the scope corresponding to the given decl context, if it
   /// happens to be an enclosing scope.  Otherwise return NULL.
   static Scope *getScopeForDeclContext(Scope *S, DeclContext *DC);
 
   /// Subroutines of ActOnDeclarator().
   TypedefDecl *ParseTypedefDecl(Scope *S, Declarator &D, QualType T,
                                 TypeSourceInfo *TInfo);
   bool isIncompatibleTypedef(const TypeDecl *Old, TypedefNameDecl *New);
 
   /// Describes the kind of merge to perform for availability
   /// attributes (including "deprecated", "unavailable", and "availability").
   enum AvailabilityMergeKind {
     /// Don't merge availability attributes at all.
     AMK_None,
     /// Merge availability attributes for a redeclaration, which requires
     /// an exact match.
     AMK_Redeclaration,
     /// Merge availability attributes for an override, which requires
     /// an exact match or a weakening of constraints.
     AMK_Override,
     /// Merge availability attributes for an implementation of
     /// a protocol requirement.
     AMK_ProtocolImplementation,
     /// Merge availability attributes for an implementation of
     /// an optional protocol requirement.
     AMK_OptionalProtocolImplementation
   };
 
   /// mergeDeclAttributes - Copy attributes from the Old decl to the New one.
   void mergeDeclAttributes(NamedDecl *New, Decl *Old,
                            AvailabilityMergeKind AMK = AMK_Redeclaration);
 
   /// MergeTypedefNameDecl - We just parsed a typedef 'New' which has the
   /// same name and scope as a previous declaration 'Old'.  Figure out
   /// how to resolve this situation, merging decls or emitting
   /// diagnostics as appropriate. If there was an error, set New to be invalid.
   void MergeTypedefNameDecl(Scope *S, TypedefNameDecl *New,
                             LookupResult &OldDecls);
 
   /// MergeFunctionDecl - We just parsed a function 'New' from
   /// declarator D which has the same name and scope as a previous
   /// declaration 'Old'.  Figure out how to resolve this situation,
   /// merging decls or emitting diagnostics as appropriate.
   ///
   /// In C++, New and Old must be declarations that are not
   /// overloaded. Use IsOverload to determine whether New and Old are
   /// overloaded, and to select the Old declaration that New should be
   /// merged with.
   ///
   /// Returns true if there was an error, false otherwise.
   bool MergeFunctionDecl(FunctionDecl *New, NamedDecl *&Old, Scope *S,
                          bool MergeTypeWithOld, bool NewDeclIsDefn);
 
   /// Completes the merge of two function declarations that are
   /// known to be compatible.
   ///
   /// This routine handles the merging of attributes and other
   /// properties of function declarations from the old declaration to
   /// the new declaration, once we know that New is in fact a
   /// redeclaration of Old.
   ///
   /// \returns false
   bool MergeCompatibleFunctionDecls(FunctionDecl *New, FunctionDecl *Old,
                                     Scope *S, bool MergeTypeWithOld);
   void mergeObjCMethodDecls(ObjCMethodDecl *New, ObjCMethodDecl *Old);
 
   /// MergeVarDecl - We just parsed a variable 'New' which has the same name
   /// and scope as a previous declaration 'Old'.  Figure out how to resolve this
   /// situation, merging decls or emitting diagnostics as appropriate.
   ///
   /// Tentative definition rules (C99 6.9.2p2) are checked by
   /// FinalizeDeclaratorGroup. Unfortunately, we can't analyze tentative
   /// definitions here, since the initializer hasn't been attached.
   void MergeVarDecl(VarDecl *New, LookupResult &Previous);
 
   /// MergeVarDeclTypes - We parsed a variable 'New' which has the same name and
   /// scope as a previous declaration 'Old'.  Figure out how to merge their
   /// types, emitting diagnostics as appropriate.
   ///
   /// Declarations using the auto type specifier (C++ [decl.spec.auto]) call
   /// back to here in AddInitializerToDecl. We can't check them before the
   /// initializer is attached.
   void MergeVarDeclTypes(VarDecl *New, VarDecl *Old, bool MergeTypeWithOld);
 
   /// We've just determined that \p Old and \p New both appear to be definitions
   /// of the same variable. Either diagnose or fix the problem.
   bool checkVarDeclRedefinition(VarDecl *OldDefn, VarDecl *NewDefn);
   void notePreviousDefinition(const NamedDecl *Old, SourceLocation New);
 
   /// Filters out lookup results that don't fall within the given scope
   /// as determined by isDeclInScope.
   void FilterLookupForScope(LookupResult &R, DeclContext *Ctx, Scope *S,
                             bool ConsiderLinkage, bool AllowInlineNamespace);
 
   /// We've determined that \p New is a redeclaration of \p Old. Check that they
   /// have compatible owning modules.
   bool CheckRedeclarationModuleOwnership(NamedDecl *New, NamedDecl *Old);
 
   /// [module.interface]p6:
   /// A redeclaration of an entity X is implicitly exported if X was introduced
   /// by an exported declaration; otherwise it shall not be exported.
   bool CheckRedeclarationExported(NamedDecl *New, NamedDecl *Old);
 
   /// A wrapper function for checking the semantic restrictions of
   /// a redeclaration within a module.
   bool CheckRedeclarationInModule(NamedDecl *New, NamedDecl *Old);
 
   /// Check the redefinition in C++20 Modules.
   ///
   /// [basic.def.odr]p14:
   /// For any definable item D with definitions in multiple translation units,
   /// - if D is a non-inline non-templated function or variable, or
   /// - if the definitions in different translation units do not satisfy the
   /// following requirements,
   ///   the program is ill-formed; a diagnostic is required only if the
   ///   definable item is attached to a named module and a prior definition is
   ///   reachable at the point where a later definition occurs.
   /// - Each such definition shall not be attached to a named module
   /// ([module.unit]).
   /// - Each such definition shall consist of the same sequence of tokens, ...
   /// ...
   ///
   /// Return true if the redefinition is not allowed. Return false otherwise.
   bool IsRedefinitionInModule(const NamedDecl *New, const NamedDecl *Old) const;
 
   bool ShouldWarnIfUnusedFileScopedDecl(const DeclaratorDecl *D) const;
 
   /// If it's a file scoped decl that must warn if not used, keep track
   /// of it.
   void MarkUnusedFileScopedDecl(const DeclaratorDecl *D);
 
   typedef llvm::function_ref<void(SourceLocation Loc, PartialDiagnostic PD)>
       DiagReceiverTy;
 
   void DiagnoseUnusedNestedTypedefs(const RecordDecl *D);
   void DiagnoseUnusedNestedTypedefs(const RecordDecl *D,
                                     DiagReceiverTy DiagReceiver);
   void DiagnoseUnusedDecl(const NamedDecl *ND);
 
   /// DiagnoseUnusedDecl - Emit warnings about declarations that are not used
   /// unless they are marked attr(unused).
   void DiagnoseUnusedDecl(const NamedDecl *ND, DiagReceiverTy DiagReceiver);
 
   /// If VD is set but not otherwise used, diagnose, for a parameter or a
   /// variable.
   void DiagnoseUnusedButSetDecl(const VarDecl *VD, DiagReceiverTy DiagReceiver);
 
   /// getNonFieldDeclScope - Retrieves the innermost scope, starting
   /// from S, where a non-field would be declared. This routine copes
   /// with the difference between C and C++ scoping rules in structs and
   /// unions. For example, the following code is well-formed in C but
   /// ill-formed in C++:
   /// @code
   /// struct S6 {
   ///   enum { BAR } e;
   /// };
   ///
   /// void test_S6() {
   ///   struct S6 a;
   ///   a.e = BAR;
   /// }
   /// @endcode
   /// For the declaration of BAR, this routine will return a different
   /// scope. The scope S will be the scope of the unnamed enumeration
   /// within S6. In C++, this routine will return the scope associated
   /// with S6, because the enumeration's scope is a transparent
   /// context but structures can contain non-field names. In C, this
   /// routine will return the translation unit scope, since the
   /// enumeration's scope is a transparent context and structures cannot
   /// contain non-field names.
   Scope *getNonFieldDeclScope(Scope *S);
 
   FunctionDecl *CreateBuiltin(IdentifierInfo *II, QualType Type, unsigned ID,
                               SourceLocation Loc);
 
   /// LazilyCreateBuiltin - The specified Builtin-ID was first used at
   /// file scope.  lazily create a decl for it. ForRedeclaration is true
   /// if we're creating this built-in in anticipation of redeclaring the
   /// built-in.
   NamedDecl *LazilyCreateBuiltin(IdentifierInfo *II, unsigned ID, Scope *S,
                                  bool ForRedeclaration, SourceLocation Loc);
 
   /// Get the outermost AttributedType node that sets a calling convention.
   /// Valid types should not have multiple attributes with different CCs.
   const AttributedType *getCallingConvAttributedType(QualType T) const;
 
   /// GetNameForDeclarator - Determine the full declaration name for the
   /// given Declarator.
   DeclarationNameInfo GetNameForDeclarator(Declarator &D);
 
   /// Retrieves the declaration name from a parsed unqualified-id.
   DeclarationNameInfo GetNameFromUnqualifiedId(const UnqualifiedId &Name);
 
   /// ParsingInitForAutoVars - a set of declarations with auto types for which
   /// we are currently parsing the initializer.
   llvm::SmallPtrSet<const Decl *, 4> ParsingInitForAutoVars;
 
   /// Look for a locally scoped extern "C" declaration by the given name.
   NamedDecl *findLocallyScopedExternCDecl(DeclarationName Name);
 
   void deduceOpenCLAddressSpace(ValueDecl *decl);
 
   /// Adjust the \c DeclContext for a function or variable that might be a
   /// function-local external declaration.
   static bool adjustContextForLocalExternDecl(DeclContext *&DC);
 
   void MarkTypoCorrectedFunctionDefinition(const NamedDecl *F);
 
   /// Checks if the variant/multiversion functions are compatible.
   bool areMultiversionVariantFunctionsCompatible(
       const FunctionDecl *OldFD, const FunctionDecl *NewFD,
       const PartialDiagnostic &NoProtoDiagID,
       const PartialDiagnosticAt &NoteCausedDiagIDAt,
       const PartialDiagnosticAt &NoSupportDiagIDAt,
       const PartialDiagnosticAt &DiffDiagIDAt, bool TemplatesSupported,
       bool ConstexprSupported, bool CLinkageMayDiffer);
 
   /// type checking declaration initializers (C99 6.7.8)
   bool CheckForConstantInitializer(
       Expr *Init, unsigned DiagID = diag::err_init_element_not_constant);
 
   QualType deduceVarTypeFromInitializer(VarDecl *VDecl, DeclarationName Name,
                                         QualType Type, TypeSourceInfo *TSI,
                                         SourceRange Range, bool DirectInit,
                                         Expr *Init);
 
   bool DeduceVariableDeclarationType(VarDecl *VDecl, bool DirectInit,
                                      Expr *Init);
 
   sema::LambdaScopeInfo *RebuildLambdaScopeInfo(CXXMethodDecl *CallOperator);
 
   // Heuristically tells if the function is `get_return_object` member of a
   // coroutine promise_type by matching the function name.
   static bool CanBeGetReturnObject(const FunctionDecl *FD);
   static bool CanBeGetReturnTypeOnAllocFailure(const FunctionDecl *FD);
 
   /// ImplicitlyDefineFunction - An undeclared identifier was used in a function
   /// call, forming a call to an implicitly defined function (per C99 6.5.1p2).
   NamedDecl *ImplicitlyDefineFunction(SourceLocation Loc, IdentifierInfo &II,
                                       Scope *S);
 
   /// If this function is a C++ replaceable global allocation function
   /// (C++2a [basic.stc.dynamic.allocation], C++2a [new.delete]),
   /// adds any function attributes that we know a priori based on the standard.
   ///
   /// We need to check for duplicate attributes both here and where user-written
   /// attributes are applied to declarations.
   void AddKnownFunctionAttributesForReplaceableGlobalAllocationFunction(
       FunctionDecl *FD);
 
   /// Adds any function attributes that we know a priori based on
   /// the declaration of this function.
   ///
   /// These attributes can apply both to implicitly-declared builtins
   /// (like __builtin___printf_chk) or to library-declared functions
   /// like NSLog or printf.
   ///
   /// We need to check for duplicate attributes both here and where user-written
   /// attributes are applied to declarations.
   void AddKnownFunctionAttributes(FunctionDecl *FD);
 
   /// VerifyBitField - verifies that a bit field expression is an ICE and has
   /// the correct width, and that the field type is valid.
   /// Returns false on success.
   ExprResult VerifyBitField(SourceLocation FieldLoc,
                             const IdentifierInfo *FieldName, QualType FieldTy,
                             bool IsMsStruct, Expr *BitWidth);
 
   /// IsValueInFlagEnum - Determine if a value is allowed as part of a flag
   /// enum. If AllowMask is true, then we also allow the complement of a valid
   /// value, to be used as a mask.
   bool IsValueInFlagEnum(const EnumDecl *ED, const llvm::APInt &Val,
                          bool AllowMask) const;
 
   /// ActOnPragmaWeakID - Called on well formed \#pragma weak ident.
   void ActOnPragmaWeakID(IdentifierInfo *WeakName, SourceLocation PragmaLoc,
                          SourceLocation WeakNameLoc);
 
   /// ActOnPragmaRedefineExtname - Called on well formed
   /// \#pragma redefine_extname oldname newname.
   void ActOnPragmaRedefineExtname(IdentifierInfo *WeakName,
                                   IdentifierInfo *AliasName,
                                   SourceLocation PragmaLoc,
                                   SourceLocation WeakNameLoc,
                                   SourceLocation AliasNameLoc);
 
   /// ActOnPragmaWeakAlias - Called on well formed \#pragma weak ident = ident.
   void ActOnPragmaWeakAlias(IdentifierInfo *WeakName, IdentifierInfo *AliasName,
                             SourceLocation PragmaLoc,
                             SourceLocation WeakNameLoc,
                             SourceLocation AliasNameLoc);
 
   /// Status of the function emission on the CUDA/HIP/OpenMP host/device attrs.
   enum class FunctionEmissionStatus {
     Emitted,
     CUDADiscarded,     // Discarded due to CUDA/HIP hostness
     OMPDiscarded,      // Discarded due to OpenMP hostness
     TemplateDiscarded, // Discarded due to uninstantiated templates
     Unknown,
   };
   FunctionEmissionStatus getEmissionStatus(const FunctionDecl *Decl,
                                            bool Final = false);
 
   // Whether the callee should be ignored in CUDA/HIP/OpenMP host/device check.
   bool shouldIgnoreInHostDeviceCheck(FunctionDecl *Callee);
 
 private:
   /// Function or variable declarations to be checked for whether the deferred
   /// diagnostics should be emitted.
   llvm::SmallSetVector<Decl *, 4> DeclsToCheckForDeferredDiags;
 
   /// Map of current shadowing declarations to shadowed declarations. Warn if
   /// it looks like the user is trying to modify the shadowing declaration.
   llvm::DenseMap<const NamedDecl *, const NamedDecl *> ShadowingDecls;
 
   // We need this to handle
   //
   // typedef struct {
   //   void *foo() { return 0; }
   // } A;
   //
   // When we see foo we don't know if after the typedef we will get 'A' or '*A'
   // for example. If 'A', foo will have external linkage. If we have '*A',
   // foo will have no linkage. Since we can't know until we get to the end
   // of the typedef, this function finds out if D might have non-external
   // linkage. Callers should verify at the end of the TU if it D has external
   // linkage or not.
   static bool mightHaveNonExternalLinkage(const DeclaratorDecl *FD);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Declaration Attribute Handling
   /// Implementations are in SemaDeclAttr.cpp
   ///@{
 
 public:
   /// Describes the kind of priority given to an availability attribute.
   ///
   /// The sum of priorities deteremines the final priority of the attribute.
   /// The final priority determines how the attribute will be merged.
   /// An attribute with a lower priority will always remove higher priority
   /// attributes for the specified platform when it is being applied. An
   /// attribute with a higher priority will not be applied if the declaration
   /// already has an availability attribute with a lower priority for the
   /// specified platform. The final prirority values are not expected to match
   /// the values in this enumeration, but instead should be treated as a plain
   /// integer value. This enumeration just names the priority weights that are
   /// used to calculate that final vaue.
   enum AvailabilityPriority : int {
     /// The availability attribute was specified explicitly next to the
     /// declaration.
     AP_Explicit = 0,
 
     /// The availability attribute was applied using '#pragma clang attribute'.
     AP_PragmaClangAttribute = 1,
 
     /// The availability attribute for a specific platform was inferred from
     /// an availability attribute for another platform.
     AP_InferredFromOtherPlatform = 2
   };
 
   /// Describes the reason a calling convention specification was ignored, used
   /// for diagnostics.
   enum class CallingConventionIgnoredReason {
     ForThisTarget = 0,
     VariadicFunction,
     ConstructorDestructor,
     BuiltinFunction
   };
 
   /// A helper function to provide Attribute Location for the Attr types
   /// AND the ParsedAttr.
   template <typename AttrInfo>
   static std::enable_if_t<std::is_base_of_v<Attr, AttrInfo>, SourceLocation>
   getAttrLoc(const AttrInfo &AL) {
     return AL.getLocation();
   }
   SourceLocation getAttrLoc(const ParsedAttr &AL);
 
   /// If Expr is a valid integer constant, get the value of the integer
   /// expression and return success or failure. May output an error.
   ///
   /// Negative argument is implicitly converted to unsigned, unless
   /// \p StrictlyUnsigned is true.
   template <typename AttrInfo>
   bool checkUInt32Argument(const AttrInfo &AI, const Expr *Expr, uint32_t &Val,
                            unsigned Idx = UINT_MAX,
                            bool StrictlyUnsigned = false) {
     std::optional<llvm::APSInt> I = llvm::APSInt(32);
     if (Expr->isTypeDependent() ||
         !(I = Expr->getIntegerConstantExpr(Context))) {
       if (Idx != UINT_MAX)
         Diag(getAttrLoc(AI), diag::err_attribute_argument_n_type)
             << &AI << Idx << AANT_ArgumentIntegerConstant
             << Expr->getSourceRange();
       else
         Diag(getAttrLoc(AI), diag::err_attribute_argument_type)
             << &AI << AANT_ArgumentIntegerConstant << Expr->getSourceRange();
       return false;
     }
 
     if (!I->isIntN(32)) {
       Diag(Expr->getExprLoc(), diag::err_ice_too_large)
           << toString(*I, 10, false) << 32 << /* Unsigned */ 1;
       return false;
     }
 
     if (StrictlyUnsigned && I->isSigned() && I->isNegative()) {
       Diag(getAttrLoc(AI), diag::err_attribute_requires_positive_integer)
           << &AI << /*non-negative*/ 1;
       return false;
     }
 
     Val = (uint32_t)I->getZExtValue();
     return true;
   }
 
   /// WeakTopLevelDecl - Translation-unit scoped declarations generated by
   /// \#pragma weak during processing of other Decls.
   /// I couldn't figure out a clean way to generate these in-line, so
   /// we store them here and handle separately -- which is a hack.
   /// It would be best to refactor this.
   SmallVector<Decl *, 2> WeakTopLevelDecl;
 
   /// WeakTopLevelDeclDecls - access to \#pragma weak-generated Decls
   SmallVectorImpl<Decl *> &WeakTopLevelDecls() { return WeakTopLevelDecl; }
 
   typedef LazyVector<TypedefNameDecl *, ExternalSemaSource,
                      &ExternalSemaSource::ReadExtVectorDecls, 2, 2>
       ExtVectorDeclsType;
 
   /// ExtVectorDecls - This is a list all the extended vector types. This allows
   /// us to associate a raw vector type with one of the ext_vector type names.
   /// This is only necessary for issuing pretty diagnostics.
   ExtVectorDeclsType ExtVectorDecls;
 
   /// Check if the argument \p E is a ASCII string literal. If not emit an error
   /// and return false, otherwise set \p Str to the value of the string literal
   /// and return true.
   bool checkStringLiteralArgumentAttr(const AttributeCommonInfo &CI,
                                       const Expr *E, StringRef &Str,
                                       SourceLocation *ArgLocation = nullptr);
 
   /// Check if the argument \p ArgNum of \p Attr is a ASCII string literal.
   /// If not emit an error and return false. If the argument is an identifier it
   /// will emit an error with a fixit hint and treat it as if it was a string
   /// literal.
   bool checkStringLiteralArgumentAttr(const ParsedAttr &Attr, unsigned ArgNum,
                                       StringRef &Str,
                                       SourceLocation *ArgLocation = nullptr);
 
   /// Determine if type T is a valid subject for a nonnull and similar
   /// attributes. By default, we look through references (the behavior used by
   /// nonnull), but if the second parameter is true, then we treat a reference
   /// type as valid.
   bool isValidPointerAttrType(QualType T, bool RefOkay = false);
 
   /// AddAssumeAlignedAttr - Adds an assume_aligned attribute to a particular
   /// declaration.
   void AddAssumeAlignedAttr(Decl *D, const AttributeCommonInfo &CI, Expr *E,
                             Expr *OE);
 
   /// AddAllocAlignAttr - Adds an alloc_align attribute to a particular
   /// declaration.
   void AddAllocAlignAttr(Decl *D, const AttributeCommonInfo &CI,
                          Expr *ParamExpr);
 
   bool CheckAttrTarget(const ParsedAttr &CurrAttr);
   bool CheckAttrNoArgs(const ParsedAttr &CurrAttr);
 
   AvailabilityAttr *mergeAvailabilityAttr(
       NamedDecl *D, const AttributeCommonInfo &CI, IdentifierInfo *Platform,
       bool Implicit, VersionTuple Introduced, VersionTuple Deprecated,
       VersionTuple Obsoleted, bool IsUnavailable, StringRef Message,
       bool IsStrict, StringRef Replacement, AvailabilityMergeKind AMK,
       int Priority, IdentifierInfo *IIEnvironment);
 
   TypeVisibilityAttr *
   mergeTypeVisibilityAttr(Decl *D, const AttributeCommonInfo &CI,
                           TypeVisibilityAttr::VisibilityType Vis);
   VisibilityAttr *mergeVisibilityAttr(Decl *D, const AttributeCommonInfo &CI,
                                       VisibilityAttr::VisibilityType Vis);
   SectionAttr *mergeSectionAttr(Decl *D, const AttributeCommonInfo &CI,
                                 StringRef Name);
 
   /// Used to implement to perform semantic checking on
   /// attribute((section("foo"))) specifiers.
   ///
   /// In this case, "foo" is passed in to be checked.  If the section
   /// specifier is invalid, return an Error that indicates the problem.
   ///
   /// This is a simple quality of implementation feature to catch errors
   /// and give good diagnostics in cases when the assembler or code generator
   /// would otherwise reject the section specifier.
   llvm::Error isValidSectionSpecifier(StringRef Str);
   bool checkSectionName(SourceLocation LiteralLoc, StringRef Str);
   CodeSegAttr *mergeCodeSegAttr(Decl *D, const AttributeCommonInfo &CI,
                                 StringRef Name);
 
   // Check for things we'd like to warn about. Multiversioning issues are
   // handled later in the process, once we know how many exist.
   bool checkTargetAttr(SourceLocation LiteralLoc, StringRef Str);
 
   /// Check Target Version attrs
   bool checkTargetVersionAttr(SourceLocation Loc, Decl *D, StringRef Str);
   bool checkTargetClonesAttrString(
       SourceLocation LiteralLoc, StringRef Str, const StringLiteral *Literal,
       Decl *D, bool &HasDefault, bool &HasCommas, bool &HasNotDefault,
       SmallVectorImpl<SmallString<64>> &StringsBuffer);
 
   ErrorAttr *mergeErrorAttr(Decl *D, const AttributeCommonInfo &CI,
                             StringRef NewUserDiagnostic);
   FormatAttr *mergeFormatAttr(Decl *D, const AttributeCommonInfo &CI,
                               IdentifierInfo *Format, int FormatIdx,
                               int FirstArg);
 
   /// AddAlignedAttr - Adds an aligned attribute to a particular declaration.
   void AddAlignedAttr(Decl *D, const AttributeCommonInfo &CI, Expr *E,
                       bool IsPackExpansion);
   void AddAlignedAttr(Decl *D, const AttributeCommonInfo &CI, TypeSourceInfo *T,
                       bool IsPackExpansion);
 
   /// AddAlignValueAttr - Adds an align_value attribute to a particular
   /// declaration.
   void AddAlignValueAttr(Decl *D, const AttributeCommonInfo &CI, Expr *E);
 
   /// AddAnnotationAttr - Adds an annotation Annot with Args arguments to D.
   void AddAnnotationAttr(Decl *D, const AttributeCommonInfo &CI,
                          StringRef Annot, MutableArrayRef<Expr *> Args);
 
   bool checkMSInheritanceAttrOnDefinition(CXXRecordDecl *RD, SourceRange Range,
                                           bool BestCase,
                                           MSInheritanceModel SemanticSpelling);
 
   void CheckAlignasUnderalignment(Decl *D);
 
   /// AddModeAttr - Adds a mode attribute to a particular declaration.
   void AddModeAttr(Decl *D, const AttributeCommonInfo &CI, IdentifierInfo *Name,
                    bool InInstantiation = false);
   AlwaysInlineAttr *mergeAlwaysInlineAttr(Decl *D,
                                           const AttributeCommonInfo &CI,
                                           const IdentifierInfo *Ident);
   MinSizeAttr *mergeMinSizeAttr(Decl *D, const AttributeCommonInfo &CI);
   OptimizeNoneAttr *mergeOptimizeNoneAttr(Decl *D,
                                           const AttributeCommonInfo &CI);
   InternalLinkageAttr *mergeInternalLinkageAttr(Decl *D, const ParsedAttr &AL);
   InternalLinkageAttr *mergeInternalLinkageAttr(Decl *D,
                                                 const InternalLinkageAttr &AL);
 
   /// Check validaty of calling convention attribute \p attr. If \p FD
   /// is not null pointer, use \p FD to determine the CUDA/HIP host/device
   /// target. Otherwise, it is specified by \p CFT.
   bool CheckCallingConvAttr(
       const ParsedAttr &attr, CallingConv &CC, const FunctionDecl *FD = nullptr,
       CUDAFunctionTarget CFT = CUDAFunctionTarget::InvalidTarget);
 
   /// Checks a regparm attribute, returning true if it is ill-formed and
   /// otherwise setting numParams to the appropriate value.
   bool CheckRegparmAttr(const ParsedAttr &attr, unsigned &value);
 
   /// Create an CUDALaunchBoundsAttr attribute.
   CUDALaunchBoundsAttr *CreateLaunchBoundsAttr(const AttributeCommonInfo &CI,
                                                Expr *MaxThreads,
                                                Expr *MinBlocks,
                                                Expr *MaxBlocks);
 
   /// AddLaunchBoundsAttr - Adds a launch_bounds attribute to a particular
   /// declaration.
   void AddLaunchBoundsAttr(Decl *D, const AttributeCommonInfo &CI,
                            Expr *MaxThreads, Expr *MinBlocks, Expr *MaxBlocks);
 
   enum class RetainOwnershipKind { NS, CF, OS };
 
   UuidAttr *mergeUuidAttr(Decl *D, const AttributeCommonInfo &CI,
                           StringRef UuidAsWritten, MSGuidDecl *GuidDecl);
 
   BTFDeclTagAttr *mergeBTFDeclTagAttr(Decl *D, const BTFDeclTagAttr &AL);
 
   DLLImportAttr *mergeDLLImportAttr(Decl *D, const AttributeCommonInfo &CI);
   DLLExportAttr *mergeDLLExportAttr(Decl *D, const AttributeCommonInfo &CI);
   MSInheritanceAttr *mergeMSInheritanceAttr(Decl *D,
                                             const AttributeCommonInfo &CI,
                                             bool BestCase,
                                             MSInheritanceModel Model);
 
   EnforceTCBAttr *mergeEnforceTCBAttr(Decl *D, const EnforceTCBAttr &AL);
   EnforceTCBLeafAttr *mergeEnforceTCBLeafAttr(Decl *D,
                                               const EnforceTCBLeafAttr &AL);
 
   /// Helper for delayed processing TransparentUnion or
   /// BPFPreserveAccessIndexAttr attribute.
   void ProcessDeclAttributeDelayed(Decl *D,
                                    const ParsedAttributesView &AttrList);
 
   // Options for ProcessDeclAttributeList().
   struct ProcessDeclAttributeOptions {
     ProcessDeclAttributeOptions()
         : IncludeCXX11Attributes(true), IgnoreTypeAttributes(false) {}
 
     ProcessDeclAttributeOptions WithIncludeCXX11Attributes(bool Val) {
       ProcessDeclAttributeOptions Result = *this;
       Result.IncludeCXX11Attributes = Val;
       return Result;
     }
 
     ProcessDeclAttributeOptions WithIgnoreTypeAttributes(bool Val) {
       ProcessDeclAttributeOptions Result = *this;
       Result.IgnoreTypeAttributes = Val;
       return Result;
     }
 
     // Should C++11 attributes be processed?
     bool IncludeCXX11Attributes;
 
     // Should any type attributes encountered be ignored?
     // If this option is false, a diagnostic will be emitted for any type
     // attributes of a kind that does not "slide" from the declaration to
     // the decl-specifier-seq.
     bool IgnoreTypeAttributes;
   };
 
   /// ProcessDeclAttributeList - Apply all the decl attributes in the specified
   /// attribute list to the specified decl, ignoring any type attributes.
   void ProcessDeclAttributeList(Scope *S, Decl *D,
                                 const ParsedAttributesView &AttrList,
                                 const ProcessDeclAttributeOptions &Options =
                                     ProcessDeclAttributeOptions());
 
   /// Annotation attributes are the only attributes allowed after an access
   /// specifier.
   bool ProcessAccessDeclAttributeList(AccessSpecDecl *ASDecl,
                                       const ParsedAttributesView &AttrList);
 
   /// checkUnusedDeclAttributes - Given a declarator which is not being
   /// used to build a declaration, complain about any decl attributes
   /// which might be lying around on it.
   void checkUnusedDeclAttributes(Declarator &D);
 
   /// DeclClonePragmaWeak - clone existing decl (maybe definition),
   /// \#pragma weak needs a non-definition decl and source may not have one.
   NamedDecl *DeclClonePragmaWeak(NamedDecl *ND, const IdentifierInfo *II,
                                  SourceLocation Loc);
 
   /// DeclApplyPragmaWeak - A declaration (maybe definition) needs \#pragma weak
   /// applied to it, possibly with an alias.
   void DeclApplyPragmaWeak(Scope *S, NamedDecl *ND, const WeakInfo &W);
 
   void ProcessPragmaWeak(Scope *S, Decl *D);
   // Decl attributes - this routine is the top level dispatcher.
   void ProcessDeclAttributes(Scope *S, Decl *D, const Declarator &PD);
 
   void PopParsingDeclaration(ParsingDeclState state, Decl *decl);
 
   /// Given a set of delayed diagnostics, re-emit them as if they had
   /// been delayed in the current context instead of in the given pool.
   /// Essentially, this just moves them to the current pool.
   void redelayDiagnostics(sema::DelayedDiagnosticPool &pool);
 
   /// Check if IdxExpr is a valid parameter index for a function or
   /// instance method D.  May output an error.
   ///
   /// \returns true if IdxExpr is a valid index.
   template <typename AttrInfo>
   bool checkFunctionOrMethodParameterIndex(const Decl *D, const AttrInfo &AI,
                                            unsigned AttrArgNum,
                                            const Expr *IdxExpr, ParamIdx &Idx,
                                            bool CanIndexImplicitThis = false) {
     assert(isFunctionOrMethodOrBlockForAttrSubject(D));
 
     // In C++ the implicit 'this' function parameter also counts.
     // Parameters are counted from one.
     bool HP = hasFunctionProto(D);
     bool HasImplicitThisParam = isInstanceMethod(D);
     bool IV = HP && isFunctionOrMethodVariadic(D);
     unsigned NumParams =
         (HP ? getFunctionOrMethodNumParams(D) : 0) + HasImplicitThisParam;
 
     std::optional<llvm::APSInt> IdxInt;
     if (IdxExpr->isTypeDependent() ||
         !(IdxInt = IdxExpr->getIntegerConstantExpr(Context))) {
       Diag(getAttrLoc(AI), diag::err_attribute_argument_n_type)
           << &AI << AttrArgNum << AANT_ArgumentIntegerConstant
           << IdxExpr->getSourceRange();
       return false;
     }
 
     unsigned IdxSource = IdxInt->getLimitedValue(UINT_MAX);
     if (IdxSource < 1 || (!IV && IdxSource > NumParams)) {
       Diag(getAttrLoc(AI), diag::err_attribute_argument_out_of_bounds)
           << &AI << AttrArgNum << IdxExpr->getSourceRange();
       return false;
     }
     if (HasImplicitThisParam && !CanIndexImplicitThis) {
       if (IdxSource == 1) {
         Diag(getAttrLoc(AI), diag::err_attribute_invalid_implicit_this_argument)
             << &AI << IdxExpr->getSourceRange();
         return false;
       }
     }
 
     Idx = ParamIdx(IdxSource, D);
     return true;
   }
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Declarations
   /// Implementations are in SemaDeclCXX.cpp
   ///@{
 
 public:
   void CheckDelegatingCtorCycles();
 
   /// Called before parsing a function declarator belonging to a function
   /// declaration.
   void ActOnStartFunctionDeclarationDeclarator(Declarator &D,
                                                unsigned TemplateParameterDepth);
 
   /// Called after parsing a function declarator belonging to a function
   /// declaration.
   void ActOnFinishFunctionDeclarationDeclarator(Declarator &D);
 
   // Act on C++ namespaces
   Decl *ActOnStartNamespaceDef(Scope *S, SourceLocation InlineLoc,
                                SourceLocation NamespaceLoc,
                                SourceLocation IdentLoc, IdentifierInfo *Ident,
                                SourceLocation LBrace,
                                const ParsedAttributesView &AttrList,
                                UsingDirectiveDecl *&UsingDecl, bool IsNested);
 
   /// ActOnFinishNamespaceDef - This callback is called after a namespace is
   /// exited. Decl is the DeclTy returned by ActOnStartNamespaceDef.
   void ActOnFinishNamespaceDef(Decl *Dcl, SourceLocation RBrace);
 
   NamespaceDecl *getStdNamespace() const;
 
   /// Retrieve the special "std" namespace, which may require us to
   /// implicitly define the namespace.
   NamespaceDecl *getOrCreateStdNamespace();
 
   CXXRecordDecl *getStdBadAlloc() const;
   EnumDecl *getStdAlignValT() const;
 
   ValueDecl *tryLookupUnambiguousFieldDecl(RecordDecl *ClassDecl,
                                            const IdentifierInfo *MemberOrBase);
 
   enum class ComparisonCategoryUsage {
     /// The '<=>' operator was used in an expression and a builtin operator
     /// was selected.
     OperatorInExpression,
     /// A defaulted 'operator<=>' needed the comparison category. This
     /// typically only applies to 'std::strong_ordering', due to the implicit
     /// fallback return value.
     DefaultedOperator,
   };
 
   /// Lookup the specified comparison category types in the standard
   ///   library, an check the VarDecls possibly returned by the operator<=>
   ///   builtins for that type.
   ///
   /// \return The type of the comparison category type corresponding to the
   ///   specified Kind, or a null type if an error occurs
   QualType CheckComparisonCategoryType(ComparisonCategoryType Kind,
                                        SourceLocation Loc,
                                        ComparisonCategoryUsage Usage);
 
   /// Tests whether Ty is an instance of std::initializer_list and, if
   /// it is and Element is not NULL, assigns the element type to Element.
   bool isStdInitializerList(QualType Ty, QualType *Element);
 
   /// Looks for the std::initializer_list template and instantiates it
   /// with Element, or emits an error if it's not found.
   ///
   /// \returns The instantiated template, or null on error.
   QualType BuildStdInitializerList(QualType Element, SourceLocation Loc);
 
   /// Determine whether Ctor is an initializer-list constructor, as
   /// defined in [dcl.init.list]p2.
   bool isInitListConstructor(const FunctionDecl *Ctor);
 
   Decl *ActOnUsingDirective(Scope *CurScope, SourceLocation UsingLoc,
                             SourceLocation NamespcLoc, CXXScopeSpec &SS,
                             SourceLocation IdentLoc,
                             IdentifierInfo *NamespcName,
                             const ParsedAttributesView &AttrList);
 
   void PushUsingDirective(Scope *S, UsingDirectiveDecl *UDir);
 
   Decl *ActOnNamespaceAliasDef(Scope *CurScope, SourceLocation NamespaceLoc,
                                SourceLocation AliasLoc, IdentifierInfo *Alias,
                                CXXScopeSpec &SS, SourceLocation IdentLoc,
                                IdentifierInfo *Ident);
 
   /// Remove decls we can't actually see from a lookup being used to declare
   /// shadow using decls.
   ///
   /// \param S - The scope of the potential shadow decl
   /// \param Previous - The lookup of a potential shadow decl's name.
   void FilterUsingLookup(Scope *S, LookupResult &lookup);
 
   /// Hides a using shadow declaration.  This is required by the current
   /// using-decl implementation when a resolvable using declaration in a
   /// class is followed by a declaration which would hide or override
   /// one or more of the using decl's targets; for example:
   ///
   ///   struct Base { void foo(int); };
   ///   struct Derived : Base {
   ///     using Base::foo;
   ///     void foo(int);
   ///   };
   ///
   /// The governing language is C++03 [namespace.udecl]p12:
   ///
   ///   When a using-declaration brings names from a base class into a
   ///   derived class scope, member functions in the derived class
   ///   override and/or hide member functions with the same name and
   ///   parameter types in a base class (rather than conflicting).
   ///
   /// There are two ways to implement this:
   ///   (1) optimistically create shadow decls when they're not hidden
   ///       by existing declarations, or
   ///   (2) don't create any shadow decls (or at least don't make them
   ///       visible) until we've fully parsed/instantiated the class.
   /// The problem with (1) is that we might have to retroactively remove
   /// a shadow decl, which requires several O(n) operations because the
   /// decl structures are (very reasonably) not designed for removal.
   /// (2) avoids this but is very fiddly and phase-dependent.
   void HideUsingShadowDecl(Scope *S, UsingShadowDecl *Shadow);
 
   /// Determines whether to create a using shadow decl for a particular
   /// decl, given the set of decls existing prior to this using lookup.
   bool CheckUsingShadowDecl(BaseUsingDecl *BUD, NamedDecl *Target,
                             const LookupResult &PreviousDecls,
                             UsingShadowDecl *&PrevShadow);
 
   /// Builds a shadow declaration corresponding to a 'using' declaration.
   UsingShadowDecl *BuildUsingShadowDecl(Scope *S, BaseUsingDecl *BUD,
                                         NamedDecl *Target,
                                         UsingShadowDecl *PrevDecl);
 
   /// Checks that the given using declaration is not an invalid
   /// redeclaration.  Note that this is checking only for the using decl
   /// itself, not for any ill-formedness among the UsingShadowDecls.
   bool CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
                                    bool HasTypenameKeyword,
                                    const CXXScopeSpec &SS,
                                    SourceLocation NameLoc,
                                    const LookupResult &Previous);
 
   /// Checks that the given nested-name qualifier used in a using decl
   /// in the current context is appropriately related to the current
   /// scope.  If an error is found, diagnoses it and returns true.
   /// R is nullptr, if the caller has not (yet) done a lookup, otherwise it's
   /// the result of that lookup. UD is likewise nullptr, except when we have an
   /// already-populated UsingDecl whose shadow decls contain the same
   /// information (i.e. we're instantiating a UsingDecl with non-dependent
   /// scope).
   bool CheckUsingDeclQualifier(SourceLocation UsingLoc, bool HasTypename,
                                const CXXScopeSpec &SS,
                                const DeclarationNameInfo &NameInfo,
                                SourceLocation NameLoc,
                                const LookupResult *R = nullptr,
                                const UsingDecl *UD = nullptr);
 
   /// Builds a using declaration.
   ///
   /// \param IsInstantiation - Whether this call arises from an
   ///   instantiation of an unresolved using declaration.  We treat
   ///   the lookup differently for these declarations.
   NamedDecl *BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
                                    SourceLocation UsingLoc,
                                    bool HasTypenameKeyword,
                                    SourceLocation TypenameLoc, CXXScopeSpec &SS,
                                    DeclarationNameInfo NameInfo,
                                    SourceLocation EllipsisLoc,
                                    const ParsedAttributesView &AttrList,
                                    bool IsInstantiation, bool IsUsingIfExists);
   NamedDecl *BuildUsingEnumDeclaration(Scope *S, AccessSpecifier AS,
                                        SourceLocation UsingLoc,
                                        SourceLocation EnumLoc,
                                        SourceLocation NameLoc,
                                        TypeSourceInfo *EnumType, EnumDecl *ED);
   NamedDecl *BuildUsingPackDecl(NamedDecl *InstantiatedFrom,
                                 ArrayRef<NamedDecl *> Expansions);
 
   /// Additional checks for a using declaration referring to a constructor name.
   bool CheckInheritingConstructorUsingDecl(UsingDecl *UD);
 
   /// Given a derived-class using shadow declaration for a constructor and the
   /// correspnding base class constructor, find or create the implicit
   /// synthesized derived class constructor to use for this initialization.
   CXXConstructorDecl *
   findInheritingConstructor(SourceLocation Loc, CXXConstructorDecl *BaseCtor,
                             ConstructorUsingShadowDecl *DerivedShadow);
 
   Decl *ActOnUsingDeclaration(Scope *CurScope, AccessSpecifier AS,
                               SourceLocation UsingLoc,
                               SourceLocation TypenameLoc, CXXScopeSpec &SS,
                               UnqualifiedId &Name, SourceLocation EllipsisLoc,
                               const ParsedAttributesView &AttrList);
   Decl *ActOnUsingEnumDeclaration(Scope *CurScope, AccessSpecifier AS,
                                   SourceLocation UsingLoc,
                                   SourceLocation EnumLoc, SourceRange TyLoc,
                                   const IdentifierInfo &II, ParsedType Ty,
                                   CXXScopeSpec *SS = nullptr);
   Decl *ActOnAliasDeclaration(Scope *CurScope, AccessSpecifier AS,
                               MultiTemplateParamsArg TemplateParams,
                               SourceLocation UsingLoc, UnqualifiedId &Name,
                               const ParsedAttributesView &AttrList,
                               TypeResult Type, Decl *DeclFromDeclSpec);
 
   /// BuildCXXConstructExpr - Creates a complete call to a constructor,
   /// including handling of its default argument expressions.
   ///
   /// \param ConstructKind - a CXXConstructExpr::ConstructionKind
   ExprResult BuildCXXConstructExpr(
       SourceLocation ConstructLoc, QualType DeclInitType, NamedDecl *FoundDecl,
       CXXConstructorDecl *Constructor, MultiExprArg Exprs,
       bool HadMultipleCandidates, bool IsListInitialization,
       bool IsStdInitListInitialization, bool RequiresZeroInit,
       CXXConstructionKind ConstructKind, SourceRange ParenRange);
 
   /// Build a CXXConstructExpr whose constructor has already been resolved if
   /// it denotes an inherited constructor.
   ExprResult BuildCXXConstructExpr(
       SourceLocation ConstructLoc, QualType DeclInitType,
       CXXConstructorDecl *Constructor, bool Elidable, MultiExprArg Exprs,
       bool HadMultipleCandidates, bool IsListInitialization,
       bool IsStdInitListInitialization, bool RequiresZeroInit,
       CXXConstructionKind ConstructKind, SourceRange ParenRange);
 
   // FIXME: Can we remove this and have the above BuildCXXConstructExpr check if
   // the constructor can be elidable?
   ExprResult BuildCXXConstructExpr(
       SourceLocation ConstructLoc, QualType DeclInitType, NamedDecl *FoundDecl,
       CXXConstructorDecl *Constructor, bool Elidable, MultiExprArg Exprs,
       bool HadMultipleCandidates, bool IsListInitialization,
       bool IsStdInitListInitialization, bool RequiresZeroInit,
       CXXConstructionKind ConstructKind, SourceRange ParenRange);
 
   ExprResult ConvertMemberDefaultInitExpression(FieldDecl *FD, Expr *InitExpr,
                                                 SourceLocation InitLoc);
 
   /// FinalizeVarWithDestructor - Prepare for calling destructor on the
   /// constructed variable.
   void FinalizeVarWithDestructor(VarDecl *VD, const RecordType *DeclInitType);
 
   /// Helper class that collects exception specifications for
   /// implicitly-declared special member functions.
   class ImplicitExceptionSpecification {
     // Pointer to allow copying
     Sema *Self;
     // We order exception specifications thus:
     // noexcept is the most restrictive, but is only used in C++11.
     // throw() comes next.
     // Then a throw(collected exceptions)
     // Finally no specification, which is expressed as noexcept(false).
     // throw(...) is used instead if any called function uses it.
     ExceptionSpecificationType ComputedEST;
     llvm::SmallPtrSet<CanQualType, 4> ExceptionsSeen;
     SmallVector<QualType, 4> Exceptions;
 
     void ClearExceptions() {
       ExceptionsSeen.clear();
       Exceptions.clear();
     }
 
   public:
     explicit ImplicitExceptionSpecification(Sema &Self)
         : Self(&Self), ComputedEST(EST_BasicNoexcept) {
       if (!Self.getLangOpts().CPlusPlus11)
         ComputedEST = EST_DynamicNone;
     }
 
     /// Get the computed exception specification type.
     ExceptionSpecificationType getExceptionSpecType() const {
       assert(!isComputedNoexcept(ComputedEST) &&
              "noexcept(expr) should not be a possible result");
       return ComputedEST;
     }
 
     /// The number of exceptions in the exception specification.
     unsigned size() const { return Exceptions.size(); }
 
     /// The set of exceptions in the exception specification.
     const QualType *data() const { return Exceptions.data(); }
 
     /// Integrate another called method into the collected data.
     void CalledDecl(SourceLocation CallLoc, const CXXMethodDecl *Method);
 
     /// Integrate an invoked expression into the collected data.
     void CalledExpr(Expr *E) { CalledStmt(E); }
 
     /// Integrate an invoked statement into the collected data.
     void CalledStmt(Stmt *S);
 
     /// Overwrite an EPI's exception specification with this
     /// computed exception specification.
     FunctionProtoType::ExceptionSpecInfo getExceptionSpec() const {
       FunctionProtoType::ExceptionSpecInfo ESI;
       ESI.Type = getExceptionSpecType();
       if (ESI.Type == EST_Dynamic) {
         ESI.Exceptions = Exceptions;
       } else if (ESI.Type == EST_None) {
         /// C++11 [except.spec]p14:
         ///   The exception-specification is noexcept(false) if the set of
         ///   potential exceptions of the special member function contains "any"
         ESI.Type = EST_NoexceptFalse;
         ESI.NoexceptExpr =
             Self->ActOnCXXBoolLiteral(SourceLocation(), tok::kw_false).get();
       }
       return ESI;
     }
   };
 
   /// Evaluate the implicit exception specification for a defaulted
   /// special member function.
   void EvaluateImplicitExceptionSpec(SourceLocation Loc, FunctionDecl *FD);
 
   /// Check the given exception-specification and update the
   /// exception specification information with the results.
   void checkExceptionSpecification(bool IsTopLevel,
                                    ExceptionSpecificationType EST,
                                    ArrayRef<ParsedType> DynamicExceptions,
                                    ArrayRef<SourceRange> DynamicExceptionRanges,
                                    Expr *NoexceptExpr,
                                    SmallVectorImpl<QualType> &Exceptions,
                                    FunctionProtoType::ExceptionSpecInfo &ESI);
 
   /// Add an exception-specification to the given member or friend function
   /// (or function template). The exception-specification was parsed
   /// after the function itself was declared.
   void actOnDelayedExceptionSpecification(
       Decl *D, ExceptionSpecificationType EST, SourceRange SpecificationRange,
       ArrayRef<ParsedType> DynamicExceptions,
       ArrayRef<SourceRange> DynamicExceptionRanges, Expr *NoexceptExpr);
 
   class InheritedConstructorInfo;
 
   /// Determine if a special member function should have a deleted
   /// definition when it is defaulted.
   bool ShouldDeleteSpecialMember(CXXMethodDecl *MD, CXXSpecialMemberKind CSM,
                                  InheritedConstructorInfo *ICI = nullptr,
                                  bool Diagnose = false);
 
   /// Produce notes explaining why a defaulted function was defined as deleted.
   void DiagnoseDeletedDefaultedFunction(FunctionDecl *FD);
 
   /// Declare the implicit default constructor for the given class.
   ///
   /// \param ClassDecl The class declaration into which the implicit
   /// default constructor will be added.
   ///
   /// \returns The implicitly-declared default constructor.
   CXXConstructorDecl *
   DeclareImplicitDefaultConstructor(CXXRecordDecl *ClassDecl);
 
   /// DefineImplicitDefaultConstructor - Checks for feasibility of
   /// defining this constructor as the default constructor.
   void DefineImplicitDefaultConstructor(SourceLocation CurrentLocation,
                                         CXXConstructorDecl *Constructor);
 
   /// Declare the implicit destructor for the given class.
   ///
   /// \param ClassDecl The class declaration into which the implicit
   /// destructor will be added.
   ///
   /// \returns The implicitly-declared destructor.
   CXXDestructorDecl *DeclareImplicitDestructor(CXXRecordDecl *ClassDecl);
 
   /// DefineImplicitDestructor - Checks for feasibility of
   /// defining this destructor as the default destructor.
   void DefineImplicitDestructor(SourceLocation CurrentLocation,
                                 CXXDestructorDecl *Destructor);
 
   /// Build an exception spec for destructors that don't have one.
   ///
   /// C++11 says that user-defined destructors with no exception spec get one
   /// that looks as if the destructor was implicitly declared.
   void AdjustDestructorExceptionSpec(CXXDestructorDecl *Destructor);
 
   /// Define the specified inheriting constructor.
   void DefineInheritingConstructor(SourceLocation UseLoc,
                                    CXXConstructorDecl *Constructor);
 
   /// Declare the implicit copy constructor for the given class.
   ///
   /// \param ClassDecl The class declaration into which the implicit
   /// copy constructor will be added.
   ///
   /// \returns The implicitly-declared copy constructor.
   CXXConstructorDecl *DeclareImplicitCopyConstructor(CXXRecordDecl *ClassDecl);
 
   /// DefineImplicitCopyConstructor - Checks for feasibility of
   /// defining this constructor as the copy constructor.
   void DefineImplicitCopyConstructor(SourceLocation CurrentLocation,
                                      CXXConstructorDecl *Constructor);
 
   /// Declare the implicit move constructor for the given class.
   ///
   /// \param ClassDecl The Class declaration into which the implicit
   /// move constructor will be added.
   ///
   /// \returns The implicitly-declared move constructor, or NULL if it wasn't
   /// declared.
   CXXConstructorDecl *DeclareImplicitMoveConstructor(CXXRecordDecl *ClassDecl);
 
   /// DefineImplicitMoveConstructor - Checks for feasibility of
   /// defining this constructor as the move constructor.
   void DefineImplicitMoveConstructor(SourceLocation CurrentLocation,
                                      CXXConstructorDecl *Constructor);
 
   /// Declare the implicit copy assignment operator for the given class.
   ///
   /// \param ClassDecl The class declaration into which the implicit
   /// copy assignment operator will be added.
   ///
   /// \returns The implicitly-declared copy assignment operator.
   CXXMethodDecl *DeclareImplicitCopyAssignment(CXXRecordDecl *ClassDecl);
 
   /// Defines an implicitly-declared copy assignment operator.
   void DefineImplicitCopyAssignment(SourceLocation CurrentLocation,
                                     CXXMethodDecl *MethodDecl);
 
   /// Declare the implicit move assignment operator for the given class.
   ///
   /// \param ClassDecl The Class declaration into which the implicit
   /// move assignment operator will be added.
   ///
   /// \returns The implicitly-declared move assignment operator, or NULL if it
   /// wasn't declared.
   CXXMethodDecl *DeclareImplicitMoveAssignment(CXXRecordDecl *ClassDecl);
 
   /// Defines an implicitly-declared move assignment operator.
   void DefineImplicitMoveAssignment(SourceLocation CurrentLocation,
                                     CXXMethodDecl *MethodDecl);
 
   /// Check a completed declaration of an implicit special member.
   void CheckImplicitSpecialMemberDeclaration(Scope *S, FunctionDecl *FD);
 
   /// Determine whether the given function is an implicitly-deleted
   /// special member function.
   bool isImplicitlyDeleted(FunctionDecl *FD);
 
   /// Check whether 'this' shows up in the type of a static member
   /// function after the (naturally empty) cv-qualifier-seq would be.
   ///
   /// \returns true if an error occurred.
   bool checkThisInStaticMemberFunctionType(CXXMethodDecl *Method);
 
   /// Whether this' shows up in the exception specification of a static
   /// member function.
   bool checkThisInStaticMemberFunctionExceptionSpec(CXXMethodDecl *Method);
 
   /// Check whether 'this' shows up in the attributes of the given
   /// static member function.
   ///
   /// \returns true if an error occurred.
   bool checkThisInStaticMemberFunctionAttributes(CXXMethodDecl *Method);
 
   bool CheckImmediateEscalatingFunctionDefinition(
       FunctionDecl *FD, const sema::FunctionScopeInfo *FSI);
 
   void DiagnoseImmediateEscalatingReason(FunctionDecl *FD);
 
   /// Given a constructor and the set of arguments provided for the
   /// constructor, convert the arguments and add any required default arguments
   /// to form a proper call to this constructor.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CompleteConstructorCall(CXXConstructorDecl *Constructor,
                                QualType DeclInitType, MultiExprArg ArgsPtr,
                                SourceLocation Loc,
                                SmallVectorImpl<Expr *> &ConvertedArgs,
                                bool AllowExplicit = false,
                                bool IsListInitialization = false);
 
   /// ActOnCXXEnterDeclInitializer - Invoked when we are about to parse an
   /// initializer for the declaration 'Dcl'.
   /// After this method is called, according to [C++ 3.4.1p13], if 'Dcl' is a
   /// static data member of class X, names should be looked up in the scope of
   /// class X.
   void ActOnCXXEnterDeclInitializer(Scope *S, Decl *Dcl);
 
   /// ActOnCXXExitDeclInitializer - Invoked after we are finished parsing an
   /// initializer for the declaration 'Dcl'.
   void ActOnCXXExitDeclInitializer(Scope *S, Decl *Dcl);
 
   /// Define the "body" of the conversion from a lambda object to a
   /// function pointer.
   ///
   /// This routine doesn't actually define a sensible body; rather, it fills
   /// in the initialization expression needed to copy the lambda object into
   /// the block, and IR generation actually generates the real body of the
   /// block pointer conversion.
   void
   DefineImplicitLambdaToFunctionPointerConversion(SourceLocation CurrentLoc,
                                                   CXXConversionDecl *Conv);
 
   /// Define the "body" of the conversion from a lambda object to a
   /// block pointer.
   ///
   /// This routine doesn't actually define a sensible body; rather, it fills
   /// in the initialization expression needed to copy the lambda object into
   /// the block, and IR generation actually generates the real body of the
   /// block pointer conversion.
   void DefineImplicitLambdaToBlockPointerConversion(SourceLocation CurrentLoc,
                                                     CXXConversionDecl *Conv);
 
   /// ActOnStartLinkageSpecification - Parsed the beginning of a C++
   /// linkage specification, including the language and (if present)
   /// the '{'. ExternLoc is the location of the 'extern', Lang is the
   /// language string literal. LBraceLoc, if valid, provides the location of
   /// the '{' brace. Otherwise, this linkage specification does not
   /// have any braces.
   Decl *ActOnStartLinkageSpecification(Scope *S, SourceLocation ExternLoc,
                                        Expr *LangStr, SourceLocation LBraceLoc);
 
   /// ActOnFinishLinkageSpecification - Complete the definition of
   /// the C++ linkage specification LinkageSpec. If RBraceLoc is
   /// valid, it's the position of the closing '}' brace in a linkage
   /// specification that uses braces.
   Decl *ActOnFinishLinkageSpecification(Scope *S, Decl *LinkageSpec,
                                         SourceLocation RBraceLoc);
 
   //===--------------------------------------------------------------------===//
   // C++ Classes
   //
 
   /// Get the class that is directly named by the current context. This is the
   /// class for which an unqualified-id in this scope could name a constructor
   /// or destructor.
   ///
   /// If the scope specifier denotes a class, this will be that class.
   /// If the scope specifier is empty, this will be the class whose
   /// member-specification we are currently within. Otherwise, there
   /// is no such class.
   CXXRecordDecl *getCurrentClass(Scope *S, const CXXScopeSpec *SS);
 
   /// isCurrentClassName - Determine whether the identifier II is the
   /// name of the class type currently being defined. In the case of
   /// nested classes, this will only return true if II is the name of
   /// the innermost class.
   bool isCurrentClassName(const IdentifierInfo &II, Scope *S,
                           const CXXScopeSpec *SS = nullptr);
 
   /// Determine whether the identifier II is a typo for the name of
   /// the class type currently being defined. If so, update it to the identifier
   /// that should have been used.
   bool isCurrentClassNameTypo(IdentifierInfo *&II, const CXXScopeSpec *SS);
 
   /// ActOnAccessSpecifier - Parsed an access specifier followed by a colon.
   bool ActOnAccessSpecifier(AccessSpecifier Access, SourceLocation ASLoc,
                             SourceLocation ColonLoc,
                             const ParsedAttributesView &Attrs);
 
   /// ActOnCXXMemberDeclarator - This is invoked when a C++ class member
   /// declarator is parsed. 'AS' is the access specifier, 'BW' specifies the
   /// bitfield width if there is one, 'InitExpr' specifies the initializer if
   /// one has been parsed, and 'InitStyle' is set if an in-class initializer is
   /// present (but parsing it has been deferred).
   NamedDecl *
   ActOnCXXMemberDeclarator(Scope *S, AccessSpecifier AS, Declarator &D,
                            MultiTemplateParamsArg TemplateParameterLists,
                            Expr *BitfieldWidth, const VirtSpecifiers &VS,
                            InClassInitStyle InitStyle);
 
   /// Enter a new C++ default initializer scope. After calling this, the
   /// caller must call \ref ActOnFinishCXXInClassMemberInitializer, even if
   /// parsing or instantiating the initializer failed.
   void ActOnStartCXXInClassMemberInitializer();
 
   /// This is invoked after parsing an in-class initializer for a
   /// non-static C++ class member, and after instantiating an in-class
   /// initializer in a class template. Such actions are deferred until the class
   /// is complete.
   void ActOnFinishCXXInClassMemberInitializer(Decl *VarDecl,
                                               SourceLocation EqualLoc,
                                               Expr *Init);
 
   /// Handle a C++ member initializer using parentheses syntax.
   MemInitResult
   ActOnMemInitializer(Decl *ConstructorD, Scope *S, CXXScopeSpec &SS,
                       IdentifierInfo *MemberOrBase, ParsedType TemplateTypeTy,
                       const DeclSpec &DS, SourceLocation IdLoc,
                       SourceLocation LParenLoc, ArrayRef<Expr *> Args,
                       SourceLocation RParenLoc, SourceLocation EllipsisLoc);
 
   /// Handle a C++ member initializer using braced-init-list syntax.
   MemInitResult ActOnMemInitializer(Decl *ConstructorD, Scope *S,
                                     CXXScopeSpec &SS,
                                     IdentifierInfo *MemberOrBase,
                                     ParsedType TemplateTypeTy,
                                     const DeclSpec &DS, SourceLocation IdLoc,
                                     Expr *InitList, SourceLocation EllipsisLoc);
 
   /// Handle a C++ member initializer.
   MemInitResult BuildMemInitializer(Decl *ConstructorD, Scope *S,
                                     CXXScopeSpec &SS,
                                     IdentifierInfo *MemberOrBase,
                                     ParsedType TemplateTypeTy,
                                     const DeclSpec &DS, SourceLocation IdLoc,
                                     Expr *Init, SourceLocation EllipsisLoc);
 
   MemInitResult BuildMemberInitializer(ValueDecl *Member, Expr *Init,
                                        SourceLocation IdLoc);
 
   MemInitResult BuildBaseInitializer(QualType BaseType,
                                      TypeSourceInfo *BaseTInfo, Expr *Init,
                                      CXXRecordDecl *ClassDecl,
                                      SourceLocation EllipsisLoc);
 
   MemInitResult BuildDelegatingInitializer(TypeSourceInfo *TInfo, Expr *Init,
                                            CXXRecordDecl *ClassDecl);
 
   bool SetDelegatingInitializer(CXXConstructorDecl *Constructor,
                                 CXXCtorInitializer *Initializer);
 
   bool SetCtorInitializers(
       CXXConstructorDecl *Constructor, bool AnyErrors,
       ArrayRef<CXXCtorInitializer *> Initializers = std::nullopt);
 
   /// MarkBaseAndMemberDestructorsReferenced - Given a record decl,
   /// mark all the non-trivial destructors of its members and bases as
   /// referenced.
   void MarkBaseAndMemberDestructorsReferenced(SourceLocation Loc,
                                               CXXRecordDecl *Record);
 
   /// Mark destructors of virtual bases of this class referenced. In the Itanium
   /// C++ ABI, this is done when emitting a destructor for any non-abstract
   /// class. In the Microsoft C++ ABI, this is done any time a class's
   /// destructor is referenced.
   void MarkVirtualBaseDestructorsReferenced(
       SourceLocation Location, CXXRecordDecl *ClassDecl,
       llvm::SmallPtrSetImpl<const RecordType *> *DirectVirtualBases = nullptr);
 
   /// Do semantic checks to allow the complete destructor variant to be emitted
   /// when the destructor is defined in another translation unit. In the Itanium
   /// C++ ABI, destructor variants are emitted together. In the MS C++ ABI, they
   /// can be emitted in separate TUs. To emit the complete variant, run a subset
   /// of the checks performed when emitting a regular destructor.
   void CheckCompleteDestructorVariant(SourceLocation CurrentLocation,
                                       CXXDestructorDecl *Dtor);
 
   /// The list of classes whose vtables have been used within
   /// this translation unit, and the source locations at which the
   /// first use occurred.
   typedef std::pair<CXXRecordDecl *, SourceLocation> VTableUse;
 
   /// The list of vtables that are required but have not yet been
   /// materialized.
   SmallVector<VTableUse, 16> VTableUses;
 
   /// The set of classes whose vtables have been used within
   /// this translation unit, and a bit that will be true if the vtable is
   /// required to be emitted (otherwise, it should be emitted only if needed
   /// by code generation).
   llvm::DenseMap<CXXRecordDecl *, bool> VTablesUsed;
 
   /// Load any externally-stored vtable uses.
   void LoadExternalVTableUses();
 
   /// Note that the vtable for the given class was used at the
   /// given location.
   void MarkVTableUsed(SourceLocation Loc, CXXRecordDecl *Class,
                       bool DefinitionRequired = false);
 
   /// Mark the exception specifications of all virtual member functions
   /// in the given class as needed.
   void MarkVirtualMemberExceptionSpecsNeeded(SourceLocation Loc,
                                              const CXXRecordDecl *RD);
 
   /// MarkVirtualMembersReferenced - Will mark all members of the given
   /// CXXRecordDecl referenced.
   void MarkVirtualMembersReferenced(SourceLocation Loc, const CXXRecordDecl *RD,
                                     bool ConstexprOnly = false);
 
   /// Define all of the vtables that have been used in this
   /// translation unit and reference any virtual members used by those
   /// vtables.
   ///
   /// \returns true if any work was done, false otherwise.
   bool DefineUsedVTables();
 
   /// AddImplicitlyDeclaredMembersToClass - Adds any implicitly-declared
   /// special functions, such as the default constructor, copy
   /// constructor, or destructor, to the given C++ class (C++
   /// [special]p1).  This routine can only be executed just before the
   /// definition of the class is complete.
   void AddImplicitlyDeclaredMembersToClass(CXXRecordDecl *ClassDecl);
 
   /// ActOnMemInitializers - Handle the member initializers for a constructor.
   void ActOnMemInitializers(Decl *ConstructorDecl, SourceLocation ColonLoc,
                             ArrayRef<CXXCtorInitializer *> MemInits,
                             bool AnyErrors);
 
   /// Check class-level dllimport/dllexport attribute. The caller must
   /// ensure that referenceDLLExportedClassMethods is called some point later
   /// when all outer classes of Class are complete.
   void checkClassLevelDLLAttribute(CXXRecordDecl *Class);
   void checkClassLevelCodeSegAttribute(CXXRecordDecl *Class);
 
   void referenceDLLExportedClassMethods();
 
   /// Perform propagation of DLL attributes from a derived class to a
   /// templated base class for MS compatibility.
   void propagateDLLAttrToBaseClassTemplate(
       CXXRecordDecl *Class, Attr *ClassAttr,
       ClassTemplateSpecializationDecl *BaseTemplateSpec,
       SourceLocation BaseLoc);
 
   /// Perform semantic checks on a class definition that has been
   /// completing, introducing implicitly-declared members, checking for
   /// abstract types, etc.
   ///
   /// \param S The scope in which the class was parsed. Null if we didn't just
   ///        parse a class definition.
   /// \param Record The completed class.
   void CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record);
 
   /// Check that the C++ class annoated with "trivial_abi" satisfies all the
   /// conditions that are needed for the attribute to have an effect.
   void checkIllFormedTrivialABIStruct(CXXRecordDecl &RD);
 
   /// Check that VTable Pointer authentication is only being set on the first
   /// first instantiation of the vtable
   void checkIncorrectVTablePointerAuthenticationAttribute(CXXRecordDecl &RD);
 
   void ActOnFinishCXXMemberSpecification(Scope *S, SourceLocation RLoc,
                                          Decl *TagDecl, SourceLocation LBrac,
                                          SourceLocation RBrac,
                                          const ParsedAttributesView &AttrList);
 
   /// Perform any semantic analysis which needs to be delayed until all
   /// pending class member declarations have been parsed.
   void ActOnFinishCXXMemberDecls();
   void ActOnFinishCXXNonNestedClass();
 
   /// This is used to implement the constant expression evaluation part of the
   /// attribute enable_if extension. There is nothing in standard C++ which
   /// would require reentering parameters.
   void ActOnReenterCXXMethodParameter(Scope *S, ParmVarDecl *Param);
   unsigned ActOnReenterTemplateScope(Decl *Template,
                                      llvm::function_ref<Scope *()> EnterScope);
   void ActOnStartDelayedMemberDeclarations(Scope *S, Decl *Record);
 
   /// ActOnStartDelayedCXXMethodDeclaration - We have completed
   /// parsing a top-level (non-nested) C++ class, and we are now
   /// parsing those parts of the given Method declaration that could
   /// not be parsed earlier (C++ [class.mem]p2), such as default
   /// arguments. This action should enter the scope of the given
   /// Method declaration as if we had just parsed the qualified method
   /// name. However, it should not bring the parameters into scope;
   /// that will be performed by ActOnDelayedCXXMethodParameter.
   void ActOnStartDelayedCXXMethodDeclaration(Scope *S, Decl *Method);
   void ActOnDelayedCXXMethodParameter(Scope *S, Decl *Param);
   void ActOnFinishDelayedMemberDeclarations(Scope *S, Decl *Record);
 
   /// ActOnFinishDelayedCXXMethodDeclaration - We have finished
   /// processing the delayed method declaration for Method. The method
   /// declaration is now considered finished. There may be a separate
   /// ActOnStartOfFunctionDef action later (not necessarily
   /// immediately!) for this method, if it was also defined inside the
   /// class body.
   void ActOnFinishDelayedCXXMethodDeclaration(Scope *S, Decl *Method);
   void ActOnFinishDelayedMemberInitializers(Decl *Record);
 
   bool EvaluateStaticAssertMessageAsString(Expr *Message, std::string &Result,
                                            ASTContext &Ctx,
                                            bool ErrorOnInvalidMessage);
   Decl *ActOnStaticAssertDeclaration(SourceLocation StaticAssertLoc,
                                      Expr *AssertExpr, Expr *AssertMessageExpr,
                                      SourceLocation RParenLoc);
   Decl *BuildStaticAssertDeclaration(SourceLocation StaticAssertLoc,
                                      Expr *AssertExpr, Expr *AssertMessageExpr,
                                      SourceLocation RParenLoc, bool Failed);
 
   /// Try to print more useful information about a failed static_assert
   /// with expression \E
   void DiagnoseStaticAssertDetails(const Expr *E);
 
   /// Handle a friend type declaration.  This works in tandem with
   /// ActOnTag.
   ///
   /// Notes on friend class templates:
   ///
   /// We generally treat friend class declarations as if they were
   /// declaring a class.  So, for example, the elaborated type specifier
   /// in a friend declaration is required to obey the restrictions of a
   /// class-head (i.e. no typedefs in the scope chain), template
   /// parameters are required to match up with simple template-ids, &c.
   /// However, unlike when declaring a template specialization, it's
   /// okay to refer to a template specialization without an empty
   /// template parameter declaration, e.g.
   ///   friend class A<T>::B<unsigned>;
   /// We permit this as a special case; if there are any template
   /// parameters present at all, require proper matching, i.e.
   ///   template <> template \<class T> friend class A<int>::B;
   Decl *ActOnFriendTypeDecl(Scope *S, const DeclSpec &DS,
                             MultiTemplateParamsArg TemplateParams);
   NamedDecl *ActOnFriendFunctionDecl(Scope *S, Declarator &D,
                                      MultiTemplateParamsArg TemplateParams);
 
   /// CheckConstructorDeclarator - Called by ActOnDeclarator to check
   /// the well-formedness of the constructor declarator @p D with type @p
   /// R. If there are any errors in the declarator, this routine will
   /// emit diagnostics and set the invalid bit to true.  In any case, the type
   /// will be updated to reflect a well-formed type for the constructor and
   /// returned.
   QualType CheckConstructorDeclarator(Declarator &D, QualType R,
                                       StorageClass &SC);
 
   /// CheckConstructor - Checks a fully-formed constructor for
   /// well-formedness, issuing any diagnostics required. Returns true if
   /// the constructor declarator is invalid.
   void CheckConstructor(CXXConstructorDecl *Constructor);
 
   /// CheckDestructorDeclarator - Called by ActOnDeclarator to check
   /// the well-formednes of the destructor declarator @p D with type @p
   /// R. If there are any errors in the declarator, this routine will
   /// emit diagnostics and set the declarator to invalid.  Even if this happens,
   /// will be updated to reflect a well-formed type for the destructor and
   /// returned.
   QualType CheckDestructorDeclarator(Declarator &D, QualType R,
                                      StorageClass &SC);
 
   /// CheckDestructor - Checks a fully-formed destructor definition for
   /// well-formedness, issuing any diagnostics required.  Returns true
   /// on error.
   bool CheckDestructor(CXXDestructorDecl *Destructor);
 
   /// CheckConversionDeclarator - Called by ActOnDeclarator to check the
   /// well-formednes of the conversion function declarator @p D with
   /// type @p R. If there are any errors in the declarator, this routine
   /// will emit diagnostics and return true. Otherwise, it will return
   /// false. Either way, the type @p R will be updated to reflect a
   /// well-formed type for the conversion operator.
   void CheckConversionDeclarator(Declarator &D, QualType &R, StorageClass &SC);
 
   /// ActOnConversionDeclarator - Called by ActOnDeclarator to complete
   /// the declaration of the given C++ conversion function. This routine
   /// is responsible for recording the conversion function in the C++
   /// class, if possible.
   Decl *ActOnConversionDeclarator(CXXConversionDecl *Conversion);
 
   /// Check the validity of a declarator that we parsed for a deduction-guide.
   /// These aren't actually declarators in the grammar, so we need to check that
   /// the user didn't specify any pieces that are not part of the
   /// deduction-guide grammar. Return true on invalid deduction-guide.
   bool CheckDeductionGuideDeclarator(Declarator &D, QualType &R,
                                      StorageClass &SC);
 
   void CheckExplicitlyDefaultedFunction(Scope *S, FunctionDecl *MD);
 
   bool CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
                                              CXXSpecialMemberKind CSM,
                                              SourceLocation DefaultLoc);
   void CheckDelayedMemberExceptionSpecs();
 
   /// Kinds of defaulted comparison operator functions.
   enum class DefaultedComparisonKind : unsigned char {
     /// This is not a defaultable comparison operator.
     None,
     /// This is an operator== that should be implemented as a series of
     /// subobject comparisons.
     Equal,
     /// This is an operator<=> that should be implemented as a series of
     /// subobject comparisons.
     ThreeWay,
     /// This is an operator!= that should be implemented as a rewrite in terms
     /// of a == comparison.
     NotEqual,
     /// This is an <, <=, >, or >= that should be implemented as a rewrite in
     /// terms of a <=> comparison.
     Relational,
   };
 
   bool CheckExplicitlyDefaultedComparison(Scope *S, FunctionDecl *MD,
                                           DefaultedComparisonKind DCK);
   void DeclareImplicitEqualityComparison(CXXRecordDecl *RD,
                                          FunctionDecl *Spaceship);
   void DefineDefaultedComparison(SourceLocation Loc, FunctionDecl *FD,
                                  DefaultedComparisonKind DCK);
 
   void CheckExplicitObjectMemberFunction(Declarator &D, DeclarationName Name,
                                          QualType R, bool IsLambda,
                                          DeclContext *DC = nullptr);
   void CheckExplicitObjectMemberFunction(DeclContext *DC, Declarator &D,
                                          DeclarationName Name, QualType R);
   void CheckExplicitObjectLambda(Declarator &D);
 
   //===--------------------------------------------------------------------===//
   // C++ Derived Classes
   //
 
   /// Check the validity of a C++ base class specifier.
   ///
   /// \returns a new CXXBaseSpecifier if well-formed, emits diagnostics
   /// and returns NULL otherwise.
   CXXBaseSpecifier *CheckBaseSpecifier(CXXRecordDecl *Class,
                                        SourceRange SpecifierRange, bool Virtual,
                                        AccessSpecifier Access,
                                        TypeSourceInfo *TInfo,
                                        SourceLocation EllipsisLoc);
 
   /// ActOnBaseSpecifier - Parsed a base specifier. A base specifier is
   /// one entry in the base class list of a class specifier, for
   /// example:
   ///    class foo : public bar, virtual private baz {
   /// 'public bar' and 'virtual private baz' are each base-specifiers.
   BaseResult ActOnBaseSpecifier(Decl *classdecl, SourceRange SpecifierRange,
                                 const ParsedAttributesView &Attrs, bool Virtual,
                                 AccessSpecifier Access, ParsedType basetype,
                                 SourceLocation BaseLoc,
                                 SourceLocation EllipsisLoc);
 
   /// Performs the actual work of attaching the given base class
   /// specifiers to a C++ class.
   bool AttachBaseSpecifiers(CXXRecordDecl *Class,
                             MutableArrayRef<CXXBaseSpecifier *> Bases);
 
   /// ActOnBaseSpecifiers - Attach the given base specifiers to the
   /// class, after checking whether there are any duplicate base
   /// classes.
   void ActOnBaseSpecifiers(Decl *ClassDecl,
                            MutableArrayRef<CXXBaseSpecifier *> Bases);
 
   /// Determine whether the type \p Derived is a C++ class that is
   /// derived from the type \p Base.
   bool IsDerivedFrom(SourceLocation Loc, QualType Derived, QualType Base);
 
   /// Determine whether the type \p Derived is a C++ class that is
   /// derived from the type \p Base.
   bool IsDerivedFrom(SourceLocation Loc, QualType Derived, QualType Base,
                      CXXBasePaths &Paths);
 
   // FIXME: I don't like this name.
   void BuildBasePathArray(const CXXBasePaths &Paths, CXXCastPath &BasePath);
 
   bool CheckDerivedToBaseConversion(QualType Derived, QualType Base,
                                     SourceLocation Loc, SourceRange Range,
                                     CXXCastPath *BasePath = nullptr,
                                     bool IgnoreAccess = false);
 
   /// CheckDerivedToBaseConversion - Check whether the Derived-to-Base
   /// conversion (where Derived and Base are class types) is
   /// well-formed, meaning that the conversion is unambiguous (and
   /// that all of the base classes are accessible). Returns true
   /// and emits a diagnostic if the code is ill-formed, returns false
   /// otherwise. Loc is the location where this routine should point to
   /// if there is an error, and Range is the source range to highlight
   /// if there is an error.
   ///
   /// If either InaccessibleBaseID or AmbiguousBaseConvID are 0, then the
   /// diagnostic for the respective type of error will be suppressed, but the
   /// check for ill-formed code will still be performed.
   bool CheckDerivedToBaseConversion(QualType Derived, QualType Base,
                                     unsigned InaccessibleBaseID,
                                     unsigned AmbiguousBaseConvID,
                                     SourceLocation Loc, SourceRange Range,
                                     DeclarationName Name, CXXCastPath *BasePath,
                                     bool IgnoreAccess = false);
 
   /// Builds a string representing ambiguous paths from a
   /// specific derived class to different subobjects of the same base
   /// class.
   ///
   /// This function builds a string that can be used in error messages
   /// to show the different paths that one can take through the
   /// inheritance hierarchy to go from the derived class to different
   /// subobjects of a base class. The result looks something like this:
   /// @code
   /// struct D -> struct B -> struct A
   /// struct D -> struct C -> struct A
   /// @endcode
   std::string getAmbiguousPathsDisplayString(CXXBasePaths &Paths);
 
   bool CheckOverridingFunctionAttributes(CXXMethodDecl *New,
                                          const CXXMethodDecl *Old);
 
   /// CheckOverridingFunctionReturnType - Checks whether the return types are
   /// covariant, according to C++ [class.virtual]p5.
   bool CheckOverridingFunctionReturnType(const CXXMethodDecl *New,
                                          const CXXMethodDecl *Old);
 
   // Check that the overriding method has no explicit object parameter.
   bool CheckExplicitObjectOverride(CXXMethodDecl *New,
                                    const CXXMethodDecl *Old);
 
   /// Mark the given method pure.
   ///
   /// \param Method the method to be marked pure.
   ///
   /// \param InitRange the source range that covers the "0" initializer.
   bool CheckPureMethod(CXXMethodDecl *Method, SourceRange InitRange);
 
   /// CheckOverrideControl - Check C++11 override control semantics.
   void CheckOverrideControl(NamedDecl *D);
 
   /// DiagnoseAbsenceOfOverrideControl - Diagnose if 'override' keyword was
   /// not used in the declaration of an overriding method.
   void DiagnoseAbsenceOfOverrideControl(NamedDecl *D, bool Inconsistent);
 
   /// CheckIfOverriddenFunctionIsMarkedFinal - Checks whether a virtual member
   /// function overrides a virtual member function marked 'final', according to
   /// C++11 [class.virtual]p4.
   bool CheckIfOverriddenFunctionIsMarkedFinal(const CXXMethodDecl *New,
                                               const CXXMethodDecl *Old);
 
   enum AbstractDiagSelID {
     AbstractNone = -1,
     AbstractReturnType,
     AbstractParamType,
     AbstractVariableType,
     AbstractFieldType,
     AbstractIvarType,
     AbstractSynthesizedIvarType,
     AbstractArrayType
   };
 
   struct TypeDiagnoser;
 
   bool isAbstractType(SourceLocation Loc, QualType T);
   bool RequireNonAbstractType(SourceLocation Loc, QualType T,
                               TypeDiagnoser &Diagnoser);
   template <typename... Ts>
   bool RequireNonAbstractType(SourceLocation Loc, QualType T, unsigned DiagID,
                               const Ts &...Args) {
     BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireNonAbstractType(Loc, T, Diagnoser);
   }
 
   void DiagnoseAbstractType(const CXXRecordDecl *RD);
 
   //===--------------------------------------------------------------------===//
   // C++ Overloaded Operators [C++ 13.5]
   //
 
   /// CheckOverloadedOperatorDeclaration - Check whether the declaration
   /// of this overloaded operator is well-formed. If so, returns false;
   /// otherwise, emits appropriate diagnostics and returns true.
   bool CheckOverloadedOperatorDeclaration(FunctionDecl *FnDecl);
 
   /// CheckLiteralOperatorDeclaration - Check whether the declaration
   /// of this literal operator function is well-formed. If so, returns
   /// false; otherwise, emits appropriate diagnostics and returns true.
   bool CheckLiteralOperatorDeclaration(FunctionDecl *FnDecl);
 
   /// ActOnExplicitBoolSpecifier - Build an ExplicitSpecifier from an expression
   /// found in an explicit(bool) specifier.
   ExplicitSpecifier ActOnExplicitBoolSpecifier(Expr *E);
 
   /// tryResolveExplicitSpecifier - Attempt to resolve the explict specifier.
   /// Returns true if the explicit specifier is now resolved.
   bool tryResolveExplicitSpecifier(ExplicitSpecifier &ExplicitSpec);
 
   /// ActOnCXXConditionDeclarationExpr - Parsed a condition declaration of a
   /// C++ if/switch/while/for statement.
   /// e.g: "if (int x = f()) {...}"
   DeclResult ActOnCXXConditionDeclaration(Scope *S, Declarator &D);
 
   // Emitting members of dllexported classes is delayed until the class
   // (including field initializers) is fully parsed.
   SmallVector<CXXRecordDecl *, 4> DelayedDllExportClasses;
   SmallVector<CXXMethodDecl *, 4> DelayedDllExportMemberFunctions;
 
   /// Merge the exception specifications of two variable declarations.
   ///
   /// This is called when there's a redeclaration of a VarDecl. The function
   /// checks if the redeclaration might have an exception specification and
   /// validates compatibility and merges the specs if necessary.
   void MergeVarDeclExceptionSpecs(VarDecl *New, VarDecl *Old);
 
   /// MergeCXXFunctionDecl - Merge two declarations of the same C++
   /// function, once we already know that they have the same
   /// type. Subroutine of MergeFunctionDecl. Returns true if there was an
   /// error, false otherwise.
   bool MergeCXXFunctionDecl(FunctionDecl *New, FunctionDecl *Old, Scope *S);
 
   /// Helpers for dealing with blocks and functions.
   void CheckCXXDefaultArguments(FunctionDecl *FD);
 
   /// CheckExtraCXXDefaultArguments - Check for any extra default
   /// arguments in the declarator, which is not a function declaration
   /// or definition and therefore is not permitted to have default
   /// arguments. This routine should be invoked for every declarator
   /// that is not a function declaration or definition.
   void CheckExtraCXXDefaultArguments(Declarator &D);
 
   CXXSpecialMemberKind getSpecialMember(const CXXMethodDecl *MD) {
     return getDefaultedFunctionKind(MD).asSpecialMember();
   }
 
   /// Perform semantic analysis for the variable declaration that
   /// occurs within a C++ catch clause, returning the newly-created
   /// variable.
   VarDecl *BuildExceptionDeclaration(Scope *S, TypeSourceInfo *TInfo,
                                      SourceLocation StartLoc,
                                      SourceLocation IdLoc,
                                      const IdentifierInfo *Id);
 
   /// ActOnExceptionDeclarator - Parsed the exception-declarator in a C++ catch
   /// handler.
   Decl *ActOnExceptionDeclarator(Scope *S, Declarator &D);
 
   void DiagnoseReturnInConstructorExceptionHandler(CXXTryStmt *TryBlock);
 
   /// Handle a friend tag declaration where the scope specifier was
   /// templated.
   DeclResult ActOnTemplatedFriendTag(Scope *S, SourceLocation FriendLoc,
                                      unsigned TagSpec, SourceLocation TagLoc,
                                      CXXScopeSpec &SS, IdentifierInfo *Name,
                                      SourceLocation NameLoc,
                                      const ParsedAttributesView &Attr,
                                      MultiTemplateParamsArg TempParamLists);
 
   MSPropertyDecl *HandleMSProperty(Scope *S, RecordDecl *TagD,
                                    SourceLocation DeclStart, Declarator &D,
                                    Expr *BitfieldWidth,
                                    InClassInitStyle InitStyle,
                                    AccessSpecifier AS,
                                    const ParsedAttr &MSPropertyAttr);
 
   /// Diagnose why the specified class does not have a trivial special member of
   /// the given kind.
   void DiagnoseNontrivial(const CXXRecordDecl *Record,
                           CXXSpecialMemberKind CSM);
 
   enum TrivialABIHandling {
     /// The triviality of a method unaffected by "trivial_abi".
     TAH_IgnoreTrivialABI,
 
     /// The triviality of a method affected by "trivial_abi".
     TAH_ConsiderTrivialABI
   };
 
   /// Determine whether a defaulted or deleted special member function is
   /// trivial, as specified in C++11 [class.ctor]p5, C++11 [class.copy]p12,
   /// C++11 [class.copy]p25, and C++11 [class.dtor]p5.
   bool SpecialMemberIsTrivial(CXXMethodDecl *MD, CXXSpecialMemberKind CSM,
                               TrivialABIHandling TAH = TAH_IgnoreTrivialABI,
                               bool Diagnose = false);
 
   /// For a defaulted function, the kind of defaulted function that it is.
   class DefaultedFunctionKind {
     LLVM_PREFERRED_TYPE(CXXSpecialMemberKind)
     unsigned SpecialMember : 8;
     unsigned Comparison : 8;
 
   public:
     DefaultedFunctionKind()
         : SpecialMember(llvm::to_underlying(CXXSpecialMemberKind::Invalid)),
           Comparison(llvm::to_underlying(DefaultedComparisonKind::None)) {}
     DefaultedFunctionKind(CXXSpecialMemberKind CSM)
         : SpecialMember(llvm::to_underlying(CSM)),
           Comparison(llvm::to_underlying(DefaultedComparisonKind::None)) {}
     DefaultedFunctionKind(DefaultedComparisonKind Comp)
         : SpecialMember(llvm::to_underlying(CXXSpecialMemberKind::Invalid)),
           Comparison(llvm::to_underlying(Comp)) {}
 
     bool isSpecialMember() const {
       return static_cast<CXXSpecialMemberKind>(SpecialMember) !=
              CXXSpecialMemberKind::Invalid;
     }
     bool isComparison() const {
       return static_cast<DefaultedComparisonKind>(Comparison) !=
              DefaultedComparisonKind::None;
     }
 
     explicit operator bool() const {
       return isSpecialMember() || isComparison();
     }
 
     CXXSpecialMemberKind asSpecialMember() const {
       return static_cast<CXXSpecialMemberKind>(SpecialMember);
     }
     DefaultedComparisonKind asComparison() const {
       return static_cast<DefaultedComparisonKind>(Comparison);
     }
 
     /// Get the index of this function kind for use in diagnostics.
     unsigned getDiagnosticIndex() const {
       static_assert(llvm::to_underlying(CXXSpecialMemberKind::Invalid) >
                         llvm::to_underlying(CXXSpecialMemberKind::Destructor),
                     "invalid should have highest index");
       static_assert((unsigned)DefaultedComparisonKind::None == 0,
                     "none should be equal to zero");
       return SpecialMember + Comparison;
     }
   };
 
   /// Determine the kind of defaulting that would be done for a given function.
   ///
   /// If the function is both a default constructor and a copy / move
   /// constructor (due to having a default argument for the first parameter),
   /// this picks CXXSpecialMemberKind::DefaultConstructor.
   ///
   /// FIXME: Check that case is properly handled by all callers.
   DefaultedFunctionKind getDefaultedFunctionKind(const FunctionDecl *FD);
 
   /// Handle a C++11 empty-declaration and attribute-declaration.
   Decl *ActOnEmptyDeclaration(Scope *S, const ParsedAttributesView &AttrList,
                               SourceLocation SemiLoc);
 
   enum class CheckConstexprKind {
     /// Diagnose issues that are non-constant or that are extensions.
     Diagnose,
     /// Identify whether this function satisfies the formal rules for constexpr
     /// functions in the current lanugage mode (with no extensions).
     CheckValid
   };
 
   // Check whether a function declaration satisfies the requirements of a
   // constexpr function definition or a constexpr constructor definition. If so,
   // return true. If not, produce appropriate diagnostics (unless asked not to
   // by Kind) and return false.
   //
   // This implements C++11 [dcl.constexpr]p3,4, as amended by DR1360.
   bool CheckConstexprFunctionDefinition(const FunctionDecl *FD,
                                         CheckConstexprKind Kind);
 
   /// Diagnose methods which overload virtual methods in a base class
   /// without overriding any.
   void DiagnoseHiddenVirtualMethods(CXXMethodDecl *MD);
 
   /// Check if a method overloads virtual methods in a base class without
   /// overriding any.
   void
   FindHiddenVirtualMethods(CXXMethodDecl *MD,
                            SmallVectorImpl<CXXMethodDecl *> &OverloadedMethods);
   void
   NoteHiddenVirtualMethods(CXXMethodDecl *MD,
                            SmallVectorImpl<CXXMethodDecl *> &OverloadedMethods);
 
   /// ActOnParamDefaultArgument - Check whether the default argument
   /// provided for a function parameter is well-formed. If so, attach it
   /// to the parameter declaration.
   void ActOnParamDefaultArgument(Decl *param, SourceLocation EqualLoc,
                                  Expr *defarg);
 
   /// ActOnParamUnparsedDefaultArgument - We've seen a default
   /// argument for a function parameter, but we can't parse it yet
   /// because we're inside a class definition. Note that this default
   /// argument will be parsed later.
   void ActOnParamUnparsedDefaultArgument(Decl *param, SourceLocation EqualLoc,
                                          SourceLocation ArgLoc);
 
   /// ActOnParamDefaultArgumentError - Parsing or semantic analysis of
   /// the default argument for the parameter param failed.
   void ActOnParamDefaultArgumentError(Decl *param, SourceLocation EqualLoc,
                                       Expr *DefaultArg);
   ExprResult ConvertParamDefaultArgument(ParmVarDecl *Param, Expr *DefaultArg,
                                          SourceLocation EqualLoc);
   void SetParamDefaultArgument(ParmVarDecl *Param, Expr *DefaultArg,
                                SourceLocation EqualLoc);
 
   void ActOnPureSpecifier(Decl *D, SourceLocation PureSpecLoc);
   void SetDeclDeleted(Decl *dcl, SourceLocation DelLoc,
                       StringLiteral *Message = nullptr);
   void SetDeclDefaulted(Decl *dcl, SourceLocation DefaultLoc);
 
   void SetFunctionBodyKind(Decl *D, SourceLocation Loc, FnBodyKind BodyKind,
                            StringLiteral *DeletedMessage = nullptr);
   void ActOnStartTrailingRequiresClause(Scope *S, Declarator &D);
   ExprResult ActOnFinishTrailingRequiresClause(ExprResult ConstraintExpr);
   ExprResult ActOnRequiresClause(ExprResult ConstraintExpr);
 
   NamedDecl *
   ActOnDecompositionDeclarator(Scope *S, Declarator &D,
                                MultiTemplateParamsArg TemplateParamLists);
   void DiagPlaceholderVariableDefinition(SourceLocation Loc);
   bool DiagRedefinedPlaceholderFieldDecl(SourceLocation Loc,
                                          RecordDecl *ClassDecl,
                                          const IdentifierInfo *Name);
 
   void CheckCompleteDecompositionDeclaration(DecompositionDecl *DD);
 
   /// Stack containing information needed when in C++2a an 'auto' is encountered
   /// in a function declaration parameter type specifier in order to invent a
   /// corresponding template parameter in the enclosing abbreviated function
   /// template. This information is also present in LambdaScopeInfo, stored in
   /// the FunctionScopes stack.
   SmallVector<InventedTemplateParameterInfo, 4> InventedParameterInfos;
 
   /// FieldCollector - Collects CXXFieldDecls during parsing of C++ classes.
   std::unique_ptr<CXXFieldCollector> FieldCollector;
 
   typedef llvm::SmallSetVector<const NamedDecl *, 16> NamedDeclSetType;
   /// Set containing all declared private fields that are not used.
   NamedDeclSetType UnusedPrivateFields;
 
   typedef llvm::SmallPtrSet<const CXXRecordDecl *, 8> RecordDeclSetTy;
 
   /// PureVirtualClassDiagSet - a set of class declarations which we have
   /// emitted a list of pure virtual functions. Used to prevent emitting the
   /// same list more than once.
   std::unique_ptr<RecordDeclSetTy> PureVirtualClassDiagSet;
 
   typedef LazyVector<CXXConstructorDecl *, ExternalSemaSource,
                      &ExternalSemaSource::ReadDelegatingConstructors, 2, 2>
       DelegatingCtorDeclsType;
 
   /// All the delegating constructors seen so far in the file, used for
   /// cycle detection at the end of the TU.
   DelegatingCtorDeclsType DelegatingCtorDecls;
 
   /// The C++ "std" namespace, where the standard library resides.
   LazyDeclPtr StdNamespace;
 
   /// The C++ "std::initializer_list" template, which is defined in
   /// \<initializer_list>.
   ClassTemplateDecl *StdInitializerList;
 
   // Contains the locations of the beginning of unparsed default
   // argument locations.
   llvm::DenseMap<ParmVarDecl *, SourceLocation> UnparsedDefaultArgLocs;
 
   /// UndefinedInternals - all the used, undefined objects which require a
   /// definition in this translation unit.
   llvm::MapVector<NamedDecl *, SourceLocation> UndefinedButUsed;
 
   typedef llvm::PointerIntPair<CXXRecordDecl *, 3, CXXSpecialMemberKind>
       SpecialMemberDecl;
 
   /// The C++ special members which we are currently in the process of
   /// declaring. If this process recursively triggers the declaration of the
   /// same special member, we should act as if it is not yet declared.
   llvm::SmallPtrSet<SpecialMemberDecl, 4> SpecialMembersBeingDeclared;
 
   void NoteDeletedInheritingConstructor(CXXConstructorDecl *CD);
 
   void ActOnDefaultCtorInitializers(Decl *CDtorDecl);
 
   typedef ProcessingContextState ParsingClassState;
   ParsingClassState PushParsingClass() {
     ParsingClassDepth++;
     return DelayedDiagnostics.pushUndelayed();
   }
   void PopParsingClass(ParsingClassState state) {
     ParsingClassDepth--;
     DelayedDiagnostics.popUndelayed(state);
   }
 
   ValueDecl *tryLookupCtorInitMemberDecl(CXXRecordDecl *ClassDecl,
                                          CXXScopeSpec &SS,
                                          ParsedType TemplateTypeTy,
                                          IdentifierInfo *MemberOrBase);
 
 private:
   void setupImplicitSpecialMemberType(CXXMethodDecl *SpecialMem,
                                       QualType ResultTy,
                                       ArrayRef<QualType> Args);
 
   // A cache representing if we've fully checked the various comparison category
   // types stored in ASTContext. The bit-index corresponds to the integer value
   // of a ComparisonCategoryType enumerator.
   llvm::SmallBitVector FullyCheckedComparisonCategories;
 
   /// Check if there is a field shadowing.
   void CheckShadowInheritedFields(const SourceLocation &Loc,
                                   DeclarationName FieldName,
                                   const CXXRecordDecl *RD,
                                   bool DeclIsField = true);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Exception Specifications
   /// Implementations are in SemaExceptionSpec.cpp
   ///@{
 
 public:
   /// All the overriding functions seen during a class definition
   /// that had their exception spec checks delayed, plus the overridden
   /// function.
   SmallVector<std::pair<const CXXMethodDecl *, const CXXMethodDecl *>, 2>
       DelayedOverridingExceptionSpecChecks;
 
   /// All the function redeclarations seen during a class definition that had
   /// their exception spec checks delayed, plus the prior declaration they
   /// should be checked against. Except during error recovery, the new decl
   /// should always be a friend declaration, as that's the only valid way to
   /// redeclare a special member before its class is complete.
   SmallVector<std::pair<FunctionDecl *, FunctionDecl *>, 2>
       DelayedEquivalentExceptionSpecChecks;
 
   /// Determine if we're in a case where we need to (incorrectly) eagerly
   /// parse an exception specification to work around a libstdc++ bug.
   bool isLibstdcxxEagerExceptionSpecHack(const Declarator &D);
 
   /// Check the given noexcept-specifier, convert its expression, and compute
   /// the appropriate ExceptionSpecificationType.
   ExprResult ActOnNoexceptSpec(Expr *NoexceptExpr,
                                ExceptionSpecificationType &EST);
 
   CanThrowResult canThrow(const Stmt *E);
   /// Determine whether the callee of a particular function call can throw.
   /// E, D and Loc are all optional.
   static CanThrowResult canCalleeThrow(Sema &S, const Expr *E, const Decl *D,
                                        SourceLocation Loc = SourceLocation());
   const FunctionProtoType *ResolveExceptionSpec(SourceLocation Loc,
                                                 const FunctionProtoType *FPT);
   void UpdateExceptionSpec(FunctionDecl *FD,
                            const FunctionProtoType::ExceptionSpecInfo &ESI);
 
   /// CheckSpecifiedExceptionType - Check if the given type is valid in an
   /// exception specification. Incomplete types, or pointers to incomplete types
   /// other than void are not allowed.
   ///
   /// \param[in,out] T  The exception type. This will be decayed to a pointer
   /// type
   ///                   when the input is an array or a function type.
   bool CheckSpecifiedExceptionType(QualType &T, SourceRange Range);
 
   /// CheckDistantExceptionSpec - Check if the given type is a pointer or
   /// pointer to member to a function with an exception specification. This
   /// means that it is invalid to add another level of indirection.
   bool CheckDistantExceptionSpec(QualType T);
   bool CheckEquivalentExceptionSpec(FunctionDecl *Old, FunctionDecl *New);
 
   /// CheckEquivalentExceptionSpec - Check if the two types have equivalent
   /// exception specifications. Exception specifications are equivalent if
   /// they allow exactly the same set of exception types. It does not matter how
   /// that is achieved. See C++ [except.spec]p2.
   bool CheckEquivalentExceptionSpec(const FunctionProtoType *Old,
                                     SourceLocation OldLoc,
                                     const FunctionProtoType *New,
                                     SourceLocation NewLoc);
   bool CheckEquivalentExceptionSpec(const PartialDiagnostic &DiagID,
                                     const PartialDiagnostic &NoteID,
                                     const FunctionProtoType *Old,
                                     SourceLocation OldLoc,
                                     const FunctionProtoType *New,
                                     SourceLocation NewLoc);
   bool handlerCanCatch(QualType HandlerType, QualType ExceptionType);
 
   /// CheckExceptionSpecSubset - Check whether the second function type's
   /// exception specification is a subset (or equivalent) of the first function
   /// type. This is used by override and pointer assignment checks.
   bool CheckExceptionSpecSubset(
       const PartialDiagnostic &DiagID, const PartialDiagnostic &NestedDiagID,
       const PartialDiagnostic &NoteID, const PartialDiagnostic &NoThrowDiagID,
       const FunctionProtoType *Superset, bool SkipSupersetFirstParameter,
       SourceLocation SuperLoc, const FunctionProtoType *Subset,
       bool SkipSubsetFirstParameter, SourceLocation SubLoc);
 
   /// CheckParamExceptionSpec - Check if the parameter and return types of the
   /// two functions have equivalent exception specs. This is part of the
   /// assignment and override compatibility check. We do not check the
   /// parameters of parameter function pointers recursively, as no sane
   /// programmer would even be able to write such a function type.
   bool CheckParamExceptionSpec(
       const PartialDiagnostic &NestedDiagID, const PartialDiagnostic &NoteID,
       const FunctionProtoType *Target, bool SkipTargetFirstParameter,
       SourceLocation TargetLoc, const FunctionProtoType *Source,
       bool SkipSourceFirstParameter, SourceLocation SourceLoc);
 
   bool CheckExceptionSpecCompatibility(Expr *From, QualType ToType);
 
   /// CheckOverridingFunctionExceptionSpec - Checks whether the exception
   /// spec is a subset of base spec.
   bool CheckOverridingFunctionExceptionSpec(const CXXMethodDecl *New,
                                             const CXXMethodDecl *Old);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Expressions
   /// Implementations are in SemaExpr.cpp
   ///@{
 
 public:
   /// Describes how the expressions currently being parsed are
   /// evaluated at run-time, if at all.
   enum class ExpressionEvaluationContext {
     /// The current expression and its subexpressions occur within an
     /// unevaluated operand (C++11 [expr]p7), such as the subexpression of
     /// \c sizeof, where the type of the expression may be significant but
     /// no code will be generated to evaluate the value of the expression at
     /// run time.
     Unevaluated,
 
     /// The current expression occurs within a braced-init-list within
     /// an unevaluated operand. This is mostly like a regular unevaluated
     /// context, except that we still instantiate constexpr functions that are
     /// referenced here so that we can perform narrowing checks correctly.
     UnevaluatedList,
 
     /// The current expression occurs within a discarded statement.
     /// This behaves largely similarly to an unevaluated operand in preventing
     /// definitions from being required, but not in other ways.
     DiscardedStatement,
 
     /// The current expression occurs within an unevaluated
     /// operand that unconditionally permits abstract references to
     /// fields, such as a SIZE operator in MS-style inline assembly.
     UnevaluatedAbstract,
 
     /// The current context is "potentially evaluated" in C++11 terms,
     /// but the expression is evaluated at compile-time (like the values of
     /// cases in a switch statement).
     ConstantEvaluated,
 
     /// In addition of being constant evaluated, the current expression
     /// occurs in an immediate function context - either a consteval function
     /// or a consteval if statement.
     ImmediateFunctionContext,
 
     /// The current expression is potentially evaluated at run time,
     /// which means that code may be generated to evaluate the value of the
     /// expression at run time.
     PotentiallyEvaluated,
 
     /// The current expression is potentially evaluated, but any
     /// declarations referenced inside that expression are only used if
     /// in fact the current expression is used.
     ///
     /// This value is used when parsing default function arguments, for which
     /// we would like to provide diagnostics (e.g., passing non-POD arguments
     /// through varargs) but do not want to mark declarations as "referenced"
     /// until the default argument is used.
     PotentiallyEvaluatedIfUsed
   };
 
   /// Store a set of either DeclRefExprs or MemberExprs that contain a reference
   /// to a variable (constant) that may or may not be odr-used in this Expr, and
   /// we won't know until all lvalue-to-rvalue and discarded value conversions
   /// have been applied to all subexpressions of the enclosing full expression.
   /// This is cleared at the end of each full expression.
   using MaybeODRUseExprSet = llvm::SmallSetVector<Expr *, 4>;
   MaybeODRUseExprSet MaybeODRUseExprs;
 
   using ImmediateInvocationCandidate = llvm::PointerIntPair<ConstantExpr *, 1>;
 
   /// Data structure used to record current or nested
   /// expression evaluation contexts.
   struct ExpressionEvaluationContextRecord {
     /// The expression evaluation context.
     ExpressionEvaluationContext Context;
 
     /// Whether the enclosing context needed a cleanup.
     CleanupInfo ParentCleanup;
 
     /// The number of active cleanup objects when we entered
     /// this expression evaluation context.
     unsigned NumCleanupObjects;
 
     /// The number of typos encountered during this expression evaluation
     /// context (i.e. the number of TypoExprs created).
     unsigned NumTypos;
 
     MaybeODRUseExprSet SavedMaybeODRUseExprs;
 
     /// The lambdas that are present within this context, if it
     /// is indeed an unevaluated context.
     SmallVector<LambdaExpr *, 2> Lambdas;
 
     /// The declaration that provides context for lambda expressions
     /// and block literals if the normal declaration context does not
     /// suffice, e.g., in a default function argument.
     Decl *ManglingContextDecl;
 
     /// If we are processing a decltype type, a set of call expressions
     /// for which we have deferred checking the completeness of the return type.
     SmallVector<CallExpr *, 8> DelayedDecltypeCalls;
 
     /// If we are processing a decltype type, a set of temporary binding
     /// expressions for which we have deferred checking the destructor.
     SmallVector<CXXBindTemporaryExpr *, 8> DelayedDecltypeBinds;
 
     llvm::SmallPtrSet<const Expr *, 8> PossibleDerefs;
 
     /// Expressions appearing as the LHS of a volatile assignment in this
     /// context. We produce a warning for these when popping the context if
     /// they are not discarded-value expressions nor unevaluated operands.
     SmallVector<Expr *, 2> VolatileAssignmentLHSs;
 
     /// Set of candidates for starting an immediate invocation.
     llvm::SmallVector<ImmediateInvocationCandidate, 4>
         ImmediateInvocationCandidates;
 
     /// Set of DeclRefExprs referencing a consteval function when used in a
     /// context not already known to be immediately invoked.
     llvm::SmallPtrSet<DeclRefExpr *, 4> ReferenceToConsteval;
 
     /// P2718R0 - Lifetime extension in range-based for loops.
     /// MaterializeTemporaryExprs in for-range-init expressions which need to
     /// extend lifetime. Add MaterializeTemporaryExpr* if the value of
     /// InLifetimeExtendingContext is true.
     SmallVector<MaterializeTemporaryExpr *, 8> ForRangeLifetimeExtendTemps;
 
     /// \brief Describes whether we are in an expression constext which we have
     /// to handle differently.
     enum ExpressionKind {
       EK_Decltype,
       EK_TemplateArgument,
       EK_AttrArgument,
       EK_Other
     } ExprContext;
 
     // A context can be nested in both a discarded statement context and
     // an immediate function context, so they need to be tracked independently.
     bool InDiscardedStatement;
     bool InImmediateFunctionContext;
     bool InImmediateEscalatingFunctionContext;
 
     bool IsCurrentlyCheckingDefaultArgumentOrInitializer = false;
 
     // We are in a constant context, but we also allow
     // non constant expressions, for example for array bounds (which may be
     // VLAs).
     bool InConditionallyConstantEvaluateContext = false;
 
     /// Whether we are currently in a context in which all temporaries must be
     /// lifetime-extended, even if they're not bound to a reference (for
     /// example, in a for-range initializer).
     bool InLifetimeExtendingContext = false;
 
     // When evaluating immediate functions in the initializer of a default
     // argument or default member initializer, this is the declaration whose
     // default initializer is being evaluated and the location of the call
     // or constructor definition.
     struct InitializationContext {
       InitializationContext(SourceLocation Loc, ValueDecl *Decl,
                             DeclContext *Context)
           : Loc(Loc), Decl(Decl), Context(Context) {
         assert(Decl && Context && "invalid initialization context");
       }
 
       SourceLocation Loc;
       ValueDecl *Decl = nullptr;
       DeclContext *Context = nullptr;
     };
     std::optional<InitializationContext> DelayedDefaultInitializationContext;
 
     ExpressionEvaluationContextRecord(ExpressionEvaluationContext Context,
                                       unsigned NumCleanupObjects,
                                       CleanupInfo ParentCleanup,
                                       Decl *ManglingContextDecl,
                                       ExpressionKind ExprContext)
         : Context(Context), ParentCleanup(ParentCleanup),
           NumCleanupObjects(NumCleanupObjects), NumTypos(0),
           ManglingContextDecl(ManglingContextDecl), ExprContext(ExprContext),
           InDiscardedStatement(false), InImmediateFunctionContext(false),
           InImmediateEscalatingFunctionContext(false) {}
 
     bool isUnevaluated() const {
       return Context == ExpressionEvaluationContext::Unevaluated ||
              Context == ExpressionEvaluationContext::UnevaluatedAbstract ||
              Context == ExpressionEvaluationContext::UnevaluatedList;
     }
 
     bool isPotentiallyEvaluated() const {
       return Context == ExpressionEvaluationContext::PotentiallyEvaluated ||
              Context ==
                  ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed ||
              Context == ExpressionEvaluationContext::ConstantEvaluated;
     }
 
     bool isConstantEvaluated() const {
       return Context == ExpressionEvaluationContext::ConstantEvaluated ||
              Context == ExpressionEvaluationContext::ImmediateFunctionContext;
     }
 
     bool isImmediateFunctionContext() const {
       return Context == ExpressionEvaluationContext::ImmediateFunctionContext ||
              (Context == ExpressionEvaluationContext::DiscardedStatement &&
               InImmediateFunctionContext) ||
              // C++23 [expr.const]p14:
              // An expression or conversion is in an immediate function
              // context if it is potentially evaluated and either:
              //   * its innermost enclosing non-block scope is a function
              //     parameter scope of an immediate function, or
              //   * its enclosing statement is enclosed by the compound-
              //     statement of a consteval if statement.
              (Context == ExpressionEvaluationContext::PotentiallyEvaluated &&
               InImmediateFunctionContext);
     }
 
     bool isDiscardedStatementContext() const {
       return Context == ExpressionEvaluationContext::DiscardedStatement ||
              (Context ==
                   ExpressionEvaluationContext::ImmediateFunctionContext &&
               InDiscardedStatement);
     }
   };
 
   const ExpressionEvaluationContextRecord &currentEvaluationContext() const {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
     return ExprEvalContexts.back();
   };
 
   ExpressionEvaluationContextRecord &currentEvaluationContext() {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
     return ExprEvalContexts.back();
   };
 
   ExpressionEvaluationContextRecord &parentEvaluationContext() {
     assert(ExprEvalContexts.size() >= 2 &&
            "Must be in an expression evaluation context");
     return ExprEvalContexts[ExprEvalContexts.size() - 2];
   };
 
   const ExpressionEvaluationContextRecord &parentEvaluationContext() const {
     return const_cast<Sema *>(this)->parentEvaluationContext();
   };
 
   bool isAttrContext() const {
     return ExprEvalContexts.back().ExprContext ==
            ExpressionEvaluationContextRecord::ExpressionKind::EK_AttrArgument;
   }
 
   /// Increment when we find a reference; decrement when we find an ignored
   /// assignment.  Ultimately the value is 0 if every reference is an ignored
   /// assignment.
   llvm::DenseMap<const VarDecl *, int> RefsMinusAssignments;
 
   /// Used to control the generation of ExprWithCleanups.
   CleanupInfo Cleanup;
 
   /// ExprCleanupObjects - This is the stack of objects requiring
   /// cleanup that are created by the current full expression.
   SmallVector<ExprWithCleanups::CleanupObject, 8> ExprCleanupObjects;
 
   // AssignmentAction - This is used by all the assignment diagnostic functions
   // to represent what is actually causing the operation
   enum AssignmentAction {
     AA_Assigning,
     AA_Passing,
     AA_Returning,
     AA_Converting,
     AA_Initializing,
     AA_Sending,
     AA_Casting,
     AA_Passing_CFAudited
   };
 
   /// Determine whether the use of this declaration is valid, without
   /// emitting diagnostics.
   bool CanUseDecl(NamedDecl *D, bool TreatUnavailableAsInvalid);
   // A version of DiagnoseUseOfDecl that should be used if overload resolution
   // has been used to find this declaration, which means we don't have to bother
   // checking the trailing requires clause.
   bool DiagnoseUseOfOverloadedDecl(NamedDecl *D, SourceLocation Loc) {
     return DiagnoseUseOfDecl(
         D, Loc, /*UnknownObjCClass=*/nullptr, /*ObjCPropertyAccess=*/false,
         /*AvoidPartialAvailabilityChecks=*/false, /*ClassReceiver=*/nullptr,
         /*SkipTrailingRequiresClause=*/true);
   }
 
   /// Determine whether the use of this declaration is valid, and
   /// emit any corresponding diagnostics.
   ///
   /// This routine diagnoses various problems with referencing
   /// declarations that can occur when using a declaration. For example,
   /// it might warn if a deprecated or unavailable declaration is being
   /// used, or produce an error (and return true) if a C++0x deleted
   /// function is being used.
   ///
   /// \returns true if there was an error (this declaration cannot be
   /// referenced), false otherwise.
   bool DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
                          const ObjCInterfaceDecl *UnknownObjCClass = nullptr,
                          bool ObjCPropertyAccess = false,
                          bool AvoidPartialAvailabilityChecks = false,
                          ObjCInterfaceDecl *ClassReciever = nullptr,
                          bool SkipTrailingRequiresClause = false);
 
   /// Emit a note explaining that this function is deleted.
   void NoteDeletedFunction(FunctionDecl *FD);
 
   /// DiagnoseSentinelCalls - This routine checks whether a call or
   /// message-send is to a declaration with the sentinel attribute, and
   /// if so, it checks that the requirements of the sentinel are
   /// satisfied.
   void DiagnoseSentinelCalls(const NamedDecl *D, SourceLocation Loc,
                              ArrayRef<Expr *> Args);
 
   void PushExpressionEvaluationContext(
       ExpressionEvaluationContext NewContext, Decl *LambdaContextDecl = nullptr,
       ExpressionEvaluationContextRecord::ExpressionKind Type =
           ExpressionEvaluationContextRecord::EK_Other);
   enum ReuseLambdaContextDecl_t { ReuseLambdaContextDecl };
   void PushExpressionEvaluationContext(
       ExpressionEvaluationContext NewContext, ReuseLambdaContextDecl_t,
       ExpressionEvaluationContextRecord::ExpressionKind Type =
           ExpressionEvaluationContextRecord::EK_Other);
   void PopExpressionEvaluationContext();
 
   void DiscardCleanupsInEvaluationContext();
 
   ExprResult TransformToPotentiallyEvaluated(Expr *E);
   TypeSourceInfo *TransformToPotentiallyEvaluated(TypeSourceInfo *TInfo);
   ExprResult HandleExprEvaluationContextForTypeof(Expr *E);
 
   /// Check whether E, which is either a discarded-value expression or an
   /// unevaluated operand, is a simple-assignment to a volatlie-qualified
   /// lvalue, and if so, remove it from the list of volatile-qualified
   /// assignments that we are going to warn are deprecated.
   void CheckUnusedVolatileAssignment(Expr *E);
 
   ExprResult ActOnConstantExpression(ExprResult Res);
 
   // Functions for marking a declaration referenced.  These functions also
   // contain the relevant logic for marking if a reference to a function or
   // variable is an odr-use (in the C++11 sense).  There are separate variants
   // for expressions referring to a decl; these exist because odr-use marking
   // needs to be delayed for some constant variables when we build one of the
   // named expressions.
   //
   // MightBeOdrUse indicates whether the use could possibly be an odr-use, and
   // should usually be true. This only needs to be set to false if the lack of
   // odr-use cannot be determined from the current context (for instance,
   // because the name denotes a virtual function and was written without an
   // explicit nested-name-specifier).
   void MarkAnyDeclReferenced(SourceLocation Loc, Decl *D, bool MightBeOdrUse);
 
   /// Mark a function referenced, and check whether it is odr-used
   /// (C++ [basic.def.odr]p2, C99 6.9p3)
   void MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
                               bool MightBeOdrUse = true);
 
   /// Mark a variable referenced, and check whether it is odr-used
   /// (C++ [basic.def.odr]p2, C99 6.9p3).  Note that this should not be
   /// used directly for normal expressions referring to VarDecl.
   void MarkVariableReferenced(SourceLocation Loc, VarDecl *Var);
 
   /// Perform reference-marking and odr-use handling for a DeclRefExpr.
   ///
   /// Note, this may change the dependence of the DeclRefExpr, and so needs to
   /// be handled with care if the DeclRefExpr is not newly-created.
   void MarkDeclRefReferenced(DeclRefExpr *E, const Expr *Base = nullptr);
 
   /// Perform reference-marking and odr-use handling for a MemberExpr.
   void MarkMemberReferenced(MemberExpr *E);
 
   /// Perform reference-marking and odr-use handling for a FunctionParmPackExpr.
   void MarkFunctionParmPackReferenced(FunctionParmPackExpr *E);
   void MarkCaptureUsedInEnclosingContext(ValueDecl *Capture, SourceLocation Loc,
                                          unsigned CapturingScopeIndex);
 
   ExprResult CheckLValueToRValueConversionOperand(Expr *E);
   void CleanupVarDeclMarking();
 
   enum TryCaptureKind {
     TryCapture_Implicit,
     TryCapture_ExplicitByVal,
     TryCapture_ExplicitByRef
   };
 
   /// Try to capture the given variable.
   ///
   /// \param Var The variable to capture.
   ///
   /// \param Loc The location at which the capture occurs.
   ///
   /// \param Kind The kind of capture, which may be implicit (for either a
   /// block or a lambda), or explicit by-value or by-reference (for a lambda).
   ///
   /// \param EllipsisLoc The location of the ellipsis, if one is provided in
   /// an explicit lambda capture.
   ///
   /// \param BuildAndDiagnose Whether we are actually supposed to add the
   /// captures or diagnose errors. If false, this routine merely check whether
   /// the capture can occur without performing the capture itself or complaining
   /// if the variable cannot be captured.
   ///
   /// \param CaptureType Will be set to the type of the field used to capture
   /// this variable in the innermost block or lambda. Only valid when the
   /// variable can be captured.
   ///
   /// \param DeclRefType Will be set to the type of a reference to the capture
   /// from within the current scope. Only valid when the variable can be
   /// captured.
   ///
   /// \param FunctionScopeIndexToStopAt If non-null, it points to the index
   /// of the FunctionScopeInfo stack beyond which we do not attempt to capture.
   /// This is useful when enclosing lambdas must speculatively capture
   /// variables that may or may not be used in certain specializations of
   /// a nested generic lambda.
   ///
   /// \returns true if an error occurred (i.e., the variable cannot be
   /// captured) and false if the capture succeeded.
   bool tryCaptureVariable(ValueDecl *Var, SourceLocation Loc,
                           TryCaptureKind Kind, SourceLocation EllipsisLoc,
                           bool BuildAndDiagnose, QualType &CaptureType,
                           QualType &DeclRefType,
                           const unsigned *const FunctionScopeIndexToStopAt);
 
   /// Try to capture the given variable.
   bool tryCaptureVariable(ValueDecl *Var, SourceLocation Loc,
                           TryCaptureKind Kind = TryCapture_Implicit,
                           SourceLocation EllipsisLoc = SourceLocation());
 
   /// Checks if the variable must be captured.
   bool NeedToCaptureVariable(ValueDecl *Var, SourceLocation Loc);
 
   /// Given a variable, determine the type that a reference to that
   /// variable will have in the given scope.
   QualType getCapturedDeclRefType(ValueDecl *Var, SourceLocation Loc);
 
   /// Mark all of the declarations referenced within a particular AST node as
   /// referenced. Used when template instantiation instantiates a non-dependent
   /// type -- entities referenced by the type are now referenced.
   void MarkDeclarationsReferencedInType(SourceLocation Loc, QualType T);
 
   /// Mark any declarations that appear within this expression or any
   /// potentially-evaluated subexpressions as "referenced".
   ///
   /// \param SkipLocalVariables If true, don't mark local variables as
   /// 'referenced'.
   /// \param StopAt Subexpressions that we shouldn't recurse into.
   void MarkDeclarationsReferencedInExpr(
       Expr *E, bool SkipLocalVariables = false,
       ArrayRef<const Expr *> StopAt = std::nullopt);
 
   /// Try to convert an expression \p E to type \p Ty. Returns the result of the
   /// conversion.
   ExprResult tryConvertExprToType(Expr *E, QualType Ty);
 
   /// Conditionally issue a diagnostic based on the statements's reachability
   /// analysis.
   ///
   /// \param Stmts If Stmts is non-empty, delay reporting the diagnostic until
   /// the function body is parsed, and then do a basic reachability analysis to
   /// determine if the statement is reachable. If it is unreachable, the
   /// diagnostic will not be emitted.
   bool DiagIfReachable(SourceLocation Loc, ArrayRef<const Stmt *> Stmts,
                        const PartialDiagnostic &PD);
 
   /// Conditionally issue a diagnostic based on the current
   /// evaluation context.
   ///
   /// \param Statement If Statement is non-null, delay reporting the
   /// diagnostic until the function body is parsed, and then do a basic
   /// reachability analysis to determine if the statement is reachable.
   /// If it is unreachable, the diagnostic will not be emitted.
   bool DiagRuntimeBehavior(SourceLocation Loc, const Stmt *Statement,
                            const PartialDiagnostic &PD);
   /// Similar, but diagnostic is only produced if all the specified statements
   /// are reachable.
   bool DiagRuntimeBehavior(SourceLocation Loc, ArrayRef<const Stmt *> Stmts,
                            const PartialDiagnostic &PD);
 
   // Primary Expressions.
   SourceRange getExprRange(Expr *E) const;
 
   ExprResult ActOnIdExpression(Scope *S, CXXScopeSpec &SS,
                                SourceLocation TemplateKWLoc, UnqualifiedId &Id,
                                bool HasTrailingLParen, bool IsAddressOfOperand,
                                CorrectionCandidateCallback *CCC = nullptr,
                                bool IsInlineAsmIdentifier = false,
                                Token *KeywordReplacement = nullptr);
 
   /// Decomposes the given name into a DeclarationNameInfo, its location, and
   /// possibly a list of template arguments.
   ///
   /// If this produces template arguments, it is permitted to call
   /// DecomposeTemplateName.
   ///
   /// This actually loses a lot of source location information for
   /// non-standard name kinds; we should consider preserving that in
   /// some way.
   void DecomposeUnqualifiedId(const UnqualifiedId &Id,
                               TemplateArgumentListInfo &Buffer,
                               DeclarationNameInfo &NameInfo,
                               const TemplateArgumentListInfo *&TemplateArgs);
 
   /// Diagnose a lookup that found results in an enclosing class during error
   /// recovery. This usually indicates that the results were found in a
   /// dependent base class that could not be searched as part of a template
   /// definition. Always issues a diagnostic (though this may be only a warning
   /// in MS compatibility mode).
   ///
   /// Return \c true if the error is unrecoverable, or \c false if the caller
   /// should attempt to recover using these lookup results.
   bool DiagnoseDependentMemberLookup(const LookupResult &R);
 
   /// Diagnose an empty lookup.
   ///
   /// \return false if new lookup candidates were found
   bool
   DiagnoseEmptyLookup(Scope *S, CXXScopeSpec &SS, LookupResult &R,
                       CorrectionCandidateCallback &CCC,
                       TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr,
                       ArrayRef<Expr *> Args = std::nullopt,
                       DeclContext *LookupCtx = nullptr,
                       TypoExpr **Out = nullptr);
 
   /// If \p D cannot be odr-used in the current expression evaluation context,
   /// return a reason explaining why. Otherwise, return NOUR_None.
   NonOdrUseReason getNonOdrUseReasonInCurrentContext(ValueDecl *D);
 
   DeclRefExpr *BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                                 SourceLocation Loc,
                                 const CXXScopeSpec *SS = nullptr);
   DeclRefExpr *
   BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                    const DeclarationNameInfo &NameInfo,
                    const CXXScopeSpec *SS = nullptr,
                    NamedDecl *FoundD = nullptr,
                    SourceLocation TemplateKWLoc = SourceLocation(),
                    const TemplateArgumentListInfo *TemplateArgs = nullptr);
 
   /// BuildDeclRefExpr - Build an expression that references a
   /// declaration that does not require a closure capture.
   DeclRefExpr *
   BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                    const DeclarationNameInfo &NameInfo,
                    NestedNameSpecifierLoc NNS, NamedDecl *FoundD = nullptr,
                    SourceLocation TemplateKWLoc = SourceLocation(),
                    const TemplateArgumentListInfo *TemplateArgs = nullptr);
 
   bool UseArgumentDependentLookup(const CXXScopeSpec &SS, const LookupResult &R,
                                   bool HasTrailingLParen);
 
   /// BuildQualifiedDeclarationNameExpr - Build a C++ qualified
   /// declaration name, generally during template instantiation.
   /// There's a large number of things which don't need to be done along
   /// this path.
   ExprResult BuildQualifiedDeclarationNameExpr(
       CXXScopeSpec &SS, const DeclarationNameInfo &NameInfo,
       bool IsAddressOfOperand, TypeSourceInfo **RecoveryTSI = nullptr);
 
   ExprResult BuildDeclarationNameExpr(const CXXScopeSpec &SS, LookupResult &R,
                                       bool NeedsADL,
                                       bool AcceptInvalidDecl = false);
 
   /// Complete semantic analysis for a reference to the given declaration.
   ExprResult BuildDeclarationNameExpr(
       const CXXScopeSpec &SS, const DeclarationNameInfo &NameInfo, NamedDecl *D,
       NamedDecl *FoundD = nullptr,
       const TemplateArgumentListInfo *TemplateArgs = nullptr,
       bool AcceptInvalidDecl = false);
 
   // ExpandFunctionLocalPredefinedMacros - Returns a new vector of Tokens,
   // where Tokens representing function local predefined macros (such as
   // __FUNCTION__) are replaced (expanded) with string-literal Tokens.
   std::vector<Token> ExpandFunctionLocalPredefinedMacros(ArrayRef<Token> Toks);
 
   ExprResult BuildPredefinedExpr(SourceLocation Loc, PredefinedIdentKind IK);
   ExprResult ActOnPredefinedExpr(SourceLocation Loc, tok::TokenKind Kind);
   ExprResult ActOnIntegerConstant(SourceLocation Loc, uint64_t Val);
 
   bool CheckLoopHintExpr(Expr *E, SourceLocation Loc, bool AllowZero);
 
   ExprResult ActOnNumericConstant(const Token &Tok, Scope *UDLScope = nullptr);
   ExprResult ActOnCharacterConstant(const Token &Tok,
                                     Scope *UDLScope = nullptr);
   ExprResult ActOnParenExpr(SourceLocation L, SourceLocation R, Expr *E);
   ExprResult ActOnParenListExpr(SourceLocation L, SourceLocation R,
                                 MultiExprArg Val);
 
   /// ActOnStringLiteral - The specified tokens were lexed as pasted string
   /// fragments (e.g. "foo" "bar" L"baz").  The result string has to handle
   /// string concatenation ([C99 5.1.1.2, translation phase #6]), so it may come
   /// from multiple tokens.  However, the common case is that StringToks points
   /// to one string.
   ExprResult ActOnStringLiteral(ArrayRef<Token> StringToks,
                                 Scope *UDLScope = nullptr);
 
   ExprResult ActOnUnevaluatedStringLiteral(ArrayRef<Token> StringToks);
 
   /// ControllingExprOrType is either an opaque pointer coming out of a
   /// ParsedType or an Expr *. FIXME: it'd be better to split this interface
   /// into two so we don't take a void *, but that's awkward because one of
   /// the operands is either a ParsedType or an Expr *, which doesn't lend
   /// itself to generic code very well.
   ExprResult ActOnGenericSelectionExpr(SourceLocation KeyLoc,
                                        SourceLocation DefaultLoc,
                                        SourceLocation RParenLoc,
                                        bool PredicateIsExpr,
                                        void *ControllingExprOrType,
                                        ArrayRef<ParsedType> ArgTypes,
                                        ArrayRef<Expr *> ArgExprs);
   /// ControllingExprOrType is either a TypeSourceInfo * or an Expr *. FIXME:
   /// it'd be better to split this interface into two so we don't take a
   /// void *, but see the FIXME on ActOnGenericSelectionExpr as to why that
   /// isn't a trivial change.
   ExprResult CreateGenericSelectionExpr(SourceLocation KeyLoc,
                                         SourceLocation DefaultLoc,
                                         SourceLocation RParenLoc,
                                         bool PredicateIsExpr,
                                         void *ControllingExprOrType,
                                         ArrayRef<TypeSourceInfo *> Types,
                                         ArrayRef<Expr *> Exprs);
 
   // Binary/Unary Operators.  'Tok' is the token for the operator.
   ExprResult CreateBuiltinUnaryOp(SourceLocation OpLoc, UnaryOperatorKind Opc,
                                   Expr *InputExpr, bool IsAfterAmp = false);
   ExprResult BuildUnaryOp(Scope *S, SourceLocation OpLoc, UnaryOperatorKind Opc,
                           Expr *Input, bool IsAfterAmp = false);
 
   /// Unary Operators.  'Tok' is the token for the operator.
   ExprResult ActOnUnaryOp(Scope *S, SourceLocation OpLoc, tok::TokenKind Op,
                           Expr *Input, bool IsAfterAmp = false);
 
   /// Determine whether the given expression is a qualified member
   /// access expression, of a form that could be turned into a pointer to member
   /// with the address-of operator.
   bool isQualifiedMemberAccess(Expr *E);
   bool CheckUseOfCXXMethodAsAddressOfOperand(SourceLocation OpLoc,
                                              const Expr *Op,
                                              const CXXMethodDecl *MD);
 
   /// CheckAddressOfOperand - The operand of & must be either a function
   /// designator or an lvalue designating an object. If it is an lvalue, the
   /// object cannot be declared with storage class register or be a bit field.
   /// Note: The usual conversions are *not* applied to the operand of the &
   /// operator (C99 6.3.2.1p[2-4]), and its result is never an lvalue.
   /// In C++, the operand might be an overloaded function name, in which case
   /// we allow the '&' but retain the overloaded-function type.
   QualType CheckAddressOfOperand(ExprResult &Operand, SourceLocation OpLoc);
 
   /// ActOnAlignasTypeArgument - Handle @c alignas(type-id) and @c
   /// _Alignas(type-name) .
   /// [dcl.align] An alignment-specifier of the form
   /// alignas(type-id) has the same effect as alignas(alignof(type-id)).
   ///
   /// [N1570 6.7.5] _Alignas(type-name) is equivalent to
   /// _Alignas(_Alignof(type-name)).
   bool ActOnAlignasTypeArgument(StringRef KWName, ParsedType Ty,
                                 SourceLocation OpLoc, SourceRange R);
   bool CheckAlignasTypeArgument(StringRef KWName, TypeSourceInfo *TInfo,
                                 SourceLocation OpLoc, SourceRange R);
 
   /// Build a sizeof or alignof expression given a type operand.
   ExprResult CreateUnaryExprOrTypeTraitExpr(TypeSourceInfo *TInfo,
                                             SourceLocation OpLoc,
                                             UnaryExprOrTypeTrait ExprKind,
                                             SourceRange R);
 
   /// Build a sizeof or alignof expression given an expression
   /// operand.
   ExprResult CreateUnaryExprOrTypeTraitExpr(Expr *E, SourceLocation OpLoc,
                                             UnaryExprOrTypeTrait ExprKind);
 
   /// ActOnUnaryExprOrTypeTraitExpr - Handle @c sizeof(type) and @c sizeof @c
   /// expr and the same for @c alignof and @c __alignof
   /// Note that the ArgRange is invalid if isType is false.
   ExprResult ActOnUnaryExprOrTypeTraitExpr(SourceLocation OpLoc,
                                            UnaryExprOrTypeTrait ExprKind,
                                            bool IsType, void *TyOrEx,
                                            SourceRange ArgRange);
 
   /// Check for operands with placeholder types and complain if found.
   /// Returns ExprError() if there was an error and no recovery was possible.
   ExprResult CheckPlaceholderExpr(Expr *E);
   bool CheckVecStepExpr(Expr *E);
 
   /// Check the constraints on expression operands to unary type expression
   /// and type traits.
   ///
   /// Completes any types necessary and validates the constraints on the operand
   /// expression. The logic mostly mirrors the type-based overload, but may
   /// modify the expression as it completes the type for that expression through
   /// template instantiation, etc.
   bool CheckUnaryExprOrTypeTraitOperand(Expr *E, UnaryExprOrTypeTrait ExprKind);
 
   /// Check the constraints on operands to unary expression and type
   /// traits.
   ///
   /// This will complete any types necessary, and validate the various
   /// constraints on those operands.
   ///
   /// The UsualUnaryConversions() function is *not* called by this routine.
   /// C99 6.3.2.1p[2-4] all state:
   ///   Except when it is the operand of the sizeof operator ...
   ///
   /// C++ [expr.sizeof]p4
   ///   The lvalue-to-rvalue, array-to-pointer, and function-to-pointer
   ///   standard conversions are not applied to the operand of sizeof.
   ///
   /// This policy is followed for all of the unary trait expressions.
   bool CheckUnaryExprOrTypeTraitOperand(QualType ExprType, SourceLocation OpLoc,
                                         SourceRange ExprRange,
                                         UnaryExprOrTypeTrait ExprKind,
                                         StringRef KWName);
 
   ExprResult ActOnPostfixUnaryOp(Scope *S, SourceLocation OpLoc,
                                  tok::TokenKind Kind, Expr *Input);
 
   ExprResult ActOnArraySubscriptExpr(Scope *S, Expr *Base, SourceLocation LLoc,
                                      MultiExprArg ArgExprs,
                                      SourceLocation RLoc);
   ExprResult CreateBuiltinArraySubscriptExpr(Expr *Base, SourceLocation LLoc,
                                              Expr *Idx, SourceLocation RLoc);
 
   ExprResult CreateBuiltinMatrixSubscriptExpr(Expr *Base, Expr *RowIdx,
                                               Expr *ColumnIdx,
                                               SourceLocation RBLoc);
 
   /// ConvertArgumentsForCall - Converts the arguments specified in
   /// Args/NumArgs to the parameter types of the function FDecl with
   /// function prototype Proto. Call is the call expression itself, and
   /// Fn is the function expression. For a C++ member function, this
   /// routine does not attempt to convert the object argument. Returns
   /// true if the call is ill-formed.
   bool ConvertArgumentsForCall(CallExpr *Call, Expr *Fn, FunctionDecl *FDecl,
                                const FunctionProtoType *Proto,
                                ArrayRef<Expr *> Args, SourceLocation RParenLoc,
                                bool ExecConfig = false);
 
   /// CheckStaticArrayArgument - If the given argument corresponds to a static
   /// array parameter, check that it is non-null, and that if it is formed by
   /// array-to-pointer decay, the underlying array is sufficiently large.
   ///
   /// C99 6.7.5.3p7: If the keyword static also appears within the [ and ] of
   /// the array type derivation, then for each call to the function, the value
   /// of the corresponding actual argument shall provide access to the first
   /// element of an array with at least as many elements as specified by the
   /// size expression.
   void CheckStaticArrayArgument(SourceLocation CallLoc, ParmVarDecl *Param,
                                 const Expr *ArgExpr);
 
   /// ActOnCallExpr - Handle a call to Fn with the specified array of arguments.
   /// This provides the location of the left/right parens and a list of comma
   /// locations.
   ExprResult ActOnCallExpr(Scope *S, Expr *Fn, SourceLocation LParenLoc,
                            MultiExprArg ArgExprs, SourceLocation RParenLoc,
                            Expr *ExecConfig = nullptr);
 
   /// BuildCallExpr - Handle a call to Fn with the specified array of arguments.
   /// This provides the location of the left/right parens and a list of comma
   /// locations.
   ExprResult BuildCallExpr(Scope *S, Expr *Fn, SourceLocation LParenLoc,
                            MultiExprArg ArgExprs, SourceLocation RParenLoc,
                            Expr *ExecConfig = nullptr,
                            bool IsExecConfig = false,
                            bool AllowRecovery = false);
 
   /// BuildBuiltinCallExpr - Create a call to a builtin function specified by Id
   //  with the specified CallArgs
   Expr *BuildBuiltinCallExpr(SourceLocation Loc, Builtin::ID Id,
                              MultiExprArg CallArgs);
 
   using ADLCallKind = CallExpr::ADLCallKind;
 
   /// BuildResolvedCallExpr - Build a call to a resolved expression,
   /// i.e. an expression not of \p OverloadTy.  The expression should
   /// unary-convert to an expression of function-pointer or
   /// block-pointer type.
   ///
   /// \param NDecl the declaration being called, if available
   ExprResult
   BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl, SourceLocation LParenLoc,
                         ArrayRef<Expr *> Arg, SourceLocation RParenLoc,
                         Expr *Config = nullptr, bool IsExecConfig = false,
                         ADLCallKind UsesADL = ADLCallKind::NotADL);
 
   ExprResult ActOnCastExpr(Scope *S, SourceLocation LParenLoc, Declarator &D,
                            ParsedType &Ty, SourceLocation RParenLoc,
                            Expr *CastExpr);
 
   /// Prepares for a scalar cast, performing all the necessary stages
   /// except the final cast and returning the kind required.
   CastKind PrepareScalarCast(ExprResult &src, QualType destType);
 
   /// Build an altivec or OpenCL literal.
   ExprResult BuildVectorLiteral(SourceLocation LParenLoc,
                                 SourceLocation RParenLoc, Expr *E,
                                 TypeSourceInfo *TInfo);
 
   /// This is not an AltiVec-style cast or or C++ direct-initialization, so turn
   /// the ParenListExpr into a sequence of comma binary operators.
   ExprResult MaybeConvertParenListExprToParenExpr(Scope *S, Expr *ME);
 
   ExprResult ActOnCompoundLiteral(SourceLocation LParenLoc, ParsedType Ty,
                                   SourceLocation RParenLoc, Expr *InitExpr);
 
   ExprResult BuildCompoundLiteralExpr(SourceLocation LParenLoc,
                                       TypeSourceInfo *TInfo,
                                       SourceLocation RParenLoc,
                                       Expr *LiteralExpr);
 
   ExprResult ActOnInitList(SourceLocation LBraceLoc, MultiExprArg InitArgList,
                            SourceLocation RBraceLoc);
 
   ExprResult BuildInitList(SourceLocation LBraceLoc, MultiExprArg InitArgList,
                            SourceLocation RBraceLoc);
 
   /// Binary Operators.  'Tok' is the token for the operator.
   ExprResult ActOnBinOp(Scope *S, SourceLocation TokLoc, tok::TokenKind Kind,
                         Expr *LHSExpr, Expr *RHSExpr);
   ExprResult BuildBinOp(Scope *S, SourceLocation OpLoc, BinaryOperatorKind Opc,
                         Expr *LHSExpr, Expr *RHSExpr);
 
   /// CreateBuiltinBinOp - Creates a new built-in binary operation with
   /// operator @p Opc at location @c TokLoc. This routine only supports
   /// built-in operations; ActOnBinOp handles overloaded operators.
   ExprResult CreateBuiltinBinOp(SourceLocation OpLoc, BinaryOperatorKind Opc,
                                 Expr *LHSExpr, Expr *RHSExpr);
   void LookupBinOp(Scope *S, SourceLocation OpLoc, BinaryOperatorKind Opc,
                    UnresolvedSetImpl &Functions);
 
   /// Look for instances where it is likely the comma operator is confused with
   /// another operator.  There is an explicit list of acceptable expressions for
   /// the left hand side of the comma operator, otherwise emit a warning.
   void DiagnoseCommaOperator(const Expr *LHS, SourceLocation Loc);
 
   /// ActOnConditionalOp - Parse a ?: operation.  Note that 'LHS' may be null
   /// in the case of a the GNU conditional expr extension.
   ExprResult ActOnConditionalOp(SourceLocation QuestionLoc,
                                 SourceLocation ColonLoc, Expr *CondExpr,
                                 Expr *LHSExpr, Expr *RHSExpr);
 
   /// ActOnAddrLabel - Parse the GNU address of label extension: "&&foo".
   ExprResult ActOnAddrLabel(SourceLocation OpLoc, SourceLocation LabLoc,
                             LabelDecl *TheDecl);
 
   void ActOnStartStmtExpr();
   ExprResult ActOnStmtExpr(Scope *S, SourceLocation LPLoc, Stmt *SubStmt,
                            SourceLocation RPLoc);
   ExprResult BuildStmtExpr(SourceLocation LPLoc, Stmt *SubStmt,
                            SourceLocation RPLoc, unsigned TemplateDepth);
   // Handle the final expression in a statement expression.
   ExprResult ActOnStmtExprResult(ExprResult E);
   void ActOnStmtExprError();
 
   // __builtin_offsetof(type, identifier(.identifier|[expr])*)
   struct OffsetOfComponent {
     SourceLocation LocStart, LocEnd;
     bool isBrackets; // true if [expr], false if .ident
     union {
       IdentifierInfo *IdentInfo;
       Expr *E;
     } U;
   };
 
   /// __builtin_offsetof(type, a.b[123][456].c)
   ExprResult BuildBuiltinOffsetOf(SourceLocation BuiltinLoc,
                                   TypeSourceInfo *TInfo,
                                   ArrayRef<OffsetOfComponent> Components,
                                   SourceLocation RParenLoc);
   ExprResult ActOnBuiltinOffsetOf(Scope *S, SourceLocation BuiltinLoc,
                                   SourceLocation TypeLoc,
                                   ParsedType ParsedArgTy,
                                   ArrayRef<OffsetOfComponent> Components,
                                   SourceLocation RParenLoc);
 
   // __builtin_choose_expr(constExpr, expr1, expr2)
   ExprResult ActOnChooseExpr(SourceLocation BuiltinLoc, Expr *CondExpr,
                              Expr *LHSExpr, Expr *RHSExpr,
                              SourceLocation RPLoc);
 
   // __builtin_va_arg(expr, type)
   ExprResult ActOnVAArg(SourceLocation BuiltinLoc, Expr *E, ParsedType Ty,
                         SourceLocation RPLoc);
   ExprResult BuildVAArgExpr(SourceLocation BuiltinLoc, Expr *E,
                             TypeSourceInfo *TInfo, SourceLocation RPLoc);
 
   // __builtin_LINE(), __builtin_FUNCTION(), __builtin_FUNCSIG(),
   // __builtin_FILE(), __builtin_COLUMN(), __builtin_source_location()
   ExprResult ActOnSourceLocExpr(SourceLocIdentKind Kind,
                                 SourceLocation BuiltinLoc,
                                 SourceLocation RPLoc);
 
   // #embed
   ExprResult ActOnEmbedExpr(SourceLocation EmbedKeywordLoc,
                             StringLiteral *BinaryData);
 
   // Build a potentially resolved SourceLocExpr.
   ExprResult BuildSourceLocExpr(SourceLocIdentKind Kind, QualType ResultTy,
                                 SourceLocation BuiltinLoc, SourceLocation RPLoc,
                                 DeclContext *ParentContext);
 
   // __null
   ExprResult ActOnGNUNullExpr(SourceLocation TokenLoc);
 
   bool CheckCaseExpression(Expr *E);
 
   //===------------------------- "Block" Extension ------------------------===//
 
   /// ActOnBlockStart - This callback is invoked when a block literal is
   /// started.
   void ActOnBlockStart(SourceLocation CaretLoc, Scope *CurScope);
 
   /// ActOnBlockArguments - This callback allows processing of block arguments.
   /// If there are no arguments, this is still invoked.
   void ActOnBlockArguments(SourceLocation CaretLoc, Declarator &ParamInfo,
                            Scope *CurScope);
 
   /// ActOnBlockError - If there is an error parsing a block, this callback
   /// is invoked to pop the information about the block from the action impl.
   void ActOnBlockError(SourceLocation CaretLoc, Scope *CurScope);
 
   /// ActOnBlockStmtExpr - This is called when the body of a block statement
   /// literal was successfully completed.  ^(int x){...}
   ExprResult ActOnBlockStmtExpr(SourceLocation CaretLoc, Stmt *Body,
                                 Scope *CurScope);
 
   //===---------------------------- Clang Extensions ----------------------===//
 
   /// ActOnConvertVectorExpr - create a new convert-vector expression from the
   /// provided arguments.
   ///
   /// __builtin_convertvector( value, dst type )
   ///
   ExprResult ActOnConvertVectorExpr(Expr *E, ParsedType ParsedDestTy,
                                     SourceLocation BuiltinLoc,
                                     SourceLocation RParenLoc);
 
   //===---------------------------- OpenCL Features -----------------------===//
 
   /// Parse a __builtin_astype expression.
   ///
   /// __builtin_astype( value, dst type )
   ///
   ExprResult ActOnAsTypeExpr(Expr *E, ParsedType ParsedDestTy,
                              SourceLocation BuiltinLoc,
                              SourceLocation RParenLoc);
 
   /// Create a new AsTypeExpr node (bitcast) from the arguments.
   ExprResult BuildAsTypeExpr(Expr *E, QualType DestTy,
                              SourceLocation BuiltinLoc,
                              SourceLocation RParenLoc);
 
   /// Attempts to produce a RecoveryExpr after some AST node cannot be created.
   ExprResult CreateRecoveryExpr(SourceLocation Begin, SourceLocation End,
                                 ArrayRef<Expr *> SubExprs,
                                 QualType T = QualType());
 
   /// Cast a base object to a member's actual type.
   ///
   /// There are two relevant checks:
   ///
   /// C++ [class.access.base]p7:
   ///
   ///   If a class member access operator [...] is used to access a non-static
   ///   data member or non-static member function, the reference is ill-formed
   ///   if the left operand [...] cannot be implicitly converted to a pointer to
   ///   the naming class of the right operand.
   ///
   /// C++ [expr.ref]p7:
   ///
   ///   If E2 is a non-static data member or a non-static member function, the
   ///   program is ill-formed if the class of which E2 is directly a member is
   ///   an ambiguous base (11.8) of the naming class (11.9.3) of E2.
   ///
   /// Note that the latter check does not consider access; the access of the
   /// "real" base class is checked as appropriate when checking the access of
   /// the member name.
   ExprResult PerformObjectMemberConversion(Expr *From,
                                            NestedNameSpecifier *Qualifier,
                                            NamedDecl *FoundDecl,
                                            NamedDecl *Member);
 
   /// CheckCallReturnType - Checks that a call expression's return type is
   /// complete. Returns true on failure. The location passed in is the location
   /// that best represents the call.
   bool CheckCallReturnType(QualType ReturnType, SourceLocation Loc,
                            CallExpr *CE, FunctionDecl *FD);
 
   /// Emit a warning for all pending noderef expressions that we recorded.
   void WarnOnPendingNoDerefs(ExpressionEvaluationContextRecord &Rec);
 
   ExprResult BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field);
 
   /// Instantiate or parse a C++ default argument expression as necessary.
   /// Return true on error.
   bool CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
                               ParmVarDecl *Param, Expr *Init = nullptr,
                               bool SkipImmediateInvocations = true);
 
   /// BuildCXXDefaultArgExpr - Creates a CXXDefaultArgExpr, instantiating
   /// the default expr if needed.
   ExprResult BuildCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
                                     ParmVarDecl *Param, Expr *Init = nullptr);
 
   /// Wrap the expression in a ConstantExpr if it is a potential immediate
   /// invocation.
   ExprResult CheckForImmediateInvocation(ExprResult E, FunctionDecl *Decl);
 
   void MarkExpressionAsImmediateEscalating(Expr *E);
 
   // Check that the SME attributes for PSTATE.ZA and PSTATE.SM are compatible.
   bool IsInvalidSMECallConversion(QualType FromType, QualType ToType);
 
   /// Abstract base class used for diagnosing integer constant
   /// expression violations.
   class VerifyICEDiagnoser {
   public:
     bool Suppress;
 
     VerifyICEDiagnoser(bool Suppress = false) : Suppress(Suppress) {}
 
     virtual SemaDiagnosticBuilder
     diagnoseNotICEType(Sema &S, SourceLocation Loc, QualType T);
     virtual SemaDiagnosticBuilder diagnoseNotICE(Sema &S,
                                                  SourceLocation Loc) = 0;
     virtual SemaDiagnosticBuilder diagnoseFold(Sema &S, SourceLocation Loc);
     virtual ~VerifyICEDiagnoser() {}
   };
 
   enum AllowFoldKind {
     NoFold,
     AllowFold,
   };
 
   /// VerifyIntegerConstantExpression - Verifies that an expression is an ICE,
   /// and reports the appropriate diagnostics. Returns false on success.
   /// Can optionally return the value of the expression.
   ExprResult VerifyIntegerConstantExpression(Expr *E, llvm::APSInt *Result,
                                              VerifyICEDiagnoser &Diagnoser,
                                              AllowFoldKind CanFold = NoFold);
   ExprResult VerifyIntegerConstantExpression(Expr *E, llvm::APSInt *Result,
                                              unsigned DiagID,
                                              AllowFoldKind CanFold = NoFold);
   ExprResult VerifyIntegerConstantExpression(Expr *E,
                                              llvm::APSInt *Result = nullptr,
                                              AllowFoldKind CanFold = NoFold);
   ExprResult VerifyIntegerConstantExpression(Expr *E,
                                              AllowFoldKind CanFold = NoFold) {
     return VerifyIntegerConstantExpression(E, nullptr, CanFold);
   }
 
   /// DiagnoseAssignmentAsCondition - Given that an expression is
   /// being used as a boolean condition, warn if it's an assignment.
   void DiagnoseAssignmentAsCondition(Expr *E);
 
   /// Redundant parentheses over an equality comparison can indicate
   /// that the user intended an assignment used as condition.
   void DiagnoseEqualityWithExtraParens(ParenExpr *ParenE);
 
   class FullExprArg {
   public:
     FullExprArg() : E(nullptr) {}
     FullExprArg(Sema &actions) : E(nullptr) {}
 
     ExprResult release() { return E; }
 
     Expr *get() const { return E; }
 
     Expr *operator->() { return E; }
 
   private:
     // FIXME: No need to make the entire Sema class a friend when it's just
     // Sema::MakeFullExpr that needs access to the constructor below.
     friend class Sema;
 
     explicit FullExprArg(Expr *expr) : E(expr) {}
 
     Expr *E;
   };
 
   FullExprArg MakeFullExpr(Expr *Arg) {
     return MakeFullExpr(Arg, Arg ? Arg->getExprLoc() : SourceLocation());
   }
   FullExprArg MakeFullExpr(Expr *Arg, SourceLocation CC) {
     return FullExprArg(
         ActOnFinishFullExpr(Arg, CC, /*DiscardedValue*/ false).get());
   }
   FullExprArg MakeFullDiscardedValueExpr(Expr *Arg) {
     ExprResult FE =
         ActOnFinishFullExpr(Arg, Arg ? Arg->getExprLoc() : SourceLocation(),
                             /*DiscardedValue*/ true);
     return FullExprArg(FE.get());
   }
 
   class ConditionResult {
     Decl *ConditionVar;
     FullExprArg Condition;
     bool Invalid;
     std::optional<bool> KnownValue;
 
     friend class Sema;
     ConditionResult(Sema &S, Decl *ConditionVar, FullExprArg Condition,
                     bool IsConstexpr)
         : ConditionVar(ConditionVar), Condition(Condition), Invalid(false) {
       if (IsConstexpr && Condition.get()) {
         if (std::optional<llvm::APSInt> Val =
                 Condition.get()->getIntegerConstantExpr(S.Context)) {
           KnownValue = !!(*Val);
         }
       }
     }
     explicit ConditionResult(bool Invalid)
         : ConditionVar(nullptr), Condition(nullptr), Invalid(Invalid),
           KnownValue(std::nullopt) {}
 
   public:
     ConditionResult() : ConditionResult(false) {}
     bool isInvalid() const { return Invalid; }
     std::pair<VarDecl *, Expr *> get() const {
       return std::make_pair(cast_or_null<VarDecl>(ConditionVar),
                             Condition.get());
     }
     std::optional<bool> getKnownValue() const { return KnownValue; }
   };
   static ConditionResult ConditionError() { return ConditionResult(true); }
 
   /// CheckBooleanCondition - Diagnose problems involving the use of
   /// the given expression as a boolean condition (e.g. in an if
   /// statement).  Also performs the standard function and array
   /// decays, possibly changing the input variable.
   ///
   /// \param Loc - A location associated with the condition, e.g. the
   /// 'if' keyword.
   /// \return true iff there were any errors
   ExprResult CheckBooleanCondition(SourceLocation Loc, Expr *E,
                                    bool IsConstexpr = false);
 
   enum class ConditionKind {
     Boolean,     ///< A boolean condition, from 'if', 'while', 'for', or 'do'.
     ConstexprIf, ///< A constant boolean condition from 'if constexpr'.
     Switch       ///< An integral condition for a 'switch' statement.
   };
 
   ConditionResult ActOnCondition(Scope *S, SourceLocation Loc, Expr *SubExpr,
                                  ConditionKind CK, bool MissingOK = false);
 
   QualType CheckConditionalOperands( // C99 6.5.15
       ExprResult &Cond, ExprResult &LHS, ExprResult &RHS, ExprValueKind &VK,
       ExprObjectKind &OK, SourceLocation QuestionLoc);
 
   /// Emit a specialized diagnostic when one expression is a null pointer
   /// constant and the other is not a pointer.  Returns true if a diagnostic is
   /// emitted.
   bool DiagnoseConditionalForNull(const Expr *LHSExpr, const Expr *RHSExpr,
                                   SourceLocation QuestionLoc);
 
   /// type checking for vector binary operators.
   QualType CheckVectorOperands(ExprResult &LHS, ExprResult &RHS,
                                SourceLocation Loc, bool IsCompAssign,
                                bool AllowBothBool, bool AllowBoolConversion,
                                bool AllowBoolOperation, bool ReportInvalid);
 
   /// Return a signed ext_vector_type that is of identical size and number of
   /// elements. For floating point vectors, return an integer type of identical
   /// size and number of elements. In the non ext_vector_type case, search from
   /// the largest type to the smallest type to avoid cases where long long ==
   /// long, where long gets picked over long long.
   QualType GetSignedVectorType(QualType V);
   QualType GetSignedSizelessVectorType(QualType V);
 
   /// CheckVectorCompareOperands - vector comparisons are a clang extension that
   /// operates on extended vector types.  Instead of producing an IntTy result,
   /// like a scalar comparison, a vector comparison produces a vector of integer
   /// types.
   QualType CheckVectorCompareOperands(ExprResult &LHS, ExprResult &RHS,
                                       SourceLocation Loc,
                                       BinaryOperatorKind Opc);
   QualType CheckSizelessVectorCompareOperands(ExprResult &LHS, ExprResult &RHS,
                                               SourceLocation Loc,
                                               BinaryOperatorKind Opc);
   QualType CheckVectorLogicalOperands(ExprResult &LHS, ExprResult &RHS,
                                       SourceLocation Loc);
 
   /// Context in which we're performing a usual arithmetic conversion.
   enum ArithConvKind {
     /// An arithmetic operation.
     ACK_Arithmetic,
     /// A bitwise operation.
     ACK_BitwiseOp,
     /// A comparison.
     ACK_Comparison,
     /// A conditional (?:) operator.
     ACK_Conditional,
     /// A compound assignment expression.
     ACK_CompAssign,
   };
 
   // type checking for sizeless vector binary operators.
   QualType CheckSizelessVectorOperands(ExprResult &LHS, ExprResult &RHS,
                                        SourceLocation Loc, bool IsCompAssign,
                                        ArithConvKind OperationKind);
 
   /// Type checking for matrix binary operators.
   QualType CheckMatrixElementwiseOperands(ExprResult &LHS, ExprResult &RHS,
                                           SourceLocation Loc,
                                           bool IsCompAssign);
   QualType CheckMatrixMultiplyOperands(ExprResult &LHS, ExprResult &RHS,
                                        SourceLocation Loc, bool IsCompAssign);
 
   /// Are the two types SVE-bitcast-compatible types? I.e. is bitcasting from
   /// the first SVE type (e.g. an SVE VLAT) to the second type (e.g. an SVE
   /// VLST) allowed?
   ///
   /// This will also return false if the two given types do not make sense from
   /// the perspective of SVE bitcasts.
   bool isValidSveBitcast(QualType srcType, QualType destType);
 
   /// Are the two types matrix types and do they have the same dimensions i.e.
   /// do they have the same number of rows and the same number of columns?
   bool areMatrixTypesOfTheSameDimension(QualType srcTy, QualType destTy);
 
   bool areVectorTypesSameSize(QualType srcType, QualType destType);
 
   /// Are the two types lax-compatible vector types?  That is, given
   /// that one of them is a vector, do they have equal storage sizes,
   /// where the storage size is the number of elements times the element
   /// size?
   ///
   /// This will also return false if either of the types is neither a
   /// vector nor a real type.
   bool areLaxCompatibleVectorTypes(QualType srcType, QualType destType);
 
   /// Is this a legal conversion between two types, one of which is
   /// known to be a vector type?
   bool isLaxVectorConversion(QualType srcType, QualType destType);
 
   // This returns true if at least one of the types is an altivec vector.
   bool anyAltivecTypes(QualType srcType, QualType destType);
 
   // type checking C++ declaration initializers (C++ [dcl.init]).
 
   /// Check a cast of an unknown-any type.  We intentionally only
   /// trigger this for C-style casts.
   ExprResult checkUnknownAnyCast(SourceRange TypeRange, QualType CastType,
                                  Expr *CastExpr, CastKind &CastKind,
                                  ExprValueKind &VK, CXXCastPath &Path);
 
   /// Force an expression with unknown-type to an expression of the
   /// given type.
   ExprResult forceUnknownAnyToType(Expr *E, QualType ToType);
 
   /// Type-check an expression that's being passed to an
   /// __unknown_anytype parameter.
   ExprResult checkUnknownAnyArg(SourceLocation callLoc, Expr *result,
                                 QualType &paramType);
 
   // CheckMatrixCast - Check type constraints for matrix casts.
   // We allow casting between matrixes of the same dimensions i.e. when they
   // have the same number of rows and column. Returns true if the cast is
   // invalid.
   bool CheckMatrixCast(SourceRange R, QualType DestTy, QualType SrcTy,
                        CastKind &Kind);
 
   // CheckVectorCast - check type constraints for vectors.
   // Since vectors are an extension, there are no C standard reference for this.
   // We allow casting between vectors and integer datatypes of the same size.
   // returns true if the cast is invalid
   bool CheckVectorCast(SourceRange R, QualType VectorTy, QualType Ty,
                        CastKind &Kind);
 
   /// Prepare `SplattedExpr` for a vector splat operation, adding
   /// implicit casts if necessary.
   ExprResult prepareVectorSplat(QualType VectorTy, Expr *SplattedExpr);
 
   // CheckExtVectorCast - check type constraints for extended vectors.
   // Since vectors are an extension, there are no C standard reference for this.
   // We allow casting between vectors and integer datatypes of the same size,
   // or vectors and the element type of that vector.
   // returns the cast expr
   ExprResult CheckExtVectorCast(SourceRange R, QualType DestTy, Expr *CastExpr,
                                 CastKind &Kind);
 
   QualType PreferredConditionType(ConditionKind K) const {
     return K == ConditionKind::Switch ? Context.IntTy : Context.BoolTy;
   }
 
   // UsualUnaryConversions - promotes integers (C99 6.3.1.1p2) and converts
   // functions and arrays to their respective pointers (C99 6.3.2.1).
   ExprResult UsualUnaryConversions(Expr *E);
 
   /// CallExprUnaryConversions - a special case of an unary conversion
   /// performed on a function designator of a call expression.
   ExprResult CallExprUnaryConversions(Expr *E);
 
   // DefaultFunctionArrayConversion - converts functions and arrays
   // to their respective pointers (C99 6.3.2.1).
   ExprResult DefaultFunctionArrayConversion(Expr *E, bool Diagnose = true);
 
   // DefaultFunctionArrayLvalueConversion - converts functions and
   // arrays to their respective pointers and performs the
   // lvalue-to-rvalue conversion.
   ExprResult DefaultFunctionArrayLvalueConversion(Expr *E,
                                                   bool Diagnose = true);
 
   // DefaultLvalueConversion - performs lvalue-to-rvalue conversion on
   // the operand. This function is a no-op if the operand has a function type
   // or an array type.
   ExprResult DefaultLvalueConversion(Expr *E);
 
   // DefaultArgumentPromotion (C99 6.5.2.2p6). Used for function calls that
   // do not have a prototype. Integer promotions are performed on each
   // argument, and arguments that have type float are promoted to double.
   ExprResult DefaultArgumentPromotion(Expr *E);
 
   VariadicCallType getVariadicCallType(FunctionDecl *FDecl,
                                        const FunctionProtoType *Proto,
                                        Expr *Fn);
 
   // Used for determining in which context a type is allowed to be passed to a
   // vararg function.
   enum VarArgKind {
     VAK_Valid,
     VAK_ValidInCXX11,
     VAK_Undefined,
     VAK_MSVCUndefined,
     VAK_Invalid
   };
 
   /// Determine the degree of POD-ness for an expression.
   /// Incomplete types are considered POD, since this check can be performed
   /// when we're in an unevaluated context.
   VarArgKind isValidVarArgType(const QualType &Ty);
 
   /// Check to see if the given expression is a valid argument to a variadic
   /// function, issuing a diagnostic if not.
   void checkVariadicArgument(const Expr *E, VariadicCallType CT);
 
   /// GatherArgumentsForCall - Collector argument expressions for various
   /// form of call prototypes.
   bool GatherArgumentsForCall(SourceLocation CallLoc, FunctionDecl *FDecl,
                               const FunctionProtoType *Proto,
                               unsigned FirstParam, ArrayRef<Expr *> Args,
                               SmallVectorImpl<Expr *> &AllArgs,
                               VariadicCallType CallType = VariadicDoesNotApply,
                               bool AllowExplicit = false,
                               bool IsListInitialization = false);
 
   // DefaultVariadicArgumentPromotion - Like DefaultArgumentPromotion, but
   // will create a runtime trap if the resulting type is not a POD type.
   ExprResult DefaultVariadicArgumentPromotion(Expr *E, VariadicCallType CT,
                                               FunctionDecl *FDecl);
 
   // UsualArithmeticConversions - performs the UsualUnaryConversions on it's
   // operands and then handles various conversions that are common to binary
   // operators (C99 6.3.1.8). If both operands aren't arithmetic, this
   // routine returns the first non-arithmetic type found. The client is
   // responsible for emitting appropriate error diagnostics.
   QualType UsualArithmeticConversions(ExprResult &LHS, ExprResult &RHS,
                                       SourceLocation Loc, ArithConvKind ACK);
 
   /// AssignConvertType - All of the 'assignment' semantic checks return this
   /// enum to indicate whether the assignment was allowed.  These checks are
   /// done for simple assignments, as well as initialization, return from
   /// function, argument passing, etc.  The query is phrased in terms of a
   /// source and destination type.
   enum AssignConvertType {
     /// Compatible - the types are compatible according to the standard.
     Compatible,
 
     /// PointerToInt - The assignment converts a pointer to an int, which we
     /// accept as an extension.
     PointerToInt,
 
     /// IntToPointer - The assignment converts an int to a pointer, which we
     /// accept as an extension.
     IntToPointer,
 
     /// FunctionVoidPointer - The assignment is between a function pointer and
     /// void*, which the standard doesn't allow, but we accept as an extension.
     FunctionVoidPointer,
 
     /// IncompatiblePointer - The assignment is between two pointers types that
     /// are not compatible, but we accept them as an extension.
     IncompatiblePointer,
 
     /// IncompatibleFunctionPointer - The assignment is between two function
     /// pointers types that are not compatible, but we accept them as an
     /// extension.
     IncompatibleFunctionPointer,
 
     /// IncompatibleFunctionPointerStrict - The assignment is between two
     /// function pointer types that are not identical, but are compatible,
     /// unless compiled with -fsanitize=cfi, in which case the type mismatch
     /// may trip an indirect call runtime check.
     IncompatibleFunctionPointerStrict,
 
     /// IncompatiblePointerSign - The assignment is between two pointers types
     /// which point to integers which have a different sign, but are otherwise
     /// identical. This is a subset of the above, but broken out because it's by
     /// far the most common case of incompatible pointers.
     IncompatiblePointerSign,
 
     /// CompatiblePointerDiscardsQualifiers - The assignment discards
     /// c/v/r qualifiers, which we accept as an extension.
     CompatiblePointerDiscardsQualifiers,
 
     /// IncompatiblePointerDiscardsQualifiers - The assignment
     /// discards qualifiers that we don't permit to be discarded,
     /// like address spaces.
     IncompatiblePointerDiscardsQualifiers,
 
     /// IncompatibleNestedPointerAddressSpaceMismatch - The assignment
     /// changes address spaces in nested pointer types which is not allowed.
     /// For instance, converting __private int ** to __generic int ** is
     /// illegal even though __private could be converted to __generic.
     IncompatibleNestedPointerAddressSpaceMismatch,
 
     /// IncompatibleNestedPointerQualifiers - The assignment is between two
     /// nested pointer types, and the qualifiers other than the first two
     /// levels differ e.g. char ** -> const char **, but we accept them as an
     /// extension.
     IncompatibleNestedPointerQualifiers,
 
     /// IncompatibleVectors - The assignment is between two vector types that
     /// have the same size, which we accept as an extension.
     IncompatibleVectors,
 
     /// IntToBlockPointer - The assignment converts an int to a block
     /// pointer. We disallow this.
     IntToBlockPointer,
 
     /// IncompatibleBlockPointer - The assignment is between two block
     /// pointers types that are not compatible.
     IncompatibleBlockPointer,
 
     /// IncompatibleObjCQualifiedId - The assignment is between a qualified
     /// id type and something else (that is incompatible with it). For example,
     /// "id <XXX>" = "Foo *", where "Foo *" doesn't implement the XXX protocol.
     IncompatibleObjCQualifiedId,
 
     /// IncompatibleObjCWeakRef - Assigning a weak-unavailable object to an
     /// object with __weak qualifier.
     IncompatibleObjCWeakRef,
 
     /// Incompatible - We reject this conversion outright, it is invalid to
     /// represent it in the AST.
     Incompatible
   };
 
   /// DiagnoseAssignmentResult - Emit a diagnostic, if required, for the
   /// assignment conversion type specified by ConvTy.  This returns true if the
   /// conversion was invalid or false if the conversion was accepted.
   bool DiagnoseAssignmentResult(AssignConvertType ConvTy, SourceLocation Loc,
                                 QualType DstType, QualType SrcType,
                                 Expr *SrcExpr, AssignmentAction Action,
                                 bool *Complained = nullptr);
 
   /// CheckAssignmentConstraints - Perform type checking for assignment,
   /// argument passing, variable initialization, and function return values.
   /// C99 6.5.16.
   AssignConvertType CheckAssignmentConstraints(SourceLocation Loc,
                                                QualType LHSType,
                                                QualType RHSType);
 
   /// Check assignment constraints and optionally prepare for a conversion of
   /// the RHS to the LHS type. The conversion is prepared for if ConvertRHS
   /// is true.
   AssignConvertType CheckAssignmentConstraints(QualType LHSType,
                                                ExprResult &RHS, CastKind &Kind,
                                                bool ConvertRHS = true);
 
   /// Check assignment constraints for an assignment of RHS to LHSType.
   ///
   /// \param LHSType The destination type for the assignment.
   /// \param RHS The source expression for the assignment.
   /// \param Diagnose If \c true, diagnostics may be produced when checking
   ///        for assignability. If a diagnostic is produced, \p RHS will be
   ///        set to ExprError(). Note that this function may still return
   ///        without producing a diagnostic, even for an invalid assignment.
   /// \param DiagnoseCFAudited If \c true, the target is a function parameter
   ///        in an audited Core Foundation API and does not need to be checked
   ///        for ARC retain issues.
   /// \param ConvertRHS If \c true, \p RHS will be updated to model the
   ///        conversions necessary to perform the assignment. If \c false,
   ///        \p Diagnose must also be \c false.
   AssignConvertType CheckSingleAssignmentConstraints(
       QualType LHSType, ExprResult &RHS, bool Diagnose = true,
       bool DiagnoseCFAudited = false, bool ConvertRHS = true);
 
   // If the lhs type is a transparent union, check whether we
   // can initialize the transparent union with the given expression.
   AssignConvertType CheckTransparentUnionArgumentConstraints(QualType ArgType,
                                                              ExprResult &RHS);
 
   /// the following "Check" methods will return a valid/converted QualType
   /// or a null QualType (indicating an error diagnostic was issued).
 
   /// type checking binary operators (subroutines of CreateBuiltinBinOp).
   QualType InvalidOperands(SourceLocation Loc, ExprResult &LHS,
                            ExprResult &RHS);
 
   /// Diagnose cases where a scalar was implicitly converted to a vector and
   /// diagnose the underlying types. Otherwise, diagnose the error
   /// as invalid vector logical operands for non-C++ cases.
   QualType InvalidLogicalVectorOperands(SourceLocation Loc, ExprResult &LHS,
                                         ExprResult &RHS);
 
   QualType CheckMultiplyDivideOperands( // C99 6.5.5
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc, bool IsCompAssign,
       bool IsDivide);
   QualType CheckRemainderOperands( // C99 6.5.5
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       bool IsCompAssign = false);
   QualType CheckAdditionOperands( // C99 6.5.6
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc, QualType *CompLHSTy = nullptr);
   QualType CheckSubtractionOperands( // C99 6.5.6
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       QualType *CompLHSTy = nullptr);
   QualType CheckShiftOperands( // C99 6.5.7
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc, bool IsCompAssign = false);
   void CheckPtrComparisonWithNullChar(ExprResult &E, ExprResult &NullE);
   QualType CheckCompareOperands( // C99 6.5.8/9
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc);
   QualType CheckBitwiseOperands( // C99 6.5.[10...12]
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc);
   QualType CheckLogicalOperands( // C99 6.5.[13,14]
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc);
   // CheckAssignmentOperands is used for both simple and compound assignment.
   // For simple assignment, pass both expressions and a null converted type.
   // For compound assignment, pass both expressions and the converted type.
   QualType CheckAssignmentOperands( // C99 6.5.16.[1,2]
       Expr *LHSExpr, ExprResult &RHS, SourceLocation Loc, QualType CompoundType,
       BinaryOperatorKind Opc);
 
   /// To be used for checking whether the arguments being passed to
   /// function exceeds the number of parameters expected for it.
   static bool TooManyArguments(size_t NumParams, size_t NumArgs,
                                bool PartialOverloading = false) {
     // We check whether we're just after a comma in code-completion.
     if (NumArgs > 0 && PartialOverloading)
       return NumArgs + 1 > NumParams; // If so, we view as an extra argument.
     return NumArgs > NumParams;
   }
 
   /// Whether the AST is currently being rebuilt to correct immediate
   /// invocations. Immediate invocation candidates and references to consteval
   /// functions aren't tracked when this is set.
   bool RebuildingImmediateInvocation = false;
 
   bool isAlwaysConstantEvaluatedContext() const {
     const ExpressionEvaluationContextRecord &Ctx = currentEvaluationContext();
     return (Ctx.isConstantEvaluated() || isConstantEvaluatedOverride) &&
            !Ctx.InConditionallyConstantEvaluateContext;
   }
 
   /// Determines whether we are currently in a context that
   /// is not evaluated as per C++ [expr] p5.
   bool isUnevaluatedContext() const {
     return currentEvaluationContext().isUnevaluated();
   }
 
   bool isImmediateFunctionContext() const {
     return currentEvaluationContext().isImmediateFunctionContext();
   }
 
   bool isInLifetimeExtendingContext() const {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
     return ExprEvalContexts.back().InLifetimeExtendingContext;
   }
 
   bool isCheckingDefaultArgumentOrInitializer() const {
     const ExpressionEvaluationContextRecord &Ctx = currentEvaluationContext();
     return (Ctx.Context ==
             ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed) ||
            Ctx.IsCurrentlyCheckingDefaultArgumentOrInitializer;
   }
 
   std::optional<ExpressionEvaluationContextRecord::InitializationContext>
   InnermostDeclarationWithDelayedImmediateInvocations() const {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
     for (const auto &Ctx : llvm::reverse(ExprEvalContexts)) {
       if (Ctx.Context == ExpressionEvaluationContext::PotentiallyEvaluated &&
           Ctx.DelayedDefaultInitializationContext)
         return Ctx.DelayedDefaultInitializationContext;
       if (Ctx.isConstantEvaluated() || Ctx.isImmediateFunctionContext() ||
           Ctx.isUnevaluated())
         break;
     }
     return std::nullopt;
   }
 
   std::optional<ExpressionEvaluationContextRecord::InitializationContext>
   OutermostDeclarationWithDelayedImmediateInvocations() const {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
     std::optional<ExpressionEvaluationContextRecord::InitializationContext> Res;
     for (auto &Ctx : llvm::reverse(ExprEvalContexts)) {
       if (Ctx.Context == ExpressionEvaluationContext::PotentiallyEvaluated &&
           !Ctx.DelayedDefaultInitializationContext && Res)
         break;
       if (Ctx.isConstantEvaluated() || Ctx.isImmediateFunctionContext() ||
           Ctx.isUnevaluated())
         break;
       Res = Ctx.DelayedDefaultInitializationContext;
     }
     return Res;
   }
 
   /// keepInLifetimeExtendingContext - Pull down InLifetimeExtendingContext
   /// flag from previous context.
   void keepInLifetimeExtendingContext() {
     if (ExprEvalContexts.size() > 2 &&
         parentEvaluationContext().InLifetimeExtendingContext) {
       auto &LastRecord = ExprEvalContexts.back();
       auto &PrevRecord = parentEvaluationContext();
       LastRecord.InLifetimeExtendingContext =
           PrevRecord.InLifetimeExtendingContext;
     }
   }
 
   DefaultedComparisonKind getDefaultedComparisonKind(const FunctionDecl *FD) {
     return getDefaultedFunctionKind(FD).asComparison();
   }
 
   /// Returns a field in a CXXRecordDecl that has the same name as the decl \p
   /// SelfAssigned when inside a CXXMethodDecl.
   const FieldDecl *
   getSelfAssignmentClassMemberCandidate(const ValueDecl *SelfAssigned);
 
   void MaybeSuggestAddingStaticToDecl(const FunctionDecl *D);
 
   template <typename... Ts>
   bool RequireCompleteSizedType(SourceLocation Loc, QualType T, unsigned DiagID,
                                 const Ts &...Args) {
     SizelessTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireCompleteType(Loc, T, CompleteTypeKind::Normal, Diagnoser);
   }
 
   template <typename... Ts>
   bool RequireCompleteSizedExprType(Expr *E, unsigned DiagID,
                                     const Ts &...Args) {
     SizelessTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireCompleteExprType(E, CompleteTypeKind::Normal, Diagnoser);
   }
 
   /// Abstract class used to diagnose incomplete types.
   struct TypeDiagnoser {
     TypeDiagnoser() {}
 
     virtual void diagnose(Sema &S, SourceLocation Loc, QualType T) = 0;
     virtual ~TypeDiagnoser() {}
   };
 
   template <typename... Ts> class BoundTypeDiagnoser : public TypeDiagnoser {
   protected:
     unsigned DiagID;
     std::tuple<const Ts &...> Args;
 
     template <std::size_t... Is>
     void emit(const SemaDiagnosticBuilder &DB,
               std::index_sequence<Is...>) const {
       // Apply all tuple elements to the builder in order.
       bool Dummy[] = {false, (DB << getPrintable(std::get<Is>(Args)))...};
       (void)Dummy;
     }
 
   public:
     BoundTypeDiagnoser(unsigned DiagID, const Ts &...Args)
         : TypeDiagnoser(), DiagID(DiagID), Args(Args...) {
       assert(DiagID != 0 && "no diagnostic for type diagnoser");
     }
 
     void diagnose(Sema &S, SourceLocation Loc, QualType T) override {
       const SemaDiagnosticBuilder &DB = S.Diag(Loc, DiagID);
       emit(DB, std::index_sequence_for<Ts...>());
       DB << T;
     }
   };
 
   /// A derivative of BoundTypeDiagnoser for which the diagnostic's type
   /// parameter is preceded by a 0/1 enum that is 1 if the type is sizeless.
   /// For example, a diagnostic with no other parameters would generally have
   /// the form "...%select{incomplete|sizeless}0 type %1...".
   template <typename... Ts>
   class SizelessTypeDiagnoser : public BoundTypeDiagnoser<Ts...> {
   public:
     SizelessTypeDiagnoser(unsigned DiagID, const Ts &...Args)
         : BoundTypeDiagnoser<Ts...>(DiagID, Args...) {}
 
     void diagnose(Sema &S, SourceLocation Loc, QualType T) override {
       const SemaDiagnosticBuilder &DB = S.Diag(Loc, this->DiagID);
       this->emit(DB, std::index_sequence_for<Ts...>());
       DB << T->isSizelessType() << T;
     }
   };
 
   /// Check an argument list for placeholders that we won't try to
   /// handle later.
   bool CheckArgsForPlaceholders(MultiExprArg args);
 
   /// The C++ "std::source_location::__impl" struct, defined in
   /// \<source_location>.
   RecordDecl *StdSourceLocationImplDecl;
 
   /// A stack of expression evaluation contexts.
   SmallVector<ExpressionEvaluationContextRecord, 8> ExprEvalContexts;
 
   // Set of failed immediate invocations to avoid double diagnosing.
   llvm::SmallPtrSet<ConstantExpr *, 4> FailedImmediateInvocations;
 
   /// List of SourceLocations where 'self' is implicitly retained inside a
   /// block.
   llvm::SmallVector<std::pair<SourceLocation, const BlockDecl *>, 1>
       ImplicitlyRetainedSelfLocs;
 
   /// Do an explicit extend of the given block pointer if we're in ARC.
   void maybeExtendBlockObject(ExprResult &E);
 
 private:
   static BinaryOperatorKind ConvertTokenKindToBinaryOpcode(tok::TokenKind Kind);
 
   /// Methods for marking which expressions involve dereferencing a pointer
   /// marked with the 'noderef' attribute. Expressions are checked bottom up as
   /// they are parsed, meaning that a noderef pointer may not be accessed. For
   /// example, in `&*p` where `p` is a noderef pointer, we will first parse the
   /// `*p`, but need to check that `address of` is called on it. This requires
   /// keeping a container of all pending expressions and checking if the address
   /// of them are eventually taken.
   void CheckSubscriptAccessOfNoDeref(const ArraySubscriptExpr *E);
   void CheckAddressOfNoDeref(const Expr *E);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Expressions
   /// Implementations are in SemaExprCXX.cpp
   ///@{
 
 public:
   /// The C++ "std::bad_alloc" class, which is defined by the C++
   /// standard library.
   LazyDeclPtr StdBadAlloc;
 
   /// The C++ "std::align_val_t" enum class, which is defined by the C++
   /// standard library.
   LazyDeclPtr StdAlignValT;
 
   /// The C++ "type_info" declaration, which is defined in \<typeinfo>.
   RecordDecl *CXXTypeInfoDecl;
 
   /// A flag to remember whether the implicit forms of operator new and delete
   /// have been declared.
   bool GlobalNewDeleteDeclared;
 
   /// Delete-expressions to be analyzed at the end of translation unit
   ///
   /// This list contains class members, and locations of delete-expressions
   /// that could not be proven as to whether they mismatch with new-expression
   /// used in initializer of the field.
   llvm::MapVector<FieldDecl *, DeleteLocs> DeleteExprs;
 
   /// Handle the result of the special case name lookup for inheriting
   /// constructor declarations. 'NS::X::X' and 'NS::X<...>::X' are treated as
   /// constructor names in member using declarations, even if 'X' is not the
   /// name of the corresponding type.
   ParsedType getInheritingConstructorName(CXXScopeSpec &SS,
                                           SourceLocation NameLoc,
                                           const IdentifierInfo &Name);
 
   ParsedType getConstructorName(const IdentifierInfo &II,
                                 SourceLocation NameLoc, Scope *S,
                                 CXXScopeSpec &SS, bool EnteringContext);
   ParsedType getDestructorName(const IdentifierInfo &II, SourceLocation NameLoc,
                                Scope *S, CXXScopeSpec &SS,
                                ParsedType ObjectType, bool EnteringContext);
 
   ParsedType getDestructorTypeForDecltype(const DeclSpec &DS,
                                           ParsedType ObjectType);
 
   /// Build a C++ typeid expression with a type operand.
   ExprResult BuildCXXTypeId(QualType TypeInfoType, SourceLocation TypeidLoc,
                             TypeSourceInfo *Operand, SourceLocation RParenLoc);
 
   /// Build a C++ typeid expression with an expression operand.
   ExprResult BuildCXXTypeId(QualType TypeInfoType, SourceLocation TypeidLoc,
                             Expr *Operand, SourceLocation RParenLoc);
 
   /// ActOnCXXTypeid - Parse typeid( something ).
   ExprResult ActOnCXXTypeid(SourceLocation OpLoc, SourceLocation LParenLoc,
                             bool isType, void *TyOrExpr,
                             SourceLocation RParenLoc);
 
   /// Build a Microsoft __uuidof expression with a type operand.
   ExprResult BuildCXXUuidof(QualType TypeInfoType, SourceLocation TypeidLoc,
                             TypeSourceInfo *Operand, SourceLocation RParenLoc);
 
   /// Build a Microsoft __uuidof expression with an expression operand.
   ExprResult BuildCXXUuidof(QualType TypeInfoType, SourceLocation TypeidLoc,
                             Expr *Operand, SourceLocation RParenLoc);
 
   /// ActOnCXXUuidof - Parse __uuidof( something ).
   ExprResult ActOnCXXUuidof(SourceLocation OpLoc, SourceLocation LParenLoc,
                             bool isType, void *TyOrExpr,
                             SourceLocation RParenLoc);
 
   //// ActOnCXXThis -  Parse 'this' pointer.
   ExprResult ActOnCXXThis(SourceLocation Loc);
 
   /// Check whether the type of 'this' is valid in the current context.
   bool CheckCXXThisType(SourceLocation Loc, QualType Type);
 
   /// Build a CXXThisExpr and mark it referenced in the current context.
   Expr *BuildCXXThisExpr(SourceLocation Loc, QualType Type, bool IsImplicit);
   void MarkThisReferenced(CXXThisExpr *This);
 
   /// Try to retrieve the type of the 'this' pointer.
   ///
   /// \returns The type of 'this', if possible. Otherwise, returns a NULL type.
   QualType getCurrentThisType();
 
   /// When non-NULL, the C++ 'this' expression is allowed despite the
   /// current context not being a non-static member function. In such cases,
   /// this provides the type used for 'this'.
   QualType CXXThisTypeOverride;
 
   /// RAII object used to temporarily allow the C++ 'this' expression
   /// to be used, with the given qualifiers on the current class type.
   class CXXThisScopeRAII {
     Sema &S;
     QualType OldCXXThisTypeOverride;
     bool Enabled;
 
   public:
     /// Introduce a new scope where 'this' may be allowed (when enabled),
     /// using the given declaration (which is either a class template or a
     /// class) along with the given qualifiers.
     /// along with the qualifiers placed on '*this'.
     CXXThisScopeRAII(Sema &S, Decl *ContextDecl, Qualifiers CXXThisTypeQuals,
                      bool Enabled = true);
 
     ~CXXThisScopeRAII();
   };
 
   /// Make sure the value of 'this' is actually available in the current
   /// context, if it is a potentially evaluated context.
   ///
   /// \param Loc The location at which the capture of 'this' occurs.
   ///
   /// \param Explicit Whether 'this' is explicitly captured in a lambda
   /// capture list.
   ///
   /// \param FunctionScopeIndexToStopAt If non-null, it points to the index
   /// of the FunctionScopeInfo stack beyond which we do not attempt to capture.
   /// This is useful when enclosing lambdas must speculatively capture
   /// 'this' that may or may not be used in certain specializations of
   /// a nested generic lambda (depending on whether the name resolves to
   /// a non-static member function or a static function).
   /// \return returns 'true' if failed, 'false' if success.
   bool CheckCXXThisCapture(
       SourceLocation Loc, bool Explicit = false, bool BuildAndDiagnose = true,
       const unsigned *const FunctionScopeIndexToStopAt = nullptr,
       bool ByCopy = false);
 
   /// Determine whether the given type is the type of *this that is used
   /// outside of the body of a member function for a type that is currently
   /// being defined.
   bool isThisOutsideMemberFunctionBody(QualType BaseType);
 
   /// ActOnCXXBoolLiteral - Parse {true,false} literals.
   ExprResult ActOnCXXBoolLiteral(SourceLocation OpLoc, tok::TokenKind Kind);
 
   /// ActOnCXXNullPtrLiteral - Parse 'nullptr'.
   ExprResult ActOnCXXNullPtrLiteral(SourceLocation Loc);
 
   //// ActOnCXXThrow -  Parse throw expressions.
   ExprResult ActOnCXXThrow(Scope *S, SourceLocation OpLoc, Expr *expr);
   ExprResult BuildCXXThrow(SourceLocation OpLoc, Expr *Ex,
                            bool IsThrownVarInScope);
 
   /// CheckCXXThrowOperand - Validate the operand of a throw.
   bool CheckCXXThrowOperand(SourceLocation ThrowLoc, QualType ThrowTy, Expr *E);
 
   /// ActOnCXXTypeConstructExpr - Parse construction of a specified type.
   /// Can be interpreted either as function-style casting ("int(x)")
   /// or class type construction ("ClassType(x,y,z)")
   /// or creation of a value-initialized type ("int()").
   ExprResult ActOnCXXTypeConstructExpr(ParsedType TypeRep,
                                        SourceLocation LParenOrBraceLoc,
                                        MultiExprArg Exprs,
                                        SourceLocation RParenOrBraceLoc,
                                        bool ListInitialization);
 
   ExprResult BuildCXXTypeConstructExpr(TypeSourceInfo *Type,
                                        SourceLocation LParenLoc,
                                        MultiExprArg Exprs,
                                        SourceLocation RParenLoc,
                                        bool ListInitialization);
 
   /// Parsed a C++ 'new' expression (C++ 5.3.4).
   ///
   /// E.g.:
   /// @code new (memory) int[size][4] @endcode
   /// or
   /// @code ::new Foo(23, "hello") @endcode
   ///
   /// \param StartLoc The first location of the expression.
   /// \param UseGlobal True if 'new' was prefixed with '::'.
   /// \param PlacementLParen Opening paren of the placement arguments.
   /// \param PlacementArgs Placement new arguments.
   /// \param PlacementRParen Closing paren of the placement arguments.
   /// \param TypeIdParens If the type is in parens, the source range.
   /// \param D The type to be allocated, as well as array dimensions.
   /// \param Initializer The initializing expression or initializer-list, or
   ///   null if there is none.
   ExprResult ActOnCXXNew(SourceLocation StartLoc, bool UseGlobal,
                          SourceLocation PlacementLParen,
                          MultiExprArg PlacementArgs,
                          SourceLocation PlacementRParen,
                          SourceRange TypeIdParens, Declarator &D,
                          Expr *Initializer);
   ExprResult
   BuildCXXNew(SourceRange Range, bool UseGlobal, SourceLocation PlacementLParen,
               MultiExprArg PlacementArgs, SourceLocation PlacementRParen,
               SourceRange TypeIdParens, QualType AllocType,
               TypeSourceInfo *AllocTypeInfo, std::optional<Expr *> ArraySize,
               SourceRange DirectInitRange, Expr *Initializer);
 
   /// Determine whether \p FD is an aligned allocation or deallocation
   /// function that is unavailable.
   bool isUnavailableAlignedAllocationFunction(const FunctionDecl &FD) const;
 
   /// Produce diagnostics if \p FD is an aligned allocation or deallocation
   /// function that is unavailable.
   void diagnoseUnavailableAlignedAllocation(const FunctionDecl &FD,
                                             SourceLocation Loc);
 
   /// Checks that a type is suitable as the allocated type
   /// in a new-expression.
   bool CheckAllocatedType(QualType AllocType, SourceLocation Loc,
                           SourceRange R);
 
   /// The scope in which to find allocation functions.
   enum AllocationFunctionScope {
     /// Only look for allocation functions in the global scope.
     AFS_Global,
     /// Only look for allocation functions in the scope of the
     /// allocated class.
     AFS_Class,
     /// Look for allocation functions in both the global scope
     /// and in the scope of the allocated class.
     AFS_Both
   };
 
   /// Finds the overloads of operator new and delete that are appropriate
   /// for the allocation.
   bool FindAllocationFunctions(SourceLocation StartLoc, SourceRange Range,
                                AllocationFunctionScope NewScope,
                                AllocationFunctionScope DeleteScope,
                                QualType AllocType, bool IsArray,
                                bool &PassAlignment, MultiExprArg PlaceArgs,
                                FunctionDecl *&OperatorNew,
                                FunctionDecl *&OperatorDelete,
                                bool Diagnose = true);
 
   /// DeclareGlobalNewDelete - Declare the global forms of operator new and
   /// delete. These are:
   /// @code
   ///   // C++03:
   ///   void* operator new(std::size_t) throw(std::bad_alloc);
   ///   void* operator new[](std::size_t) throw(std::bad_alloc);
   ///   void operator delete(void *) throw();
   ///   void operator delete[](void *) throw();
   ///   // C++11:
   ///   void* operator new(std::size_t);
   ///   void* operator new[](std::size_t);
   ///   void operator delete(void *) noexcept;
   ///   void operator delete[](void *) noexcept;
   ///   // C++1y:
   ///   void* operator new(std::size_t);
   ///   void* operator new[](std::size_t);
   ///   void operator delete(void *) noexcept;
   ///   void operator delete[](void *) noexcept;
   ///   void operator delete(void *, std::size_t) noexcept;
   ///   void operator delete[](void *, std::size_t) noexcept;
   /// @endcode
   /// Note that the placement and nothrow forms of new are *not* implicitly
   /// declared. Their use requires including \<new\>.
   void DeclareGlobalNewDelete();
   void DeclareGlobalAllocationFunction(DeclarationName Name, QualType Return,
                                        ArrayRef<QualType> Params);
 
   bool FindDeallocationFunction(SourceLocation StartLoc, CXXRecordDecl *RD,
                                 DeclarationName Name, FunctionDecl *&Operator,
                                 bool Diagnose = true, bool WantSize = false,
                                 bool WantAligned = false);
   FunctionDecl *FindUsualDeallocationFunction(SourceLocation StartLoc,
                                               bool CanProvideSize,
                                               bool Overaligned,
                                               DeclarationName Name);
   FunctionDecl *FindDeallocationFunctionForDestructor(SourceLocation StartLoc,
                                                       CXXRecordDecl *RD);
 
   /// ActOnCXXDelete - Parsed a C++ 'delete' expression (C++ 5.3.5), as in:
   /// @code ::delete ptr; @endcode
   /// or
   /// @code delete [] ptr; @endcode
   ExprResult ActOnCXXDelete(SourceLocation StartLoc, bool UseGlobal,
                             bool ArrayForm, Expr *Operand);
   void CheckVirtualDtorCall(CXXDestructorDecl *dtor, SourceLocation Loc,
                             bool IsDelete, bool CallCanBeVirtual,
                             bool WarnOnNonAbstractTypes,
                             SourceLocation DtorLoc);
 
   ExprResult ActOnNoexceptExpr(SourceLocation KeyLoc, SourceLocation LParen,
                                Expr *Operand, SourceLocation RParen);
   ExprResult BuildCXXNoexceptExpr(SourceLocation KeyLoc, Expr *Operand,
                                   SourceLocation RParen);
 
   ExprResult ActOnStartCXXMemberReference(Scope *S, Expr *Base,
                                           SourceLocation OpLoc,
                                           tok::TokenKind OpKind,
                                           ParsedType &ObjectType,
                                           bool &MayBePseudoDestructor);
 
   ExprResult BuildPseudoDestructorExpr(
       Expr *Base, SourceLocation OpLoc, tok::TokenKind OpKind,
       const CXXScopeSpec &SS, TypeSourceInfo *ScopeType, SourceLocation CCLoc,
       SourceLocation TildeLoc, PseudoDestructorTypeStorage DestroyedType);
 
   ExprResult ActOnPseudoDestructorExpr(
       Scope *S, Expr *Base, SourceLocation OpLoc, tok::TokenKind OpKind,
       CXXScopeSpec &SS, UnqualifiedId &FirstTypeName, SourceLocation CCLoc,
       SourceLocation TildeLoc, UnqualifiedId &SecondTypeName);
 
   ExprResult ActOnPseudoDestructorExpr(Scope *S, Expr *Base,
                                        SourceLocation OpLoc,
                                        tok::TokenKind OpKind,
                                        SourceLocation TildeLoc,
                                        const DeclSpec &DS);
 
   /// MaybeCreateExprWithCleanups - If the current full-expression
   /// requires any cleanups, surround it with a ExprWithCleanups node.
   /// Otherwise, just returns the passed-in expression.
   Expr *MaybeCreateExprWithCleanups(Expr *SubExpr);
   Stmt *MaybeCreateStmtWithCleanups(Stmt *SubStmt);
   ExprResult MaybeCreateExprWithCleanups(ExprResult SubExpr);
 
   ExprResult ActOnFinishFullExpr(Expr *Expr, bool DiscardedValue) {
     return ActOnFinishFullExpr(
         Expr, Expr ? Expr->getExprLoc() : SourceLocation(), DiscardedValue);
   }
   ExprResult ActOnFinishFullExpr(Expr *Expr, SourceLocation CC,
                                  bool DiscardedValue, bool IsConstexpr = false,
                                  bool IsTemplateArgument = false);
   StmtResult ActOnFinishFullStmt(Stmt *Stmt);
 
   /// Process the expression contained within a decltype. For such expressions,
   /// certain semantic checks on temporaries are delayed until this point, and
   /// are omitted for the 'topmost' call in the decltype expression. If the
   /// topmost call bound a temporary, strip that temporary off the expression.
   ExprResult ActOnDecltypeExpression(Expr *E);
 
   bool checkLiteralOperatorId(const CXXScopeSpec &SS, const UnqualifiedId &Id,
                               bool IsUDSuffix);
 
   bool isUsualDeallocationFunction(const CXXMethodDecl *FD);
 
   ConditionResult ActOnConditionVariable(Decl *ConditionVar,
                                          SourceLocation StmtLoc,
                                          ConditionKind CK);
 
   /// Check the use of the given variable as a C++ condition in an if,
   /// while, do-while, or switch statement.
   ExprResult CheckConditionVariable(VarDecl *ConditionVar,
                                     SourceLocation StmtLoc, ConditionKind CK);
 
   /// CheckCXXBooleanCondition - Returns true if conversion to bool is invalid.
   ExprResult CheckCXXBooleanCondition(Expr *CondExpr, bool IsConstexpr = false);
 
   /// Helper function to determine whether this is the (deprecated) C++
   /// conversion from a string literal to a pointer to non-const char or
   /// non-const wchar_t (for narrow and wide string literals,
   /// respectively).
   bool IsStringLiteralToNonConstPointerConversion(Expr *From, QualType ToType);
 
   /// PerformImplicitConversion - Perform an implicit conversion of the
   /// expression From to the type ToType using the pre-computed implicit
   /// conversion sequence ICS. Returns the converted
   /// expression. Action is the kind of conversion we're performing,
   /// used in the error message.
   ExprResult PerformImplicitConversion(
       Expr *From, QualType ToType, const ImplicitConversionSequence &ICS,
       AssignmentAction Action,
       CheckedConversionKind CCK = CheckedConversionKind::Implicit);
 
   /// PerformImplicitConversion - Perform an implicit conversion of the
   /// expression From to the type ToType by following the standard
   /// conversion sequence SCS. Returns the converted
   /// expression. Flavor is the context in which we're performing this
   /// conversion, for use in error messages.
   ExprResult PerformImplicitConversion(Expr *From, QualType ToType,
                                        const StandardConversionSequence &SCS,
                                        AssignmentAction Action,
                                        CheckedConversionKind CCK);
 
   bool CheckTypeTraitArity(unsigned Arity, SourceLocation Loc, size_t N);
 
   /// Parsed one of the type trait support pseudo-functions.
   ExprResult ActOnTypeTrait(TypeTrait Kind, SourceLocation KWLoc,
                             ArrayRef<ParsedType> Args,
                             SourceLocation RParenLoc);
   ExprResult BuildTypeTrait(TypeTrait Kind, SourceLocation KWLoc,
                             ArrayRef<TypeSourceInfo *> Args,
                             SourceLocation RParenLoc);
 
   /// ActOnArrayTypeTrait - Parsed one of the binary type trait support
   /// pseudo-functions.
   ExprResult ActOnArrayTypeTrait(ArrayTypeTrait ATT, SourceLocation KWLoc,
                                  ParsedType LhsTy, Expr *DimExpr,
                                  SourceLocation RParen);
 
   ExprResult BuildArrayTypeTrait(ArrayTypeTrait ATT, SourceLocation KWLoc,
                                  TypeSourceInfo *TSInfo, Expr *DimExpr,
                                  SourceLocation RParen);
 
   /// ActOnExpressionTrait - Parsed one of the unary type trait support
   /// pseudo-functions.
   ExprResult ActOnExpressionTrait(ExpressionTrait OET, SourceLocation KWLoc,
                                   Expr *Queried, SourceLocation RParen);
 
   ExprResult BuildExpressionTrait(ExpressionTrait OET, SourceLocation KWLoc,
                                   Expr *Queried, SourceLocation RParen);
 
   QualType CheckPointerToMemberOperands( // C++ 5.5
       ExprResult &LHS, ExprResult &RHS, ExprValueKind &VK, SourceLocation OpLoc,
       bool isIndirect);
   QualType CheckVectorConditionalTypes(ExprResult &Cond, ExprResult &LHS,
                                        ExprResult &RHS,
                                        SourceLocation QuestionLoc);
 
   QualType CheckSizelessVectorConditionalTypes(ExprResult &Cond,
                                                ExprResult &LHS, ExprResult &RHS,
                                                SourceLocation QuestionLoc);
 
   /// Check the operands of ?: under C++ semantics.
   ///
   /// See C++ [expr.cond]. Note that LHS is never null, even for the GNU x ?: y
   /// extension. In this case, LHS == Cond. (But they're not aliases.)
   ///
   /// This function also implements GCC's vector extension and the
   /// OpenCL/ext_vector_type extension for conditionals. The vector extensions
   /// permit the use of a?b:c where the type of a is that of a integer vector
   /// with the same number of elements and size as the vectors of b and c. If
   /// one of either b or c is a scalar it is implicitly converted to match the
   /// type of the vector. Otherwise the expression is ill-formed. If both b and
   /// c are scalars, then b and c are checked and converted to the type of a if
   /// possible.
   ///
   /// The expressions are evaluated differently for GCC's and OpenCL's
   /// extensions. For the GCC extension, the ?: operator is evaluated as
   ///   (a[0] != 0 ? b[0] : c[0], .. , a[n] != 0 ? b[n] : c[n]).
   /// For the OpenCL extensions, the ?: operator is evaluated as
   ///   (most-significant-bit-set(a[0])  ? b[0] : c[0], .. ,
   ///    most-significant-bit-set(a[n]) ? b[n] : c[n]).
   QualType CXXCheckConditionalOperands( // C++ 5.16
       ExprResult &cond, ExprResult &lhs, ExprResult &rhs, ExprValueKind &VK,
       ExprObjectKind &OK, SourceLocation questionLoc);
 
   /// Find a merged pointer type and convert the two expressions to it.
   ///
   /// This finds the composite pointer type for \p E1 and \p E2 according to
   /// C++2a [expr.type]p3. It converts both expressions to this type and returns
   /// it.  It does not emit diagnostics (FIXME: that's not true if \p
   /// ConvertArgs is \c true).
   ///
   /// \param Loc The location of the operator requiring these two expressions to
   /// be converted to the composite pointer type.
   ///
   /// \param ConvertArgs If \c false, do not convert E1 and E2 to the target
   /// type.
   QualType FindCompositePointerType(SourceLocation Loc, Expr *&E1, Expr *&E2,
                                     bool ConvertArgs = true);
   QualType FindCompositePointerType(SourceLocation Loc, ExprResult &E1,
                                     ExprResult &E2, bool ConvertArgs = true) {
     Expr *E1Tmp = E1.get(), *E2Tmp = E2.get();
     QualType Composite =
         FindCompositePointerType(Loc, E1Tmp, E2Tmp, ConvertArgs);
     E1 = E1Tmp;
     E2 = E2Tmp;
     return Composite;
   }
 
   /// MaybeBindToTemporary - If the passed in expression has a record type with
   /// a non-trivial destructor, this will return CXXBindTemporaryExpr. Otherwise
   /// it simply returns the passed in expression.
   ExprResult MaybeBindToTemporary(Expr *E);
 
   /// IgnoredValueConversions - Given that an expression's result is
   /// syntactically ignored, perform any conversions that are
   /// required.
   ExprResult IgnoredValueConversions(Expr *E);
 
   ExprResult CheckUnevaluatedOperand(Expr *E);
 
   /// Process any TypoExprs in the given Expr and its children,
   /// generating diagnostics as appropriate and returning a new Expr if there
   /// were typos that were all successfully corrected and ExprError if one or
   /// more typos could not be corrected.
   ///
   /// \param E The Expr to check for TypoExprs.
   ///
   /// \param InitDecl A VarDecl to avoid because the Expr being corrected is its
   /// initializer.
   ///
   /// \param RecoverUncorrectedTypos If true, when typo correction fails, it
   /// will rebuild the given Expr with all TypoExprs degraded to RecoveryExprs.
   ///
   /// \param Filter A function applied to a newly rebuilt Expr to determine if
   /// it is an acceptable/usable result from a single combination of typo
   /// corrections. As long as the filter returns ExprError, different
   /// combinations of corrections will be tried until all are exhausted.
   ExprResult CorrectDelayedTyposInExpr(
       Expr *E, VarDecl *InitDecl = nullptr,
       bool RecoverUncorrectedTypos = false,
       llvm::function_ref<ExprResult(Expr *)> Filter =
           [](Expr *E) -> ExprResult { return E; });
 
   ExprResult CorrectDelayedTyposInExpr(
       ExprResult ER, VarDecl *InitDecl = nullptr,
       bool RecoverUncorrectedTypos = false,
       llvm::function_ref<ExprResult(Expr *)> Filter =
           [](Expr *E) -> ExprResult { return E; }) {
     return ER.isInvalid()
                ? ER
                : CorrectDelayedTyposInExpr(ER.get(), InitDecl,
                                            RecoverUncorrectedTypos, Filter);
   }
 
   /// Describes the result of an "if-exists" condition check.
   enum IfExistsResult {
     /// The symbol exists.
     IER_Exists,
 
     /// The symbol does not exist.
     IER_DoesNotExist,
 
     /// The name is a dependent name, so the results will differ
     /// from one instantiation to the next.
     IER_Dependent,
 
     /// An error occurred.
     IER_Error
   };
 
   IfExistsResult
   CheckMicrosoftIfExistsSymbol(Scope *S, CXXScopeSpec &SS,
                                const DeclarationNameInfo &TargetNameInfo);
 
   IfExistsResult CheckMicrosoftIfExistsSymbol(Scope *S,
                                               SourceLocation KeywordLoc,
                                               bool IsIfExists, CXXScopeSpec &SS,
                                               UnqualifiedId &Name);
 
   RequiresExprBodyDecl *
   ActOnStartRequiresExpr(SourceLocation RequiresKWLoc,
                          ArrayRef<ParmVarDecl *> LocalParameters,
                          Scope *BodyScope);
   void ActOnFinishRequiresExpr();
   concepts::Requirement *ActOnSimpleRequirement(Expr *E);
   concepts::Requirement *ActOnTypeRequirement(SourceLocation TypenameKWLoc,
                                               CXXScopeSpec &SS,
                                               SourceLocation NameLoc,
                                               const IdentifierInfo *TypeName,
                                               TemplateIdAnnotation *TemplateId);
   concepts::Requirement *ActOnCompoundRequirement(Expr *E,
                                                   SourceLocation NoexceptLoc);
   concepts::Requirement *ActOnCompoundRequirement(
       Expr *E, SourceLocation NoexceptLoc, CXXScopeSpec &SS,
       TemplateIdAnnotation *TypeConstraint, unsigned Depth);
   concepts::Requirement *ActOnNestedRequirement(Expr *Constraint);
   concepts::ExprRequirement *BuildExprRequirement(
       Expr *E, bool IsSatisfied, SourceLocation NoexceptLoc,
       concepts::ExprRequirement::ReturnTypeRequirement ReturnTypeRequirement);
   concepts::ExprRequirement *BuildExprRequirement(
       concepts::Requirement::SubstitutionDiagnostic *ExprSubstDiag,
       bool IsSatisfied, SourceLocation NoexceptLoc,
       concepts::ExprRequirement::ReturnTypeRequirement ReturnTypeRequirement);
   concepts::TypeRequirement *BuildTypeRequirement(TypeSourceInfo *Type);
   concepts::TypeRequirement *BuildTypeRequirement(
       concepts::Requirement::SubstitutionDiagnostic *SubstDiag);
   concepts::NestedRequirement *BuildNestedRequirement(Expr *E);
   concepts::NestedRequirement *
   BuildNestedRequirement(StringRef InvalidConstraintEntity,
                          const ASTConstraintSatisfaction &Satisfaction);
   ExprResult ActOnRequiresExpr(SourceLocation RequiresKWLoc,
                                RequiresExprBodyDecl *Body,
                                SourceLocation LParenLoc,
                                ArrayRef<ParmVarDecl *> LocalParameters,
                                SourceLocation RParenLoc,
                                ArrayRef<concepts::Requirement *> Requirements,
                                SourceLocation ClosingBraceLoc);
 
 private:
   ExprResult BuiltinOperatorNewDeleteOverloaded(ExprResult TheCallResult,
                                                 bool IsDelete);
 
   void AnalyzeDeleteExprMismatch(const CXXDeleteExpr *DE);
   void AnalyzeDeleteExprMismatch(FieldDecl *Field, SourceLocation DeleteLoc,
                                  bool DeleteWasArrayForm);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Member Access Expressions
   /// Implementations are in SemaExprMember.cpp
   ///@{
 
 public:
   /// Check whether an expression might be an implicit class member access.
   bool isPotentialImplicitMemberAccess(const CXXScopeSpec &SS, LookupResult &R,
                                        bool IsAddressOfOperand);
 
   /// Builds an expression which might be an implicit member expression.
   ExprResult BuildPossibleImplicitMemberExpr(
       const CXXScopeSpec &SS, SourceLocation TemplateKWLoc, LookupResult &R,
       const TemplateArgumentListInfo *TemplateArgs, const Scope *S);
 
   /// Builds an implicit member access expression.  The current context
   /// is known to be an instance method, and the given unqualified lookup
   /// set is known to contain only instance members, at least one of which
   /// is from an appropriate type.
   ExprResult
   BuildImplicitMemberExpr(const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                           LookupResult &R,
                           const TemplateArgumentListInfo *TemplateArgs,
                           bool IsDefiniteInstance, const Scope *S);
 
   ExprResult ActOnDependentMemberExpr(
       Expr *Base, QualType BaseType, bool IsArrow, SourceLocation OpLoc,
       const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
       NamedDecl *FirstQualifierInScope, const DeclarationNameInfo &NameInfo,
       const TemplateArgumentListInfo *TemplateArgs);
 
   /// The main callback when the parser finds something like
   ///   expression . [nested-name-specifier] identifier
   ///   expression -> [nested-name-specifier] identifier
   /// where 'identifier' encompasses a fairly broad spectrum of
   /// possibilities, including destructor and operator references.
   ///
   /// \param OpKind either tok::arrow or tok::period
   /// \param ObjCImpDecl the current Objective-C \@implementation
   ///   decl; this is an ugly hack around the fact that Objective-C
   ///   \@implementations aren't properly put in the context chain
   ExprResult ActOnMemberAccessExpr(Scope *S, Expr *Base, SourceLocation OpLoc,
                                    tok::TokenKind OpKind, CXXScopeSpec &SS,
                                    SourceLocation TemplateKWLoc,
                                    UnqualifiedId &Member, Decl *ObjCImpDecl);
 
   MemberExpr *
   BuildMemberExpr(Expr *Base, bool IsArrow, SourceLocation OpLoc,
                   NestedNameSpecifierLoc NNS, SourceLocation TemplateKWLoc,
                   ValueDecl *Member, DeclAccessPair FoundDecl,
                   bool HadMultipleCandidates,
                   const DeclarationNameInfo &MemberNameInfo, QualType Ty,
                   ExprValueKind VK, ExprObjectKind OK,
                   const TemplateArgumentListInfo *TemplateArgs = nullptr);
 
   // Check whether the declarations we found through a nested-name
   // specifier in a member expression are actually members of the base
   // type.  The restriction here is:
   //
   //   C++ [expr.ref]p2:
   //     ... In these cases, the id-expression shall name a
   //     member of the class or of one of its base classes.
   //
   // So it's perfectly legitimate for the nested-name specifier to name
   // an unrelated class, and for us to find an overload set including
   // decls from classes which are not superclasses, as long as the decl
   // we actually pick through overload resolution is from a superclass.
   bool CheckQualifiedMemberReference(Expr *BaseExpr, QualType BaseType,
                                      const CXXScopeSpec &SS,
                                      const LookupResult &R);
 
   // This struct is for use by ActOnMemberAccess to allow
   // BuildMemberReferenceExpr to be able to reinvoke ActOnMemberAccess after
   // changing the access operator from a '.' to a '->' (to see if that is the
   // change needed to fix an error about an unknown member, e.g. when the class
   // defines a custom operator->).
   struct ActOnMemberAccessExtraArgs {
     Scope *S;
     UnqualifiedId &Id;
     Decl *ObjCImpDecl;
   };
 
   ExprResult BuildMemberReferenceExpr(
       Expr *Base, QualType BaseType, SourceLocation OpLoc, bool IsArrow,
       CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
       NamedDecl *FirstQualifierInScope, const DeclarationNameInfo &NameInfo,
       const TemplateArgumentListInfo *TemplateArgs, const Scope *S,
       ActOnMemberAccessExtraArgs *ExtraArgs = nullptr);
 
   ExprResult
   BuildMemberReferenceExpr(Expr *Base, QualType BaseType, SourceLocation OpLoc,
                            bool IsArrow, const CXXScopeSpec &SS,
                            SourceLocation TemplateKWLoc,
                            NamedDecl *FirstQualifierInScope, LookupResult &R,
                            const TemplateArgumentListInfo *TemplateArgs,
                            const Scope *S, bool SuppressQualifierCheck = false,
                            ActOnMemberAccessExtraArgs *ExtraArgs = nullptr);
 
   ExprResult BuildFieldReferenceExpr(Expr *BaseExpr, bool IsArrow,
                                      SourceLocation OpLoc,
                                      const CXXScopeSpec &SS, FieldDecl *Field,
                                      DeclAccessPair FoundDecl,
                                      const DeclarationNameInfo &MemberNameInfo);
 
   /// Perform conversions on the LHS of a member access expression.
   ExprResult PerformMemberExprBaseConversion(Expr *Base, bool IsArrow);
 
   ExprResult BuildAnonymousStructUnionMemberReference(
       const CXXScopeSpec &SS, SourceLocation nameLoc,
       IndirectFieldDecl *indirectField,
       DeclAccessPair FoundDecl = DeclAccessPair::make(nullptr, AS_none),
       Expr *baseObjectExpr = nullptr, SourceLocation opLoc = SourceLocation());
 
 private:
   void CheckMemberAccessOfNoDeref(const MemberExpr *E);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Initializers
   /// Implementations are in SemaInit.cpp
   ///@{
 
 public:
   /// Stack of types that correspond to the parameter entities that are
   /// currently being copy-initialized. Can be empty.
   llvm::SmallVector<QualType, 4> CurrentParameterCopyTypes;
 
   llvm::DenseMap<unsigned, CXXDeductionGuideDecl *>
       AggregateDeductionCandidates;
 
   bool IsStringInit(Expr *Init, const ArrayType *AT);
 
   /// Determine whether we can perform aggregate initialization for the purposes
   /// of overload resolution.
   bool CanPerformAggregateInitializationForOverloadResolution(
       const InitializedEntity &Entity, InitListExpr *From);
 
   ExprResult ActOnDesignatedInitializer(Designation &Desig,
                                         SourceLocation EqualOrColonLoc,
                                         bool GNUSyntax, ExprResult Init);
 
   /// Check that the lifetime of the initializer (and its subobjects) is
   /// sufficient for initializing the entity, and perform lifetime extension
   /// (when permitted) if not.
   void checkInitializerLifetime(const InitializedEntity &Entity, Expr *Init);
 
   MaterializeTemporaryExpr *
   CreateMaterializeTemporaryExpr(QualType T, Expr *Temporary,
                                  bool BoundToLvalueReference);
 
   /// If \p E is a prvalue denoting an unmaterialized temporary, materialize
   /// it as an xvalue. In C++98, the result will still be a prvalue, because
   /// we don't have xvalues there.
   ExprResult TemporaryMaterializationConversion(Expr *E);
 
   ExprResult PerformQualificationConversion(
       Expr *E, QualType Ty, ExprValueKind VK = VK_PRValue,
       CheckedConversionKind CCK = CheckedConversionKind::Implicit);
 
   bool CanPerformCopyInitialization(const InitializedEntity &Entity,
                                     ExprResult Init);
   ExprResult PerformCopyInitialization(const InitializedEntity &Entity,
                                        SourceLocation EqualLoc, ExprResult Init,
                                        bool TopLevelOfInitList = false,
                                        bool AllowExplicit = false);
 
   QualType DeduceTemplateSpecializationFromInitializer(
       TypeSourceInfo *TInfo, const InitializedEntity &Entity,
       const InitializationKind &Kind, MultiExprArg Init);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Lambda Expressions
   /// Implementations are in SemaLambda.cpp
   ///@{
 
 public:
   /// Create a new lambda closure type.
   CXXRecordDecl *createLambdaClosureType(SourceRange IntroducerRange,
                                          TypeSourceInfo *Info,
                                          unsigned LambdaDependencyKind,
                                          LambdaCaptureDefault CaptureDefault);
 
   /// Number lambda for linkage purposes if necessary.
   void handleLambdaNumbering(CXXRecordDecl *Class, CXXMethodDecl *Method,
                              std::optional<CXXRecordDecl::LambdaNumbering>
                                  NumberingOverride = std::nullopt);
 
   /// Endow the lambda scope info with the relevant properties.
   void buildLambdaScope(sema::LambdaScopeInfo *LSI, CXXMethodDecl *CallOperator,
                         SourceRange IntroducerRange,
                         LambdaCaptureDefault CaptureDefault,
                         SourceLocation CaptureDefaultLoc, bool ExplicitParams,
                         bool Mutable);
 
   CXXMethodDecl *CreateLambdaCallOperator(SourceRange IntroducerRange,
                                           CXXRecordDecl *Class);
 
   void AddTemplateParametersToLambdaCallOperator(
       CXXMethodDecl *CallOperator, CXXRecordDecl *Class,
       TemplateParameterList *TemplateParams);
 
   void CompleteLambdaCallOperator(
       CXXMethodDecl *Method, SourceLocation LambdaLoc,
       SourceLocation CallOperatorLoc, Expr *TrailingRequiresClause,
       TypeSourceInfo *MethodTyInfo, ConstexprSpecKind ConstexprKind,
       StorageClass SC, ArrayRef<ParmVarDecl *> Params,
       bool HasExplicitResultType);
 
   /// Returns true if the explicit object parameter was invalid.
   bool DiagnoseInvalidExplicitObjectParameterInLambda(CXXMethodDecl *Method,
                                                       SourceLocation CallLoc);
 
   /// Perform initialization analysis of the init-capture and perform
   /// any implicit conversions such as an lvalue-to-rvalue conversion if
   /// not being used to initialize a reference.
   ParsedType actOnLambdaInitCaptureInitialization(
       SourceLocation Loc, bool ByRef, SourceLocation EllipsisLoc,
       IdentifierInfo *Id, LambdaCaptureInitKind InitKind, Expr *&Init) {
     return ParsedType::make(buildLambdaInitCaptureInitialization(
         Loc, ByRef, EllipsisLoc, std::nullopt, Id,
         InitKind != LambdaCaptureInitKind::CopyInit, Init));
   }
   QualType buildLambdaInitCaptureInitialization(
       SourceLocation Loc, bool ByRef, SourceLocation EllipsisLoc,
       std::optional<unsigned> NumExpansions, IdentifierInfo *Id,
       bool DirectInit, Expr *&Init);
 
   /// Create a dummy variable within the declcontext of the lambda's
   ///  call operator, for name lookup purposes for a lambda init capture.
   ///
   ///  CodeGen handles emission of lambda captures, ignoring these dummy
   ///  variables appropriately.
   VarDecl *createLambdaInitCaptureVarDecl(
       SourceLocation Loc, QualType InitCaptureType, SourceLocation EllipsisLoc,
       IdentifierInfo *Id, unsigned InitStyle, Expr *Init, DeclContext *DeclCtx);
 
   /// Add an init-capture to a lambda scope.
   void addInitCapture(sema::LambdaScopeInfo *LSI, VarDecl *Var, bool ByRef);
 
   /// Note that we have finished the explicit captures for the
   /// given lambda.
   void finishLambdaExplicitCaptures(sema::LambdaScopeInfo *LSI);
 
   /// Deduce a block or lambda's return type based on the return
   /// statements present in the body.
   void deduceClosureReturnType(sema::CapturingScopeInfo &CSI);
 
   /// Once the Lambdas capture are known, we can start to create the closure,
   /// call operator method, and keep track of the captures.
   /// We do the capture lookup here, but they are not actually captured until
   /// after we know what the qualifiers of the call operator are.
   void ActOnLambdaExpressionAfterIntroducer(LambdaIntroducer &Intro,
                                             Scope *CurContext);
 
   /// This is called after parsing the explicit template parameter list
   /// on a lambda (if it exists) in C++2a.
   void ActOnLambdaExplicitTemplateParameterList(LambdaIntroducer &Intro,
                                                 SourceLocation LAngleLoc,
                                                 ArrayRef<NamedDecl *> TParams,
                                                 SourceLocation RAngleLoc,
                                                 ExprResult RequiresClause);
 
   void ActOnLambdaClosureQualifiers(LambdaIntroducer &Intro,
                                     SourceLocation MutableLoc);
 
   void ActOnLambdaClosureParameters(
       Scope *LambdaScope,
       MutableArrayRef<DeclaratorChunk::ParamInfo> ParamInfo);
 
   /// ActOnStartOfLambdaDefinition - This is called just before we start
   /// parsing the body of a lambda; it analyzes the explicit captures and
   /// arguments, and sets up various data-structures for the body of the
   /// lambda.
   void ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
                                     Declarator &ParamInfo, const DeclSpec &DS);
 
   /// ActOnLambdaError - If there is an error parsing a lambda, this callback
   /// is invoked to pop the information about the lambda.
   void ActOnLambdaError(SourceLocation StartLoc, Scope *CurScope,
                         bool IsInstantiation = false);
 
   /// ActOnLambdaExpr - This is called when the body of a lambda expression
   /// was successfully completed.
   ExprResult ActOnLambdaExpr(SourceLocation StartLoc, Stmt *Body);
 
   /// Does copying/destroying the captured variable have side effects?
   bool CaptureHasSideEffects(const sema::Capture &From);
 
   /// Diagnose if an explicit lambda capture is unused. Returns true if a
   /// diagnostic is emitted.
   bool DiagnoseUnusedLambdaCapture(SourceRange CaptureRange,
                                    const sema::Capture &From);
 
   /// Build a FieldDecl suitable to hold the given capture.
   FieldDecl *BuildCaptureField(RecordDecl *RD, const sema::Capture &Capture);
 
   /// Initialize the given capture with a suitable expression.
   ExprResult BuildCaptureInit(const sema::Capture &Capture,
                               SourceLocation ImplicitCaptureLoc,
                               bool IsOpenMPMapping = false);
 
   /// Complete a lambda-expression having processed and attached the
   /// lambda body.
   ExprResult BuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
                              sema::LambdaScopeInfo *LSI);
 
   /// Get the return type to use for a lambda's conversion function(s) to
   /// function pointer type, given the type of the call operator.
   QualType
   getLambdaConversionFunctionResultType(const FunctionProtoType *CallOpType,
                                         CallingConv CC);
 
   ExprResult BuildBlockForLambdaConversion(SourceLocation CurrentLocation,
                                            SourceLocation ConvLocation,
                                            CXXConversionDecl *Conv, Expr *Src);
 
   class LambdaScopeForCallOperatorInstantiationRAII
       : private FunctionScopeRAII {
   public:
     LambdaScopeForCallOperatorInstantiationRAII(
         Sema &SemasRef, FunctionDecl *FD, MultiLevelTemplateArgumentList MLTAL,
         LocalInstantiationScope &Scope,
         bool ShouldAddDeclsFromParentScope = true);
   };
 
   /// Compute the mangling number context for a lambda expression or
   /// block literal. Also return the extra mangling decl if any.
   ///
   /// \param DC - The DeclContext containing the lambda expression or
   /// block literal.
   std::tuple<MangleNumberingContext *, Decl *>
   getCurrentMangleNumberContext(const DeclContext *DC);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Name Lookup
   ///
   /// These routines provide name lookup that is used during semantic
   /// analysis to resolve the various kinds of names (identifiers,
   /// overloaded operator names, constructor names, etc.) into zero or
   /// more declarations within a particular scope. The major entry
   /// points are LookupName, which performs unqualified name lookup,
   /// and LookupQualifiedName, which performs qualified name lookup.
   ///
   /// All name lookup is performed based on some specific criteria,
   /// which specify what names will be visible to name lookup and how
   /// far name lookup should work. These criteria are important both
   /// for capturing language semantics (certain lookups will ignore
   /// certain names, for example) and for performance, since name
   /// lookup is often a bottleneck in the compilation of C++. Name
   /// lookup criteria is specified via the LookupCriteria enumeration.
   ///
   /// The results of name lookup can vary based on the kind of name
   /// lookup performed, the current language, and the translation
   /// unit. In C, for example, name lookup will either return nothing
   /// (no entity found) or a single declaration. In C++, name lookup
   /// can additionally refer to a set of overloaded functions or
   /// result in an ambiguity. All of the possible results of name
   /// lookup are captured by the LookupResult class, which provides
   /// the ability to distinguish among them.
   ///
   /// Implementations are in SemaLookup.cpp
   ///@{
 
 public:
   /// Tracks whether we are in a context where typo correction is
   /// disabled.
   bool DisableTypoCorrection;
 
   /// The number of typos corrected by CorrectTypo.
   unsigned TyposCorrected;
 
   typedef llvm::SmallSet<SourceLocation, 2> SrcLocSet;
   typedef llvm::DenseMap<IdentifierInfo *, SrcLocSet> IdentifierSourceLocations;
 
   /// A cache containing identifiers for which typo correction failed and
   /// their locations, so that repeated attempts to correct an identifier in a
   /// given location are ignored if typo correction already failed for it.
   IdentifierSourceLocations TypoCorrectionFailures;
 
   /// SpecialMemberOverloadResult - The overloading result for a special member
   /// function.
   ///
   /// This is basically a wrapper around PointerIntPair. The lowest bits of the
   /// integer are used to determine whether overload resolution succeeded.
   class SpecialMemberOverloadResult {
   public:
     enum Kind { NoMemberOrDeleted, Ambiguous, Success };
 
   private:
     llvm::PointerIntPair<CXXMethodDecl *, 2> Pair;
 
   public:
     SpecialMemberOverloadResult() {}
     SpecialMemberOverloadResult(CXXMethodDecl *MD)
         : Pair(MD, MD->isDeleted() ? NoMemberOrDeleted : Success) {}
 
     CXXMethodDecl *getMethod() const { return Pair.getPointer(); }
     void setMethod(CXXMethodDecl *MD) { Pair.setPointer(MD); }
 
     Kind getKind() const { return static_cast<Kind>(Pair.getInt()); }
     void setKind(Kind K) { Pair.setInt(K); }
   };
 
   class SpecialMemberOverloadResultEntry : public llvm::FastFoldingSetNode,
                                            public SpecialMemberOverloadResult {
   public:
     SpecialMemberOverloadResultEntry(const llvm::FoldingSetNodeID &ID)
         : FastFoldingSetNode(ID) {}
   };
 
   /// A cache of special member function overload resolution results
   /// for C++ records.
   llvm::FoldingSet<SpecialMemberOverloadResultEntry> SpecialMemberCache;
 
   /// Holds TypoExprs that are created from `createDelayedTypo`. This is used by
   /// `TransformTypos` in order to keep track of any TypoExprs that are created
   /// recursively during typo correction and wipe them away if the correction
   /// fails.
   llvm::SmallVector<TypoExpr *, 2> TypoExprs;
 
   enum class AcceptableKind { Visible, Reachable };
 
   // Members have to be NamespaceDecl* or TranslationUnitDecl*.
   // TODO: make this is a typesafe union.
   typedef llvm::SmallSetVector<DeclContext *, 16> AssociatedNamespaceSet;
   typedef llvm::SmallSetVector<CXXRecordDecl *, 16> AssociatedClassSet;
 
   /// Describes the kind of name lookup to perform.
   enum LookupNameKind {
     /// Ordinary name lookup, which finds ordinary names (functions,
     /// variables, typedefs, etc.) in C and most kinds of names
     /// (functions, variables, members, types, etc.) in C++.
     LookupOrdinaryName = 0,
     /// Tag name lookup, which finds the names of enums, classes,
     /// structs, and unions.
     LookupTagName,
     /// Label name lookup.
     LookupLabel,
     /// Member name lookup, which finds the names of
     /// class/struct/union members.
     LookupMemberName,
     /// Look up of an operator name (e.g., operator+) for use with
     /// operator overloading. This lookup is similar to ordinary name
     /// lookup, but will ignore any declarations that are class members.
     LookupOperatorName,
     /// Look up a name following ~ in a destructor name. This is an ordinary
     /// lookup, but prefers tags to typedefs.
     LookupDestructorName,
     /// Look up of a name that precedes the '::' scope resolution
     /// operator in C++. This lookup completely ignores operator, object,
     /// function, and enumerator names (C++ [basic.lookup.qual]p1).
     LookupNestedNameSpecifierName,
     /// Look up a namespace name within a C++ using directive or
     /// namespace alias definition, ignoring non-namespace names (C++
     /// [basic.lookup.udir]p1).
     LookupNamespaceName,
     /// Look up all declarations in a scope with the given name,
     /// including resolved using declarations.  This is appropriate
     /// for checking redeclarations for a using declaration.
     LookupUsingDeclName,
     /// Look up an ordinary name that is going to be redeclared as a
     /// name with linkage. This lookup ignores any declarations that
     /// are outside of the current scope unless they have linkage. See
     /// C99 6.2.2p4-5 and C++ [basic.link]p6.
     LookupRedeclarationWithLinkage,
     /// Look up a friend of a local class. This lookup does not look
     /// outside the innermost non-class scope. See C++11 [class.friend]p11.
     LookupLocalFriendName,
     /// Look up the name of an Objective-C protocol.
     LookupObjCProtocolName,
     /// Look up implicit 'self' parameter of an objective-c method.
     LookupObjCImplicitSelfParam,
     /// Look up the name of an OpenMP user-defined reduction operation.
     LookupOMPReductionName,
     /// Look up the name of an OpenMP user-defined mapper.
     LookupOMPMapperName,
     /// Look up any declaration with any name.
     LookupAnyName
   };
 
   /// The possible outcomes of name lookup for a literal operator.
   enum LiteralOperatorLookupResult {
     /// The lookup resulted in an error.
     LOLR_Error,
     /// The lookup found no match but no diagnostic was issued.
     LOLR_ErrorNoDiagnostic,
     /// The lookup found a single 'cooked' literal operator, which
     /// expects a normal literal to be built and passed to it.
     LOLR_Cooked,
     /// The lookup found a single 'raw' literal operator, which expects
     /// a string literal containing the spelling of the literal token.
     LOLR_Raw,
     /// The lookup found an overload set of literal operator templates,
     /// which expect the characters of the spelling of the literal token to be
     /// passed as a non-type template argument pack.
     LOLR_Template,
     /// The lookup found an overload set of literal operator templates,
     /// which expect the character type and characters of the spelling of the
     /// string literal token to be passed as template arguments.
     LOLR_StringTemplatePack,
   };
 
   SpecialMemberOverloadResult
   LookupSpecialMember(CXXRecordDecl *D, CXXSpecialMemberKind SM, bool ConstArg,
                       bool VolatileArg, bool RValueThis, bool ConstThis,
                       bool VolatileThis);
 
   typedef std::function<void(const TypoCorrection &)> TypoDiagnosticGenerator;
   typedef std::function<ExprResult(Sema &, TypoExpr *, TypoCorrection)>
       TypoRecoveryCallback;
 
   RedeclarationKind forRedeclarationInCurContext() const;
 
   /// Look up a name, looking for a single declaration.  Return
   /// null if the results were absent, ambiguous, or overloaded.
   ///
   /// It is preferable to use the elaborated form and explicitly handle
   /// ambiguity and overloaded.
   NamedDecl *LookupSingleName(
       Scope *S, DeclarationName Name, SourceLocation Loc,
       LookupNameKind NameKind,
       RedeclarationKind Redecl = RedeclarationKind::NotForRedeclaration);
 
   /// Lookup a builtin function, when name lookup would otherwise
   /// fail.
   bool LookupBuiltin(LookupResult &R);
   void LookupNecessaryTypesForBuiltin(Scope *S, unsigned ID);
 
   /// Perform unqualified name lookup starting from a given
   /// scope.
   ///
   /// Unqualified name lookup (C++ [basic.lookup.unqual], C99 6.2.1) is
   /// used to find names within the current scope. For example, 'x' in
   /// @code
   /// int x;
   /// int f() {
   ///   return x; // unqualified name look finds 'x' in the global scope
   /// }
   /// @endcode
   ///
   /// Different lookup criteria can find different names. For example, a
   /// particular scope can have both a struct and a function of the same
   /// name, and each can be found by certain lookup criteria. For more
   /// information about lookup criteria, see the documentation for the
   /// class LookupCriteria.
   ///
   /// @param S        The scope from which unqualified name lookup will
   /// begin. If the lookup criteria permits, name lookup may also search
   /// in the parent scopes.
   ///
   /// @param [in,out] R Specifies the lookup to perform (e.g., the name to
   /// look up and the lookup kind), and is updated with the results of lookup
   /// including zero or more declarations and possibly additional information
   /// used to diagnose ambiguities.
   ///
   /// @returns \c true if lookup succeeded and false otherwise.
   bool LookupName(LookupResult &R, Scope *S, bool AllowBuiltinCreation = false,
                   bool ForceNoCPlusPlus = false);
 
   /// Perform qualified name lookup into a given context.
   ///
   /// Qualified name lookup (C++ [basic.lookup.qual]) is used to find
   /// names when the context of those names is explicit specified, e.g.,
   /// "std::vector" or "x->member", or as part of unqualified name lookup.
   ///
   /// Different lookup criteria can find different names. For example, a
   /// particular scope can have both a struct and a function of the same
   /// name, and each can be found by certain lookup criteria. For more
   /// information about lookup criteria, see the documentation for the
   /// class LookupCriteria.
   ///
   /// \param R captures both the lookup criteria and any lookup results found.
   ///
   /// \param LookupCtx The context in which qualified name lookup will
   /// search. If the lookup criteria permits, name lookup may also search
   /// in the parent contexts or (for C++ classes) base classes.
   ///
   /// \param InUnqualifiedLookup true if this is qualified name lookup that
   /// occurs as part of unqualified name lookup.
   ///
   /// \returns true if lookup succeeded, false if it failed.
   bool LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
                            bool InUnqualifiedLookup = false);
 
   /// Performs qualified name lookup or special type of lookup for
   /// "__super::" scope specifier.
   ///
   /// This routine is a convenience overload meant to be called from contexts
   /// that need to perform a qualified name lookup with an optional C++ scope
   /// specifier that might require special kind of lookup.
   ///
   /// \param R captures both the lookup criteria and any lookup results found.
   ///
   /// \param LookupCtx The context in which qualified name lookup will
   /// search.
   ///
   /// \param SS An optional C++ scope-specifier.
   ///
   /// \returns true if lookup succeeded, false if it failed.
   bool LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
                            CXXScopeSpec &SS);
 
   /// Performs name lookup for a name that was parsed in the
   /// source code, and may contain a C++ scope specifier.
   ///
   /// This routine is a convenience routine meant to be called from
   /// contexts that receive a name and an optional C++ scope specifier
   /// (e.g., "N::M::x"). It will then perform either qualified or
   /// unqualified name lookup (with LookupQualifiedName or LookupName,
   /// respectively) on the given name and return those results. It will
   /// perform a special type of lookup for "__super::" scope specifier.
   ///
   /// @param S        The scope from which unqualified name lookup will
   /// begin.
   ///
   /// @param SS       An optional C++ scope-specifier, e.g., "::N::M".
   ///
   /// @param EnteringContext Indicates whether we are going to enter the
   /// context of the scope-specifier SS (if present).
   ///
   /// @returns True if any decls were found (but possibly ambiguous)
   bool LookupParsedName(LookupResult &R, Scope *S, CXXScopeSpec *SS,
                         QualType ObjectType, bool AllowBuiltinCreation = false,
                         bool EnteringContext = false);
 
   /// Perform qualified name lookup into all base classes of the given
   /// class.
   ///
   /// \param R captures both the lookup criteria and any lookup results found.
   ///
   /// \param Class The context in which qualified name lookup will
   /// search. Name lookup will search in all base classes merging the results.
   ///
   /// @returns True if any decls were found (but possibly ambiguous)
   bool LookupInSuper(LookupResult &R, CXXRecordDecl *Class);
 
   void LookupOverloadedOperatorName(OverloadedOperatorKind Op, Scope *S,
                                     UnresolvedSetImpl &Functions);
 
   /// LookupOrCreateLabel - Do a name lookup of a label with the specified name.
   /// If GnuLabelLoc is a valid source location, then this is a definition
   /// of an __label__ label name, otherwise it is a normal label definition
   /// or use.
   LabelDecl *LookupOrCreateLabel(IdentifierInfo *II, SourceLocation IdentLoc,
                                  SourceLocation GnuLabelLoc = SourceLocation());
 
   /// Look up the constructors for the given class.
   DeclContextLookupResult LookupConstructors(CXXRecordDecl *Class);
 
   /// Look up the default constructor for the given class.
   CXXConstructorDecl *LookupDefaultConstructor(CXXRecordDecl *Class);
 
   /// Look up the copying constructor for the given class.
   CXXConstructorDecl *LookupCopyingConstructor(CXXRecordDecl *Class,
                                                unsigned Quals);
 
   /// Look up the copying assignment operator for the given class.
   CXXMethodDecl *LookupCopyingAssignment(CXXRecordDecl *Class, unsigned Quals,
                                          bool RValueThis, unsigned ThisQuals);
 
   /// Look up the moving constructor for the given class.
   CXXConstructorDecl *LookupMovingConstructor(CXXRecordDecl *Class,
                                               unsigned Quals);
 
   /// Look up the moving assignment operator for the given class.
   CXXMethodDecl *LookupMovingAssignment(CXXRecordDecl *Class, unsigned Quals,
                                         bool RValueThis, unsigned ThisQuals);
 
   /// Look for the destructor of the given class.
   ///
   /// During semantic analysis, this routine should be used in lieu of
   /// CXXRecordDecl::getDestructor().
   ///
   /// \returns The destructor for this class.
   CXXDestructorDecl *LookupDestructor(CXXRecordDecl *Class);
 
   /// Force the declaration of any implicitly-declared members of this
   /// class.
   void ForceDeclarationOfImplicitMembers(CXXRecordDecl *Class);
 
   /// Make a merged definition of an existing hidden definition \p ND
   /// visible at the specified location.
   void makeMergedDefinitionVisible(NamedDecl *ND);
 
   /// Check ODR hashes for C/ObjC when merging types from modules.
   /// Differently from C++, actually parse the body and reject in case
   /// of a mismatch.
   template <typename T,
             typename = std::enable_if_t<std::is_base_of<NamedDecl, T>::value>>
   bool ActOnDuplicateODRHashDefinition(T *Duplicate, T *Previous) {
     if (Duplicate->getODRHash() != Previous->getODRHash())
       return false;
 
     // Make the previous decl visible.
     makeMergedDefinitionVisible(Previous);
     return true;
   }
 
   /// Get the set of additional modules that should be checked during
   /// name lookup. A module and its imports become visible when instanting a
   /// template defined within it.
   llvm::DenseSet<Module *> &getLookupModules();
 
   bool hasVisibleMergedDefinition(const NamedDecl *Def);
   bool hasMergedDefinitionInCurrentModule(const NamedDecl *Def);
 
   /// Determine if the template parameter \p D has a visible default argument.
   bool
   hasVisibleDefaultArgument(const NamedDecl *D,
                             llvm::SmallVectorImpl<Module *> *Modules = nullptr);
   /// Determine if the template parameter \p D has a reachable default argument.
   bool hasReachableDefaultArgument(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
   /// Determine if the template parameter \p D has a reachable default argument.
   bool hasAcceptableDefaultArgument(const NamedDecl *D,
                                     llvm::SmallVectorImpl<Module *> *Modules,
                                     Sema::AcceptableKind Kind);
 
   /// Determine if there is a visible declaration of \p D that is an explicit
   /// specialization declaration for a specialization of a template. (For a
   /// member specialization, use hasVisibleMemberSpecialization.)
   bool hasVisibleExplicitSpecialization(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
   /// Determine if there is a reachable declaration of \p D that is an explicit
   /// specialization declaration for a specialization of a template. (For a
   /// member specialization, use hasReachableMemberSpecialization.)
   bool hasReachableExplicitSpecialization(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
 
   /// Determine if there is a visible declaration of \p D that is a member
   /// specialization declaration (as opposed to an instantiated declaration).
   bool hasVisibleMemberSpecialization(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
   /// Determine if there is a reachable declaration of \p D that is a member
   /// specialization declaration (as opposed to an instantiated declaration).
   bool hasReachableMemberSpecialization(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
 
   bool isModuleVisible(const Module *M, bool ModulePrivate = false);
 
   /// Determine whether any declaration of an entity is visible.
   bool
   hasVisibleDeclaration(const NamedDecl *D,
                         llvm::SmallVectorImpl<Module *> *Modules = nullptr) {
     return isVisible(D) || hasVisibleDeclarationSlow(D, Modules);
   }
 
   bool hasVisibleDeclarationSlow(const NamedDecl *D,
                                  llvm::SmallVectorImpl<Module *> *Modules);
   /// Determine whether any declaration of an entity is reachable.
   bool
   hasReachableDeclaration(const NamedDecl *D,
                           llvm::SmallVectorImpl<Module *> *Modules = nullptr) {
     return isReachable(D) || hasReachableDeclarationSlow(D, Modules);
   }
   bool hasReachableDeclarationSlow(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
 
   void diagnoseTypo(const TypoCorrection &Correction,
                     const PartialDiagnostic &TypoDiag,
                     bool ErrorRecovery = true);
 
   /// Diagnose a successfully-corrected typo. Separated from the correction
   /// itself to allow external validation of the result, etc.
   ///
   /// \param Correction The result of performing typo correction.
   /// \param TypoDiag The diagnostic to produce. This will have the corrected
   ///        string added to it (and usually also a fixit).
   /// \param PrevNote A note to use when indicating the location of the entity
   ///        to which we are correcting. Will have the correction string added
   ///        to it.
   /// \param ErrorRecovery If \c true (the default), the caller is going to
   ///        recover from the typo as if the corrected string had been typed.
   ///        In this case, \c PDiag must be an error, and we will attach a fixit
   ///        to it.
   void diagnoseTypo(const TypoCorrection &Correction,
                     const PartialDiagnostic &TypoDiag,
                     const PartialDiagnostic &PrevNote,
                     bool ErrorRecovery = true);
 
   /// Find the associated classes and namespaces for
   /// argument-dependent lookup for a call with the given set of
   /// arguments.
   ///
   /// This routine computes the sets of associated classes and associated
   /// namespaces searched by argument-dependent lookup
   /// (C++ [basic.lookup.argdep]) for a given set of arguments.
   void FindAssociatedClassesAndNamespaces(
       SourceLocation InstantiationLoc, ArrayRef<Expr *> Args,
       AssociatedNamespaceSet &AssociatedNamespaces,
       AssociatedClassSet &AssociatedClasses);
 
   /// Produce a diagnostic describing the ambiguity that resulted
   /// from name lookup.
   ///
   /// \param Result The result of the ambiguous lookup to be diagnosed.
   void DiagnoseAmbiguousLookup(LookupResult &Result);
 
   /// LookupLiteralOperator - Determine which literal operator should be used
   /// for a user-defined literal, per C++11 [lex.ext].
   ///
   /// Normal overload resolution is not used to select which literal operator to
   /// call for a user-defined literal. Look up the provided literal operator
   /// name, and filter the results to the appropriate set for the given argument
   /// types.
   LiteralOperatorLookupResult
   LookupLiteralOperator(Scope *S, LookupResult &R, ArrayRef<QualType> ArgTys,
                         bool AllowRaw, bool AllowTemplate,
                         bool AllowStringTemplate, bool DiagnoseMissing,
                         StringLiteral *StringLit = nullptr);
 
   void ArgumentDependentLookup(DeclarationName Name, SourceLocation Loc,
                                ArrayRef<Expr *> Args, ADLResult &Functions);
 
   void LookupVisibleDecls(Scope *S, LookupNameKind Kind,
                           VisibleDeclConsumer &Consumer,
                           bool IncludeGlobalScope = true,
                           bool LoadExternal = true);
   void LookupVisibleDecls(DeclContext *Ctx, LookupNameKind Kind,
                           VisibleDeclConsumer &Consumer,
                           bool IncludeGlobalScope = true,
                           bool IncludeDependentBases = false,
                           bool LoadExternal = true);
 
   enum CorrectTypoKind {
     CTK_NonError,     // CorrectTypo used in a non error recovery situation.
     CTK_ErrorRecovery // CorrectTypo used in normal error recovery.
   };
 
   /// Try to "correct" a typo in the source code by finding
   /// visible declarations whose names are similar to the name that was
   /// present in the source code.
   ///
   /// \param TypoName the \c DeclarationNameInfo structure that contains
   /// the name that was present in the source code along with its location.
   ///
   /// \param LookupKind the name-lookup criteria used to search for the name.
   ///
   /// \param S the scope in which name lookup occurs.
   ///
   /// \param SS the nested-name-specifier that precedes the name we're
   /// looking for, if present.
   ///
   /// \param CCC A CorrectionCandidateCallback object that provides further
   /// validation of typo correction candidates. It also provides flags for
   /// determining the set of keywords permitted.
   ///
   /// \param MemberContext if non-NULL, the context in which to look for
   /// a member access expression.
   ///
   /// \param EnteringContext whether we're entering the context described by
   /// the nested-name-specifier SS.
   ///
   /// \param OPT when non-NULL, the search for visible declarations will
   /// also walk the protocols in the qualified interfaces of \p OPT.
   ///
   /// \returns a \c TypoCorrection containing the corrected name if the typo
   /// along with information such as the \c NamedDecl where the corrected name
   /// was declared, and any additional \c NestedNameSpecifier needed to access
   /// it (C++ only). The \c TypoCorrection is empty if there is no correction.
   TypoCorrection CorrectTypo(const DeclarationNameInfo &Typo,
                              Sema::LookupNameKind LookupKind, Scope *S,
                              CXXScopeSpec *SS, CorrectionCandidateCallback &CCC,
                              CorrectTypoKind Mode,
                              DeclContext *MemberContext = nullptr,
                              bool EnteringContext = false,
                              const ObjCObjectPointerType *OPT = nullptr,
                              bool RecordFailure = true);
 
   /// Try to "correct" a typo in the source code by finding
   /// visible declarations whose names are similar to the name that was
   /// present in the source code.
   ///
   /// \param TypoName the \c DeclarationNameInfo structure that contains
   /// the name that was present in the source code along with its location.
   ///
   /// \param LookupKind the name-lookup criteria used to search for the name.
   ///
   /// \param S the scope in which name lookup occurs.
   ///
   /// \param SS the nested-name-specifier that precedes the name we're
   /// looking for, if present.
   ///
   /// \param CCC A CorrectionCandidateCallback object that provides further
   /// validation of typo correction candidates. It also provides flags for
   /// determining the set of keywords permitted.
   ///
   /// \param TDG A TypoDiagnosticGenerator functor that will be used to print
   /// diagnostics when the actual typo correction is attempted.
   ///
   /// \param TRC A TypoRecoveryCallback functor that will be used to build an
   /// Expr from a typo correction candidate.
   ///
   /// \param MemberContext if non-NULL, the context in which to look for
   /// a member access expression.
   ///
   /// \param EnteringContext whether we're entering the context described by
   /// the nested-name-specifier SS.
   ///
   /// \param OPT when non-NULL, the search for visible declarations will
   /// also walk the protocols in the qualified interfaces of \p OPT.
   ///
   /// \returns a new \c TypoExpr that will later be replaced in the AST with an
   /// Expr representing the result of performing typo correction, or nullptr if
   /// typo correction is not possible. If nullptr is returned, no diagnostics
   /// will be emitted and it is the responsibility of the caller to emit any
   /// that are needed.
   TypoExpr *CorrectTypoDelayed(
       const DeclarationNameInfo &Typo, Sema::LookupNameKind LookupKind,
       Scope *S, CXXScopeSpec *SS, CorrectionCandidateCallback &CCC,
       TypoDiagnosticGenerator TDG, TypoRecoveryCallback TRC,
       CorrectTypoKind Mode, DeclContext *MemberContext = nullptr,
       bool EnteringContext = false, const ObjCObjectPointerType *OPT = nullptr);
 
   /// Kinds of missing import. Note, the values of these enumerators correspond
   /// to %select values in diagnostics.
   enum class MissingImportKind {
     Declaration,
     Definition,
     DefaultArgument,
     ExplicitSpecialization,
     PartialSpecialization
   };
 
   /// Diagnose that the specified declaration needs to be visible but
   /// isn't, and suggest a module import that would resolve the problem.
   void diagnoseMissingImport(SourceLocation Loc, const NamedDecl *Decl,
                              MissingImportKind MIK, bool Recover = true);
   void diagnoseMissingImport(SourceLocation Loc, const NamedDecl *Decl,
                              SourceLocation DeclLoc, ArrayRef<Module *> Modules,
                              MissingImportKind MIK, bool Recover);
 
   struct TypoExprState {
     std::unique_ptr<TypoCorrectionConsumer> Consumer;
     TypoDiagnosticGenerator DiagHandler;
     TypoRecoveryCallback RecoveryHandler;
     TypoExprState();
     TypoExprState(TypoExprState &&other) noexcept;
     TypoExprState &operator=(TypoExprState &&other) noexcept;
   };
 
   const TypoExprState &getTypoExprState(TypoExpr *TE) const;
 
   /// Clears the state of the given TypoExpr.
   void clearDelayedTypo(TypoExpr *TE);
 
   /// Called on #pragma clang __debug dump II
   void ActOnPragmaDump(Scope *S, SourceLocation Loc, IdentifierInfo *II);
 
   /// Called on #pragma clang __debug dump E
   void ActOnPragmaDump(Expr *E);
 
 private:
   // The set of known/encountered (unique, canonicalized) NamespaceDecls.
   //
   // The boolean value will be true to indicate that the namespace was loaded
   // from an AST/PCH file, or false otherwise.
   llvm::MapVector<NamespaceDecl *, bool> KnownNamespaces;
 
   /// Whether we have already loaded known namespaces from an extenal
   /// source.
   bool LoadedExternalKnownNamespaces;
 
   bool CppLookupName(LookupResult &R, Scope *S);
 
   /// Determine if we could use all the declarations in the module.
   bool isUsableModule(const Module *M);
 
   /// Helper for CorrectTypo and CorrectTypoDelayed used to create and
   /// populate a new TypoCorrectionConsumer. Returns nullptr if typo correction
   /// should be skipped entirely.
   std::unique_ptr<TypoCorrectionConsumer> makeTypoCorrectionConsumer(
       const DeclarationNameInfo &Typo, Sema::LookupNameKind LookupKind,
       Scope *S, CXXScopeSpec *SS, CorrectionCandidateCallback &CCC,
       DeclContext *MemberContext, bool EnteringContext,
       const ObjCObjectPointerType *OPT, bool ErrorRecovery);
 
   /// The set of unhandled TypoExprs and their associated state.
   llvm::MapVector<TypoExpr *, TypoExprState> DelayedTypos;
 
   /// Creates a new TypoExpr AST node.
   TypoExpr *createDelayedTypo(std::unique_ptr<TypoCorrectionConsumer> TCC,
                               TypoDiagnosticGenerator TDG,
                               TypoRecoveryCallback TRC, SourceLocation TypoLoc);
 
   /// Cache for module units which is usable for current module.
   llvm::DenseSet<const Module *> UsableModuleUnitsCache;
 
   /// Record the typo correction failure and return an empty correction.
   TypoCorrection FailedCorrection(IdentifierInfo *Typo, SourceLocation TypoLoc,
                                   bool RecordFailure = true) {
     if (RecordFailure)
       TypoCorrectionFailures[Typo].insert(TypoLoc);
     return TypoCorrection();
   }
 
   bool isAcceptableSlow(const NamedDecl *D, AcceptableKind Kind);
 
   /// Determine whether two declarations should be linked together, given that
   /// the old declaration might not be visible and the new declaration might
   /// not have external linkage.
   bool shouldLinkPossiblyHiddenDecl(const NamedDecl *Old,
                                     const NamedDecl *New) {
     if (isVisible(Old))
       return true;
     // See comment in below overload for why it's safe to compute the linkage
     // of the new declaration here.
     if (New->isExternallyDeclarable()) {
       assert(Old->isExternallyDeclarable() &&
              "should not have found a non-externally-declarable previous decl");
       return true;
     }
     return false;
   }
   bool shouldLinkPossiblyHiddenDecl(LookupResult &Old, const NamedDecl *New);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Modules
   /// Implementations are in SemaModule.cpp
   ///@{
 
 public:
   /// Get the module unit whose scope we are currently within.
   Module *getCurrentModule() const {
     return ModuleScopes.empty() ? nullptr : ModuleScopes.back().Module;
   }
 
   /// Is the module scope we are an implementation unit?
   bool currentModuleIsImplementation() const {
     return ModuleScopes.empty()
                ? false
                : ModuleScopes.back().Module->isModuleImplementation();
   }
 
   // When loading a non-modular PCH files, this is used to restore module
   // visibility.
   void makeModuleVisible(Module *Mod, SourceLocation ImportLoc) {
     VisibleModules.setVisible(Mod, ImportLoc);
   }
 
   enum class ModuleDeclKind {
     Interface,               ///< 'export module X;'
     Implementation,          ///< 'module X;'
     PartitionInterface,      ///< 'export module X:Y;'
     PartitionImplementation, ///< 'module X:Y;'
   };
 
   /// An enumeration to represent the transition of states in parsing module
   /// fragments and imports.  If we are not parsing a C++20 TU, or we find
   /// an error in state transition, the state is set to NotACXX20Module.
   enum class ModuleImportState {
     FirstDecl,      ///< Parsing the first decl in a TU.
     GlobalFragment, ///< after 'module;' but before 'module X;'
     ImportAllowed,  ///< after 'module X;' but before any non-import decl.
     ImportFinished, ///< after any non-import decl.
     PrivateFragmentImportAllowed,  ///< after 'module :private;' but before any
                                    ///< non-import decl.
     PrivateFragmentImportFinished, ///< after 'module :private;' but a
                                    ///< non-import decl has already been seen.
     NotACXX20Module ///< Not a C++20 TU, or an invalid state was found.
   };
 
   /// The parser has processed a module-declaration that begins the definition
   /// of a module interface or implementation.
   DeclGroupPtrTy ActOnModuleDecl(SourceLocation StartLoc,
                                  SourceLocation ModuleLoc, ModuleDeclKind MDK,
                                  ModuleIdPath Path, ModuleIdPath Partition,
                                  ModuleImportState &ImportState);
 
   /// The parser has processed a global-module-fragment declaration that begins
   /// the definition of the global module fragment of the current module unit.
   /// \param ModuleLoc The location of the 'module' keyword.
   DeclGroupPtrTy ActOnGlobalModuleFragmentDecl(SourceLocation ModuleLoc);
 
   /// The parser has processed a private-module-fragment declaration that begins
   /// the definition of the private module fragment of the current module unit.
   /// \param ModuleLoc The location of the 'module' keyword.
   /// \param PrivateLoc The location of the 'private' keyword.
   DeclGroupPtrTy ActOnPrivateModuleFragmentDecl(SourceLocation ModuleLoc,
                                                 SourceLocation PrivateLoc);
 
   /// The parser has processed a module import declaration.
   ///
   /// \param StartLoc The location of the first token in the declaration. This
   ///        could be the location of an '@', 'export', or 'import'.
   /// \param ExportLoc The location of the 'export' keyword, if any.
   /// \param ImportLoc The location of the 'import' keyword.
   /// \param Path The module toplevel name as an access path.
   /// \param IsPartition If the name is for a partition.
   DeclResult ActOnModuleImport(SourceLocation StartLoc,
                                SourceLocation ExportLoc,
                                SourceLocation ImportLoc, ModuleIdPath Path,
                                bool IsPartition = false);
   DeclResult ActOnModuleImport(SourceLocation StartLoc,
                                SourceLocation ExportLoc,
                                SourceLocation ImportLoc, Module *M,
                                ModuleIdPath Path = {});
 
   /// The parser has processed a module import translated from a
   /// #include or similar preprocessing directive.
   void ActOnAnnotModuleInclude(SourceLocation DirectiveLoc, Module *Mod);
   void BuildModuleInclude(SourceLocation DirectiveLoc, Module *Mod);
 
   /// The parsed has entered a submodule.
   void ActOnAnnotModuleBegin(SourceLocation DirectiveLoc, Module *Mod);
   /// The parser has left a submodule.
   void ActOnAnnotModuleEnd(SourceLocation DirectiveLoc, Module *Mod);
 
   /// Create an implicit import of the given module at the given
   /// source location, for error recovery, if possible.
   ///
   /// This routine is typically used when an entity found by name lookup
   /// is actually hidden within a module that we know about but the user
   /// has forgotten to import.
   void createImplicitModuleImportForErrorRecovery(SourceLocation Loc,
                                                   Module *Mod);
 
   /// We have parsed the start of an export declaration, including the '{'
   /// (if present).
   Decl *ActOnStartExportDecl(Scope *S, SourceLocation ExportLoc,
                              SourceLocation LBraceLoc);
 
   /// Complete the definition of an export declaration.
   Decl *ActOnFinishExportDecl(Scope *S, Decl *ExportDecl,
                               SourceLocation RBraceLoc);
 
 private:
   /// The parser has begun a translation unit to be compiled as a C++20
   /// Header Unit, helper for ActOnStartOfTranslationUnit() only.
   void HandleStartOfHeaderUnit();
 
   struct ModuleScope {
     SourceLocation BeginLoc;
     clang::Module *Module = nullptr;
     VisibleModuleSet OuterVisibleModules;
   };
   /// The modules we're currently parsing.
   llvm::SmallVector<ModuleScope, 16> ModuleScopes;
 
   /// For an interface unit, this is the implicitly imported interface unit.
   clang::Module *ThePrimaryInterface = nullptr;
 
   /// The explicit global module fragment of the current translation unit.
   /// The explicit Global Module Fragment, as specified in C++
   /// [module.global.frag].
   clang::Module *TheGlobalModuleFragment = nullptr;
 
   /// The implicit global module fragments of the current translation unit.
   ///
   /// The contents in the implicit global module fragment can't be discarded.
   clang::Module *TheImplicitGlobalModuleFragment = nullptr;
 
   /// Namespace definitions that we will export when they finish.
   llvm::SmallPtrSet<const NamespaceDecl *, 8> DeferredExportedNamespaces;
 
   /// In a C++ standard module, inline declarations require a definition to be
   /// present at the end of a definition domain.  This set holds the decls to
   /// be checked at the end of the TU.
   llvm::SmallPtrSet<const FunctionDecl *, 8> PendingInlineFuncDecls;
 
   /// Helper function to judge if we are in module purview.
   /// Return false if we are not in a module.
   bool isCurrentModulePurview() const;
 
   /// Enter the scope of the explicit global module fragment.
   Module *PushGlobalModuleFragment(SourceLocation BeginLoc);
   /// Leave the scope of the explicit global module fragment.
   void PopGlobalModuleFragment();
 
   /// Enter the scope of an implicit global module fragment.
   Module *PushImplicitGlobalModuleFragment(SourceLocation BeginLoc);
   /// Leave the scope of an implicit global module fragment.
   void PopImplicitGlobalModuleFragment();
 
   VisibleModuleSet VisibleModules;
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Overloading
   /// Implementations are in SemaOverload.cpp
   ///@{
 
 public:
   /// Whether deferrable diagnostics should be deferred.
   bool DeferDiags = false;
 
   /// RAII class to control scope of DeferDiags.
   class DeferDiagsRAII {
     Sema &S;
     bool SavedDeferDiags = false;
 
   public:
     DeferDiagsRAII(Sema &S, bool DeferDiags)
         : S(S), SavedDeferDiags(S.DeferDiags) {
       S.DeferDiags = DeferDiags;
     }
     ~DeferDiagsRAII() { S.DeferDiags = SavedDeferDiags; }
   };
 
   /// Flag indicating if Sema is building a recovery call expression.
   ///
   /// This flag is used to avoid building recovery call expressions
   /// if Sema is already doing so, which would cause infinite recursions.
   bool IsBuildingRecoveryCallExpr;
 
   enum OverloadKind {
     /// This is a legitimate overload: the existing declarations are
     /// functions or function templates with different signatures.
     Ovl_Overload,
 
     /// This is not an overload because the signature exactly matches
     /// an existing declaration.
     Ovl_Match,
 
     /// This is not an overload because the lookup results contain a
     /// non-function.
     Ovl_NonFunction
   };
 
   /// Determine whether the given New declaration is an overload of the
   /// declarations in Old. This routine returns Ovl_Match or Ovl_NonFunction if
   /// New and Old cannot be overloaded, e.g., if New has the same signature as
   /// some function in Old (C++ 1.3.10) or if the Old declarations aren't
   /// functions (or function templates) at all. When it does return Ovl_Match or
   /// Ovl_NonFunction, MatchedDecl will point to the decl that New cannot be
   /// overloaded with. This decl may be a UsingShadowDecl on top of the
   /// underlying declaration.
   ///
   /// Example: Given the following input:
   ///
   ///   void f(int, float); // #1
   ///   void f(int, int); // #2
   ///   int f(int, int); // #3
   ///
   /// When we process #1, there is no previous declaration of "f", so IsOverload
   /// will not be used.
   ///
   /// When we process #2, Old contains only the FunctionDecl for #1. By
   /// comparing the parameter types, we see that #1 and #2 are overloaded (since
   /// they have different signatures), so this routine returns Ovl_Overload;
   /// MatchedDecl is unchanged.
   ///
   /// When we process #3, Old is an overload set containing #1 and #2. We
   /// compare the signatures of #3 to #1 (they're overloaded, so we do nothing)
   /// and then #3 to #2. Since the signatures of #3 and #2 are identical (return
   /// types of functions are not part of the signature), IsOverload returns
   /// Ovl_Match and MatchedDecl will be set to point to the FunctionDecl for #2.
   ///
   /// 'NewIsUsingShadowDecl' indicates that 'New' is being introduced into a
   /// class by a using declaration. The rules for whether to hide shadow
   /// declarations ignore some properties which otherwise figure into a function
   /// template's signature.
   OverloadKind CheckOverload(Scope *S, FunctionDecl *New,
                              const LookupResult &OldDecls, NamedDecl *&OldDecl,
                              bool UseMemberUsingDeclRules);
   bool IsOverload(FunctionDecl *New, FunctionDecl *Old,
                   bool UseMemberUsingDeclRules, bool ConsiderCudaAttrs = true);
 
   // Checks whether MD constitutes an override the base class method BaseMD.
   // When checking for overrides, the object object members are ignored.
   bool IsOverride(FunctionDecl *MD, FunctionDecl *BaseMD,
                   bool UseMemberUsingDeclRules, bool ConsiderCudaAttrs = true);
 
   enum class AllowedExplicit {
     /// Allow no explicit functions to be used.
     None,
     /// Allow explicit conversion functions but not explicit constructors.
     Conversions,
     /// Allow both explicit conversion functions and explicit constructors.
     All
   };
 
   ImplicitConversionSequence TryImplicitConversion(
       Expr *From, QualType ToType, bool SuppressUserConversions,
       AllowedExplicit AllowExplicit, bool InOverloadResolution, bool CStyle,
       bool AllowObjCWritebackConversion);
 
   /// PerformImplicitConversion - Perform an implicit conversion of the
   /// expression From to the type ToType. Returns the
   /// converted expression. Flavor is the kind of conversion we're
   /// performing, used in the error message. If @p AllowExplicit,
   /// explicit user-defined conversions are permitted.
   ExprResult PerformImplicitConversion(Expr *From, QualType ToType,
                                        AssignmentAction Action,
                                        bool AllowExplicit = false);
 
   /// IsIntegralPromotion - Determines whether the conversion from the
   /// expression From (whose potentially-adjusted type is FromType) to
   /// ToType is an integral promotion (C++ 4.5). If so, returns true and
   /// sets PromotedType to the promoted type.
   bool IsIntegralPromotion(Expr *From, QualType FromType, QualType ToType);
 
   /// IsFloatingPointPromotion - Determines whether the conversion from
   /// FromType to ToType is a floating point promotion (C++ 4.6). If so,
   /// returns true and sets PromotedType to the promoted type.
   bool IsFloatingPointPromotion(QualType FromType, QualType ToType);
 
   /// Determine if a conversion is a complex promotion.
   ///
   /// A complex promotion is defined as a complex -> complex conversion
   /// where the conversion between the underlying real types is a
   /// floating-point or integral promotion.
   bool IsComplexPromotion(QualType FromType, QualType ToType);
 
   /// IsPointerConversion - Determines whether the conversion of the
   /// expression From, which has the (possibly adjusted) type FromType,
   /// can be converted to the type ToType via a pointer conversion (C++
   /// 4.10). If so, returns true and places the converted type (that
   /// might differ from ToType in its cv-qualifiers at some level) into
   /// ConvertedType.
   ///
   /// This routine also supports conversions to and from block pointers
   /// and conversions with Objective-C's 'id', 'id<protocols...>', and
   /// pointers to interfaces. FIXME: Once we've determined the
   /// appropriate overloading rules for Objective-C, we may want to
   /// split the Objective-C checks into a different routine; however,
   /// GCC seems to consider all of these conversions to be pointer
   /// conversions, so for now they live here. IncompatibleObjC will be
   /// set if the conversion is an allowed Objective-C conversion that
   /// should result in a warning.
   bool IsPointerConversion(Expr *From, QualType FromType, QualType ToType,
                            bool InOverloadResolution, QualType &ConvertedType,
                            bool &IncompatibleObjC);
 
   /// isObjCPointerConversion - Determines whether this is an
   /// Objective-C pointer conversion. Subroutine of IsPointerConversion,
   /// with the same arguments and return values.
   bool isObjCPointerConversion(QualType FromType, QualType ToType,
                                QualType &ConvertedType, bool &IncompatibleObjC);
   bool IsBlockPointerConversion(QualType FromType, QualType ToType,
                                 QualType &ConvertedType);
 
   /// FunctionParamTypesAreEqual - This routine checks two function proto types
   /// for equality of their parameter types. Caller has already checked that
   /// they have same number of parameters.  If the parameters are different,
   /// ArgPos will have the parameter index of the first different parameter.
   /// If `Reversed` is true, the parameters of `NewType` will be compared in
   /// reverse order. That's useful if one of the functions is being used as a
   /// C++20 synthesized operator overload with a reversed parameter order.
   bool FunctionParamTypesAreEqual(ArrayRef<QualType> Old,
                                   ArrayRef<QualType> New,
                                   unsigned *ArgPos = nullptr,
                                   bool Reversed = false);
 
   bool FunctionParamTypesAreEqual(const FunctionProtoType *OldType,
                                   const FunctionProtoType *NewType,
                                   unsigned *ArgPos = nullptr,
                                   bool Reversed = false);
 
   bool FunctionNonObjectParamTypesAreEqual(const FunctionDecl *OldFunction,
                                            const FunctionDecl *NewFunction,
                                            unsigned *ArgPos = nullptr,
                                            bool Reversed = false);
 
   /// HandleFunctionTypeMismatch - Gives diagnostic information for differeing
   /// function types.  Catches different number of parameter, mismatch in
   /// parameter types, and different return types.
   void HandleFunctionTypeMismatch(PartialDiagnostic &PDiag, QualType FromType,
                                   QualType ToType);
 
   /// CheckPointerConversion - Check the pointer conversion from the
   /// expression From to the type ToType. This routine checks for
   /// ambiguous or inaccessible derived-to-base pointer
   /// conversions for which IsPointerConversion has already returned
   /// true. It returns true and produces a diagnostic if there was an
   /// error, or returns false otherwise.
   bool CheckPointerConversion(Expr *From, QualType ToType, CastKind &Kind,
                               CXXCastPath &BasePath, bool IgnoreBaseAccess,
                               bool Diagnose = true);
 
   /// IsMemberPointerConversion - Determines whether the conversion of the
   /// expression From, which has the (possibly adjusted) type FromType, can be
   /// converted to the type ToType via a member pointer conversion (C++ 4.11).
   /// If so, returns true and places the converted type (that might differ from
   /// ToType in its cv-qualifiers at some level) into ConvertedType.
   bool IsMemberPointerConversion(Expr *From, QualType FromType, QualType ToType,
                                  bool InOverloadResolution,
                                  QualType &ConvertedType);
 
   /// CheckMemberPointerConversion - Check the member pointer conversion from
   /// the expression From to the type ToType. This routine checks for ambiguous
   /// or virtual or inaccessible base-to-derived member pointer conversions for
   /// which IsMemberPointerConversion has already returned true. It returns true
   /// and produces a diagnostic if there was an error, or returns false
   /// otherwise.
   bool CheckMemberPointerConversion(Expr *From, QualType ToType, CastKind &Kind,
                                     CXXCastPath &BasePath,
                                     bool IgnoreBaseAccess);
 
   /// IsQualificationConversion - Determines whether the conversion from
   /// an rvalue of type FromType to ToType is a qualification conversion
   /// (C++ 4.4).
   ///
   /// \param ObjCLifetimeConversion Output parameter that will be set to
   /// indicate when the qualification conversion involves a change in the
   /// Objective-C object lifetime.
   bool IsQualificationConversion(QualType FromType, QualType ToType,
                                  bool CStyle, bool &ObjCLifetimeConversion);
 
   /// Determine whether the conversion from FromType to ToType is a valid
   /// conversion that strips "noexcept" or "noreturn" off the nested function
   /// type.
   bool IsFunctionConversion(QualType FromType, QualType ToType,
                             QualType &ResultTy);
   bool DiagnoseMultipleUserDefinedConversion(Expr *From, QualType ToType);
   void DiagnoseUseOfDeletedFunction(SourceLocation Loc, SourceRange Range,
                                     DeclarationName Name,
                                     OverloadCandidateSet &CandidateSet,
                                     FunctionDecl *Fn, MultiExprArg Args,
                                     bool IsMember = false);
 
   ExprResult InitializeExplicitObjectArgument(Sema &S, Expr *Obj,
                                               FunctionDecl *Fun);
   ExprResult PerformImplicitObjectArgumentInitialization(
       Expr *From, NestedNameSpecifier *Qualifier, NamedDecl *FoundDecl,
       CXXMethodDecl *Method);
 
   /// PerformContextuallyConvertToBool - Perform a contextual conversion
   /// of the expression From to bool (C++0x [conv]p3).
   ExprResult PerformContextuallyConvertToBool(Expr *From);
 
   /// PerformContextuallyConvertToObjCPointer - Perform a contextual
   /// conversion of the expression From to an Objective-C pointer type.
   /// Returns a valid but null ExprResult if no conversion sequence exists.
   ExprResult PerformContextuallyConvertToObjCPointer(Expr *From);
 
   /// Contexts in which a converted constant expression is required.
   enum CCEKind {
     CCEK_CaseValue,    ///< Expression in a case label.
     CCEK_Enumerator,   ///< Enumerator value with fixed underlying type.
     CCEK_TemplateArg,  ///< Value of a non-type template parameter.
     CCEK_ArrayBound,   ///< Array bound in array declarator or new-expression.
     CCEK_ExplicitBool, ///< Condition in an explicit(bool) specifier.
     CCEK_Noexcept,     ///< Condition in a noexcept(bool) specifier.
     CCEK_StaticAssertMessageSize, ///< Call to size() in a static assert
                                   ///< message.
     CCEK_StaticAssertMessageData, ///< Call to data() in a static assert
                                   ///< message.
   };
 
   ExprResult BuildConvertedConstantExpression(Expr *From, QualType T,
                                               CCEKind CCE,
                                               NamedDecl *Dest = nullptr);
 
   ExprResult CheckConvertedConstantExpression(Expr *From, QualType T,
                                               llvm::APSInt &Value, CCEKind CCE);
   ExprResult CheckConvertedConstantExpression(Expr *From, QualType T,
                                               APValue &Value, CCEKind CCE,
                                               NamedDecl *Dest = nullptr);
 
   /// EvaluateConvertedConstantExpression - Evaluate an Expression
   /// That is a converted constant expression
   /// (which was built with BuildConvertedConstantExpression)
   ExprResult
   EvaluateConvertedConstantExpression(Expr *E, QualType T, APValue &Value,
                                       CCEKind CCE, bool RequireInt,
                                       const APValue &PreNarrowingValue);
 
   /// Abstract base class used to perform a contextual implicit
   /// conversion from an expression to any type passing a filter.
   class ContextualImplicitConverter {
   public:
     bool Suppress;
     bool SuppressConversion;
 
     ContextualImplicitConverter(bool Suppress = false,
                                 bool SuppressConversion = false)
         : Suppress(Suppress), SuppressConversion(SuppressConversion) {}
 
     /// Determine whether the specified type is a valid destination type
     /// for this conversion.
     virtual bool match(QualType T) = 0;
 
     /// Emits a diagnostic complaining that the expression does not have
     /// integral or enumeration type.
     virtual SemaDiagnosticBuilder diagnoseNoMatch(Sema &S, SourceLocation Loc,
                                                   QualType T) = 0;
 
     /// Emits a diagnostic when the expression has incomplete class type.
     virtual SemaDiagnosticBuilder
     diagnoseIncomplete(Sema &S, SourceLocation Loc, QualType T) = 0;
 
     /// Emits a diagnostic when the only matching conversion function
     /// is explicit.
     virtual SemaDiagnosticBuilder diagnoseExplicitConv(Sema &S,
                                                        SourceLocation Loc,
                                                        QualType T,
                                                        QualType ConvTy) = 0;
 
     /// Emits a note for the explicit conversion function.
     virtual SemaDiagnosticBuilder
     noteExplicitConv(Sema &S, CXXConversionDecl *Conv, QualType ConvTy) = 0;
 
     /// Emits a diagnostic when there are multiple possible conversion
     /// functions.
     virtual SemaDiagnosticBuilder diagnoseAmbiguous(Sema &S, SourceLocation Loc,
                                                     QualType T) = 0;
 
     /// Emits a note for one of the candidate conversions.
     virtual SemaDiagnosticBuilder
     noteAmbiguous(Sema &S, CXXConversionDecl *Conv, QualType ConvTy) = 0;
 
     /// Emits a diagnostic when we picked a conversion function
     /// (for cases when we are not allowed to pick a conversion function).
     virtual SemaDiagnosticBuilder diagnoseConversion(Sema &S,
                                                      SourceLocation Loc,
                                                      QualType T,
                                                      QualType ConvTy) = 0;
 
     virtual ~ContextualImplicitConverter() {}
   };
 
   class ICEConvertDiagnoser : public ContextualImplicitConverter {
     bool AllowScopedEnumerations;
 
   public:
     ICEConvertDiagnoser(bool AllowScopedEnumerations, bool Suppress,
                         bool SuppressConversion)
         : ContextualImplicitConverter(Suppress, SuppressConversion),
           AllowScopedEnumerations(AllowScopedEnumerations) {}
 
     /// Match an integral or (possibly scoped) enumeration type.
     bool match(QualType T) override;
 
     SemaDiagnosticBuilder diagnoseNoMatch(Sema &S, SourceLocation Loc,
                                           QualType T) override {
       return diagnoseNotInt(S, Loc, T);
     }
 
     /// Emits a diagnostic complaining that the expression does not have
     /// integral or enumeration type.
     virtual SemaDiagnosticBuilder diagnoseNotInt(Sema &S, SourceLocation Loc,
                                                  QualType T) = 0;
   };
 
   /// Perform a contextual implicit conversion.
   ExprResult
   PerformContextualImplicitConversion(SourceLocation Loc, Expr *FromE,
                                       ContextualImplicitConverter &Converter);
 
   /// ReferenceCompareResult - Expresses the result of comparing two
   /// types (cv1 T1 and cv2 T2) to determine their compatibility for the
   /// purposes of initialization by reference (C++ [dcl.init.ref]p4).
   enum ReferenceCompareResult {
     /// Ref_Incompatible - The two types are incompatible, so direct
     /// reference binding is not possible.
     Ref_Incompatible = 0,
     /// Ref_Related - The two types are reference-related, which means
     /// that their unqualified forms (T1 and T2) are either the same
     /// or T1 is a base class of T2.
     Ref_Related,
     /// Ref_Compatible - The two types are reference-compatible.
     Ref_Compatible
   };
 
   // Fake up a scoped enumeration that still contextually converts to bool.
   struct ReferenceConversionsScope {
     /// The conversions that would be performed on an lvalue of type T2 when
     /// binding a reference of type T1 to it, as determined when evaluating
     /// whether T1 is reference-compatible with T2.
     enum ReferenceConversions {
       Qualification = 0x1,
       NestedQualification = 0x2,
       Function = 0x4,
       DerivedToBase = 0x8,
       ObjC = 0x10,
       ObjCLifetime = 0x20,
 
       LLVM_MARK_AS_BITMASK_ENUM(/*LargestValue=*/ObjCLifetime)
     };
   };
   using ReferenceConversions = ReferenceConversionsScope::ReferenceConversions;
 
   /// CompareReferenceRelationship - Compare the two types T1 and T2 to
   /// determine whether they are reference-compatible,
   /// reference-related, or incompatible, for use in C++ initialization by
   /// reference (C++ [dcl.ref.init]p4). Neither type can be a reference
   /// type, and the first type (T1) is the pointee type of the reference
   /// type being initialized.
   ReferenceCompareResult
   CompareReferenceRelationship(SourceLocation Loc, QualType T1, QualType T2,
                                ReferenceConversions *Conv = nullptr);
 
   /// AddOverloadCandidate - Adds the given function to the set of
   /// candidate functions, using the given function call arguments.  If
   /// @p SuppressUserConversions, then don't allow user-defined
   /// conversions via constructors or conversion operators.
   ///
   /// \param PartialOverloading true if we are performing "partial" overloading
   /// based on an incomplete set of function arguments. This feature is used by
   /// code completion.
   void AddOverloadCandidate(
       FunctionDecl *Function, DeclAccessPair FoundDecl, ArrayRef<Expr *> Args,
       OverloadCandidateSet &CandidateSet, bool SuppressUserConversions = false,
       bool PartialOverloading = false, bool AllowExplicit = true,
       bool AllowExplicitConversion = false,
       ADLCallKind IsADLCandidate = ADLCallKind::NotADL,
       ConversionSequenceList EarlyConversions = std::nullopt,
       OverloadCandidateParamOrder PO = {},
       bool AggregateCandidateDeduction = false);
 
   /// Add all of the function declarations in the given function set to
   /// the overload candidate set.
   void AddFunctionCandidates(
       const UnresolvedSetImpl &Functions, ArrayRef<Expr *> Args,
       OverloadCandidateSet &CandidateSet,
       TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr,
       bool SuppressUserConversions = false, bool PartialOverloading = false,
       bool FirstArgumentIsBase = false);
 
   /// AddMethodCandidate - Adds a named decl (which is some kind of
   /// method) as a method candidate to the given overload set.
   void AddMethodCandidate(DeclAccessPair FoundDecl, QualType ObjectType,
                           Expr::Classification ObjectClassification,
                           ArrayRef<Expr *> Args,
                           OverloadCandidateSet &CandidateSet,
                           bool SuppressUserConversion = false,
                           OverloadCandidateParamOrder PO = {});
 
   /// AddMethodCandidate - Adds the given C++ member function to the set
   /// of candidate functions, using the given function call arguments
   /// and the object argument (@c Object). For example, in a call
   /// @c o.f(a1,a2), @c Object will contain @c o and @c Args will contain
   /// both @c a1 and @c a2. If @p SuppressUserConversions, then don't
   /// allow user-defined conversions via constructors or conversion
   /// operators.
   void
   AddMethodCandidate(CXXMethodDecl *Method, DeclAccessPair FoundDecl,
                      CXXRecordDecl *ActingContext, QualType ObjectType,
                      Expr::Classification ObjectClassification,
                      ArrayRef<Expr *> Args, OverloadCandidateSet &CandidateSet,
                      bool SuppressUserConversions = false,
                      bool PartialOverloading = false,
                      ConversionSequenceList EarlyConversions = std::nullopt,
                      OverloadCandidateParamOrder PO = {});
 
   /// Add a C++ member function template as a candidate to the candidate
   /// set, using template argument deduction to produce an appropriate member
   /// function template specialization.
   void AddMethodTemplateCandidate(
       FunctionTemplateDecl *MethodTmpl, DeclAccessPair FoundDecl,
       CXXRecordDecl *ActingContext,
       TemplateArgumentListInfo *ExplicitTemplateArgs, QualType ObjectType,
       Expr::Classification ObjectClassification, ArrayRef<Expr *> Args,
       OverloadCandidateSet &CandidateSet, bool SuppressUserConversions = false,
       bool PartialOverloading = false, OverloadCandidateParamOrder PO = {});
 
   /// Add a C++ function template specialization as a candidate
   /// in the candidate set, using template argument deduction to produce
   /// an appropriate function template specialization.
   void AddTemplateOverloadCandidate(
       FunctionTemplateDecl *FunctionTemplate, DeclAccessPair FoundDecl,
       TemplateArgumentListInfo *ExplicitTemplateArgs, ArrayRef<Expr *> Args,
       OverloadCandidateSet &CandidateSet, bool SuppressUserConversions = false,
       bool PartialOverloading = false, bool AllowExplicit = true,
       ADLCallKind IsADLCandidate = ADLCallKind::NotADL,
       OverloadCandidateParamOrder PO = {},
       bool AggregateCandidateDeduction = false);
 
   /// Check that implicit conversion sequences can be formed for each argument
   /// whose corresponding parameter has a non-dependent type, per DR1391's
   /// [temp.deduct.call]p10.
   bool CheckNonDependentConversions(
       FunctionTemplateDecl *FunctionTemplate, ArrayRef<QualType> ParamTypes,
       ArrayRef<Expr *> Args, OverloadCandidateSet &CandidateSet,
       ConversionSequenceList &Conversions, bool SuppressUserConversions,
       CXXRecordDecl *ActingContext = nullptr, QualType ObjectType = QualType(),
       Expr::Classification ObjectClassification = {},
       OverloadCandidateParamOrder PO = {});
 
   /// AddConversionCandidate - Add a C++ conversion function as a
   /// candidate in the candidate set (C++ [over.match.conv],
   /// C++ [over.match.copy]). From is the expression we're converting from,
   /// and ToType is the type that we're eventually trying to convert to
   /// (which may or may not be the same type as the type that the
   /// conversion function produces).
   void AddConversionCandidate(
       CXXConversionDecl *Conversion, DeclAccessPair FoundDecl,
       CXXRecordDecl *ActingContext, Expr *From, QualType ToType,
       OverloadCandidateSet &CandidateSet, bool AllowObjCConversionOnExplicit,
       bool AllowExplicit, bool AllowResultConversion = true);
 
   /// Adds a conversion function template specialization
   /// candidate to the overload set, using template argument deduction
   /// to deduce the template arguments of the conversion function
   /// template from the type that we are converting to (C++
   /// [temp.deduct.conv]).
   void AddTemplateConversionCandidate(
       FunctionTemplateDecl *FunctionTemplate, DeclAccessPair FoundDecl,
       CXXRecordDecl *ActingContext, Expr *From, QualType ToType,
       OverloadCandidateSet &CandidateSet, bool AllowObjCConversionOnExplicit,
       bool AllowExplicit, bool AllowResultConversion = true);
 
   /// AddSurrogateCandidate - Adds a "surrogate" candidate function that
   /// converts the given @c Object to a function pointer via the
   /// conversion function @c Conversion, and then attempts to call it
   /// with the given arguments (C++ [over.call.object]p2-4). Proto is
   /// the type of function that we'll eventually be calling.
   void AddSurrogateCandidate(CXXConversionDecl *Conversion,
                              DeclAccessPair FoundDecl,
                              CXXRecordDecl *ActingContext,
                              const FunctionProtoType *Proto, Expr *Object,
                              ArrayRef<Expr *> Args,
                              OverloadCandidateSet &CandidateSet);
 
   /// Add all of the non-member operator function declarations in the given
   /// function set to the overload candidate set.
   void AddNonMemberOperatorCandidates(
       const UnresolvedSetImpl &Functions, ArrayRef<Expr *> Args,
       OverloadCandidateSet &CandidateSet,
       TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr);
 
   /// Add overload candidates for overloaded operators that are
   /// member functions.
   ///
   /// Add the overloaded operator candidates that are member functions
   /// for the operator Op that was used in an operator expression such
   /// as "x Op y". , Args/NumArgs provides the operator arguments, and
   /// CandidateSet will store the added overload candidates. (C++
   /// [over.match.oper]).
   void AddMemberOperatorCandidates(OverloadedOperatorKind Op,
                                    SourceLocation OpLoc, ArrayRef<Expr *> Args,
                                    OverloadCandidateSet &CandidateSet,
                                    OverloadCandidateParamOrder PO = {});
 
   /// AddBuiltinCandidate - Add a candidate for a built-in
   /// operator. ResultTy and ParamTys are the result and parameter types
   /// of the built-in candidate, respectively. Args and NumArgs are the
   /// arguments being passed to the candidate. IsAssignmentOperator
   /// should be true when this built-in candidate is an assignment
   /// operator. NumContextualBoolArguments is the number of arguments
   /// (at the beginning of the argument list) that will be contextually
   /// converted to bool.
   void AddBuiltinCandidate(QualType *ParamTys, ArrayRef<Expr *> Args,
                            OverloadCandidateSet &CandidateSet,
                            bool IsAssignmentOperator = false,
                            unsigned NumContextualBoolArguments = 0);
 
   /// AddBuiltinOperatorCandidates - Add the appropriate built-in
   /// operator overloads to the candidate set (C++ [over.built]), based
   /// on the operator @p Op and the arguments given. For example, if the
   /// operator is a binary '+', this routine might add "int
   /// operator+(int, int)" to cover integer addition.
   void AddBuiltinOperatorCandidates(OverloadedOperatorKind Op,
                                     SourceLocation OpLoc, ArrayRef<Expr *> Args,
                                     OverloadCandidateSet &CandidateSet);
 
   /// Add function candidates found via argument-dependent lookup
   /// to the set of overloading candidates.
   ///
   /// This routine performs argument-dependent name lookup based on the
   /// given function name (which may also be an operator name) and adds
   /// all of the overload candidates found by ADL to the overload
   /// candidate set (C++ [basic.lookup.argdep]).
   void AddArgumentDependentLookupCandidates(
       DeclarationName Name, SourceLocation Loc, ArrayRef<Expr *> Args,
       TemplateArgumentListInfo *ExplicitTemplateArgs,
       OverloadCandidateSet &CandidateSet, bool PartialOverloading = false);
 
   /// Check the enable_if expressions on the given function. Returns the first
   /// failing attribute, or NULL if they were all successful.
   EnableIfAttr *CheckEnableIf(FunctionDecl *Function, SourceLocation CallLoc,
                               ArrayRef<Expr *> Args,
                               bool MissingImplicitThis = false);
 
   /// Emit diagnostics for the diagnose_if attributes on Function, ignoring any
   /// non-ArgDependent DiagnoseIfAttrs.
   ///
   /// Argument-dependent diagnose_if attributes should be checked each time a
   /// function is used as a direct callee of a function call.
   ///
   /// Returns true if any errors were emitted.
   bool diagnoseArgDependentDiagnoseIfAttrs(const FunctionDecl *Function,
                                            const Expr *ThisArg,
                                            ArrayRef<const Expr *> Args,
                                            SourceLocation Loc);
 
   /// Emit diagnostics for the diagnose_if attributes on Function, ignoring any
   /// ArgDependent DiagnoseIfAttrs.
   ///
   /// Argument-independent diagnose_if attributes should be checked on every use
   /// of a function.
   ///
   /// Returns true if any errors were emitted.
   bool diagnoseArgIndependentDiagnoseIfAttrs(const NamedDecl *ND,
                                              SourceLocation Loc);
 
   /// Determine if \p A and \p B are equivalent internal linkage declarations
   /// from different modules, and thus an ambiguity error can be downgraded to
   /// an extension warning.
   bool isEquivalentInternalLinkageDeclaration(const NamedDecl *A,
                                               const NamedDecl *B);
   void diagnoseEquivalentInternalLinkageDeclarations(
       SourceLocation Loc, const NamedDecl *D,
       ArrayRef<const NamedDecl *> Equiv);
 
   // Emit as a 'note' the specific overload candidate
   void NoteOverloadCandidate(
       const NamedDecl *Found, const FunctionDecl *Fn,
       OverloadCandidateRewriteKind RewriteKind = OverloadCandidateRewriteKind(),
       QualType DestType = QualType(), bool TakingAddress = false);
 
   // Emit as a series of 'note's all template and non-templates identified by
   // the expression Expr
   void NoteAllOverloadCandidates(Expr *E, QualType DestType = QualType(),
                                  bool TakingAddress = false);
 
   /// Returns whether the given function's address can be taken or not,
   /// optionally emitting a diagnostic if the address can't be taken.
   ///
   /// Returns false if taking the address of the function is illegal.
   bool checkAddressOfFunctionIsAvailable(const FunctionDecl *Function,
                                          bool Complain = false,
                                          SourceLocation Loc = SourceLocation());
 
   // [PossiblyAFunctionType]  -->   [Return]
   // NonFunctionType --> NonFunctionType
   // R (A) --> R(A)
   // R (*)(A) --> R (A)
   // R (&)(A) --> R (A)
   // R (S::*)(A) --> R (A)
   QualType ExtractUnqualifiedFunctionType(QualType PossiblyAFunctionType);
 
   /// ResolveAddressOfOverloadedFunction - Try to resolve the address of
   /// an overloaded function (C++ [over.over]), where @p From is an
   /// expression with overloaded function type and @p ToType is the type
   /// we're trying to resolve to. For example:
   ///
   /// @code
   /// int f(double);
   /// int f(int);
   ///
   /// int (*pfd)(double) = f; // selects f(double)
   /// @endcode
   ///
   /// This routine returns the resulting FunctionDecl if it could be
   /// resolved, and NULL otherwise. When @p Complain is true, this
   /// routine will emit diagnostics if there is an error.
   FunctionDecl *
   ResolveAddressOfOverloadedFunction(Expr *AddressOfExpr, QualType TargetType,
                                      bool Complain, DeclAccessPair &Found,
                                      bool *pHadMultipleCandidates = nullptr);
 
   /// Given an expression that refers to an overloaded function, try to
   /// resolve that function to a single function that can have its address
   /// taken. This will modify `Pair` iff it returns non-null.
   ///
   /// This routine can only succeed if from all of the candidates in the
   /// overload set for SrcExpr that can have their addresses taken, there is one
   /// candidate that is more constrained than the rest.
   FunctionDecl *
   resolveAddressOfSingleOverloadCandidate(Expr *E, DeclAccessPair &FoundResult);
 
   /// Given an overloaded function, tries to turn it into a non-overloaded
   /// function reference using resolveAddressOfSingleOverloadCandidate. This
   /// will perform access checks, diagnose the use of the resultant decl, and,
   /// if requested, potentially perform a function-to-pointer decay.
   ///
   /// Returns false if resolveAddressOfSingleOverloadCandidate fails.
   /// Otherwise, returns true. This may emit diagnostics and return true.
   bool resolveAndFixAddressOfSingleOverloadCandidate(
       ExprResult &SrcExpr, bool DoFunctionPointerConversion = false);
 
   /// Given an expression that refers to an overloaded function, try to
   /// resolve that overloaded function expression down to a single function.
   ///
   /// This routine can only resolve template-ids that refer to a single function
   /// template, where that template-id refers to a single template whose
   /// template arguments are either provided by the template-id or have
   /// defaults, as described in C++0x [temp.arg.explicit]p3.
   ///
   /// If no template-ids are found, no diagnostics are emitted and NULL is
   /// returned.
   FunctionDecl *ResolveSingleFunctionTemplateSpecialization(
       OverloadExpr *ovl, bool Complain = false, DeclAccessPair *Found = nullptr,
       TemplateSpecCandidateSet *FailedTSC = nullptr);
 
   // Resolve and fix an overloaded expression that can be resolved
   // because it identifies a single function template specialization.
   //
   // Last three arguments should only be supplied if Complain = true
   //
   // Return true if it was logically possible to so resolve the
   // expression, regardless of whether or not it succeeded.  Always
   // returns true if 'complain' is set.
   bool ResolveAndFixSingleFunctionTemplateSpecialization(
       ExprResult &SrcExpr, bool DoFunctionPointerConversion = false,
       bool Complain = false, SourceRange OpRangeForComplaining = SourceRange(),
       QualType DestTypeForComplaining = QualType(),
       unsigned DiagIDForComplaining = 0);
 
   /// Add the overload candidates named by callee and/or found by argument
   /// dependent lookup to the given overload set.
   void AddOverloadedCallCandidates(UnresolvedLookupExpr *ULE,
                                    ArrayRef<Expr *> Args,
                                    OverloadCandidateSet &CandidateSet,
                                    bool PartialOverloading = false);
 
   /// Add the call candidates from the given set of lookup results to the given
   /// overload set. Non-function lookup results are ignored.
   void AddOverloadedCallCandidates(
       LookupResult &R, TemplateArgumentListInfo *ExplicitTemplateArgs,
       ArrayRef<Expr *> Args, OverloadCandidateSet &CandidateSet);
 
   // An enum used to represent the different possible results of building a
   // range-based for loop.
   enum ForRangeStatus {
     FRS_Success,
     FRS_NoViableFunction,
     FRS_DiagnosticIssued
   };
 
   /// Build a call to 'begin' or 'end' for a C++11 for-range statement. If the
   /// given LookupResult is non-empty, it is assumed to describe a member which
   /// will be invoked. Otherwise, the function will be found via argument
   /// dependent lookup.
   /// CallExpr is set to a valid expression and FRS_Success returned on success,
   /// otherwise CallExpr is set to ExprError() and some non-success value
   /// is returned.
   ForRangeStatus BuildForRangeBeginEndCall(SourceLocation Loc,
                                            SourceLocation RangeLoc,
                                            const DeclarationNameInfo &NameInfo,
                                            LookupResult &MemberLookup,
                                            OverloadCandidateSet *CandidateSet,
                                            Expr *Range, ExprResult *CallExpr);
 
   /// BuildOverloadedCallExpr - Given the call expression that calls Fn
   /// (which eventually refers to the declaration Func) and the call
   /// arguments Args/NumArgs, attempt to resolve the function call down
   /// to a specific function. If overload resolution succeeds, returns
   /// the call expression produced by overload resolution.
   /// Otherwise, emits diagnostics and returns ExprError.
   ExprResult BuildOverloadedCallExpr(
       Scope *S, Expr *Fn, UnresolvedLookupExpr *ULE, SourceLocation LParenLoc,
       MultiExprArg Args, SourceLocation RParenLoc, Expr *ExecConfig,
       bool AllowTypoCorrection = true, bool CalleesAddressIsTaken = false);
 
   /// Constructs and populates an OverloadedCandidateSet from
   /// the given function.
   /// \returns true when an the ExprResult output parameter has been set.
   bool buildOverloadedCallSet(Scope *S, Expr *Fn, UnresolvedLookupExpr *ULE,
                               MultiExprArg Args, SourceLocation RParenLoc,
                               OverloadCandidateSet *CandidateSet,
                               ExprResult *Result);
 
   ExprResult CreateUnresolvedLookupExpr(CXXRecordDecl *NamingClass,
                                         NestedNameSpecifierLoc NNSLoc,
                                         DeclarationNameInfo DNI,
                                         const UnresolvedSetImpl &Fns,
                                         bool PerformADL = true);
 
   /// Create a unary operation that may resolve to an overloaded
   /// operator.
   ///
   /// \param OpLoc The location of the operator itself (e.g., '*').
   ///
   /// \param Opc The UnaryOperatorKind that describes this operator.
   ///
   /// \param Fns The set of non-member functions that will be
   /// considered by overload resolution. The caller needs to build this
   /// set based on the context using, e.g.,
   /// LookupOverloadedOperatorName() and ArgumentDependentLookup(). This
   /// set should not contain any member functions; those will be added
   /// by CreateOverloadedUnaryOp().
   ///
   /// \param Input The input argument.
   ExprResult CreateOverloadedUnaryOp(SourceLocation OpLoc,
                                      UnaryOperatorKind Opc,
                                      const UnresolvedSetImpl &Fns, Expr *input,
                                      bool RequiresADL = true);
 
   /// Perform lookup for an overloaded binary operator.
   void LookupOverloadedBinOp(OverloadCandidateSet &CandidateSet,
                              OverloadedOperatorKind Op,
                              const UnresolvedSetImpl &Fns,
                              ArrayRef<Expr *> Args, bool RequiresADL = true);
 
   /// Create a binary operation that may resolve to an overloaded
   /// operator.
   ///
   /// \param OpLoc The location of the operator itself (e.g., '+').
   ///
   /// \param Opc The BinaryOperatorKind that describes this operator.
   ///
   /// \param Fns The set of non-member functions that will be
   /// considered by overload resolution. The caller needs to build this
   /// set based on the context using, e.g.,
   /// LookupOverloadedOperatorName() and ArgumentDependentLookup(). This
   /// set should not contain any member functions; those will be added
   /// by CreateOverloadedBinOp().
   ///
   /// \param LHS Left-hand argument.
   /// \param RHS Right-hand argument.
   /// \param PerformADL Whether to consider operator candidates found by ADL.
   /// \param AllowRewrittenCandidates Whether to consider candidates found by
   ///        C++20 operator rewrites.
   /// \param DefaultedFn If we are synthesizing a defaulted operator function,
   ///        the function in question. Such a function is never a candidate in
   ///        our overload resolution. This also enables synthesizing a three-way
   ///        comparison from < and == as described in C++20 [class.spaceship]p1.
   ExprResult CreateOverloadedBinOp(SourceLocation OpLoc, BinaryOperatorKind Opc,
                                    const UnresolvedSetImpl &Fns, Expr *LHS,
                                    Expr *RHS, bool RequiresADL = true,
                                    bool AllowRewrittenCandidates = true,
                                    FunctionDecl *DefaultedFn = nullptr);
   ExprResult BuildSynthesizedThreeWayComparison(SourceLocation OpLoc,
                                                 const UnresolvedSetImpl &Fns,
                                                 Expr *LHS, Expr *RHS,
                                                 FunctionDecl *DefaultedFn);
 
   ExprResult CreateOverloadedArraySubscriptExpr(SourceLocation LLoc,
                                                 SourceLocation RLoc, Expr *Base,
                                                 MultiExprArg Args);
 
   /// BuildCallToMemberFunction - Build a call to a member
   /// function. MemExpr is the expression that refers to the member
   /// function (and includes the object parameter), Args/NumArgs are the
   /// arguments to the function call (not including the object
   /// parameter). The caller needs to validate that the member
   /// expression refers to a non-static member function or an overloaded
   /// member function.
   ExprResult BuildCallToMemberFunction(
       Scope *S, Expr *MemExpr, SourceLocation LParenLoc, MultiExprArg Args,
       SourceLocation RParenLoc, Expr *ExecConfig = nullptr,
       bool IsExecConfig = false, bool AllowRecovery = false);
 
   /// BuildCallToObjectOfClassType - Build a call to an object of class
   /// type (C++ [over.call.object]), which can end up invoking an
   /// overloaded function call operator (@c operator()) or performing a
   /// user-defined conversion on the object argument.
   ExprResult BuildCallToObjectOfClassType(Scope *S, Expr *Object,
                                           SourceLocation LParenLoc,
                                           MultiExprArg Args,
                                           SourceLocation RParenLoc);
 
   /// BuildOverloadedArrowExpr - Build a call to an overloaded @c operator->
   ///  (if one exists), where @c Base is an expression of class type and
   /// @c Member is the name of the member we're trying to find.
   ExprResult BuildOverloadedArrowExpr(Scope *S, Expr *Base,
                                       SourceLocation OpLoc,
                                       bool *NoArrowOperatorFound = nullptr);
 
   ExprResult BuildCXXMemberCallExpr(Expr *Exp, NamedDecl *FoundDecl,
                                     CXXConversionDecl *Method,
                                     bool HadMultipleCandidates);
 
   /// BuildLiteralOperatorCall - Build a UserDefinedLiteral by creating a call
   /// to a literal operator described by the provided lookup results.
   ExprResult BuildLiteralOperatorCall(
       LookupResult &R, DeclarationNameInfo &SuffixInfo, ArrayRef<Expr *> Args,
       SourceLocation LitEndLoc,
       TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr);
 
   /// FixOverloadedFunctionReference - E is an expression that refers to
   /// a C++ overloaded function (possibly with some parentheses and
   /// perhaps a '&' around it). We have resolved the overloaded function
   /// to the function declaration Fn, so patch up the expression E to
   /// refer (possibly indirectly) to Fn. Returns the new expr.
   ExprResult FixOverloadedFunctionReference(Expr *E, DeclAccessPair FoundDecl,
                                             FunctionDecl *Fn);
   ExprResult FixOverloadedFunctionReference(ExprResult,
                                             DeclAccessPair FoundDecl,
                                             FunctionDecl *Fn);
 
   /// - Returns a selector which best matches given argument list or
   /// nullptr if none could be found
   ObjCMethodDecl *SelectBestMethod(Selector Sel, MultiExprArg Args,
                                    bool IsInstance,
                                    SmallVectorImpl<ObjCMethodDecl *> &Methods);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Statements
   /// Implementations are in SemaStmt.cpp
   ///@{
 
 public:
   /// Stack of active SEH __finally scopes.  Can be empty.
   SmallVector<Scope *, 2> CurrentSEHFinally;
 
   StmtResult ActOnExprStmt(ExprResult Arg, bool DiscardedValue = true);
   StmtResult ActOnExprStmtError();
 
   StmtResult ActOnNullStmt(SourceLocation SemiLoc,
                            bool HasLeadingEmptyMacro = false);
 
   StmtResult ActOnDeclStmt(DeclGroupPtrTy Decl, SourceLocation StartLoc,
                            SourceLocation EndLoc);
   void ActOnForEachDeclStmt(DeclGroupPtrTy Decl);
 
   /// DiagnoseUnusedExprResult - If the statement passed in is an expression
   /// whose result is unused, warn.
   void DiagnoseUnusedExprResult(const Stmt *S, unsigned DiagID);
 
   void ActOnStartOfCompoundStmt(bool IsStmtExpr);
   void ActOnAfterCompoundStatementLeadingPragmas();
   void ActOnFinishOfCompoundStmt();
   StmtResult ActOnCompoundStmt(SourceLocation L, SourceLocation R,
                                ArrayRef<Stmt *> Elts, bool isStmtExpr);
 
   sema::CompoundScopeInfo &getCurCompoundScope() const;
 
   ExprResult ActOnCaseExpr(SourceLocation CaseLoc, ExprResult Val);
   StmtResult ActOnCaseStmt(SourceLocation CaseLoc, ExprResult LHS,
                            SourceLocation DotDotDotLoc, ExprResult RHS,
                            SourceLocation ColonLoc);
 
   /// ActOnCaseStmtBody - This installs a statement as the body of a case.
   void ActOnCaseStmtBody(Stmt *CaseStmt, Stmt *SubStmt);
 
   StmtResult ActOnDefaultStmt(SourceLocation DefaultLoc,
                               SourceLocation ColonLoc, Stmt *SubStmt,
                               Scope *CurScope);
   StmtResult ActOnLabelStmt(SourceLocation IdentLoc, LabelDecl *TheDecl,
                             SourceLocation ColonLoc, Stmt *SubStmt);
 
   StmtResult BuildAttributedStmt(SourceLocation AttrsLoc,
                                  ArrayRef<const Attr *> Attrs, Stmt *SubStmt);
   StmtResult ActOnAttributedStmt(const ParsedAttributes &AttrList,
                                  Stmt *SubStmt);
 
   /// Check whether the given statement can have musttail applied to it,
   /// issuing a diagnostic and returning false if not. In the success case,
   /// the statement is rewritten to remove implicit nodes from the return
   /// value.
   bool checkAndRewriteMustTailAttr(Stmt *St, const Attr &MTA);
 
   StmtResult ActOnIfStmt(SourceLocation IfLoc, IfStatementKind StatementKind,
                          SourceLocation LParenLoc, Stmt *InitStmt,
                          ConditionResult Cond, SourceLocation RParenLoc,
                          Stmt *ThenVal, SourceLocation ElseLoc, Stmt *ElseVal);
   StmtResult BuildIfStmt(SourceLocation IfLoc, IfStatementKind StatementKind,
                          SourceLocation LParenLoc, Stmt *InitStmt,
                          ConditionResult Cond, SourceLocation RParenLoc,
                          Stmt *ThenVal, SourceLocation ElseLoc, Stmt *ElseVal);
 
   ExprResult CheckSwitchCondition(SourceLocation SwitchLoc, Expr *Cond);
 
   StmtResult ActOnStartOfSwitchStmt(SourceLocation SwitchLoc,
                                     SourceLocation LParenLoc, Stmt *InitStmt,
                                     ConditionResult Cond,
                                     SourceLocation RParenLoc);
   StmtResult ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
                                    Stmt *Body);
 
   /// DiagnoseAssignmentEnum - Warn if assignment to enum is a constant
   /// integer not in the range of enum values.
   void DiagnoseAssignmentEnum(QualType DstType, QualType SrcType,
                               Expr *SrcExpr);
 
   StmtResult ActOnWhileStmt(SourceLocation WhileLoc, SourceLocation LParenLoc,
                             ConditionResult Cond, SourceLocation RParenLoc,
                             Stmt *Body);
   StmtResult ActOnDoStmt(SourceLocation DoLoc, Stmt *Body,
                          SourceLocation WhileLoc, SourceLocation CondLParen,
                          Expr *Cond, SourceLocation CondRParen);
 
   StmtResult ActOnForStmt(SourceLocation ForLoc, SourceLocation LParenLoc,
                           Stmt *First, ConditionResult Second,
                           FullExprArg Third, SourceLocation RParenLoc,
                           Stmt *Body);
 
   /// In an Objective C collection iteration statement:
   ///   for (x in y)
   /// x can be an arbitrary l-value expression.  Bind it up as a
   /// full-expression.
   StmtResult ActOnForEachLValueExpr(Expr *E);
 
   enum BuildForRangeKind {
     /// Initial building of a for-range statement.
     BFRK_Build,
     /// Instantiation or recovery rebuild of a for-range statement. Don't
     /// attempt any typo-correction.
     BFRK_Rebuild,
     /// Determining whether a for-range statement could be built. Avoid any
     /// unnecessary or irreversible actions.
     BFRK_Check
   };
 
   /// ActOnCXXForRangeStmt - Check and build a C++11 for-range statement.
   ///
   /// C++11 [stmt.ranged]:
   ///   A range-based for statement is equivalent to
   ///
   ///   {
   ///     auto && __range = range-init;
   ///     for ( auto __begin = begin-expr,
   ///           __end = end-expr;
   ///           __begin != __end;
   ///           ++__begin ) {
   ///       for-range-declaration = *__begin;
   ///       statement
   ///     }
   ///   }
   ///
   /// The body of the loop is not available yet, since it cannot be analysed
   /// until we have determined the type of the for-range-declaration.
   StmtResult ActOnCXXForRangeStmt(
       Scope *S, SourceLocation ForLoc, SourceLocation CoawaitLoc,
       Stmt *InitStmt, Stmt *LoopVar, SourceLocation ColonLoc, Expr *Collection,
       SourceLocation RParenLoc, BuildForRangeKind Kind,
       ArrayRef<MaterializeTemporaryExpr *> LifetimeExtendTemps = {});
 
   /// BuildCXXForRangeStmt - Build or instantiate a C++11 for-range statement.
   StmtResult BuildCXXForRangeStmt(
       SourceLocation ForLoc, SourceLocation CoawaitLoc, Stmt *InitStmt,
       SourceLocation ColonLoc, Stmt *RangeDecl, Stmt *Begin, Stmt *End,
       Expr *Cond, Expr *Inc, Stmt *LoopVarDecl, SourceLocation RParenLoc,
       BuildForRangeKind Kind,
       ArrayRef<MaterializeTemporaryExpr *> LifetimeExtendTemps = {});
 
   /// FinishCXXForRangeStmt - Attach the body to a C++0x for-range statement.
   /// This is a separate step from ActOnCXXForRangeStmt because analysis of the
   /// body cannot be performed until after the type of the range variable is
   /// determined.
   StmtResult FinishCXXForRangeStmt(Stmt *ForRange, Stmt *Body);
 
   StmtResult ActOnGotoStmt(SourceLocation GotoLoc, SourceLocation LabelLoc,
                            LabelDecl *TheDecl);
   StmtResult ActOnIndirectGotoStmt(SourceLocation GotoLoc,
                                    SourceLocation StarLoc, Expr *DestExp);
   StmtResult ActOnContinueStmt(SourceLocation ContinueLoc, Scope *CurScope);
   StmtResult ActOnBreakStmt(SourceLocation BreakLoc, Scope *CurScope);
 
   struct NamedReturnInfo {
     const VarDecl *Candidate;
 
     enum Status : uint8_t { None, MoveEligible, MoveEligibleAndCopyElidable };
     Status S;
 
     bool isMoveEligible() const { return S != None; };
     bool isCopyElidable() const { return S == MoveEligibleAndCopyElidable; }
   };
   enum class SimplerImplicitMoveMode { ForceOff, Normal, ForceOn };
 
   /// Determine whether the given expression might be move-eligible or
   /// copy-elidable in either a (co_)return statement or throw expression,
   /// without considering function return type, if applicable.
   ///
   /// \param E The expression being returned from the function or block,
   /// being thrown, or being co_returned from a coroutine. This expression
   /// might be modified by the implementation.
   ///
   /// \param Mode Overrides detection of current language mode
   /// and uses the rules for C++23.
   ///
   /// \returns An aggregate which contains the Candidate and isMoveEligible
   /// and isCopyElidable methods. If Candidate is non-null, it means
   /// isMoveEligible() would be true under the most permissive language
   /// standard.
   NamedReturnInfo getNamedReturnInfo(
       Expr *&E, SimplerImplicitMoveMode Mode = SimplerImplicitMoveMode::Normal);
 
   /// Determine whether the given NRVO candidate variable is move-eligible or
   /// copy-elidable, without considering function return type.
   ///
   /// \param VD The NRVO candidate variable.
   ///
   /// \returns An aggregate which contains the Candidate and isMoveEligible
   /// and isCopyElidable methods. If Candidate is non-null, it means
   /// isMoveEligible() would be true under the most permissive language
   /// standard.
   NamedReturnInfo getNamedReturnInfo(const VarDecl *VD);
 
   /// Updates given NamedReturnInfo's move-eligible and
   /// copy-elidable statuses, considering the function
   /// return type criteria as applicable to return statements.
   ///
   /// \param Info The NamedReturnInfo object to update.
   ///
   /// \param ReturnType This is the return type of the function.
   /// \returns The copy elision candidate, in case the initial return expression
   /// was copy elidable, or nullptr otherwise.
   const VarDecl *getCopyElisionCandidate(NamedReturnInfo &Info,
                                          QualType ReturnType);
 
   /// Perform the initialization of a potentially-movable value, which
   /// is the result of return value.
   ///
   /// This routine implements C++20 [class.copy.elision]p3, which attempts to
   /// treat returned lvalues as rvalues in certain cases (to prefer move
   /// construction), then falls back to treating them as lvalues if that failed.
   ExprResult
   PerformMoveOrCopyInitialization(const InitializedEntity &Entity,
                                   const NamedReturnInfo &NRInfo, Expr *Value,
                                   bool SupressSimplerImplicitMoves = false);
 
   TypeLoc getReturnTypeLoc(FunctionDecl *FD) const;
 
   /// Deduce the return type for a function from a returned expression, per
   /// C++1y [dcl.spec.auto]p6.
   bool DeduceFunctionTypeFromReturnExpr(FunctionDecl *FD,
                                         SourceLocation ReturnLoc, Expr *RetExpr,
                                         const AutoType *AT);
 
   StmtResult ActOnReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
                              Scope *CurScope);
   StmtResult BuildReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
                              bool AllowRecovery = false);
 
   /// ActOnCapScopeReturnStmt - Utility routine to type-check return statements
   /// for capturing scopes.
   StmtResult ActOnCapScopeReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
                                      NamedReturnInfo &NRInfo,
                                      bool SupressSimplerImplicitMoves);
 
   /// ActOnCXXCatchBlock - Takes an exception declaration and a handler block
   /// and creates a proper catch handler from them.
   StmtResult ActOnCXXCatchBlock(SourceLocation CatchLoc, Decl *ExDecl,
                                 Stmt *HandlerBlock);
 
   /// ActOnCXXTryBlock - Takes a try compound-statement and a number of
   /// handlers and creates a try statement from them.
   StmtResult ActOnCXXTryBlock(SourceLocation TryLoc, Stmt *TryBlock,
                               ArrayRef<Stmt *> Handlers);
 
   StmtResult ActOnSEHTryBlock(bool IsCXXTry, // try (true) or __try (false) ?
                               SourceLocation TryLoc, Stmt *TryBlock,
                               Stmt *Handler);
   StmtResult ActOnSEHExceptBlock(SourceLocation Loc, Expr *FilterExpr,
                                  Stmt *Block);
   void ActOnStartSEHFinallyBlock();
   void ActOnAbortSEHFinallyBlock();
   StmtResult ActOnFinishSEHFinallyBlock(SourceLocation Loc, Stmt *Block);
   StmtResult ActOnSEHLeaveStmt(SourceLocation Loc, Scope *CurScope);
 
   StmtResult BuildMSDependentExistsStmt(SourceLocation KeywordLoc,
                                         bool IsIfExists,
                                         NestedNameSpecifierLoc QualifierLoc,
                                         DeclarationNameInfo NameInfo,
                                         Stmt *Nested);
   StmtResult ActOnMSDependentExistsStmt(SourceLocation KeywordLoc,
                                         bool IsIfExists, CXXScopeSpec &SS,
                                         UnqualifiedId &Name, Stmt *Nested);
 
   void ActOnCapturedRegionStart(SourceLocation Loc, Scope *CurScope,
                                 CapturedRegionKind Kind, unsigned NumParams);
   typedef std::pair<StringRef, QualType> CapturedParamNameType;
   void ActOnCapturedRegionStart(SourceLocation Loc, Scope *CurScope,
                                 CapturedRegionKind Kind,
                                 ArrayRef<CapturedParamNameType> Params,
                                 unsigned OpenMPCaptureLevel = 0);
   StmtResult ActOnCapturedRegionEnd(Stmt *S);
   void ActOnCapturedRegionError();
   RecordDecl *CreateCapturedStmtRecordDecl(CapturedDecl *&CD,
                                            SourceLocation Loc,
                                            unsigned NumParams);
 
 private:
   /// Check whether the given statement can have musttail applied to it,
   /// issuing a diagnostic and returning false if not.
   bool checkMustTailAttr(const Stmt *St, const Attr &MTA);
 
   /// Check if the given expression contains 'break' or 'continue'
   /// statement that produces control flow different from GCC.
   void CheckBreakContinueBinding(Expr *E);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name `inline asm` Statement
   /// Implementations are in SemaStmtAsm.cpp
   ///@{
 
 public:
   StmtResult ActOnGCCAsmStmt(SourceLocation AsmLoc, bool IsSimple,
                              bool IsVolatile, unsigned NumOutputs,
                              unsigned NumInputs, IdentifierInfo **Names,
                              MultiExprArg Constraints, MultiExprArg Exprs,
                              Expr *AsmString, MultiExprArg Clobbers,
                              unsigned NumLabels, SourceLocation RParenLoc);
 
   void FillInlineAsmIdentifierInfo(Expr *Res,
                                    llvm::InlineAsmIdentifierInfo &Info);
   ExprResult LookupInlineAsmIdentifier(CXXScopeSpec &SS,
                                        SourceLocation TemplateKWLoc,
                                        UnqualifiedId &Id,
                                        bool IsUnevaluatedContext);
   bool LookupInlineAsmField(StringRef Base, StringRef Member, unsigned &Offset,
                             SourceLocation AsmLoc);
   ExprResult LookupInlineAsmVarDeclField(Expr *RefExpr, StringRef Member,
                                          SourceLocation AsmLoc);
   StmtResult ActOnMSAsmStmt(SourceLocation AsmLoc, SourceLocation LBraceLoc,
                             ArrayRef<Token> AsmToks, StringRef AsmString,
                             unsigned NumOutputs, unsigned NumInputs,
                             ArrayRef<StringRef> Constraints,
                             ArrayRef<StringRef> Clobbers,
                             ArrayRef<Expr *> Exprs, SourceLocation EndLoc);
   LabelDecl *GetOrCreateMSAsmLabel(StringRef ExternalLabelName,
                                    SourceLocation Location, bool AlwaysCreate);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Statement Attribute Handling
   /// Implementations are in SemaStmtAttr.cpp
   ///@{
 
 public:
   bool CheckNoInlineAttr(const Stmt *OrigSt, const Stmt *CurSt,
                          const AttributeCommonInfo &A);
   bool CheckAlwaysInlineAttr(const Stmt *OrigSt, const Stmt *CurSt,
                              const AttributeCommonInfo &A);
 
   CodeAlignAttr *BuildCodeAlignAttr(const AttributeCommonInfo &CI, Expr *E);
   bool CheckRebuiltStmtAttributes(ArrayRef<const Attr *> Attrs);
 
   /// Process the attributes before creating an attributed statement. Returns
   /// the semantic attributes that have been processed.
   void ProcessStmtAttributes(Stmt *Stmt, const ParsedAttributes &InAttrs,
                              SmallVectorImpl<const Attr *> &OutAttrs);
 
   ExprResult ActOnCXXAssumeAttr(Stmt *St, const ParsedAttr &A,
                                 SourceRange Range);
   ExprResult BuildCXXAssumeExpr(Expr *Assumption,
                                 const IdentifierInfo *AttrName,
                                 SourceRange Range);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Templates
   /// Implementations are in SemaTemplate.cpp
   ///@{
 
 public:
   // Saves the current floating-point pragma stack and clear it in this Sema.
   class FpPragmaStackSaveRAII {
   public:
     FpPragmaStackSaveRAII(Sema &S)
         : S(S), SavedStack(std::move(S.FpPragmaStack)) {
       S.FpPragmaStack.Stack.clear();
     }
     ~FpPragmaStackSaveRAII() { S.FpPragmaStack = std::move(SavedStack); }
 
   private:
     Sema &S;
     PragmaStack<FPOptionsOverride> SavedStack;
   };
 
   void resetFPOptions(FPOptions FPO) {
     CurFPFeatures = FPO;
     FpPragmaStack.CurrentValue = FPO.getChangesFrom(FPOptions(LangOpts));
   }
 
   ArrayRef<InventedTemplateParameterInfo> getInventedParameterInfos() const {
     return llvm::ArrayRef(InventedParameterInfos.begin() +
                               InventedParameterInfosStart,
                           InventedParameterInfos.end());
   }
 
   /// The number of SFINAE diagnostics that have been trapped.
   unsigned NumSFINAEErrors;
 
   ArrayRef<sema::FunctionScopeInfo *> getFunctionScopes() const {
     return llvm::ArrayRef(FunctionScopes.begin() + FunctionScopesStart,
                           FunctionScopes.end());
   }
 
   typedef llvm::MapVector<const FunctionDecl *,
                           std::unique_ptr<LateParsedTemplate>>
       LateParsedTemplateMapT;
   LateParsedTemplateMapT LateParsedTemplateMap;
 
   /// Determine the number of levels of enclosing template parameters. This is
   /// only usable while parsing. Note that this does not include dependent
   /// contexts in which no template parameters have yet been declared, such as
   /// in a terse function template or generic lambda before the first 'auto' is
   /// encountered.
   unsigned getTemplateDepth(Scope *S) const;
 
   void FilterAcceptableTemplateNames(LookupResult &R,
                                      bool AllowFunctionTemplates = true,
                                      bool AllowDependent = true);
   bool hasAnyAcceptableTemplateNames(LookupResult &R,
                                      bool AllowFunctionTemplates = true,
                                      bool AllowDependent = true,
                                      bool AllowNonTemplateFunctions = false);
   /// Try to interpret the lookup result D as a template-name.
   ///
   /// \param D A declaration found by name lookup.
   /// \param AllowFunctionTemplates Whether function templates should be
   ///        considered valid results.
   /// \param AllowDependent Whether unresolved using declarations (that might
   ///        name templates) should be considered valid results.
   static NamedDecl *getAsTemplateNameDecl(NamedDecl *D,
                                           bool AllowFunctionTemplates = true,
                                           bool AllowDependent = true);
 
   enum TemplateNameIsRequiredTag { TemplateNameIsRequired };
   /// Whether and why a template name is required in this lookup.
   class RequiredTemplateKind {
   public:
     /// Template name is required if TemplateKWLoc is valid.
     RequiredTemplateKind(SourceLocation TemplateKWLoc = SourceLocation())
         : TemplateKW(TemplateKWLoc) {}
     /// Template name is unconditionally required.
     RequiredTemplateKind(TemplateNameIsRequiredTag) {}
 
     SourceLocation getTemplateKeywordLoc() const {
       return TemplateKW.value_or(SourceLocation());
     }
     bool hasTemplateKeyword() const {
       return getTemplateKeywordLoc().isValid();
     }
     bool isRequired() const { return TemplateKW != SourceLocation(); }
     explicit operator bool() const { return isRequired(); }
 
   private:
     std::optional<SourceLocation> TemplateKW;
   };
 
   enum class AssumedTemplateKind {
     /// This is not assumed to be a template name.
     None,
     /// This is assumed to be a template name because lookup found nothing.
     FoundNothing,
     /// This is assumed to be a template name because lookup found one or more
     /// functions (but no function templates).
     FoundFunctions,
   };
 
   bool
   LookupTemplateName(LookupResult &R, Scope *S, CXXScopeSpec &SS,
                      QualType ObjectType, bool EnteringContext,
                      RequiredTemplateKind RequiredTemplate = SourceLocation(),
                      AssumedTemplateKind *ATK = nullptr,
                      bool AllowTypoCorrection = true);
 
   TemplateNameKind isTemplateName(Scope *S, CXXScopeSpec &SS,
                                   bool hasTemplateKeyword,
                                   const UnqualifiedId &Name,
                                   ParsedType ObjectType, bool EnteringContext,
                                   TemplateTy &Template,
                                   bool &MemberOfUnknownSpecialization,
                                   bool Disambiguation = false);
 
   /// Try to resolve an undeclared template name as a type template.
   ///
   /// Sets II to the identifier corresponding to the template name, and updates
   /// Name to a corresponding (typo-corrected) type template name and TNK to
   /// the corresponding kind, if possible.
   void ActOnUndeclaredTypeTemplateName(Scope *S, TemplateTy &Name,
                                        TemplateNameKind &TNK,
                                        SourceLocation NameLoc,
                                        IdentifierInfo *&II);
 
   bool resolveAssumedTemplateNameAsType(Scope *S, TemplateName &Name,
                                         SourceLocation NameLoc,
                                         bool Diagnose = true);
 
   /// Determine whether a particular identifier might be the name in a C++1z
   /// deduction-guide declaration.
   bool isDeductionGuideName(Scope *S, const IdentifierInfo &Name,
                             SourceLocation NameLoc, CXXScopeSpec &SS,
                             ParsedTemplateTy *Template = nullptr);
 
   bool DiagnoseUnknownTemplateName(const IdentifierInfo &II,
                                    SourceLocation IILoc, Scope *S,
                                    const CXXScopeSpec *SS,
                                    TemplateTy &SuggestedTemplate,
                                    TemplateNameKind &SuggestedKind);
 
   /// Determine whether we would be unable to instantiate this template (because
   /// it either has no definition, or is in the process of being instantiated).
   bool DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
                                       NamedDecl *Instantiation,
                                       bool InstantiatedFromMember,
                                       const NamedDecl *Pattern,
                                       const NamedDecl *PatternDef,
                                       TemplateSpecializationKind TSK,
                                       bool Complain = true);
 
   /// DiagnoseTemplateParameterShadow - Produce a diagnostic complaining
   /// that the template parameter 'PrevDecl' is being shadowed by a new
   /// declaration at location Loc. Returns true to indicate that this is
   /// an error, and false otherwise.
   ///
   /// \param Loc The location of the declaration that shadows a template
   ///            parameter.
   ///
   /// \param PrevDecl The template parameter that the declaration shadows.
   ///
   /// \param SupportedForCompatibility Whether to issue the diagnostic as
   ///        a warning for compatibility with older versions of clang.
   ///        Ignored when MSVC compatibility is enabled.
   void DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl,
                                        bool SupportedForCompatibility = false);
 
   /// AdjustDeclIfTemplate - If the given decl happens to be a template, reset
   /// the parameter D to reference the templated declaration and return a
   /// pointer to the template declaration. Otherwise, do nothing to D and return
   /// null.
   TemplateDecl *AdjustDeclIfTemplate(Decl *&Decl);
 
   /// ActOnTypeParameter - Called when a C++ template type parameter
   /// (e.g., "typename T") has been parsed. Typename specifies whether
   /// the keyword "typename" was used to declare the type parameter
   /// (otherwise, "class" was used), and KeyLoc is the location of the
   /// "class" or "typename" keyword. ParamName is the name of the
   /// parameter (NULL indicates an unnamed template parameter) and
   /// ParamNameLoc is the location of the parameter name (if any).
   /// If the type parameter has a default argument, it will be added
   /// later via ActOnTypeParameterDefault.
   NamedDecl *ActOnTypeParameter(Scope *S, bool Typename,
                                 SourceLocation EllipsisLoc,
                                 SourceLocation KeyLoc,
                                 IdentifierInfo *ParamName,
                                 SourceLocation ParamNameLoc, unsigned Depth,
                                 unsigned Position, SourceLocation EqualLoc,
                                 ParsedType DefaultArg, bool HasTypeConstraint);
 
   bool CheckTypeConstraint(TemplateIdAnnotation *TypeConstraint);
 
   bool ActOnTypeConstraint(const CXXScopeSpec &SS,
                            TemplateIdAnnotation *TypeConstraint,
                            TemplateTypeParmDecl *ConstrainedParameter,
                            SourceLocation EllipsisLoc);
   bool BuildTypeConstraint(const CXXScopeSpec &SS,
                            TemplateIdAnnotation *TypeConstraint,
                            TemplateTypeParmDecl *ConstrainedParameter,
                            SourceLocation EllipsisLoc,
                            bool AllowUnexpandedPack);
 
   /// Attach a type-constraint to a template parameter.
   /// \returns true if an error occurred. This can happen if the
   /// immediately-declared constraint could not be formed (e.g. incorrect number
   /// of arguments for the named concept).
   bool AttachTypeConstraint(NestedNameSpecifierLoc NS,
                             DeclarationNameInfo NameInfo,
                             ConceptDecl *NamedConcept, NamedDecl *FoundDecl,
                             const TemplateArgumentListInfo *TemplateArgs,
                             TemplateTypeParmDecl *ConstrainedParameter,
                             SourceLocation EllipsisLoc);
 
   bool AttachTypeConstraint(AutoTypeLoc TL,
                             NonTypeTemplateParmDecl *NewConstrainedParm,
                             NonTypeTemplateParmDecl *OrigConstrainedParm,
                             SourceLocation EllipsisLoc);
 
   /// Require the given type to be a structural type, and diagnose if it is not.
   ///
   /// \return \c true if an error was produced.
   bool RequireStructuralType(QualType T, SourceLocation Loc);
 
   /// Check that the type of a non-type template parameter is
   /// well-formed.
   ///
   /// \returns the (possibly-promoted) parameter type if valid;
   /// otherwise, produces a diagnostic and returns a NULL type.
   QualType CheckNonTypeTemplateParameterType(TypeSourceInfo *&TSI,
                                              SourceLocation Loc);
   QualType CheckNonTypeTemplateParameterType(QualType T, SourceLocation Loc);
 
   NamedDecl *ActOnNonTypeTemplateParameter(Scope *S, Declarator &D,
                                            unsigned Depth, unsigned Position,
                                            SourceLocation EqualLoc,
                                            Expr *DefaultArg);
 
   /// ActOnTemplateTemplateParameter - Called when a C++ template template
   /// parameter (e.g. T in template <template \<typename> class T> class array)
   /// has been parsed. S is the current scope.
   NamedDecl *ActOnTemplateTemplateParameter(
       Scope *S, SourceLocation TmpLoc, TemplateParameterList *Params,
       bool Typename, SourceLocation EllipsisLoc, IdentifierInfo *ParamName,
       SourceLocation ParamNameLoc, unsigned Depth, unsigned Position,
       SourceLocation EqualLoc, ParsedTemplateArgument DefaultArg);
 
   /// ActOnTemplateParameterList - Builds a TemplateParameterList, optionally
   /// constrained by RequiresClause, that contains the template parameters in
   /// Params.
   TemplateParameterList *ActOnTemplateParameterList(
       unsigned Depth, SourceLocation ExportLoc, SourceLocation TemplateLoc,
       SourceLocation LAngleLoc, ArrayRef<NamedDecl *> Params,
       SourceLocation RAngleLoc, Expr *RequiresClause);
 
   /// The context in which we are checking a template parameter list.
   enum TemplateParamListContext {
     TPC_ClassTemplate,
     TPC_VarTemplate,
     TPC_FunctionTemplate,
     TPC_ClassTemplateMember,
     TPC_FriendClassTemplate,
     TPC_FriendFunctionTemplate,
     TPC_FriendFunctionTemplateDefinition,
     TPC_TypeAliasTemplate
   };
 
   /// Checks the validity of a template parameter list, possibly
   /// considering the template parameter list from a previous
   /// declaration.
   ///
   /// If an "old" template parameter list is provided, it must be
   /// equivalent (per TemplateParameterListsAreEqual) to the "new"
   /// template parameter list.
   ///
   /// \param NewParams Template parameter list for a new template
   /// declaration. This template parameter list will be updated with any
   /// default arguments that are carried through from the previous
   /// template parameter list.
   ///
   /// \param OldParams If provided, template parameter list from a
   /// previous declaration of the same template. Default template
   /// arguments will be merged from the old template parameter list to
   /// the new template parameter list.
   ///
   /// \param TPC Describes the context in which we are checking the given
   /// template parameter list.
   ///
   /// \param SkipBody If we might have already made a prior merged definition
   /// of this template visible, the corresponding body-skipping information.
   /// Default argument redefinition is not an error when skipping such a body,
   /// because (under the ODR) we can assume the default arguments are the same
   /// as the prior merged definition.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CheckTemplateParameterList(TemplateParameterList *NewParams,
                                   TemplateParameterList *OldParams,
                                   TemplateParamListContext TPC,
                                   SkipBodyInfo *SkipBody = nullptr);
 
   /// Match the given template parameter lists to the given scope
   /// specifier, returning the template parameter list that applies to the
   /// name.
   ///
   /// \param DeclStartLoc the start of the declaration that has a scope
   /// specifier or a template parameter list.
   ///
   /// \param DeclLoc The location of the declaration itself.
   ///
   /// \param SS the scope specifier that will be matched to the given template
   /// parameter lists. This scope specifier precedes a qualified name that is
   /// being declared.
   ///
   /// \param TemplateId The template-id following the scope specifier, if there
   /// is one. Used to check for a missing 'template<>'.
   ///
   /// \param ParamLists the template parameter lists, from the outermost to the
   /// innermost template parameter lists.
   ///
   /// \param IsFriend Whether to apply the slightly different rules for
   /// matching template parameters to scope specifiers in friend
   /// declarations.
   ///
   /// \param IsMemberSpecialization will be set true if the scope specifier
   /// denotes a fully-specialized type, and therefore this is a declaration of
   /// a member specialization.
   ///
   /// \returns the template parameter list, if any, that corresponds to the
   /// name that is preceded by the scope specifier @p SS. This template
   /// parameter list may have template parameters (if we're declaring a
   /// template) or may have no template parameters (if we're declaring a
   /// template specialization), or may be NULL (if what we're declaring isn't
   /// itself a template).
   TemplateParameterList *MatchTemplateParametersToScopeSpecifier(
       SourceLocation DeclStartLoc, SourceLocation DeclLoc,
       const CXXScopeSpec &SS, TemplateIdAnnotation *TemplateId,
       ArrayRef<TemplateParameterList *> ParamLists, bool IsFriend,
       bool &IsMemberSpecialization, bool &Invalid,
       bool SuppressDiagnostic = false);
 
   /// Returns the template parameter list with all default template argument
   /// information.
   TemplateParameterList *GetTemplateParameterList(TemplateDecl *TD);
 
   DeclResult CheckClassTemplate(
       Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
       CXXScopeSpec &SS, IdentifierInfo *Name, SourceLocation NameLoc,
       const ParsedAttributesView &Attr, TemplateParameterList *TemplateParams,
       AccessSpecifier AS, SourceLocation ModulePrivateLoc,
       SourceLocation FriendLoc, unsigned NumOuterTemplateParamLists,
       TemplateParameterList **OuterTemplateParamLists,
       SkipBodyInfo *SkipBody = nullptr);
 
   /// Translates template arguments as provided by the parser
   /// into template arguments used by semantic analysis.
   void translateTemplateArguments(const ASTTemplateArgsPtr &In,
                                   TemplateArgumentListInfo &Out);
 
   /// Convert a parsed type into a parsed template argument. This is mostly
   /// trivial, except that we may have parsed a C++17 deduced class template
   /// specialization type, in which case we should form a template template
   /// argument instead of a type template argument.
   ParsedTemplateArgument ActOnTemplateTypeArgument(TypeResult ParsedType);
 
   void NoteAllFoundTemplates(TemplateName Name);
 
   QualType CheckTemplateIdType(TemplateName Template,
                                SourceLocation TemplateLoc,
                                TemplateArgumentListInfo &TemplateArgs);
 
   TypeResult
   ActOnTemplateIdType(Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                       TemplateTy Template, const IdentifierInfo *TemplateII,
                       SourceLocation TemplateIILoc, SourceLocation LAngleLoc,
                       ASTTemplateArgsPtr TemplateArgs, SourceLocation RAngleLoc,
                       bool IsCtorOrDtorName = false, bool IsClassName = false,
                       ImplicitTypenameContext AllowImplicitTypename =
                           ImplicitTypenameContext::No);
 
   /// Parsed an elaborated-type-specifier that refers to a template-id,
   /// such as \c class T::template apply<U>.
   TypeResult ActOnTagTemplateIdType(
       TagUseKind TUK, TypeSpecifierType TagSpec, SourceLocation TagLoc,
       CXXScopeSpec &SS, SourceLocation TemplateKWLoc, TemplateTy TemplateD,
       SourceLocation TemplateLoc, SourceLocation LAngleLoc,
       ASTTemplateArgsPtr TemplateArgsIn, SourceLocation RAngleLoc);
 
   DeclResult ActOnVarTemplateSpecialization(
       Scope *S, Declarator &D, TypeSourceInfo *DI, LookupResult &Previous,
       SourceLocation TemplateKWLoc, TemplateParameterList *TemplateParams,
       StorageClass SC, bool IsPartialSpecialization);
 
   /// Get the specialization of the given variable template corresponding to
   /// the specified argument list, or a null-but-valid result if the arguments
   /// are dependent.
   DeclResult CheckVarTemplateId(VarTemplateDecl *Template,
                                 SourceLocation TemplateLoc,
                                 SourceLocation TemplateNameLoc,
                                 const TemplateArgumentListInfo &TemplateArgs);
 
   /// Form a reference to the specialization of the given variable template
   /// corresponding to the specified argument list, or a null-but-valid result
   /// if the arguments are dependent.
   ExprResult CheckVarTemplateId(const CXXScopeSpec &SS,
                                 const DeclarationNameInfo &NameInfo,
                                 VarTemplateDecl *Template, NamedDecl *FoundD,
                                 SourceLocation TemplateLoc,
                                 const TemplateArgumentListInfo *TemplateArgs);
 
   ExprResult
   CheckConceptTemplateId(const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                          const DeclarationNameInfo &ConceptNameInfo,
                          NamedDecl *FoundDecl, ConceptDecl *NamedConcept,
                          const TemplateArgumentListInfo *TemplateArgs);
 
   void diagnoseMissingTemplateArguments(TemplateName Name, SourceLocation Loc);
   void diagnoseMissingTemplateArguments(const CXXScopeSpec &SS,
                                         bool TemplateKeyword, TemplateDecl *TD,
                                         SourceLocation Loc);
 
   ExprResult BuildTemplateIdExpr(const CXXScopeSpec &SS,
                                  SourceLocation TemplateKWLoc, LookupResult &R,
                                  bool RequiresADL,
                                  const TemplateArgumentListInfo *TemplateArgs);
 
   // We actually only call this from template instantiation.
   ExprResult
   BuildQualifiedTemplateIdExpr(CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                                const DeclarationNameInfo &NameInfo,
                                const TemplateArgumentListInfo *TemplateArgs,
                                bool IsAddressOfOperand);
 
   /// Form a template name from a name that is syntactically required to name a
   /// template, either due to use of the 'template' keyword or because a name in
   /// this syntactic context is assumed to name a template (C++
   /// [temp.names]p2-4).
   ///
   /// This action forms a template name given the name of the template and its
   /// optional scope specifier. This is used when the 'template' keyword is used
   /// or when the parsing context unambiguously treats a following '<' as
   /// introducing a template argument list. Note that this may produce a
   /// non-dependent template name if we can perform the lookup now and identify
   /// the named template.
   ///
   /// For example, given "x.MetaFun::template apply", the scope specifier
   /// \p SS will be "MetaFun::", \p TemplateKWLoc contains the location
   /// of the "template" keyword, and "apply" is the \p Name.
   TemplateNameKind ActOnTemplateName(Scope *S, CXXScopeSpec &SS,
                                      SourceLocation TemplateKWLoc,
                                      const UnqualifiedId &Name,
                                      ParsedType ObjectType,
                                      bool EnteringContext, TemplateTy &Template,
                                      bool AllowInjectedClassName = false);
 
   DeclResult ActOnClassTemplateSpecialization(
       Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
       SourceLocation ModulePrivateLoc, CXXScopeSpec &SS,
       TemplateIdAnnotation &TemplateId, const ParsedAttributesView &Attr,
       MultiTemplateParamsArg TemplateParameterLists,
       SkipBodyInfo *SkipBody = nullptr);
 
   /// Check the non-type template arguments of a class template
   /// partial specialization according to C++ [temp.class.spec]p9.
   ///
   /// \param TemplateNameLoc the location of the template name.
   /// \param PrimaryTemplate the template parameters of the primary class
   ///        template.
   /// \param NumExplicit the number of explicitly-specified template arguments.
   /// \param TemplateArgs the template arguments of the class template
   ///        partial specialization.
   ///
   /// \returns \c true if there was an error, \c false otherwise.
   bool CheckTemplatePartialSpecializationArgs(SourceLocation Loc,
                                               TemplateDecl *PrimaryTemplate,
                                               unsigned NumExplicitArgs,
                                               ArrayRef<TemplateArgument> Args);
   void CheckTemplatePartialSpecialization(
       ClassTemplatePartialSpecializationDecl *Partial);
   void CheckTemplatePartialSpecialization(
       VarTemplatePartialSpecializationDecl *Partial);
 
   Decl *ActOnTemplateDeclarator(Scope *S,
                                 MultiTemplateParamsArg TemplateParameterLists,
                                 Declarator &D);
 
   /// Diagnose cases where we have an explicit template specialization
   /// before/after an explicit template instantiation, producing diagnostics
   /// for those cases where they are required and determining whether the
   /// new specialization/instantiation will have any effect.
   ///
   /// \param NewLoc the location of the new explicit specialization or
   /// instantiation.
   ///
   /// \param NewTSK the kind of the new explicit specialization or
   /// instantiation.
   ///
   /// \param PrevDecl the previous declaration of the entity.
   ///
   /// \param PrevTSK the kind of the old explicit specialization or
   /// instantiatin.
   ///
   /// \param PrevPointOfInstantiation if valid, indicates where the previous
   /// declaration was instantiated (either implicitly or explicitly).
   ///
   /// \param HasNoEffect will be set to true to indicate that the new
   /// specialization or instantiation has no effect and should be ignored.
   ///
   /// \returns true if there was an error that should prevent the introduction
   /// of the new declaration into the AST, false otherwise.
   bool CheckSpecializationInstantiationRedecl(
       SourceLocation NewLoc,
       TemplateSpecializationKind ActOnExplicitInstantiationNewTSK,
       NamedDecl *PrevDecl, TemplateSpecializationKind PrevTSK,
       SourceLocation PrevPtOfInstantiation, bool &SuppressNew);
 
   /// Perform semantic analysis for the given dependent function
   /// template specialization.
   ///
   /// The only possible way to get a dependent function template specialization
   /// is with a friend declaration, like so:
   ///
   /// \code
   ///   template \<class T> void foo(T);
   ///   template \<class T> class A {
   ///     friend void foo<>(T);
   ///   };
   /// \endcode
   ///
   /// There really isn't any useful analysis we can do here, so we
   /// just store the information.
   bool CheckDependentFunctionTemplateSpecialization(
       FunctionDecl *FD, const TemplateArgumentListInfo *ExplicitTemplateArgs,
       LookupResult &Previous);
 
   /// Perform semantic analysis for the given function template
   /// specialization.
   ///
   /// This routine performs all of the semantic analysis required for an
   /// explicit function template specialization. On successful completion,
   /// the function declaration \p FD will become a function template
   /// specialization.
   ///
   /// \param FD the function declaration, which will be updated to become a
   /// function template specialization.
   ///
   /// \param ExplicitTemplateArgs the explicitly-provided template arguments,
   /// if any. Note that this may be valid info even when 0 arguments are
   /// explicitly provided as in, e.g., \c void sort<>(char*, char*);
   /// as it anyway contains info on the angle brackets locations.
   ///
   /// \param Previous the set of declarations that may be specialized by
   /// this function specialization.
   ///
   /// \param QualifiedFriend whether this is a lookup for a qualified friend
   /// declaration with no explicit template argument list that might be
   /// befriending a function template specialization.
   bool CheckFunctionTemplateSpecialization(
       FunctionDecl *FD, TemplateArgumentListInfo *ExplicitTemplateArgs,
       LookupResult &Previous, bool QualifiedFriend = false);
 
   /// Perform semantic analysis for the given non-template member
   /// specialization.
   ///
   /// This routine performs all of the semantic analysis required for an
   /// explicit member function specialization. On successful completion,
   /// the function declaration \p FD will become a member function
   /// specialization.
   ///
   /// \param Member the member declaration, which will be updated to become a
   /// specialization.
   ///
   /// \param Previous the set of declarations, one of which may be specialized
   /// by this function specialization;  the set will be modified to contain the
   /// redeclared member.
   bool CheckMemberSpecialization(NamedDecl *Member, LookupResult &Previous);
   void CompleteMemberSpecialization(NamedDecl *Member, LookupResult &Previous);
 
   // Explicit instantiation of a class template specialization
   DeclResult ActOnExplicitInstantiation(
       Scope *S, SourceLocation ExternLoc, SourceLocation TemplateLoc,
       unsigned TagSpec, SourceLocation KWLoc, const CXXScopeSpec &SS,
       TemplateTy Template, SourceLocation TemplateNameLoc,
       SourceLocation LAngleLoc, ASTTemplateArgsPtr TemplateArgs,
       SourceLocation RAngleLoc, const ParsedAttributesView &Attr);
 
   // Explicit instantiation of a member class of a class template.
   DeclResult ActOnExplicitInstantiation(Scope *S, SourceLocation ExternLoc,
                                         SourceLocation TemplateLoc,
                                         unsigned TagSpec, SourceLocation KWLoc,
                                         CXXScopeSpec &SS, IdentifierInfo *Name,
                                         SourceLocation NameLoc,
                                         const ParsedAttributesView &Attr);
 
   DeclResult ActOnExplicitInstantiation(Scope *S, SourceLocation ExternLoc,
                                         SourceLocation TemplateLoc,
                                         Declarator &D);
 
   /// If the given template parameter has a default template
   /// argument, substitute into that default template argument and
   /// return the corresponding template argument.
   TemplateArgumentLoc SubstDefaultTemplateArgumentIfAvailable(
       TemplateDecl *Template, SourceLocation TemplateLoc,
       SourceLocation RAngleLoc, Decl *Param,
       ArrayRef<TemplateArgument> SugaredConverted,
       ArrayRef<TemplateArgument> CanonicalConverted, bool &HasDefaultArg);
 
   /// Returns the top most location responsible for the definition of \p N.
   /// If \p N is a a template specialization, this is the location
   /// of the top of the instantiation stack.
   /// Otherwise, the location of \p N is returned.
   SourceLocation getTopMostPointOfInstantiation(const NamedDecl *) const;
 
   /// Specifies the context in which a particular template
   /// argument is being checked.
   enum CheckTemplateArgumentKind {
     /// The template argument was specified in the code or was
     /// instantiated with some deduced template arguments.
     CTAK_Specified,
 
     /// The template argument was deduced via template argument
     /// deduction.
     CTAK_Deduced,
 
     /// The template argument was deduced from an array bound
     /// via template argument deduction.
     CTAK_DeducedFromArrayBound
   };
 
   /// Check that the given template argument corresponds to the given
   /// template parameter.
   ///
   /// \param Param The template parameter against which the argument will be
   /// checked.
   ///
   /// \param Arg The template argument, which may be updated due to conversions.
   ///
   /// \param Template The template in which the template argument resides.
   ///
   /// \param TemplateLoc The location of the template name for the template
   /// whose argument list we're matching.
   ///
   /// \param RAngleLoc The location of the right angle bracket ('>') that closes
   /// the template argument list.
   ///
   /// \param ArgumentPackIndex The index into the argument pack where this
   /// argument will be placed. Only valid if the parameter is a parameter pack.
   ///
   /// \param Converted The checked, converted argument will be added to the
   /// end of this small vector.
   ///
   /// \param CTAK Describes how we arrived at this particular template argument:
   /// explicitly written, deduced, etc.
   ///
   /// \returns true on error, false otherwise.
   bool
   CheckTemplateArgument(NamedDecl *Param, TemplateArgumentLoc &Arg,
                         NamedDecl *Template, SourceLocation TemplateLoc,
                         SourceLocation RAngleLoc, unsigned ArgumentPackIndex,
                         SmallVectorImpl<TemplateArgument> &SugaredConverted,
                         SmallVectorImpl<TemplateArgument> &CanonicalConverted,
                         CheckTemplateArgumentKind CTAK);
 
   /// Check that the given template arguments can be provided to
   /// the given template, converting the arguments along the way.
   ///
   /// \param Template The template to which the template arguments are being
   /// provided.
   ///
   /// \param TemplateLoc The location of the template name in the source.
   ///
   /// \param TemplateArgs The list of template arguments. If the template is
   /// a template template parameter, this function may extend the set of
   /// template arguments to also include substituted, defaulted template
   /// arguments.
   ///
   /// \param PartialTemplateArgs True if the list of template arguments is
   /// intentionally partial, e.g., because we're checking just the initial
   /// set of template arguments.
   ///
   /// \param Converted Will receive the converted, canonicalized template
   /// arguments.
   ///
   /// \param UpdateArgsWithConversions If \c true, update \p TemplateArgs to
   /// contain the converted forms of the template arguments as written.
   /// Otherwise, \p TemplateArgs will not be modified.
   ///
   /// \param ConstraintsNotSatisfied If provided, and an error occurred, will
   /// receive true if the cause for the error is the associated constraints of
   /// the template not being satisfied by the template arguments.
   ///
   /// \param PartialOrderingTTP If true, assume these template arguments are
   /// the injected template arguments for a template template parameter.
   /// This will relax the requirement that all its possible uses are valid:
   /// TTP checking is loose, and assumes that invalid uses will be diagnosed
   /// during instantiation.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CheckTemplateArgumentList(
       TemplateDecl *Template, SourceLocation TemplateLoc,
       TemplateArgumentListInfo &TemplateArgs, bool PartialTemplateArgs,
       SmallVectorImpl<TemplateArgument> &SugaredConverted,
       SmallVectorImpl<TemplateArgument> &CanonicalConverted,
       bool UpdateArgsWithConversions = true,
       bool *ConstraintsNotSatisfied = nullptr, bool PartialOrderingTTP = false);
 
   bool CheckTemplateTypeArgument(
       TemplateTypeParmDecl *Param, TemplateArgumentLoc &Arg,
       SmallVectorImpl<TemplateArgument> &SugaredConverted,
       SmallVectorImpl<TemplateArgument> &CanonicalConverted);
 
   /// Check a template argument against its corresponding
   /// template type parameter.
   ///
   /// This routine implements the semantics of C++ [temp.arg.type]. It
   /// returns true if an error occurred, and false otherwise.
   bool CheckTemplateArgument(TypeSourceInfo *Arg);
 
   /// Check a template argument against its corresponding
   /// non-type template parameter.
   ///
   /// This routine implements the semantics of C++ [temp.arg.nontype].
   /// If an error occurred, it returns ExprError(); otherwise, it
   /// returns the converted template argument. \p ParamType is the
   /// type of the non-type template parameter after it has been instantiated.
   ExprResult CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
                                    QualType InstantiatedParamType, Expr *Arg,
                                    TemplateArgument &SugaredConverted,
                                    TemplateArgument &CanonicalConverted,
                                    CheckTemplateArgumentKind CTAK);
 
   /// Check a template argument against its corresponding
   /// template template parameter.
   ///
   /// This routine implements the semantics of C++ [temp.arg.template].
   /// It returns true if an error occurred, and false otherwise.
   bool CheckTemplateTemplateArgument(TemplateTemplateParmDecl *Param,
                                      TemplateParameterList *Params,
                                      TemplateArgumentLoc &Arg, bool IsDeduced);
 
   void NoteTemplateLocation(const NamedDecl &Decl,
                             std::optional<SourceRange> ParamRange = {});
   void NoteTemplateParameterLocation(const NamedDecl &Decl);
 
   /// Given a non-type template argument that refers to a
   /// declaration and the type of its corresponding non-type template
   /// parameter, produce an expression that properly refers to that
   /// declaration.
   ExprResult BuildExpressionFromDeclTemplateArgument(
       const TemplateArgument &Arg, QualType ParamType, SourceLocation Loc,
       NamedDecl *TemplateParam = nullptr);
   ExprResult
   BuildExpressionFromNonTypeTemplateArgument(const TemplateArgument &Arg,
                                              SourceLocation Loc);
 
   /// Enumeration describing how template parameter lists are compared
   /// for equality.
   enum TemplateParameterListEqualKind {
     /// We are matching the template parameter lists of two templates
     /// that might be redeclarations.
     ///
     /// \code
     /// template<typename T> struct X;
     /// template<typename T> struct X;
     /// \endcode
     TPL_TemplateMatch,
 
     /// We are matching the template parameter lists of two template
     /// template parameters as part of matching the template parameter lists
     /// of two templates that might be redeclarations.
     ///
     /// \code
     /// template<template<int I> class TT> struct X;
     /// template<template<int Value> class Other> struct X;
     /// \endcode
     TPL_TemplateTemplateParmMatch,
 
     /// We are matching the template parameter lists of a template
     /// template argument against the template parameter lists of a template
     /// template parameter.
     ///
     /// \code
     /// template<template<int Value> class Metafun> struct X;
     /// template<int Value> struct integer_c;
     /// X<integer_c> xic;
     /// \endcode
     TPL_TemplateTemplateArgumentMatch,
 
     /// We are determining whether the template-parameters are equivalent
     /// according to C++ [temp.over.link]/6. This comparison does not consider
     /// constraints.
     ///
     /// \code
     /// template<C1 T> void f(T);
     /// template<C2 T> void f(T);
     /// \endcode
     TPL_TemplateParamsEquivalent,
   };
 
   // A struct to represent the 'new' declaration, which is either itself just
   // the named decl, or the important information we need about it in order to
   // do constraint comparisons.
   class TemplateCompareNewDeclInfo {
     const NamedDecl *ND = nullptr;
     const DeclContext *DC = nullptr;
     const DeclContext *LexicalDC = nullptr;
     SourceLocation Loc;
 
   public:
     TemplateCompareNewDeclInfo(const NamedDecl *ND) : ND(ND) {}
     TemplateCompareNewDeclInfo(const DeclContext *DeclCtx,
                                const DeclContext *LexicalDeclCtx,
                                SourceLocation Loc)
 
         : DC(DeclCtx), LexicalDC(LexicalDeclCtx), Loc(Loc) {
       assert(DC && LexicalDC &&
              "Constructor only for cases where we have the information to put "
              "in here");
     }
 
     // If this was constructed with no information, we cannot do substitution
     // for constraint comparison, so make sure we can check that.
     bool isInvalid() const { return !ND && !DC; }
 
     const NamedDecl *getDecl() const { return ND; }
 
     bool ContainsDecl(const NamedDecl *ND) const { return this->ND == ND; }
 
     const DeclContext *getLexicalDeclContext() const {
       return ND ? ND->getLexicalDeclContext() : LexicalDC;
     }
 
     const DeclContext *getDeclContext() const {
       return ND ? ND->getDeclContext() : DC;
     }
 
     SourceLocation getLocation() const { return ND ? ND->getLocation() : Loc; }
   };
 
   /// Determine whether the given template parameter lists are
   /// equivalent.
   ///
   /// \param New  The new template parameter list, typically written in the
   /// source code as part of a new template declaration.
   ///
   /// \param Old  The old template parameter list, typically found via
   /// name lookup of the template declared with this template parameter
   /// list.
   ///
   /// \param Complain  If true, this routine will produce a diagnostic if
   /// the template parameter lists are not equivalent.
   ///
   /// \param Kind describes how we are to match the template parameter lists.
   ///
   /// \param TemplateArgLoc If this source location is valid, then we
   /// are actually checking the template parameter list of a template
   /// argument (New) against the template parameter list of its
   /// corresponding template template parameter (Old). We produce
   /// slightly different diagnostics in this scenario.
   ///
   /// \returns True if the template parameter lists are equal, false
   /// otherwise.
   bool TemplateParameterListsAreEqual(
       const TemplateCompareNewDeclInfo &NewInstFrom, TemplateParameterList *New,
       const NamedDecl *OldInstFrom, TemplateParameterList *Old, bool Complain,
       TemplateParameterListEqualKind Kind,
       SourceLocation TemplateArgLoc = SourceLocation());
 
   bool TemplateParameterListsAreEqual(
       TemplateParameterList *New, TemplateParameterList *Old, bool Complain,
       TemplateParameterListEqualKind Kind,
       SourceLocation TemplateArgLoc = SourceLocation()) {
     return TemplateParameterListsAreEqual(nullptr, New, nullptr, Old, Complain,
                                           Kind, TemplateArgLoc);
   }
 
   /// Check whether a template can be declared within this scope.
   ///
   /// If the template declaration is valid in this scope, returns
   /// false. Otherwise, issues a diagnostic and returns true.
   bool CheckTemplateDeclScope(Scope *S, TemplateParameterList *TemplateParams);
 
   /// Called when the parser has parsed a C++ typename
   /// specifier, e.g., "typename T::type".
   ///
   /// \param S The scope in which this typename type occurs.
   /// \param TypenameLoc the location of the 'typename' keyword
   /// \param SS the nested-name-specifier following the typename (e.g., 'T::').
   /// \param II the identifier we're retrieving (e.g., 'type' in the example).
   /// \param IdLoc the location of the identifier.
   /// \param IsImplicitTypename context where T::type refers to a type.
   TypeResult ActOnTypenameType(
       Scope *S, SourceLocation TypenameLoc, const CXXScopeSpec &SS,
       const IdentifierInfo &II, SourceLocation IdLoc,
       ImplicitTypenameContext IsImplicitTypename = ImplicitTypenameContext::No);
 
   /// Called when the parser has parsed a C++ typename
   /// specifier that ends in a template-id, e.g.,
   /// "typename MetaFun::template apply<T1, T2>".
   ///
   /// \param S The scope in which this typename type occurs.
   /// \param TypenameLoc the location of the 'typename' keyword
   /// \param SS the nested-name-specifier following the typename (e.g., 'T::').
   /// \param TemplateLoc the location of the 'template' keyword, if any.
   /// \param TemplateName The template name.
   /// \param TemplateII The identifier used to name the template.
   /// \param TemplateIILoc The location of the template name.
   /// \param LAngleLoc The location of the opening angle bracket  ('<').
   /// \param TemplateArgs The template arguments.
   /// \param RAngleLoc The location of the closing angle bracket  ('>').
   TypeResult
   ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
                     const CXXScopeSpec &SS, SourceLocation TemplateLoc,
                     TemplateTy TemplateName, const IdentifierInfo *TemplateII,
                     SourceLocation TemplateIILoc, SourceLocation LAngleLoc,
                     ASTTemplateArgsPtr TemplateArgs, SourceLocation RAngleLoc);
 
   QualType CheckTypenameType(ElaboratedTypeKeyword Keyword,
                              SourceLocation KeywordLoc,
                              NestedNameSpecifierLoc QualifierLoc,
                              const IdentifierInfo &II, SourceLocation IILoc,
                              TypeSourceInfo **TSI, bool DeducedTSTContext);
 
   QualType CheckTypenameType(ElaboratedTypeKeyword Keyword,
                              SourceLocation KeywordLoc,
                              NestedNameSpecifierLoc QualifierLoc,
                              const IdentifierInfo &II, SourceLocation IILoc,
                              bool DeducedTSTContext = true);
 
   /// Rebuilds a type within the context of the current instantiation.
   ///
   /// The type \p T is part of the type of an out-of-line member definition of
   /// a class template (or class template partial specialization) that was
   /// parsed and constructed before we entered the scope of the class template
   /// (or partial specialization thereof). This routine will rebuild that type
   /// now that we have entered the declarator's scope, which may produce
   /// different canonical types, e.g.,
   ///
   /// \code
   /// template<typename T>
   /// struct X {
   ///   typedef T* pointer;
   ///   pointer data();
   /// };
   ///
   /// template<typename T>
   /// typename X<T>::pointer X<T>::data() { ... }
   /// \endcode
   ///
   /// Here, the type "typename X<T>::pointer" will be created as a
   /// DependentNameType, since we do not know that we can look into X<T> when we
   /// parsed the type. This function will rebuild the type, performing the
   /// lookup of "pointer" in X<T> and returning an ElaboratedType whose
   /// canonical type is the same as the canonical type of T*, allowing the
   /// return types of the out-of-line definition and the declaration to match.
   TypeSourceInfo *RebuildTypeInCurrentInstantiation(TypeSourceInfo *T,
                                                     SourceLocation Loc,
                                                     DeclarationName Name);
   bool RebuildNestedNameSpecifierInCurrentInstantiation(CXXScopeSpec &SS);
 
   ExprResult RebuildExprInCurrentInstantiation(Expr *E);
 
   /// Rebuild the template parameters now that we know we're in a current
   /// instantiation.
   bool
   RebuildTemplateParamsInCurrentInstantiation(TemplateParameterList *Params);
 
   /// Produces a formatted string that describes the binding of
   /// template parameters to template arguments.
   std::string
   getTemplateArgumentBindingsText(const TemplateParameterList *Params,
                                   const TemplateArgumentList &Args);
 
   std::string
   getTemplateArgumentBindingsText(const TemplateParameterList *Params,
                                   const TemplateArgument *Args,
                                   unsigned NumArgs);
 
   void diagnoseExprIntendedAsTemplateName(Scope *S, ExprResult TemplateName,
                                           SourceLocation Less,
                                           SourceLocation Greater);
 
   /// ActOnDependentIdExpression - Handle a dependent id-expression that
   /// was just parsed.  This is only possible with an explicit scope
   /// specifier naming a dependent type.
   ExprResult ActOnDependentIdExpression(
       const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
       const DeclarationNameInfo &NameInfo, bool isAddressOfOperand,
       const TemplateArgumentListInfo *TemplateArgs);
 
   ExprResult
   BuildDependentDeclRefExpr(const CXXScopeSpec &SS,
                             SourceLocation TemplateKWLoc,
                             const DeclarationNameInfo &NameInfo,
                             const TemplateArgumentListInfo *TemplateArgs);
 
   // Calculates whether the expression Constraint depends on an enclosing
   // template, for the purposes of [temp.friend] p9.
   // TemplateDepth is the 'depth' of the friend function, which is used to
   // compare whether a declaration reference is referring to a containing
   // template, or just the current friend function. A 'lower' TemplateDepth in
   // the AST refers to a 'containing' template. As the constraint is
   // uninstantiated, this is relative to the 'top' of the TU.
   bool
   ConstraintExpressionDependsOnEnclosingTemplate(const FunctionDecl *Friend,
                                                  unsigned TemplateDepth,
                                                  const Expr *Constraint);
 
   /// Find the failed Boolean condition within a given Boolean
   /// constant expression, and describe it with a string.
   std::pair<Expr *, std::string> findFailedBooleanCondition(Expr *Cond);
 
   void CheckDeductionGuideTemplate(FunctionTemplateDecl *TD);
 
   Decl *ActOnConceptDefinition(Scope *S,
                                MultiTemplateParamsArg TemplateParameterLists,
                                const IdentifierInfo *Name,
                                SourceLocation NameLoc, Expr *ConstraintExpr,
                                const ParsedAttributesView &Attrs);
 
   void CheckConceptRedefinition(ConceptDecl *NewDecl, LookupResult &Previous,
                                 bool &AddToScope);
 
   TypeResult ActOnDependentTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                                const CXXScopeSpec &SS,
                                const IdentifierInfo *Name,
                                SourceLocation TagLoc, SourceLocation NameLoc);
 
   void MarkAsLateParsedTemplate(FunctionDecl *FD, Decl *FnD,
                                 CachedTokens &Toks);
   void UnmarkAsLateParsedTemplate(FunctionDecl *FD);
   bool IsInsideALocalClassWithinATemplateFunction();
 
   /// We've found a use of a templated declaration that would trigger an
   /// implicit instantiation. Check that any relevant explicit specializations
   /// and partial specializations are visible/reachable, and diagnose if not.
   void checkSpecializationVisibility(SourceLocation Loc, NamedDecl *Spec);
   void checkSpecializationReachability(SourceLocation Loc, NamedDecl *Spec);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Template Argument Deduction
   /// Implementations are in SemaTemplateDeduction.cpp
   ///@{
 
 public:
   /// When true, access checking violations are treated as SFINAE
   /// failures rather than hard errors.
   bool AccessCheckingSFINAE;
 
   /// RAII class used to determine whether SFINAE has
   /// trapped any errors that occur during template argument
   /// deduction.
   class SFINAETrap {
     Sema &SemaRef;
     unsigned PrevSFINAEErrors;
     bool PrevInNonInstantiationSFINAEContext;
     bool PrevAccessCheckingSFINAE;
     bool PrevLastDiagnosticIgnored;
 
   public:
     explicit SFINAETrap(Sema &SemaRef, bool AccessCheckingSFINAE = false)
         : SemaRef(SemaRef), PrevSFINAEErrors(SemaRef.NumSFINAEErrors),
           PrevInNonInstantiationSFINAEContext(
               SemaRef.InNonInstantiationSFINAEContext),
           PrevAccessCheckingSFINAE(SemaRef.AccessCheckingSFINAE),
           PrevLastDiagnosticIgnored(
               SemaRef.getDiagnostics().isLastDiagnosticIgnored()) {
       if (!SemaRef.isSFINAEContext())
         SemaRef.InNonInstantiationSFINAEContext = true;
       SemaRef.AccessCheckingSFINAE = AccessCheckingSFINAE;
     }
 
     ~SFINAETrap() {
       SemaRef.NumSFINAEErrors = PrevSFINAEErrors;
       SemaRef.InNonInstantiationSFINAEContext =
           PrevInNonInstantiationSFINAEContext;
       SemaRef.AccessCheckingSFINAE = PrevAccessCheckingSFINAE;
       SemaRef.getDiagnostics().setLastDiagnosticIgnored(
           PrevLastDiagnosticIgnored);
     }
 
     /// Determine whether any SFINAE errors have been trapped.
     bool hasErrorOccurred() const {
       return SemaRef.NumSFINAEErrors > PrevSFINAEErrors;
     }
   };
 
   /// RAII class used to indicate that we are performing provisional
   /// semantic analysis to determine the validity of a construct, so
   /// typo-correction and diagnostics in the immediate context (not within
   /// implicitly-instantiated templates) should be suppressed.
   class TentativeAnalysisScope {
     Sema &SemaRef;
     // FIXME: Using a SFINAETrap for this is a hack.
     SFINAETrap Trap;
     bool PrevDisableTypoCorrection;
 
   public:
     explicit TentativeAnalysisScope(Sema &SemaRef)
         : SemaRef(SemaRef), Trap(SemaRef, true),
           PrevDisableTypoCorrection(SemaRef.DisableTypoCorrection) {
       SemaRef.DisableTypoCorrection = true;
     }
     ~TentativeAnalysisScope() {
       SemaRef.DisableTypoCorrection = PrevDisableTypoCorrection;
     }
   };
 
   /// For each declaration that involved template argument deduction, the
   /// set of diagnostics that were suppressed during that template argument
   /// deduction.
   ///
   /// FIXME: Serialize this structure to the AST file.
   typedef llvm::DenseMap<Decl *, SmallVector<PartialDiagnosticAt, 1>>
       SuppressedDiagnosticsMap;
   SuppressedDiagnosticsMap SuppressedDiagnostics;
 
   /// Compare types for equality with respect to possibly compatible
   /// function types (noreturn adjustment, implicit calling conventions). If any
   /// of parameter and argument is not a function, just perform type comparison.
   ///
   /// \param P the template parameter type.
   ///
   /// \param A the argument type.
   bool isSameOrCompatibleFunctionType(QualType Param, QualType Arg);
 
   /// Allocate a TemplateArgumentLoc where all locations have
   /// been initialized to the given location.
   ///
   /// \param Arg The template argument we are producing template argument
   /// location information for.
   ///
   /// \param NTTPType For a declaration template argument, the type of
   /// the non-type template parameter that corresponds to this template
   /// argument. Can be null if no type sugar is available to add to the
   /// type from the template argument.
   ///
   /// \param Loc The source location to use for the resulting template
   /// argument.
   TemplateArgumentLoc
   getTrivialTemplateArgumentLoc(const TemplateArgument &Arg, QualType NTTPType,
                                 SourceLocation Loc,
                                 NamedDecl *TemplateParam = nullptr);
 
   /// Get a template argument mapping the given template parameter to itself,
   /// e.g. for X in \c template<int X>, this would return an expression template
   /// argument referencing X.
   TemplateArgumentLoc getIdentityTemplateArgumentLoc(NamedDecl *Param,
                                                      SourceLocation Location);
 
   /// Adjust the type \p ArgFunctionType to match the calling convention,
   /// noreturn, and optionally the exception specification of \p FunctionType.
   /// Deduction often wants to ignore these properties when matching function
   /// types.
   QualType adjustCCAndNoReturn(QualType ArgFunctionType, QualType FunctionType,
                                bool AdjustExceptionSpec = false);
 
   TemplateDeductionResult
   DeduceTemplateArguments(ClassTemplatePartialSpecializationDecl *Partial,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &Info);
 
   TemplateDeductionResult
   DeduceTemplateArguments(VarTemplatePartialSpecializationDecl *Partial,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &Info);
 
   /// Deduce the template arguments of the given template from \p FromType.
   /// Used to implement the IsDeducible constraint for alias CTAD per C++
   /// [over.match.class.deduct]p4.
   ///
   /// It only supports class or type alias templates.
   TemplateDeductionResult
   DeduceTemplateArgumentsFromType(TemplateDecl *TD, QualType FromType,
                                   sema::TemplateDeductionInfo &Info);
 
   TemplateDeductionResult DeduceTemplateArguments(
       TemplateParameterList *TemplateParams, ArrayRef<TemplateArgument> Ps,
       ArrayRef<TemplateArgument> As, sema::TemplateDeductionInfo &Info,
       SmallVectorImpl<DeducedTemplateArgument> &Deduced,
       bool NumberOfArgumentsMustMatch);
 
   /// Substitute the explicitly-provided template arguments into the
   /// given function template according to C++ [temp.arg.explicit].
   ///
   /// \param FunctionTemplate the function template into which the explicit
   /// template arguments will be substituted.
   ///
   /// \param ExplicitTemplateArgs the explicitly-specified template
   /// arguments.
   ///
   /// \param Deduced the deduced template arguments, which will be populated
   /// with the converted and checked explicit template arguments.
   ///
   /// \param ParamTypes will be populated with the instantiated function
   /// parameters.
   ///
   /// \param FunctionType if non-NULL, the result type of the function template
   /// will also be instantiated and the pointed-to value will be updated with
   /// the instantiated function type.
   ///
   /// \param Info if substitution fails for any reason, this object will be
   /// populated with more information about the failure.
   ///
   /// \returns TemplateDeductionResult::Success if substitution was successful,
   /// or some failure condition.
   TemplateDeductionResult SubstituteExplicitTemplateArguments(
       FunctionTemplateDecl *FunctionTemplate,
       TemplateArgumentListInfo &ExplicitTemplateArgs,
       SmallVectorImpl<DeducedTemplateArgument> &Deduced,
       SmallVectorImpl<QualType> &ParamTypes, QualType *FunctionType,
       sema::TemplateDeductionInfo &Info);
 
   /// brief A function argument from which we performed template argument
   // deduction for a call.
   struct OriginalCallArg {
     OriginalCallArg(QualType OriginalParamType, bool DecomposedParam,
                     unsigned ArgIdx, QualType OriginalArgType)
         : OriginalParamType(OriginalParamType),
           DecomposedParam(DecomposedParam), ArgIdx(ArgIdx),
           OriginalArgType(OriginalArgType) {}
 
     QualType OriginalParamType;
     bool DecomposedParam;
     unsigned ArgIdx;
     QualType OriginalArgType;
   };
 
   /// Finish template argument deduction for a function template,
   /// checking the deduced template arguments for completeness and forming
   /// the function template specialization.
   ///
   /// \param OriginalCallArgs If non-NULL, the original call arguments against
   /// which the deduced argument types should be compared.
   TemplateDeductionResult FinishTemplateArgumentDeduction(
       FunctionTemplateDecl *FunctionTemplate,
       SmallVectorImpl<DeducedTemplateArgument> &Deduced,
       unsigned NumExplicitlySpecified, FunctionDecl *&Specialization,
       sema::TemplateDeductionInfo &Info,
       SmallVectorImpl<OriginalCallArg> const *OriginalCallArgs = nullptr,
       bool PartialOverloading = false,
       llvm::function_ref<bool()> CheckNonDependent = [] { return false; });
 
   /// Perform template argument deduction from a function call
   /// (C++ [temp.deduct.call]).
   ///
   /// \param FunctionTemplate the function template for which we are performing
   /// template argument deduction.
   ///
   /// \param ExplicitTemplateArgs the explicit template arguments provided
   /// for this call.
   ///
   /// \param Args the function call arguments
   ///
   /// \param Specialization if template argument deduction was successful,
   /// this will be set to the function template specialization produced by
   /// template argument deduction.
   ///
   /// \param Info the argument will be updated to provide additional information
   /// about template argument deduction.
   ///
   /// \param CheckNonDependent A callback to invoke to check conversions for
   /// non-dependent parameters, between deduction and substitution, per DR1391.
   /// If this returns true, substitution will be skipped and we return
   /// TemplateDeductionResult::NonDependentConversionFailure. The callback is
   /// passed the parameter types (after substituting explicit template
   /// arguments).
   ///
   /// \returns the result of template argument deduction.
   TemplateDeductionResult DeduceTemplateArguments(
       FunctionTemplateDecl *FunctionTemplate,
       TemplateArgumentListInfo *ExplicitTemplateArgs, ArrayRef<Expr *> Args,
       FunctionDecl *&Specialization, sema::TemplateDeductionInfo &Info,
       bool PartialOverloading, bool AggregateDeductionCandidate,
       QualType ObjectType, Expr::Classification ObjectClassification,
       llvm::function_ref<bool(ArrayRef<QualType>)> CheckNonDependent);
 
   /// Deduce template arguments when taking the address of a function
   /// template (C++ [temp.deduct.funcaddr]) or matching a specialization to
   /// a template.
   ///
   /// \param FunctionTemplate the function template for which we are performing
   /// template argument deduction.
   ///
   /// \param ExplicitTemplateArgs the explicitly-specified template
   /// arguments.
   ///
   /// \param ArgFunctionType the function type that will be used as the
   /// "argument" type (A) when performing template argument deduction from the
   /// function template's function type. This type may be NULL, if there is no
   /// argument type to compare against, in C++0x [temp.arg.explicit]p3.
   ///
   /// \param Specialization if template argument deduction was successful,
   /// this will be set to the function template specialization produced by
   /// template argument deduction.
   ///
   /// \param Info the argument will be updated to provide additional information
   /// about template argument deduction.
   ///
   /// \param IsAddressOfFunction If \c true, we are deducing as part of taking
   /// the address of a function template per [temp.deduct.funcaddr] and
   /// [over.over]. If \c false, we are looking up a function template
   /// specialization based on its signature, per [temp.deduct.decl].
   ///
   /// \returns the result of template argument deduction.
   TemplateDeductionResult DeduceTemplateArguments(
       FunctionTemplateDecl *FunctionTemplate,
       TemplateArgumentListInfo *ExplicitTemplateArgs, QualType ArgFunctionType,
       FunctionDecl *&Specialization, sema::TemplateDeductionInfo &Info,
       bool IsAddressOfFunction = false);
 
   /// Deduce template arguments for a templated conversion
   /// function (C++ [temp.deduct.conv]) and, if successful, produce a
   /// conversion function template specialization.
   TemplateDeductionResult DeduceTemplateArguments(
       FunctionTemplateDecl *FunctionTemplate, QualType ObjectType,
       Expr::Classification ObjectClassification, QualType ToType,
       CXXConversionDecl *&Specialization, sema::TemplateDeductionInfo &Info);
 
   /// Deduce template arguments for a function template when there is
   /// nothing to deduce against (C++0x [temp.arg.explicit]p3).
   ///
   /// \param FunctionTemplate the function template for which we are performing
   /// template argument deduction.
   ///
   /// \param ExplicitTemplateArgs the explicitly-specified template
   /// arguments.
   ///
   /// \param Specialization if template argument deduction was successful,
   /// this will be set to the function template specialization produced by
   /// template argument deduction.
   ///
   /// \param Info the argument will be updated to provide additional information
   /// about template argument deduction.
   ///
   /// \param IsAddressOfFunction If \c true, we are deducing as part of taking
   /// the address of a function template in a context where we do not have a
   /// target type, per [over.over]. If \c false, we are looking up a function
   /// template specialization based on its signature, which only happens when
   /// deducing a function parameter type from an argument that is a template-id
   /// naming a function template specialization.
   ///
   /// \returns the result of template argument deduction.
   TemplateDeductionResult
   DeduceTemplateArguments(FunctionTemplateDecl *FunctionTemplate,
                           TemplateArgumentListInfo *ExplicitTemplateArgs,
                           FunctionDecl *&Specialization,
                           sema::TemplateDeductionInfo &Info,
                           bool IsAddressOfFunction = false);
 
   /// Substitute Replacement for \p auto in \p TypeWithAuto
   QualType SubstAutoType(QualType TypeWithAuto, QualType Replacement);
   /// Substitute Replacement for auto in TypeWithAuto
   TypeSourceInfo *SubstAutoTypeSourceInfo(TypeSourceInfo *TypeWithAuto,
                                           QualType Replacement);
 
   // Substitute auto in TypeWithAuto for a Dependent auto type
   QualType SubstAutoTypeDependent(QualType TypeWithAuto);
 
   // Substitute auto in TypeWithAuto for a Dependent auto type
   TypeSourceInfo *
   SubstAutoTypeSourceInfoDependent(TypeSourceInfo *TypeWithAuto);
 
   /// Completely replace the \c auto in \p TypeWithAuto by
   /// \p Replacement. This does not retain any \c auto type sugar.
   QualType ReplaceAutoType(QualType TypeWithAuto, QualType Replacement);
   TypeSourceInfo *ReplaceAutoTypeSourceInfo(TypeSourceInfo *TypeWithAuto,
                                             QualType Replacement);
 
   /// Deduce the type for an auto type-specifier (C++11 [dcl.spec.auto]p6)
   ///
   /// Note that this is done even if the initializer is dependent. (This is
   /// necessary to support partial ordering of templates using 'auto'.)
   /// A dependent type will be produced when deducing from a dependent type.
   ///
   /// \param Type the type pattern using the auto type-specifier.
   /// \param Init the initializer for the variable whose type is to be deduced.
   /// \param Result if type deduction was successful, this will be set to the
   ///        deduced type.
   /// \param Info the argument will be updated to provide additional information
   ///        about template argument deduction.
   /// \param DependentDeduction Set if we should permit deduction in
   ///        dependent cases. This is necessary for template partial ordering
   ///        with 'auto' template parameters. The template parameter depth to be
   ///        used should be specified in the 'Info' parameter.
   /// \param IgnoreConstraints Set if we should not fail if the deduced type
   ///                          does not satisfy the type-constraint in the auto
   ///                          type.
   TemplateDeductionResult
   DeduceAutoType(TypeLoc AutoTypeLoc, Expr *Initializer, QualType &Result,
                  sema::TemplateDeductionInfo &Info,
                  bool DependentDeduction = false,
                  bool IgnoreConstraints = false,
                  TemplateSpecCandidateSet *FailedTSC = nullptr);
   void DiagnoseAutoDeductionFailure(const VarDecl *VDecl, const Expr *Init);
   bool DeduceReturnType(FunctionDecl *FD, SourceLocation Loc,
                         bool Diagnose = true);
 
   bool CheckIfFunctionSpecializationIsImmediate(FunctionDecl *FD,
                                                 SourceLocation Loc);
 
   /// Returns the more specialized class template partial specialization
   /// according to the rules of partial ordering of class template partial
   /// specializations (C++ [temp.class.order]).
   ///
   /// \param PS1 the first class template partial specialization
   ///
   /// \param PS2 the second class template partial specialization
   ///
   /// \returns the more specialized class template partial specialization. If
   /// neither partial specialization is more specialized, returns NULL.
   ClassTemplatePartialSpecializationDecl *
   getMoreSpecializedPartialSpecialization(
       ClassTemplatePartialSpecializationDecl *PS1,
       ClassTemplatePartialSpecializationDecl *PS2, SourceLocation Loc);
 
   bool isMoreSpecializedThanPrimary(ClassTemplatePartialSpecializationDecl *T,
                                     sema::TemplateDeductionInfo &Info);
 
   VarTemplatePartialSpecializationDecl *getMoreSpecializedPartialSpecialization(
       VarTemplatePartialSpecializationDecl *PS1,
       VarTemplatePartialSpecializationDecl *PS2, SourceLocation Loc);
 
   bool isMoreSpecializedThanPrimary(VarTemplatePartialSpecializationDecl *T,
                                     sema::TemplateDeductionInfo &Info);
 
   bool isTemplateTemplateParameterAtLeastAsSpecializedAs(
       TemplateParameterList *PParam, TemplateDecl *AArg, SourceLocation Loc,
       bool IsDeduced);
 
   /// Mark which template parameters are used in a given expression.
   ///
   /// \param E the expression from which template parameters will be deduced.
   ///
   /// \param Used a bit vector whose elements will be set to \c true
   /// to indicate when the corresponding template parameter will be
   /// deduced.
   void MarkUsedTemplateParameters(const Expr *E, bool OnlyDeduced,
                                   unsigned Depth, llvm::SmallBitVector &Used);
 
   /// Mark which template parameters can be deduced from a given
   /// template argument list.
   ///
   /// \param TemplateArgs the template argument list from which template
   /// parameters will be deduced.
   ///
   /// \param Used a bit vector whose elements will be set to \c true
   /// to indicate when the corresponding template parameter will be
   /// deduced.
   void MarkUsedTemplateParameters(const TemplateArgumentList &TemplateArgs,
                                   bool OnlyDeduced, unsigned Depth,
                                   llvm::SmallBitVector &Used);
   void
   MarkDeducedTemplateParameters(const FunctionTemplateDecl *FunctionTemplate,
                                 llvm::SmallBitVector &Deduced) {
     return MarkDeducedTemplateParameters(Context, FunctionTemplate, Deduced);
   }
 
   /// Marks all of the template parameters that will be deduced by a
   /// call to the given function template.
   static void
   MarkDeducedTemplateParameters(ASTContext &Ctx,
                                 const FunctionTemplateDecl *FunctionTemplate,
                                 llvm::SmallBitVector &Deduced);
 
   /// Returns the more specialized function template according
   /// to the rules of function template partial ordering (C++
   /// [temp.func.order]).
   ///
   /// \param FT1 the first function template
   ///
   /// \param FT2 the second function template
   ///
   /// \param TPOC the context in which we are performing partial ordering of
   /// function templates.
   ///
   /// \param NumCallArguments1 The number of arguments in the call to FT1, used
   /// only when \c TPOC is \c TPOC_Call. Does not include the object argument
   /// when calling a member function.
   ///
   /// \param RawObj1Ty The type of the object parameter of FT1 if a member
   /// function only used if \c TPOC is \c TPOC_Call and FT1 is a Function
   /// template from a member function
   ///
   /// \param RawObj2Ty The type of the object parameter of FT2 if a member
   /// function only used if \c TPOC is \c TPOC_Call and FT2 is a Function
   /// template from a member function
   ///
   /// \param Reversed If \c true, exactly one of FT1 and FT2 is an overload
   /// candidate with a reversed parameter order. In this case, the corresponding
   /// P/A pairs between FT1 and FT2 are reversed.
   ///
   /// \returns the more specialized function template. If neither
   /// template is more specialized, returns NULL.
   FunctionTemplateDecl *getMoreSpecializedTemplate(
       FunctionTemplateDecl *FT1, FunctionTemplateDecl *FT2, SourceLocation Loc,
       TemplatePartialOrderingContext TPOC, unsigned NumCallArguments1,
       QualType RawObj1Ty = {}, QualType RawObj2Ty = {}, bool Reversed = false);
 
   /// Retrieve the most specialized of the given function template
   /// specializations.
   ///
   /// \param SpecBegin the start iterator of the function template
   /// specializations that we will be comparing.
   ///
   /// \param SpecEnd the end iterator of the function template
   /// specializations, paired with \p SpecBegin.
   ///
   /// \param Loc the location where the ambiguity or no-specializations
   /// diagnostic should occur.
   ///
   /// \param NoneDiag partial diagnostic used to diagnose cases where there are
   /// no matching candidates.
   ///
   /// \param AmbigDiag partial diagnostic used to diagnose an ambiguity, if one
   /// occurs.
   ///
   /// \param CandidateDiag partial diagnostic used for each function template
   /// specialization that is a candidate in the ambiguous ordering. One
   /// parameter in this diagnostic should be unbound, which will correspond to
   /// the string describing the template arguments for the function template
   /// specialization.
   ///
   /// \returns the most specialized function template specialization, if
   /// found. Otherwise, returns SpecEnd.
   UnresolvedSetIterator
   getMostSpecialized(UnresolvedSetIterator SBegin, UnresolvedSetIterator SEnd,
                      TemplateSpecCandidateSet &FailedCandidates,
                      SourceLocation Loc, const PartialDiagnostic &NoneDiag,
                      const PartialDiagnostic &AmbigDiag,
                      const PartialDiagnostic &CandidateDiag,
                      bool Complain = true, QualType TargetType = QualType());
 
   /// Returns the more constrained function according to the rules of
   /// partial ordering by constraints (C++ [temp.constr.order]).
   ///
   /// \param FD1 the first function
   ///
   /// \param FD2 the second function
   ///
   /// \returns the more constrained function. If neither function is
   /// more constrained, returns NULL.
   FunctionDecl *getMoreConstrainedFunction(FunctionDecl *FD1,
                                            FunctionDecl *FD2);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Template Deduction Guide
   /// Implementations are in SemaTemplateDeductionGuide.cpp
   ///@{
 
   /// Declare implicit deduction guides for a class template if we've
   /// not already done so.
   void DeclareImplicitDeductionGuides(TemplateDecl *Template,
                                       SourceLocation Loc);
 
   FunctionTemplateDecl *DeclareAggregateDeductionGuideFromInitList(
       TemplateDecl *Template, MutableArrayRef<QualType> ParamTypes,
       SourceLocation Loc);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Template Instantiation
   /// Implementations are in SemaTemplateInstantiate.cpp
   ///@{
 
 public:
   /// A helper class for building up ExtParameterInfos.
   class ExtParameterInfoBuilder {
     SmallVector<FunctionProtoType::ExtParameterInfo, 16> Infos;
     bool HasInteresting = false;
 
   public:
     /// Set the ExtParameterInfo for the parameter at the given index,
     ///
     void set(unsigned index, FunctionProtoType::ExtParameterInfo info) {
       assert(Infos.size() <= index);
       Infos.resize(index);
       Infos.push_back(info);
 
       if (!HasInteresting)
         HasInteresting = (info != FunctionProtoType::ExtParameterInfo());
     }
 
     /// Return a pointer (suitable for setting in an ExtProtoInfo) to the
     /// ExtParameterInfo array we've built up.
     const FunctionProtoType::ExtParameterInfo *
     getPointerOrNull(unsigned numParams) {
       if (!HasInteresting)
         return nullptr;
       Infos.resize(numParams);
       return Infos.data();
     }
   };
 
   /// The current instantiation scope used to store local
   /// variables.
   LocalInstantiationScope *CurrentInstantiationScope;
 
   typedef llvm::DenseMap<ParmVarDecl *, llvm::TinyPtrVector<ParmVarDecl *>>
       UnparsedDefaultArgInstantiationsMap;
 
   /// A mapping from parameters with unparsed default arguments to the
   /// set of instantiations of each parameter.
   ///
   /// This mapping is a temporary data structure used when parsing
   /// nested class templates or nested classes of class templates,
   /// where we might end up instantiating an inner class before the
   /// default arguments of its methods have been parsed.
   UnparsedDefaultArgInstantiationsMap UnparsedDefaultArgInstantiations;
 
   /// A context in which code is being synthesized (where a source location
   /// alone is not sufficient to identify the context). This covers template
   /// instantiation and various forms of implicitly-generated functions.
   struct CodeSynthesisContext {
     /// The kind of template instantiation we are performing
     enum SynthesisKind {
       /// We are instantiating a template declaration. The entity is
       /// the declaration we're instantiating (e.g., a CXXRecordDecl).
       TemplateInstantiation,
 
       /// We are instantiating a default argument for a template
       /// parameter. The Entity is the template parameter whose argument is
       /// being instantiated, the Template is the template, and the
       /// TemplateArgs/NumTemplateArguments provide the template arguments as
       /// specified.
       DefaultTemplateArgumentInstantiation,
 
       /// We are instantiating a default argument for a function.
       /// The Entity is the ParmVarDecl, and TemplateArgs/NumTemplateArgs
       /// provides the template arguments as specified.
       DefaultFunctionArgumentInstantiation,
 
       /// We are substituting explicit template arguments provided for
       /// a function template. The entity is a FunctionTemplateDecl.
       ExplicitTemplateArgumentSubstitution,
 
       /// We are substituting template argument determined as part of
       /// template argument deduction for either a class template
       /// partial specialization or a function template. The
       /// Entity is either a {Class|Var}TemplatePartialSpecializationDecl or
       /// a TemplateDecl.
       DeducedTemplateArgumentSubstitution,
 
       /// We are substituting into a lambda expression.
       LambdaExpressionSubstitution,
 
       /// We are substituting prior template arguments into a new
       /// template parameter. The template parameter itself is either a
       /// NonTypeTemplateParmDecl or a TemplateTemplateParmDecl.
       PriorTemplateArgumentSubstitution,
 
       /// We are checking the validity of a default template argument that
       /// has been used when naming a template-id.
       DefaultTemplateArgumentChecking,
 
       /// We are computing the exception specification for a defaulted special
       /// member function.
       ExceptionSpecEvaluation,
 
       /// We are instantiating the exception specification for a function
       /// template which was deferred until it was needed.
       ExceptionSpecInstantiation,
 
       /// We are instantiating a requirement of a requires expression.
       RequirementInstantiation,
 
       /// We are checking the satisfaction of a nested requirement of a requires
       /// expression.
       NestedRequirementConstraintsCheck,
 
       /// We are declaring an implicit special member function.
       DeclaringSpecialMember,
 
       /// We are declaring an implicit 'operator==' for a defaulted
       /// 'operator<=>'.
       DeclaringImplicitEqualityComparison,
 
       /// We are defining a synthesized function (such as a defaulted special
       /// member).
       DefiningSynthesizedFunction,
 
       // We are checking the constraints associated with a constrained entity or
       // the constraint expression of a concept. This includes the checks that
       // atomic constraints have the type 'bool' and that they can be constant
       // evaluated.
       ConstraintsCheck,
 
       // We are substituting template arguments into a constraint expression.
       ConstraintSubstitution,
 
       // We are normalizing a constraint expression.
       ConstraintNormalization,
 
       // Instantiating a Requires Expression parameter clause.
       RequirementParameterInstantiation,
 
       // We are substituting into the parameter mapping of an atomic constraint
       // during normalization.
       ParameterMappingSubstitution,
 
       /// We are rewriting a comparison operator in terms of an operator<=>.
       RewritingOperatorAsSpaceship,
 
       /// We are initializing a structured binding.
       InitializingStructuredBinding,
 
       /// We are marking a class as __dllexport.
       MarkingClassDllexported,
 
       /// We are building an implied call from __builtin_dump_struct. The
       /// arguments are in CallArgs.
       BuildingBuiltinDumpStructCall,
 
       /// Added for Template instantiation observation.
       /// Memoization means we are _not_ instantiating a template because
       /// it is already instantiated (but we entered a context where we
       /// would have had to if it was not already instantiated).
       Memoization,
 
       /// We are building deduction guides for a class.
       BuildingDeductionGuides,
 
       /// We are instantiating a type alias template declaration.
       TypeAliasTemplateInstantiation,
     } Kind;
 
     /// Was the enclosing context a non-instantiation SFINAE context?
     bool SavedInNonInstantiationSFINAEContext;
 
     /// The point of instantiation or synthesis within the source code.
     SourceLocation PointOfInstantiation;
 
     /// The entity that is being synthesized.
     Decl *Entity;
 
     /// The template (or partial specialization) in which we are
     /// performing the instantiation, for substitutions of prior template
     /// arguments.
     NamedDecl *Template;
 
     union {
       /// The list of template arguments we are substituting, if they
       /// are not part of the entity.
       const TemplateArgument *TemplateArgs;
 
       /// The list of argument expressions in a synthesized call.
       const Expr *const *CallArgs;
     };
 
     // FIXME: Wrap this union around more members, or perhaps store the
     // kind-specific members in the RAII object owning the context.
     union {
       /// The number of template arguments in TemplateArgs.
       unsigned NumTemplateArgs;
 
       /// The number of expressions in CallArgs.
       unsigned NumCallArgs;
 
       /// The special member being declared or defined.
       CXXSpecialMemberKind SpecialMember;
     };
 
     ArrayRef<TemplateArgument> template_arguments() const {
       assert(Kind != DeclaringSpecialMember);
       return {TemplateArgs, NumTemplateArgs};
     }
 
     /// The template deduction info object associated with the
     /// substitution or checking of explicit or deduced template arguments.
     sema::TemplateDeductionInfo *DeductionInfo;
 
     /// The source range that covers the construct that cause
     /// the instantiation, e.g., the template-id that causes a class
     /// template instantiation.
     SourceRange InstantiationRange;
 
     CodeSynthesisContext()
         : Kind(TemplateInstantiation),
           SavedInNonInstantiationSFINAEContext(false), Entity(nullptr),
           Template(nullptr), TemplateArgs(nullptr), NumTemplateArgs(0),
           DeductionInfo(nullptr) {}
 
     /// Determines whether this template is an actual instantiation
     /// that should be counted toward the maximum instantiation depth.
     bool isInstantiationRecord() const;
   };
 
   /// A stack object to be created when performing template
   /// instantiation.
   ///
   /// Construction of an object of type \c InstantiatingTemplate
   /// pushes the current instantiation onto the stack of active
   /// instantiations. If the size of this stack exceeds the maximum
   /// number of recursive template instantiations, construction
   /// produces an error and evaluates true.
   ///
   /// Destruction of this object will pop the named instantiation off
   /// the stack.
   struct InstantiatingTemplate {
     /// Note that we are instantiating a class template,
     /// function template, variable template, alias template,
     /// or a member thereof.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           Decl *Entity,
                           SourceRange InstantiationRange = SourceRange());
 
     struct ExceptionSpecification {};
     /// Note that we are instantiating an exception specification
     /// of a function template.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           FunctionDecl *Entity, ExceptionSpecification,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating a type alias template declaration.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TypeAliasTemplateDecl *Entity,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating a default argument in a
     /// template-id.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TemplateParameter Param, TemplateDecl *Template,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are substituting either explicitly-specified or
     /// deduced template arguments during function template argument deduction.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           FunctionTemplateDecl *FunctionTemplate,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           CodeSynthesisContext::SynthesisKind Kind,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating as part of template
     /// argument deduction for a class template declaration.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TemplateDecl *Template,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating as part of template
     /// argument deduction for a class template partial
     /// specialization.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ClassTemplatePartialSpecializationDecl *PartialSpec,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating as part of template
     /// argument deduction for a variable template partial
     /// specialization.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           VarTemplatePartialSpecializationDecl *PartialSpec,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating a default argument for a function
     /// parameter.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ParmVarDecl *Param,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are substituting prior template arguments into a
     /// non-type parameter.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           NamedDecl *Template, NonTypeTemplateParmDecl *Param,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange);
 
     /// Note that we are substituting prior template arguments into a
     /// template template parameter.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           NamedDecl *Template, TemplateTemplateParmDecl *Param,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange);
 
     /// Note that we are checking the default template argument
     /// against the template parameter for a given template-id.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TemplateDecl *Template, NamedDecl *Param,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange);
 
     struct ConstraintsCheck {};
     /// \brief Note that we are checking the constraints associated with some
     /// constrained entity (a concept declaration or a template with associated
     /// constraints).
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ConstraintsCheck, NamedDecl *Template,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange);
 
     struct ConstraintSubstitution {};
     /// \brief Note that we are checking a constraint expression associated
     /// with a template declaration or as part of the satisfaction check of a
     /// concept.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ConstraintSubstitution, NamedDecl *Template,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange);
 
     struct ConstraintNormalization {};
     /// \brief Note that we are normalizing a constraint expression.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ConstraintNormalization, NamedDecl *Template,
                           SourceRange InstantiationRange);
 
     struct ParameterMappingSubstitution {};
     /// \brief Note that we are subtituting into the parameter mapping of an
     /// atomic constraint during constraint normalization.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ParameterMappingSubstitution, NamedDecl *Template,
                           SourceRange InstantiationRange);
 
     /// \brief Note that we are substituting template arguments into a part of
     /// a requirement of a requires expression.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           concepts::Requirement *Req,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// \brief Note that we are checking the satisfaction of the constraint
     /// expression inside of a nested requirement.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           concepts::NestedRequirement *Req, ConstraintsCheck,
                           SourceRange InstantiationRange = SourceRange());
 
     /// \brief Note that we are checking a requires clause.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           const RequiresExpr *E,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange);
 
     struct BuildingDeductionGuidesTag {};
     /// \brief Note that we are building deduction guides.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TemplateDecl *Entity, BuildingDeductionGuidesTag,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we have finished instantiating this template.
     void Clear();
 
     ~InstantiatingTemplate() { Clear(); }
 
     /// Determines whether we have exceeded the maximum
     /// recursive template instantiations.
     bool isInvalid() const { return Invalid; }
 
     /// Determine whether we are already instantiating this
     /// specialization in some surrounding active instantiation.
     bool isAlreadyInstantiating() const { return AlreadyInstantiating; }
 
   private:
     Sema &SemaRef;
     bool Invalid;
     bool AlreadyInstantiating;
     bool CheckInstantiationDepth(SourceLocation PointOfInstantiation,
                                  SourceRange InstantiationRange);
 
     InstantiatingTemplate(
         Sema &SemaRef, CodeSynthesisContext::SynthesisKind Kind,
         SourceLocation PointOfInstantiation, SourceRange InstantiationRange,
         Decl *Entity, NamedDecl *Template = nullptr,
         ArrayRef<TemplateArgument> TemplateArgs = std::nullopt,
         sema::TemplateDeductionInfo *DeductionInfo = nullptr);
 
     InstantiatingTemplate(const InstantiatingTemplate &) = delete;
 
     InstantiatingTemplate &operator=(const InstantiatingTemplate &) = delete;
   };
 
   bool SubstTemplateArgument(const TemplateArgumentLoc &Input,
                              const MultiLevelTemplateArgumentList &TemplateArgs,
                              TemplateArgumentLoc &Output,
                              SourceLocation Loc = {},
                              const DeclarationName &Entity = {});
   bool
   SubstTemplateArguments(ArrayRef<TemplateArgumentLoc> Args,
                          const MultiLevelTemplateArgumentList &TemplateArgs,
                          TemplateArgumentListInfo &Outputs);
 
   /// Retrieve the template argument list(s) that should be used to
   /// instantiate the definition of the given declaration.
   ///
   /// \param ND the declaration for which we are computing template
   /// instantiation arguments.
   ///
   /// \param DC In the event we don't HAVE a declaration yet, we instead provide
   ///  the decl context where it will be created.  In this case, the `Innermost`
   ///  should likely be provided.  If ND is non-null, this is ignored.
   ///
   /// \param Innermost if non-NULL, specifies a template argument list for the
   /// template declaration passed as ND.
   ///
   /// \param RelativeToPrimary true if we should get the template
   /// arguments relative to the primary template, even when we're
   /// dealing with a specialization. This is only relevant for function
   /// template specializations.
   ///
   /// \param Pattern If non-NULL, indicates the pattern from which we will be
   /// instantiating the definition of the given declaration, \p ND. This is
   /// used to determine the proper set of template instantiation arguments for
   /// friend function template specializations.
   ///
   /// \param ForConstraintInstantiation when collecting arguments,
   /// ForConstraintInstantiation indicates we should continue looking when
   /// encountering a lambda generic call operator, and continue looking for
   /// arguments on an enclosing class template.
+  ///
+  /// \param SkipForSpecialization when specified, any template specializations
+  /// in a traversal would be ignored.
+  /// \param ForDefaultArgumentSubstitution indicates we should continue looking
+  /// when encountering a specialized member function template, rather than
+  /// returning immediately.
   MultiLevelTemplateArgumentList getTemplateInstantiationArgs(
       const NamedDecl *D, const DeclContext *DC = nullptr, bool Final = false,
       std::optional<ArrayRef<TemplateArgument>> Innermost = std::nullopt,
       bool RelativeToPrimary = false, const FunctionDecl *Pattern = nullptr,
       bool ForConstraintInstantiation = false,
-      bool SkipForSpecialization = false);
+      bool SkipForSpecialization = false,
+      bool ForDefaultArgumentSubstitution = false);
 
   /// RAII object to handle the state changes required to synthesize
   /// a function body.
   class SynthesizedFunctionScope {
     Sema &S;
     Sema::ContextRAII SavedContext;
     bool PushedCodeSynthesisContext = false;
 
   public:
     SynthesizedFunctionScope(Sema &S, DeclContext *DC)
         : S(S), SavedContext(S, DC) {
       auto *FD = dyn_cast<FunctionDecl>(DC);
       S.PushFunctionScope();
       S.PushExpressionEvaluationContext(
           (FD && FD->isConsteval())
               ? ExpressionEvaluationContext::ImmediateFunctionContext
               : ExpressionEvaluationContext::PotentiallyEvaluated);
       if (FD) {
         FD->setWillHaveBody(true);
         S.ExprEvalContexts.back().InImmediateFunctionContext =
             FD->isImmediateFunction() ||
             S.ExprEvalContexts[S.ExprEvalContexts.size() - 2]
                 .isConstantEvaluated() ||
             S.ExprEvalContexts[S.ExprEvalContexts.size() - 2]
                 .isImmediateFunctionContext();
         S.ExprEvalContexts.back().InImmediateEscalatingFunctionContext =
             S.getLangOpts().CPlusPlus20 && FD->isImmediateEscalating();
       } else
         assert(isa<ObjCMethodDecl>(DC));
     }
 
     void addContextNote(SourceLocation UseLoc) {
       assert(!PushedCodeSynthesisContext);
 
       Sema::CodeSynthesisContext Ctx;
       Ctx.Kind = Sema::CodeSynthesisContext::DefiningSynthesizedFunction;
       Ctx.PointOfInstantiation = UseLoc;
       Ctx.Entity = cast<Decl>(S.CurContext);
       S.pushCodeSynthesisContext(Ctx);
 
       PushedCodeSynthesisContext = true;
     }
 
     ~SynthesizedFunctionScope() {
       if (PushedCodeSynthesisContext)
         S.popCodeSynthesisContext();
       if (auto *FD = dyn_cast<FunctionDecl>(S.CurContext)) {
         FD->setWillHaveBody(false);
         S.CheckImmediateEscalatingFunctionDefinition(FD, S.getCurFunction());
       }
       S.PopExpressionEvaluationContext();
       S.PopFunctionScopeInfo();
     }
   };
 
   /// List of active code synthesis contexts.
   ///
   /// This vector is treated as a stack. As synthesis of one entity requires
   /// synthesis of another, additional contexts are pushed onto the stack.
   SmallVector<CodeSynthesisContext, 16> CodeSynthesisContexts;
 
   /// Specializations whose definitions are currently being instantiated.
   llvm::DenseSet<std::pair<Decl *, unsigned>> InstantiatingSpecializations;
 
   /// Non-dependent types used in templates that have already been instantiated
   /// by some template instantiation.
   llvm::DenseSet<QualType> InstantiatedNonDependentTypes;
 
   /// Extra modules inspected when performing a lookup during a template
   /// instantiation. Computed lazily.
   SmallVector<Module *, 16> CodeSynthesisContextLookupModules;
 
   /// Cache of additional modules that should be used for name lookup
   /// within the current template instantiation. Computed lazily; use
   /// getLookupModules() to get a complete set.
   llvm::DenseSet<Module *> LookupModulesCache;
 
   /// Map from the most recent declaration of a namespace to the most
   /// recent visible declaration of that namespace.
   llvm::DenseMap<NamedDecl *, NamedDecl *> VisibleNamespaceCache;
 
   /// Whether we are in a SFINAE context that is not associated with
   /// template instantiation.
   ///
   /// This is used when setting up a SFINAE trap (\c see SFINAETrap) outside
   /// of a template instantiation or template argument deduction.
   bool InNonInstantiationSFINAEContext;
 
   /// The number of \p CodeSynthesisContexts that are not template
   /// instantiations and, therefore, should not be counted as part of the
   /// instantiation depth.
   ///
   /// When the instantiation depth reaches the user-configurable limit
   /// \p LangOptions::InstantiationDepth we will abort instantiation.
   // FIXME: Should we have a similar limit for other forms of synthesis?
   unsigned NonInstantiationEntries;
 
   /// The depth of the context stack at the point when the most recent
   /// error or warning was produced.
   ///
   /// This value is used to suppress printing of redundant context stacks
   /// when there are multiple errors or warnings in the same instantiation.
   // FIXME: Does this belong in Sema? It's tough to implement it anywhere else.
   unsigned LastEmittedCodeSynthesisContextDepth = 0;
 
   /// The template instantiation callbacks to trace or track
   /// instantiations (objects can be chained).
   ///
   /// This callbacks is used to print, trace or track template
   /// instantiations as they are being constructed.
   std::vector<std::unique_ptr<TemplateInstantiationCallback>>
       TemplateInstCallbacks;
 
   /// The current index into pack expansion arguments that will be
   /// used for substitution of parameter packs.
   ///
   /// The pack expansion index will be -1 to indicate that parameter packs
   /// should be instantiated as themselves. Otherwise, the index specifies
   /// which argument within the parameter pack will be used for substitution.
   int ArgumentPackSubstitutionIndex;
 
   /// RAII object used to change the argument pack substitution index
   /// within a \c Sema object.
   ///
   /// See \c ArgumentPackSubstitutionIndex for more information.
   class ArgumentPackSubstitutionIndexRAII {
     Sema &Self;
     int OldSubstitutionIndex;
 
   public:
     ArgumentPackSubstitutionIndexRAII(Sema &Self, int NewSubstitutionIndex)
         : Self(Self), OldSubstitutionIndex(Self.ArgumentPackSubstitutionIndex) {
       Self.ArgumentPackSubstitutionIndex = NewSubstitutionIndex;
     }
 
     ~ArgumentPackSubstitutionIndexRAII() {
       Self.ArgumentPackSubstitutionIndex = OldSubstitutionIndex;
     }
   };
 
   friend class ArgumentPackSubstitutionRAII;
 
   void pushCodeSynthesisContext(CodeSynthesisContext Ctx);
   void popCodeSynthesisContext();
 
   void PrintContextStack() {
     if (!CodeSynthesisContexts.empty() &&
         CodeSynthesisContexts.size() != LastEmittedCodeSynthesisContextDepth) {
       PrintInstantiationStack();
       LastEmittedCodeSynthesisContextDepth = CodeSynthesisContexts.size();
     }
     if (PragmaAttributeCurrentTargetDecl)
       PrintPragmaAttributeInstantiationPoint();
   }
   /// Prints the current instantiation stack through a series of
   /// notes.
   void PrintInstantiationStack();
 
   /// Determines whether we are currently in a context where
   /// template argument substitution failures are not considered
   /// errors.
   ///
   /// \returns An empty \c Optional if we're not in a SFINAE context.
   /// Otherwise, contains a pointer that, if non-NULL, contains the nearest
   /// template-deduction context object, which can be used to capture
   /// diagnostics that will be suppressed.
   std::optional<sema::TemplateDeductionInfo *> isSFINAEContext() const;
 
   /// Perform substitution on the type T with a given set of template
   /// arguments.
   ///
   /// This routine substitutes the given template arguments into the
   /// type T and produces the instantiated type.
   ///
   /// \param T the type into which the template arguments will be
   /// substituted. If this type is not dependent, it will be returned
   /// immediately.
   ///
   /// \param Args the template arguments that will be
   /// substituted for the top-level template parameters within T.
   ///
   /// \param Loc the location in the source code where this substitution
   /// is being performed. It will typically be the location of the
   /// declarator (if we're instantiating the type of some declaration)
   /// or the location of the type in the source code (if, e.g., we're
   /// instantiating the type of a cast expression).
   ///
   /// \param Entity the name of the entity associated with a declaration
   /// being instantiated (if any). May be empty to indicate that there
   /// is no such entity (if, e.g., this is a type that occurs as part of
   /// a cast expression) or that the entity has no name (e.g., an
   /// unnamed function parameter).
   ///
   /// \param AllowDeducedTST Whether a DeducedTemplateSpecializationType is
   /// acceptable as the top level type of the result.
   ///
   /// \returns If the instantiation succeeds, the instantiated
   /// type. Otherwise, produces diagnostics and returns a NULL type.
   TypeSourceInfo *SubstType(TypeSourceInfo *T,
                             const MultiLevelTemplateArgumentList &TemplateArgs,
                             SourceLocation Loc, DeclarationName Entity,
                             bool AllowDeducedTST = false);
 
   QualType SubstType(QualType T,
                      const MultiLevelTemplateArgumentList &TemplateArgs,
                      SourceLocation Loc, DeclarationName Entity);
 
   TypeSourceInfo *SubstType(TypeLoc TL,
                             const MultiLevelTemplateArgumentList &TemplateArgs,
                             SourceLocation Loc, DeclarationName Entity);
 
   /// A form of SubstType intended specifically for instantiating the
   /// type of a FunctionDecl.  Its purpose is solely to force the
   /// instantiation of default-argument expressions and to avoid
   /// instantiating an exception-specification.
   TypeSourceInfo *SubstFunctionDeclType(
       TypeSourceInfo *T, const MultiLevelTemplateArgumentList &TemplateArgs,
       SourceLocation Loc, DeclarationName Entity, CXXRecordDecl *ThisContext,
       Qualifiers ThisTypeQuals, bool EvaluateConstraints = true);
   void SubstExceptionSpec(FunctionDecl *New, const FunctionProtoType *Proto,
                           const MultiLevelTemplateArgumentList &Args);
   bool SubstExceptionSpec(SourceLocation Loc,
                           FunctionProtoType::ExceptionSpecInfo &ESI,
                           SmallVectorImpl<QualType> &ExceptionStorage,
                           const MultiLevelTemplateArgumentList &Args);
   ParmVarDecl *
   SubstParmVarDecl(ParmVarDecl *D,
                    const MultiLevelTemplateArgumentList &TemplateArgs,
                    int indexAdjustment, std::optional<unsigned> NumExpansions,
                    bool ExpectParameterPack, bool EvaluateConstraints = true);
 
   /// Substitute the given template arguments into the given set of
   /// parameters, producing the set of parameter types that would be generated
   /// from such a substitution.
   bool SubstParmTypes(SourceLocation Loc, ArrayRef<ParmVarDecl *> Params,
                       const FunctionProtoType::ExtParameterInfo *ExtParamInfos,
                       const MultiLevelTemplateArgumentList &TemplateArgs,
                       SmallVectorImpl<QualType> &ParamTypes,
                       SmallVectorImpl<ParmVarDecl *> *OutParams,
                       ExtParameterInfoBuilder &ParamInfos);
 
   /// Substitute the given template arguments into the default argument.
   bool SubstDefaultArgument(SourceLocation Loc, ParmVarDecl *Param,
                             const MultiLevelTemplateArgumentList &TemplateArgs,
                             bool ForCallExpr = false);
   ExprResult SubstExpr(Expr *E,
                        const MultiLevelTemplateArgumentList &TemplateArgs);
 
   // A RAII type used by the TemplateDeclInstantiator and TemplateInstantiator
   // to disable constraint evaluation, then restore the state.
   template <typename InstTy> struct ConstraintEvalRAII {
     InstTy &TI;
     bool OldValue;
 
     ConstraintEvalRAII(InstTy &TI)
         : TI(TI), OldValue(TI.getEvaluateConstraints()) {
       TI.setEvaluateConstraints(false);
     }
     ~ConstraintEvalRAII() { TI.setEvaluateConstraints(OldValue); }
   };
 
   // Must be used instead of SubstExpr at 'constraint checking' time.
   ExprResult
   SubstConstraintExpr(Expr *E,
                       const MultiLevelTemplateArgumentList &TemplateArgs);
   // Unlike the above, this does not evaluates constraints.
   ExprResult SubstConstraintExprWithoutSatisfaction(
       Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Substitute the given template arguments into a list of
   /// expressions, expanding pack expansions if required.
   ///
   /// \param Exprs The list of expressions to substitute into.
   ///
   /// \param IsCall Whether this is some form of call, in which case
   /// default arguments will be dropped.
   ///
   /// \param TemplateArgs The set of template arguments to substitute.
   ///
   /// \param Outputs Will receive all of the substituted arguments.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool SubstExprs(ArrayRef<Expr *> Exprs, bool IsCall,
                   const MultiLevelTemplateArgumentList &TemplateArgs,
                   SmallVectorImpl<Expr *> &Outputs);
 
   StmtResult SubstStmt(Stmt *S,
                        const MultiLevelTemplateArgumentList &TemplateArgs);
 
   ExprResult
   SubstInitializer(Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs,
                    bool CXXDirectInit);
 
   /// Perform substitution on the base class specifiers of the
   /// given class template specialization.
   ///
   /// Produces a diagnostic and returns true on error, returns false and
   /// attaches the instantiated base classes to the class template
   /// specialization if successful.
   bool SubstBaseSpecifiers(CXXRecordDecl *Instantiation, CXXRecordDecl *Pattern,
                            const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Instantiate the definition of a class from a given pattern.
   ///
   /// \param PointOfInstantiation The point of instantiation within the
   /// source code.
   ///
   /// \param Instantiation is the declaration whose definition is being
   /// instantiated. This will be either a class template specialization
   /// or a member class of a class template specialization.
   ///
   /// \param Pattern is the pattern from which the instantiation
   /// occurs. This will be either the declaration of a class template or
   /// the declaration of a member class of a class template.
   ///
   /// \param TemplateArgs The template arguments to be substituted into
   /// the pattern.
   ///
   /// \param TSK the kind of implicit or explicit instantiation to perform.
   ///
   /// \param Complain whether to complain if the class cannot be instantiated
   /// due to the lack of a definition.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool InstantiateClass(SourceLocation PointOfInstantiation,
                         CXXRecordDecl *Instantiation, CXXRecordDecl *Pattern,
                         const MultiLevelTemplateArgumentList &TemplateArgs,
                         TemplateSpecializationKind TSK, bool Complain = true);
 
   /// Instantiate the definition of an enum from a given pattern.
   ///
   /// \param PointOfInstantiation The point of instantiation within the
   ///        source code.
   /// \param Instantiation is the declaration whose definition is being
   ///        instantiated. This will be a member enumeration of a class
   ///        temploid specialization, or a local enumeration within a
   ///        function temploid specialization.
   /// \param Pattern The templated declaration from which the instantiation
   ///        occurs.
   /// \param TemplateArgs The template arguments to be substituted into
   ///        the pattern.
   /// \param TSK The kind of implicit or explicit instantiation to perform.
   ///
   /// \return \c true if an error occurred, \c false otherwise.
   bool InstantiateEnum(SourceLocation PointOfInstantiation,
                        EnumDecl *Instantiation, EnumDecl *Pattern,
                        const MultiLevelTemplateArgumentList &TemplateArgs,
                        TemplateSpecializationKind TSK);
 
   /// Instantiate the definition of a field from the given pattern.
   ///
   /// \param PointOfInstantiation The point of instantiation within the
   ///        source code.
   /// \param Instantiation is the declaration whose definition is being
   ///        instantiated. This will be a class of a class temploid
   ///        specialization, or a local enumeration within a function temploid
   ///        specialization.
   /// \param Pattern The templated declaration from which the instantiation
   ///        occurs.
   /// \param TemplateArgs The template arguments to be substituted into
   ///        the pattern.
   ///
   /// \return \c true if an error occurred, \c false otherwise.
   bool InstantiateInClassInitializer(
       SourceLocation PointOfInstantiation, FieldDecl *Instantiation,
       FieldDecl *Pattern, const MultiLevelTemplateArgumentList &TemplateArgs);
 
   bool usesPartialOrExplicitSpecialization(
       SourceLocation Loc, ClassTemplateSpecializationDecl *ClassTemplateSpec);
 
   bool InstantiateClassTemplateSpecialization(
       SourceLocation PointOfInstantiation,
       ClassTemplateSpecializationDecl *ClassTemplateSpec,
       TemplateSpecializationKind TSK, bool Complain = true);
 
   /// Instantiates the definitions of all of the member
   /// of the given class, which is an instantiation of a class template
   /// or a member class of a template.
   void
   InstantiateClassMembers(SourceLocation PointOfInstantiation,
                           CXXRecordDecl *Instantiation,
                           const MultiLevelTemplateArgumentList &TemplateArgs,
                           TemplateSpecializationKind TSK);
 
   /// Instantiate the definitions of all of the members of the
   /// given class template specialization, which was named as part of an
   /// explicit instantiation.
   void InstantiateClassTemplateSpecializationMembers(
       SourceLocation PointOfInstantiation,
       ClassTemplateSpecializationDecl *ClassTemplateSpec,
       TemplateSpecializationKind TSK);
 
   NestedNameSpecifierLoc SubstNestedNameSpecifierLoc(
       NestedNameSpecifierLoc NNS,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Do template substitution on declaration name info.
   DeclarationNameInfo
   SubstDeclarationNameInfo(const DeclarationNameInfo &NameInfo,
                            const MultiLevelTemplateArgumentList &TemplateArgs);
   TemplateName
   SubstTemplateName(NestedNameSpecifierLoc QualifierLoc, TemplateName Name,
                     SourceLocation Loc,
                     const MultiLevelTemplateArgumentList &TemplateArgs);
 
   bool SubstTypeConstraint(TemplateTypeParmDecl *Inst, const TypeConstraint *TC,
                            const MultiLevelTemplateArgumentList &TemplateArgs,
                            bool EvaluateConstraint);
 
   /// Determine whether we are currently performing template instantiation.
   bool inTemplateInstantiation() const {
     return CodeSynthesisContexts.size() > NonInstantiationEntries;
   }
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Template Declaration Instantiation
   /// Implementations are in SemaTemplateInstantiateDecl.cpp
   ///@{
 
 public:
   /// An entity for which implicit template instantiation is required.
   ///
   /// The source location associated with the declaration is the first place in
   /// the source code where the declaration was "used". It is not necessarily
   /// the point of instantiation (which will be either before or after the
   /// namespace-scope declaration that triggered this implicit instantiation),
   /// However, it is the location that diagnostics should generally refer to,
   /// because users will need to know what code triggered the instantiation.
   typedef std::pair<ValueDecl *, SourceLocation> PendingImplicitInstantiation;
 
   /// The queue of implicit template instantiations that are required
   /// but have not yet been performed.
   std::deque<PendingImplicitInstantiation> PendingInstantiations;
 
   /// Queue of implicit template instantiations that cannot be performed
   /// eagerly.
   SmallVector<PendingImplicitInstantiation, 1> LateParsedInstantiations;
 
   SmallVector<SmallVector<VTableUse, 16>, 8> SavedVTableUses;
   SmallVector<std::deque<PendingImplicitInstantiation>, 8>
       SavedPendingInstantiations;
 
   /// The queue of implicit template instantiations that are required
   /// and must be performed within the current local scope.
   ///
   /// This queue is only used for member functions of local classes in
   /// templates, which must be instantiated in the same scope as their
   /// enclosing function, so that they can reference function-local
   /// types, static variables, enumerators, etc.
   std::deque<PendingImplicitInstantiation> PendingLocalImplicitInstantiations;
 
   class LocalEagerInstantiationScope {
   public:
     LocalEagerInstantiationScope(Sema &S) : S(S) {
       SavedPendingLocalImplicitInstantiations.swap(
           S.PendingLocalImplicitInstantiations);
     }
 
     void perform() { S.PerformPendingInstantiations(/*LocalOnly=*/true); }
 
     ~LocalEagerInstantiationScope() {
       assert(S.PendingLocalImplicitInstantiations.empty() &&
              "there shouldn't be any pending local implicit instantiations");
       SavedPendingLocalImplicitInstantiations.swap(
           S.PendingLocalImplicitInstantiations);
     }
 
   private:
     Sema &S;
     std::deque<PendingImplicitInstantiation>
         SavedPendingLocalImplicitInstantiations;
   };
 
   /// Records and restores the CurFPFeatures state on entry/exit of compound
   /// statements.
   class FPFeaturesStateRAII {
   public:
     FPFeaturesStateRAII(Sema &S);
     ~FPFeaturesStateRAII();
     FPOptionsOverride getOverrides() { return OldOverrides; }
 
   private:
     Sema &S;
     FPOptions OldFPFeaturesState;
     FPOptionsOverride OldOverrides;
     LangOptions::FPEvalMethodKind OldEvalMethod;
     SourceLocation OldFPPragmaLocation;
   };
 
   class GlobalEagerInstantiationScope {
   public:
     GlobalEagerInstantiationScope(Sema &S, bool Enabled)
         : S(S), Enabled(Enabled) {
       if (!Enabled)
         return;
 
       S.SavedPendingInstantiations.emplace_back();
       S.SavedPendingInstantiations.back().swap(S.PendingInstantiations);
 
       S.SavedVTableUses.emplace_back();
       S.SavedVTableUses.back().swap(S.VTableUses);
     }
 
     void perform() {
       if (Enabled) {
         S.DefineUsedVTables();
         S.PerformPendingInstantiations();
       }
     }
 
     ~GlobalEagerInstantiationScope() {
       if (!Enabled)
         return;
 
       // Restore the set of pending vtables.
       assert(S.VTableUses.empty() &&
              "VTableUses should be empty before it is discarded.");
       S.VTableUses.swap(S.SavedVTableUses.back());
       S.SavedVTableUses.pop_back();
 
       // Restore the set of pending implicit instantiations.
       if (S.TUKind != TU_Prefix || !S.LangOpts.PCHInstantiateTemplates) {
         assert(S.PendingInstantiations.empty() &&
                "PendingInstantiations should be empty before it is discarded.");
         S.PendingInstantiations.swap(S.SavedPendingInstantiations.back());
         S.SavedPendingInstantiations.pop_back();
       } else {
         // Template instantiations in the PCH may be delayed until the TU.
         S.PendingInstantiations.swap(S.SavedPendingInstantiations.back());
         S.PendingInstantiations.insert(
             S.PendingInstantiations.end(),
             S.SavedPendingInstantiations.back().begin(),
             S.SavedPendingInstantiations.back().end());
         S.SavedPendingInstantiations.pop_back();
       }
     }
 
   private:
     Sema &S;
     bool Enabled;
   };
 
   ExplicitSpecifier instantiateExplicitSpecifier(
       const MultiLevelTemplateArgumentList &TemplateArgs, ExplicitSpecifier ES);
 
   struct LateInstantiatedAttribute {
     const Attr *TmplAttr;
     LocalInstantiationScope *Scope;
     Decl *NewDecl;
 
     LateInstantiatedAttribute(const Attr *A, LocalInstantiationScope *S,
                               Decl *D)
         : TmplAttr(A), Scope(S), NewDecl(D) {}
   };
   typedef SmallVector<LateInstantiatedAttribute, 16> LateInstantiatedAttrVec;
 
   void InstantiateAttrs(const MultiLevelTemplateArgumentList &TemplateArgs,
                         const Decl *Pattern, Decl *Inst,
                         LateInstantiatedAttrVec *LateAttrs = nullptr,
                         LocalInstantiationScope *OuterMostScope = nullptr);
 
   /// Update instantiation attributes after template was late parsed.
   ///
   /// Some attributes are evaluated based on the body of template. If it is
   /// late parsed, such attributes cannot be evaluated when declaration is
   /// instantiated. This function is used to update instantiation attributes
   /// when template definition is ready.
   void updateAttrsForLateParsedTemplate(const Decl *Pattern, Decl *Inst);
 
   void
   InstantiateAttrsForDecl(const MultiLevelTemplateArgumentList &TemplateArgs,
                           const Decl *Pattern, Decl *Inst,
                           LateInstantiatedAttrVec *LateAttrs = nullptr,
                           LocalInstantiationScope *OuterMostScope = nullptr);
 
   /// In the MS ABI, we need to instantiate default arguments of dllexported
   /// default constructors along with the constructor definition. This allows IR
   /// gen to emit a constructor closure which calls the default constructor with
   /// its default arguments.
   void InstantiateDefaultCtorDefaultArgs(CXXConstructorDecl *Ctor);
 
   bool InstantiateDefaultArgument(SourceLocation CallLoc, FunctionDecl *FD,
                                   ParmVarDecl *Param);
   void InstantiateExceptionSpec(SourceLocation PointOfInstantiation,
                                 FunctionDecl *Function);
 
   /// Instantiate (or find existing instantiation of) a function template with a
   /// given set of template arguments.
   ///
   /// Usually this should not be used, and template argument deduction should be
   /// used in its place.
   FunctionDecl *InstantiateFunctionDeclaration(
       FunctionTemplateDecl *FTD, const TemplateArgumentList *Args,
       SourceLocation Loc,
       CodeSynthesisContext::SynthesisKind CSC =
           CodeSynthesisContext::ExplicitTemplateArgumentSubstitution);
 
   /// Instantiate the definition of the given function from its
   /// template.
   ///
   /// \param PointOfInstantiation the point at which the instantiation was
   /// required. Note that this is not precisely a "point of instantiation"
   /// for the function, but it's close.
   ///
   /// \param Function the already-instantiated declaration of a
   /// function template specialization or member function of a class template
   /// specialization.
   ///
   /// \param Recursive if true, recursively instantiates any functions that
   /// are required by this instantiation.
   ///
   /// \param DefinitionRequired if true, then we are performing an explicit
   /// instantiation where the body of the function is required. Complain if
   /// there is no such body.
   void InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
                                      FunctionDecl *Function,
                                      bool Recursive = false,
                                      bool DefinitionRequired = false,
                                      bool AtEndOfTU = false);
   VarTemplateSpecializationDecl *BuildVarTemplateInstantiation(
       VarTemplateDecl *VarTemplate, VarDecl *FromVar,
       const TemplateArgumentList *PartialSpecArgs,
       const TemplateArgumentListInfo &TemplateArgsInfo,
       SmallVectorImpl<TemplateArgument> &Converted,
       SourceLocation PointOfInstantiation,
       LateInstantiatedAttrVec *LateAttrs = nullptr,
       LocalInstantiationScope *StartingScope = nullptr);
 
   /// Instantiates a variable template specialization by completing it
   /// with appropriate type information and initializer.
   VarTemplateSpecializationDecl *CompleteVarTemplateSpecializationDecl(
       VarTemplateSpecializationDecl *VarSpec, VarDecl *PatternDecl,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// BuildVariableInstantiation - Used after a new variable has been created.
   /// Sets basic variable data and decides whether to postpone the
   /// variable instantiation.
   void
   BuildVariableInstantiation(VarDecl *NewVar, VarDecl *OldVar,
                              const MultiLevelTemplateArgumentList &TemplateArgs,
                              LateInstantiatedAttrVec *LateAttrs,
                              DeclContext *Owner,
                              LocalInstantiationScope *StartingScope,
                              bool InstantiatingVarTemplate = false,
                              VarTemplateSpecializationDecl *PrevVTSD = nullptr);
 
   /// Instantiate the initializer of a variable.
   void InstantiateVariableInitializer(
       VarDecl *Var, VarDecl *OldVar,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Instantiate the definition of the given variable from its
   /// template.
   ///
   /// \param PointOfInstantiation the point at which the instantiation was
   /// required. Note that this is not precisely a "point of instantiation"
   /// for the variable, but it's close.
   ///
   /// \param Var the already-instantiated declaration of a templated variable.
   ///
   /// \param Recursive if true, recursively instantiates any functions that
   /// are required by this instantiation.
   ///
   /// \param DefinitionRequired if true, then we are performing an explicit
   /// instantiation where a definition of the variable is required. Complain
   /// if there is no such definition.
   void InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
                                      VarDecl *Var, bool Recursive = false,
                                      bool DefinitionRequired = false,
                                      bool AtEndOfTU = false);
 
   void InstantiateMemInitializers(
       CXXConstructorDecl *New, const CXXConstructorDecl *Tmpl,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Find the instantiation of the given declaration within the
   /// current instantiation.
   ///
   /// This routine is intended to be used when \p D is a declaration
   /// referenced from within a template, that needs to mapped into the
   /// corresponding declaration within an instantiation. For example,
   /// given:
   ///
   /// \code
   /// template<typename T>
   /// struct X {
   ///   enum Kind {
   ///     KnownValue = sizeof(T)
   ///   };
   ///
   ///   bool getKind() const { return KnownValue; }
   /// };
   ///
   /// template struct X<int>;
   /// \endcode
   ///
   /// In the instantiation of X<int>::getKind(), we need to map the \p
   /// EnumConstantDecl for \p KnownValue (which refers to
   /// X<T>::<Kind>::KnownValue) to its instantiation
   /// (X<int>::<Kind>::KnownValue).
   /// \p FindInstantiatedDecl performs this mapping from within the
   /// instantiation of X<int>.
   NamedDecl *
   FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
                        const MultiLevelTemplateArgumentList &TemplateArgs,
                        bool FindingInstantiatedContext = false);
 
   /// Finds the instantiation of the given declaration context
   /// within the current instantiation.
   ///
   /// \returns NULL if there was an error
   DeclContext *
   FindInstantiatedContext(SourceLocation Loc, DeclContext *DC,
                           const MultiLevelTemplateArgumentList &TemplateArgs);
 
   Decl *SubstDecl(Decl *D, DeclContext *Owner,
                   const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Substitute the name and return type of a defaulted 'operator<=>' to form
   /// an implicit 'operator=='.
   FunctionDecl *SubstSpaceshipAsEqualEqual(CXXRecordDecl *RD,
                                            FunctionDecl *Spaceship);
 
   /// Performs template instantiation for all implicit template
   /// instantiations we have seen until this point.
   void PerformPendingInstantiations(bool LocalOnly = false);
 
   TemplateParameterList *
   SubstTemplateParams(TemplateParameterList *Params, DeclContext *Owner,
                       const MultiLevelTemplateArgumentList &TemplateArgs,
                       bool EvaluateConstraints = true);
 
   void PerformDependentDiagnostics(
       const DeclContext *Pattern,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
 private:
   /// Introduce the instantiated local variables into the local
   /// instantiation scope.
   void addInstantiatedLocalVarsToScope(FunctionDecl *Function,
                                        const FunctionDecl *PatternDecl,
                                        LocalInstantiationScope &Scope);
   /// Introduce the instantiated function parameters into the local
   /// instantiation scope, and set the parameter names to those used
   /// in the template.
   bool addInstantiatedParametersToScope(
       FunctionDecl *Function, const FunctionDecl *PatternDecl,
       LocalInstantiationScope &Scope,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   int ParsingClassDepth = 0;
 
   class SavePendingParsedClassStateRAII {
   public:
     SavePendingParsedClassStateRAII(Sema &S) : S(S) { swapSavedState(); }
 
     ~SavePendingParsedClassStateRAII() {
       assert(S.DelayedOverridingExceptionSpecChecks.empty() &&
              "there shouldn't be any pending delayed exception spec checks");
       assert(S.DelayedEquivalentExceptionSpecChecks.empty() &&
              "there shouldn't be any pending delayed exception spec checks");
       swapSavedState();
     }
 
   private:
     Sema &S;
     decltype(DelayedOverridingExceptionSpecChecks)
         SavedOverridingExceptionSpecChecks;
     decltype(DelayedEquivalentExceptionSpecChecks)
         SavedEquivalentExceptionSpecChecks;
 
     void swapSavedState() {
       SavedOverridingExceptionSpecChecks.swap(
           S.DelayedOverridingExceptionSpecChecks);
       SavedEquivalentExceptionSpecChecks.swap(
           S.DelayedEquivalentExceptionSpecChecks);
     }
   };
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Variadic Templates
   /// Implementations are in SemaTemplateVariadic.cpp
   ///@{
 
 public:
   /// Determine whether an unexpanded parameter pack might be permitted in this
   /// location. Useful for error recovery.
   bool isUnexpandedParameterPackPermitted();
 
   /// The context in which an unexpanded parameter pack is
   /// being diagnosed.
   ///
   /// Note that the values of this enumeration line up with the first
   /// argument to the \c err_unexpanded_parameter_pack diagnostic.
   enum UnexpandedParameterPackContext {
     /// An arbitrary expression.
     UPPC_Expression = 0,
 
     /// The base type of a class type.
     UPPC_BaseType,
 
     /// The type of an arbitrary declaration.
     UPPC_DeclarationType,
 
     /// The type of a data member.
     UPPC_DataMemberType,
 
     /// The size of a bit-field.
     UPPC_BitFieldWidth,
 
     /// The expression in a static assertion.
     UPPC_StaticAssertExpression,
 
     /// The fixed underlying type of an enumeration.
     UPPC_FixedUnderlyingType,
 
     /// The enumerator value.
     UPPC_EnumeratorValue,
 
     /// A using declaration.
     UPPC_UsingDeclaration,
 
     /// A friend declaration.
     UPPC_FriendDeclaration,
 
     /// A declaration qualifier.
     UPPC_DeclarationQualifier,
 
     /// An initializer.
     UPPC_Initializer,
 
     /// A default argument.
     UPPC_DefaultArgument,
 
     /// The type of a non-type template parameter.
     UPPC_NonTypeTemplateParameterType,
 
     /// The type of an exception.
     UPPC_ExceptionType,
 
     /// Explicit specialization.
     UPPC_ExplicitSpecialization,
 
     /// Partial specialization.
     UPPC_PartialSpecialization,
 
     /// Microsoft __if_exists.
     UPPC_IfExists,
 
     /// Microsoft __if_not_exists.
     UPPC_IfNotExists,
 
     /// Lambda expression.
     UPPC_Lambda,
 
     /// Block expression.
     UPPC_Block,
 
     /// A type constraint.
     UPPC_TypeConstraint,
 
     // A requirement in a requires-expression.
     UPPC_Requirement,
 
     // A requires-clause.
     UPPC_RequiresClause,
   };
 
   /// Diagnose unexpanded parameter packs.
   ///
   /// \param Loc The location at which we should emit the diagnostic.
   ///
   /// \param UPPC The context in which we are diagnosing unexpanded
   /// parameter packs.
   ///
   /// \param Unexpanded the set of unexpanded parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPacks(
       SourceLocation Loc, UnexpandedParameterPackContext UPPC,
       ArrayRef<UnexpandedParameterPack> Unexpanded);
 
   /// If the given type contains an unexpanded parameter pack,
   /// diagnose the error.
   ///
   /// \param Loc The source location where a diagnostc should be emitted.
   ///
   /// \param T The type that is being checked for unexpanded parameter
   /// packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(SourceLocation Loc, TypeSourceInfo *T,
                                        UnexpandedParameterPackContext UPPC);
 
   /// If the given expression contains an unexpanded parameter
   /// pack, diagnose the error.
   ///
   /// \param E The expression that is being checked for unexpanded
   /// parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(
       Expr *E, UnexpandedParameterPackContext UPPC = UPPC_Expression);
 
   /// If the given requirees-expression contains an unexpanded reference to one
   /// of its own parameter packs, diagnose the error.
   ///
   /// \param RE The requiress-expression that is being checked for unexpanded
   /// parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPackInRequiresExpr(RequiresExpr *RE);
 
   /// If the given nested-name-specifier contains an unexpanded
   /// parameter pack, diagnose the error.
   ///
   /// \param SS The nested-name-specifier that is being checked for
   /// unexpanded parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(const CXXScopeSpec &SS,
                                        UnexpandedParameterPackContext UPPC);
 
   /// If the given name contains an unexpanded parameter pack,
   /// diagnose the error.
   ///
   /// \param NameInfo The name (with source location information) that
   /// is being checked for unexpanded parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(const DeclarationNameInfo &NameInfo,
                                        UnexpandedParameterPackContext UPPC);
 
   /// If the given template name contains an unexpanded parameter pack,
   /// diagnose the error.
   ///
   /// \param Loc The location of the template name.
   ///
   /// \param Template The template name that is being checked for unexpanded
   /// parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(SourceLocation Loc,
                                        TemplateName Template,
                                        UnexpandedParameterPackContext UPPC);
 
   /// If the given template argument contains an unexpanded parameter
   /// pack, diagnose the error.
   ///
   /// \param Arg The template argument that is being checked for unexpanded
   /// parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(TemplateArgumentLoc Arg,
                                        UnexpandedParameterPackContext UPPC);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// template argument.
   ///
   /// \param Arg The template argument that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       TemplateArgument Arg,
       SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// template argument.
   ///
   /// \param Arg The template argument that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       TemplateArgumentLoc Arg,
       SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// type.
   ///
   /// \param T The type that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       QualType T, SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// type.
   ///
   /// \param TL The type that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       TypeLoc TL, SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// nested-name-specifier.
   ///
   /// \param NNS The nested-name-specifier that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       NestedNameSpecifierLoc NNS,
       SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// name.
   ///
   /// \param NameInfo The name that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       const DeclarationNameInfo &NameInfo,
       SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// expression.
   static void collectUnexpandedParameterPacks(
       Expr *E, SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Invoked when parsing a template argument followed by an
   /// ellipsis, which creates a pack expansion.
   ///
   /// \param Arg The template argument preceding the ellipsis, which
   /// may already be invalid.
   ///
   /// \param EllipsisLoc The location of the ellipsis.
   ParsedTemplateArgument ActOnPackExpansion(const ParsedTemplateArgument &Arg,
                                             SourceLocation EllipsisLoc);
 
   /// Invoked when parsing a type followed by an ellipsis, which
   /// creates a pack expansion.
   ///
   /// \param Type The type preceding the ellipsis, which will become
   /// the pattern of the pack expansion.
   ///
   /// \param EllipsisLoc The location of the ellipsis.
   TypeResult ActOnPackExpansion(ParsedType Type, SourceLocation EllipsisLoc);
 
   /// Construct a pack expansion type from the pattern of the pack
   /// expansion.
   TypeSourceInfo *CheckPackExpansion(TypeSourceInfo *Pattern,
                                      SourceLocation EllipsisLoc,
                                      std::optional<unsigned> NumExpansions);
 
   /// Construct a pack expansion type from the pattern of the pack
   /// expansion.
   QualType CheckPackExpansion(QualType Pattern, SourceRange PatternRange,
                               SourceLocation EllipsisLoc,
                               std::optional<unsigned> NumExpansions);
 
   /// Invoked when parsing an expression followed by an ellipsis, which
   /// creates a pack expansion.
   ///
   /// \param Pattern The expression preceding the ellipsis, which will become
   /// the pattern of the pack expansion.
   ///
   /// \param EllipsisLoc The location of the ellipsis.
   ExprResult ActOnPackExpansion(Expr *Pattern, SourceLocation EllipsisLoc);
 
   /// Invoked when parsing an expression followed by an ellipsis, which
   /// creates a pack expansion.
   ///
   /// \param Pattern The expression preceding the ellipsis, which will become
   /// the pattern of the pack expansion.
   ///
   /// \param EllipsisLoc The location of the ellipsis.
   ExprResult CheckPackExpansion(Expr *Pattern, SourceLocation EllipsisLoc,
                                 std::optional<unsigned> NumExpansions);
 
   /// Determine whether we could expand a pack expansion with the
   /// given set of parameter packs into separate arguments by repeatedly
   /// transforming the pattern.
   ///
   /// \param EllipsisLoc The location of the ellipsis that identifies the
   /// pack expansion.
   ///
   /// \param PatternRange The source range that covers the entire pattern of
   /// the pack expansion.
   ///
   /// \param Unexpanded The set of unexpanded parameter packs within the
   /// pattern.
   ///
   /// \param ShouldExpand Will be set to \c true if the transformer should
   /// expand the corresponding pack expansions into separate arguments. When
   /// set, \c NumExpansions must also be set.
   ///
   /// \param RetainExpansion Whether the caller should add an unexpanded
   /// pack expansion after all of the expanded arguments. This is used
   /// when extending explicitly-specified template argument packs per
   /// C++0x [temp.arg.explicit]p9.
   ///
   /// \param NumExpansions The number of separate arguments that will be in
   /// the expanded form of the corresponding pack expansion. This is both an
   /// input and an output parameter, which can be set by the caller if the
   /// number of expansions is known a priori (e.g., due to a prior substitution)
   /// and will be set by the callee when the number of expansions is known.
   /// The callee must set this value when \c ShouldExpand is \c true; it may
   /// set this value in other cases.
   ///
   /// \returns true if an error occurred (e.g., because the parameter packs
   /// are to be instantiated with arguments of different lengths), false
   /// otherwise. If false, \c ShouldExpand (and possibly \c NumExpansions)
   /// must be set.
   bool CheckParameterPacksForExpansion(
       SourceLocation EllipsisLoc, SourceRange PatternRange,
       ArrayRef<UnexpandedParameterPack> Unexpanded,
       const MultiLevelTemplateArgumentList &TemplateArgs, bool &ShouldExpand,
       bool &RetainExpansion, std::optional<unsigned> &NumExpansions);
 
   /// Determine the number of arguments in the given pack expansion
   /// type.
   ///
   /// This routine assumes that the number of arguments in the expansion is
   /// consistent across all of the unexpanded parameter packs in its pattern.
   ///
   /// Returns an empty Optional if the type can't be expanded.
   std::optional<unsigned> getNumArgumentsInExpansion(
       QualType T, const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Determine whether the given declarator contains any unexpanded
   /// parameter packs.
   ///
   /// This routine is used by the parser to disambiguate function declarators
   /// with an ellipsis prior to the ')', e.g.,
   ///
   /// \code
   ///   void f(T...);
   /// \endcode
   ///
   /// To determine whether we have an (unnamed) function parameter pack or
   /// a variadic function.
   ///
   /// \returns true if the declarator contains any unexpanded parameter packs,
   /// false otherwise.
   bool containsUnexpandedParameterPacks(Declarator &D);
 
   /// Returns the pattern of the pack expansion for a template argument.
   ///
   /// \param OrigLoc The template argument to expand.
   ///
   /// \param Ellipsis Will be set to the location of the ellipsis.
   ///
   /// \param NumExpansions Will be set to the number of expansions that will
   /// be generated from this pack expansion, if known a priori.
   TemplateArgumentLoc getTemplateArgumentPackExpansionPattern(
       TemplateArgumentLoc OrigLoc, SourceLocation &Ellipsis,
       std::optional<unsigned> &NumExpansions) const;
 
   /// Given a template argument that contains an unexpanded parameter pack, but
   /// which has already been substituted, attempt to determine the number of
   /// elements that will be produced once this argument is fully-expanded.
   ///
   /// This is intended for use when transforming 'sizeof...(Arg)' in order to
   /// avoid actually expanding the pack where possible.
   std::optional<unsigned> getFullyPackExpandedSize(TemplateArgument Arg);
 
   /// Called when an expression computing the size of a parameter pack
   /// is parsed.
   ///
   /// \code
   /// template<typename ...Types> struct count {
   ///   static const unsigned value = sizeof...(Types);
   /// };
   /// \endcode
   ///
   //
   /// \param OpLoc The location of the "sizeof" keyword.
   /// \param Name The name of the parameter pack whose size will be determined.
   /// \param NameLoc The source location of the name of the parameter pack.
   /// \param RParenLoc The location of the closing parentheses.
   ExprResult ActOnSizeofParameterPackExpr(Scope *S, SourceLocation OpLoc,
                                           IdentifierInfo &Name,
                                           SourceLocation NameLoc,
                                           SourceLocation RParenLoc);
 
   ExprResult ActOnPackIndexingExpr(Scope *S, Expr *PackExpression,
                                    SourceLocation EllipsisLoc,
                                    SourceLocation LSquareLoc, Expr *IndexExpr,
                                    SourceLocation RSquareLoc);
 
   ExprResult BuildPackIndexingExpr(Expr *PackExpression,
                                    SourceLocation EllipsisLoc, Expr *IndexExpr,
                                    SourceLocation RSquareLoc,
                                    ArrayRef<Expr *> ExpandedExprs = {},
                                    bool EmptyPack = false);
 
   /// Handle a C++1z fold-expression: ( expr op ... op expr ).
   ExprResult ActOnCXXFoldExpr(Scope *S, SourceLocation LParenLoc, Expr *LHS,
                               tok::TokenKind Operator,
                               SourceLocation EllipsisLoc, Expr *RHS,
                               SourceLocation RParenLoc);
   ExprResult BuildCXXFoldExpr(UnresolvedLookupExpr *Callee,
                               SourceLocation LParenLoc, Expr *LHS,
                               BinaryOperatorKind Operator,
                               SourceLocation EllipsisLoc, Expr *RHS,
                               SourceLocation RParenLoc,
                               std::optional<unsigned> NumExpansions);
   ExprResult BuildEmptyCXXFoldExpr(SourceLocation EllipsisLoc,
                                    BinaryOperatorKind Operator);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Constraints and Concepts
   /// Implementations are in SemaConcept.cpp
   ///@{
 
 public:
   void PushSatisfactionStackEntry(const NamedDecl *D,
                                   const llvm::FoldingSetNodeID &ID) {
     const NamedDecl *Can = cast<NamedDecl>(D->getCanonicalDecl());
     SatisfactionStack.emplace_back(Can, ID);
   }
 
   void PopSatisfactionStackEntry() { SatisfactionStack.pop_back(); }
 
   bool SatisfactionStackContains(const NamedDecl *D,
                                  const llvm::FoldingSetNodeID &ID) const {
     const NamedDecl *Can = cast<NamedDecl>(D->getCanonicalDecl());
     return llvm::find(SatisfactionStack, SatisfactionStackEntryTy{Can, ID}) !=
            SatisfactionStack.end();
   }
 
   using SatisfactionStackEntryTy =
       std::pair<const NamedDecl *, llvm::FoldingSetNodeID>;
 
   // Resets the current SatisfactionStack for cases where we are instantiating
   // constraints as a 'side effect' of normal instantiation in a way that is not
   // indicative of recursive definition.
   class SatisfactionStackResetRAII {
     llvm::SmallVector<SatisfactionStackEntryTy, 10> BackupSatisfactionStack;
     Sema &SemaRef;
 
   public:
     SatisfactionStackResetRAII(Sema &S) : SemaRef(S) {
       SemaRef.SwapSatisfactionStack(BackupSatisfactionStack);
     }
 
     ~SatisfactionStackResetRAII() {
       SemaRef.SwapSatisfactionStack(BackupSatisfactionStack);
     }
   };
 
   void SwapSatisfactionStack(
       llvm::SmallVectorImpl<SatisfactionStackEntryTy> &NewSS) {
     SatisfactionStack.swap(NewSS);
   }
 
   /// Check whether the given expression is a valid constraint expression.
   /// A diagnostic is emitted if it is not, false is returned, and
   /// PossibleNonPrimary will be set to true if the failure might be due to a
   /// non-primary expression being used as an atomic constraint.
   bool CheckConstraintExpression(const Expr *CE, Token NextToken = Token(),
                                  bool *PossibleNonPrimary = nullptr,
                                  bool IsTrailingRequiresClause = false);
 
   /// \brief Check whether the given list of constraint expressions are
   /// satisfied (as if in a 'conjunction') given template arguments.
   /// \param Template the template-like entity that triggered the constraints
   /// check (either a concept or a constrained entity).
   /// \param ConstraintExprs a list of constraint expressions, treated as if
   /// they were 'AND'ed together.
   /// \param TemplateArgLists the list of template arguments to substitute into
   /// the constraint expression.
   /// \param TemplateIDRange The source range of the template id that
   /// caused the constraints check.
   /// \param Satisfaction if true is returned, will contain details of the
   /// satisfaction, with enough information to diagnose an unsatisfied
   /// expression.
   /// \returns true if an error occurred and satisfaction could not be checked,
   /// false otherwise.
   bool CheckConstraintSatisfaction(
       const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
       const MultiLevelTemplateArgumentList &TemplateArgLists,
       SourceRange TemplateIDRange, ConstraintSatisfaction &Satisfaction) {
     llvm::SmallVector<Expr *, 4> Converted;
     return CheckConstraintSatisfaction(Template, ConstraintExprs, Converted,
                                        TemplateArgLists, TemplateIDRange,
                                        Satisfaction);
   }
 
   /// \brief Check whether the given list of constraint expressions are
   /// satisfied (as if in a 'conjunction') given template arguments.
   /// Additionally, takes an empty list of Expressions which is populated with
   /// the instantiated versions of the ConstraintExprs.
   /// \param Template the template-like entity that triggered the constraints
   /// check (either a concept or a constrained entity).
   /// \param ConstraintExprs a list of constraint expressions, treated as if
   /// they were 'AND'ed together.
   /// \param ConvertedConstraints a out parameter that will get populated with
   /// the instantiated version of the ConstraintExprs if we successfully checked
   /// satisfaction.
   /// \param TemplateArgList the multi-level list of template arguments to
   /// substitute into the constraint expression. This should be relative to the
   /// top-level (hence multi-level), since we need to instantiate fully at the
   /// time of checking.
   /// \param TemplateIDRange The source range of the template id that
   /// caused the constraints check.
   /// \param Satisfaction if true is returned, will contain details of the
   /// satisfaction, with enough information to diagnose an unsatisfied
   /// expression.
   /// \returns true if an error occurred and satisfaction could not be checked,
   /// false otherwise.
   bool CheckConstraintSatisfaction(
       const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
       llvm::SmallVectorImpl<Expr *> &ConvertedConstraints,
       const MultiLevelTemplateArgumentList &TemplateArgList,
       SourceRange TemplateIDRange, ConstraintSatisfaction &Satisfaction);
 
   /// \brief Check whether the given non-dependent constraint expression is
   /// satisfied. Returns false and updates Satisfaction with the satisfaction
   /// verdict if successful, emits a diagnostic and returns true if an error
   /// occurred and satisfaction could not be determined.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CheckConstraintSatisfaction(const Expr *ConstraintExpr,
                                    ConstraintSatisfaction &Satisfaction);
 
   /// Check whether the given function decl's trailing requires clause is
   /// satisfied, if any. Returns false and updates Satisfaction with the
   /// satisfaction verdict if successful, emits a diagnostic and returns true if
   /// an error occurred and satisfaction could not be determined.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CheckFunctionConstraints(const FunctionDecl *FD,
                                 ConstraintSatisfaction &Satisfaction,
                                 SourceLocation UsageLoc = SourceLocation(),
                                 bool ForOverloadResolution = false);
 
   // Calculates whether two constraint expressions are equal irrespective of a
   // difference in 'depth'. This takes a pair of optional 'NamedDecl's 'Old' and
   // 'New', which are the "source" of the constraint, since this is necessary
   // for figuring out the relative 'depth' of the constraint. The depth of the
   // 'primary template' and the 'instantiated from' templates aren't necessarily
   // the same, such as a case when one is a 'friend' defined in a class.
   bool AreConstraintExpressionsEqual(const NamedDecl *Old,
                                      const Expr *OldConstr,
                                      const TemplateCompareNewDeclInfo &New,
                                      const Expr *NewConstr);
 
   // Calculates whether the friend function depends on an enclosing template for
   // the purposes of [temp.friend] p9.
   bool FriendConstraintsDependOnEnclosingTemplate(const FunctionDecl *FD);
 
   /// \brief Ensure that the given template arguments satisfy the constraints
   /// associated with the given template, emitting a diagnostic if they do not.
   ///
   /// \param Template The template to which the template arguments are being
   /// provided.
   ///
   /// \param TemplateArgs The converted, canonicalized template arguments.
   ///
   /// \param TemplateIDRange The source range of the template id that
   /// caused the constraints check.
   ///
   /// \returns true if the constrains are not satisfied or could not be checked
   /// for satisfaction, false if the constraints are satisfied.
   bool EnsureTemplateArgumentListConstraints(
       TemplateDecl *Template,
       const MultiLevelTemplateArgumentList &TemplateArgs,
       SourceRange TemplateIDRange);
 
   bool CheckInstantiatedFunctionTemplateConstraints(
       SourceLocation PointOfInstantiation, FunctionDecl *Decl,
       ArrayRef<TemplateArgument> TemplateArgs,
       ConstraintSatisfaction &Satisfaction);
 
   /// \brief Emit diagnostics explaining why a constraint expression was deemed
   /// unsatisfied.
   /// \param First whether this is the first time an unsatisfied constraint is
   /// diagnosed for this error.
   void DiagnoseUnsatisfiedConstraint(const ConstraintSatisfaction &Satisfaction,
                                      bool First = true);
 
   /// \brief Emit diagnostics explaining why a constraint expression was deemed
   /// unsatisfied.
   void
   DiagnoseUnsatisfiedConstraint(const ASTConstraintSatisfaction &Satisfaction,
                                 bool First = true);
 
   const NormalizedConstraint *getNormalizedAssociatedConstraints(
       NamedDecl *ConstrainedDecl, ArrayRef<const Expr *> AssociatedConstraints);
 
   /// \brief Check whether the given declaration's associated constraints are
   /// at least as constrained than another declaration's according to the
   /// partial ordering of constraints.
   ///
   /// \param Result If no error occurred, receives the result of true if D1 is
   /// at least constrained than D2, and false otherwise.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool IsAtLeastAsConstrained(NamedDecl *D1, MutableArrayRef<const Expr *> AC1,
                               NamedDecl *D2, MutableArrayRef<const Expr *> AC2,
                               bool &Result);
 
   /// If D1 was not at least as constrained as D2, but would've been if a pair
   /// of atomic constraints involved had been declared in a concept and not
   /// repeated in two separate places in code.
   /// \returns true if such a diagnostic was emitted, false otherwise.
   bool MaybeEmitAmbiguousAtomicConstraintsDiagnostic(
       NamedDecl *D1, ArrayRef<const Expr *> AC1, NamedDecl *D2,
       ArrayRef<const Expr *> AC2);
 
 private:
   /// Caches pairs of template-like decls whose associated constraints were
   /// checked for subsumption and whether or not the first's constraints did in
   /// fact subsume the second's.
   llvm::DenseMap<std::pair<NamedDecl *, NamedDecl *>, bool> SubsumptionCache;
   /// Caches the normalized associated constraints of declarations (concepts or
   /// constrained declarations). If an error occurred while normalizing the
   /// associated constraints of the template or concept, nullptr will be cached
   /// here.
   llvm::DenseMap<NamedDecl *, NormalizedConstraint *> NormalizationCache;
 
   llvm::ContextualFoldingSet<ConstraintSatisfaction, const ASTContext &>
       SatisfactionCache;
 
   // The current stack of constraint satisfactions, so we can exit-early.
   llvm::SmallVector<SatisfactionStackEntryTy, 10> SatisfactionStack;
 
   /// Introduce the instantiated captures of the lambda into the local
   /// instantiation scope.
   bool addInstantiatedCapturesToScope(
       FunctionDecl *Function, const FunctionDecl *PatternDecl,
       LocalInstantiationScope &Scope,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Used by SetupConstraintCheckingTemplateArgumentsAndScope to recursively(in
   /// the case of lambdas) set up the LocalInstantiationScope of the current
   /// function.
   bool
   SetupConstraintScope(FunctionDecl *FD,
                        std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
                        const MultiLevelTemplateArgumentList &MLTAL,
                        LocalInstantiationScope &Scope);
 
   /// Used during constraint checking, sets up the constraint template argument
   /// lists, and calls SetupConstraintScope to set up the
   /// LocalInstantiationScope to have the proper set of ParVarDecls configured.
   std::optional<MultiLevelTemplateArgumentList>
   SetupConstraintCheckingTemplateArgumentsAndScope(
       FunctionDecl *FD, std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
       LocalInstantiationScope &Scope);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Types
   /// Implementations are in SemaType.cpp
   ///@{
 
 public:
   /// A mapping that describes the nullability we've seen in each header file.
   FileNullabilityMap NullabilityMap;
 
   static int getPrintable(int I) { return I; }
   static unsigned getPrintable(unsigned I) { return I; }
   static bool getPrintable(bool B) { return B; }
   static const char *getPrintable(const char *S) { return S; }
   static StringRef getPrintable(StringRef S) { return S; }
   static const std::string &getPrintable(const std::string &S) { return S; }
   static const IdentifierInfo *getPrintable(const IdentifierInfo *II) {
     return II;
   }
   static DeclarationName getPrintable(DeclarationName N) { return N; }
   static QualType getPrintable(QualType T) { return T; }
   static SourceRange getPrintable(SourceRange R) { return R; }
   static SourceRange getPrintable(SourceLocation L) { return L; }
   static SourceRange getPrintable(const Expr *E) { return E->getSourceRange(); }
   static SourceRange getPrintable(TypeLoc TL) { return TL.getSourceRange(); }
 
   enum class CompleteTypeKind {
     /// Apply the normal rules for complete types.  In particular,
     /// treat all sizeless types as incomplete.
     Normal,
 
     /// Relax the normal rules for complete types so that they include
     /// sizeless built-in types.
     AcceptSizeless,
 
     // FIXME: Eventually we should flip the default to Normal and opt in
     // to AcceptSizeless rather than opt out of it.
     Default = AcceptSizeless
   };
 
   QualType BuildQualifiedType(QualType T, SourceLocation Loc, Qualifiers Qs,
                               const DeclSpec *DS = nullptr);
   QualType BuildQualifiedType(QualType T, SourceLocation Loc, unsigned CVRA,
                               const DeclSpec *DS = nullptr);
 
   /// Build a pointer type.
   ///
   /// \param T The type to which we'll be building a pointer.
   ///
   /// \param Loc The location of the entity whose type involves this
   /// pointer type or, if there is no such entity, the location of the
   /// type that will have pointer type.
   ///
   /// \param Entity The name of the entity that involves the pointer
   /// type, if known.
   ///
   /// \returns A suitable pointer type, if there are no
   /// errors. Otherwise, returns a NULL type.
   QualType BuildPointerType(QualType T, SourceLocation Loc,
                             DeclarationName Entity);
 
   /// Build a reference type.
   ///
   /// \param T The type to which we'll be building a reference.
   ///
   /// \param Loc The location of the entity whose type involves this
   /// reference type or, if there is no such entity, the location of the
   /// type that will have reference type.
   ///
   /// \param Entity The name of the entity that involves the reference
   /// type, if known.
   ///
   /// \returns A suitable reference type, if there are no
   /// errors. Otherwise, returns a NULL type.
   QualType BuildReferenceType(QualType T, bool LValueRef, SourceLocation Loc,
                               DeclarationName Entity);
 
   /// Build an array type.
   ///
   /// \param T The type of each element in the array.
   ///
   /// \param ASM C99 array size modifier (e.g., '*', 'static').
   ///
   /// \param ArraySize Expression describing the size of the array.
   ///
   /// \param Brackets The range from the opening '[' to the closing ']'.
   ///
   /// \param Entity The name of the entity that involves the array
   /// type, if known.
   ///
   /// \returns A suitable array type, if there are no errors. Otherwise,
   /// returns a NULL type.
   QualType BuildArrayType(QualType T, ArraySizeModifier ASM, Expr *ArraySize,
                           unsigned Quals, SourceRange Brackets,
                           DeclarationName Entity);
   QualType BuildVectorType(QualType T, Expr *VecSize, SourceLocation AttrLoc);
 
   /// Build an ext-vector type.
   ///
   /// Run the required checks for the extended vector type.
   QualType BuildExtVectorType(QualType T, Expr *ArraySize,
                               SourceLocation AttrLoc);
   QualType BuildMatrixType(QualType T, Expr *NumRows, Expr *NumColumns,
                            SourceLocation AttrLoc);
 
   QualType BuildCountAttributedArrayOrPointerType(QualType WrappedTy,
                                                   Expr *CountExpr,
                                                   bool CountInBytes,
                                                   bool OrNull);
 
   /// BuildAddressSpaceAttr - Builds a DependentAddressSpaceType if an
   /// expression is uninstantiated. If instantiated it will apply the
   /// appropriate address space to the type. This function allows dependent
   /// template variables to be used in conjunction with the address_space
   /// attribute
   QualType BuildAddressSpaceAttr(QualType &T, LangAS ASIdx, Expr *AddrSpace,
                                  SourceLocation AttrLoc);
 
   /// Same as above, but constructs the AddressSpace index if not provided.
   QualType BuildAddressSpaceAttr(QualType &T, Expr *AddrSpace,
                                  SourceLocation AttrLoc);
 
   bool CheckQualifiedFunctionForTypeId(QualType T, SourceLocation Loc);
 
   bool CheckFunctionReturnType(QualType T, SourceLocation Loc);
 
   /// Build a function type.
   ///
   /// This routine checks the function type according to C++ rules and
   /// under the assumption that the result type and parameter types have
   /// just been instantiated from a template. It therefore duplicates
   /// some of the behavior of GetTypeForDeclarator, but in a much
   /// simpler form that is only suitable for this narrow use case.
   ///
   /// \param T The return type of the function.
   ///
   /// \param ParamTypes The parameter types of the function. This array
   /// will be modified to account for adjustments to the types of the
   /// function parameters.
   ///
   /// \param Loc The location of the entity whose type involves this
   /// function type or, if there is no such entity, the location of the
   /// type that will have function type.
   ///
   /// \param Entity The name of the entity that involves the function
   /// type, if known.
   ///
   /// \param EPI Extra information about the function type. Usually this will
   /// be taken from an existing function with the same prototype.
   ///
   /// \returns A suitable function type, if there are no errors. The
   /// unqualified type will always be a FunctionProtoType.
   /// Otherwise, returns a NULL type.
   QualType BuildFunctionType(QualType T, MutableArrayRef<QualType> ParamTypes,
                              SourceLocation Loc, DeclarationName Entity,
                              const FunctionProtoType::ExtProtoInfo &EPI);
 
   /// Build a member pointer type \c T Class::*.
   ///
   /// \param T the type to which the member pointer refers.
   /// \param Class the class type into which the member pointer points.
   /// \param Loc the location where this type begins
   /// \param Entity the name of the entity that will have this member pointer
   /// type
   ///
   /// \returns a member pointer type, if successful, or a NULL type if there was
   /// an error.
   QualType BuildMemberPointerType(QualType T, QualType Class,
                                   SourceLocation Loc, DeclarationName Entity);
 
   /// Build a block pointer type.
   ///
   /// \param T The type to which we'll be building a block pointer.
   ///
   /// \param Loc The source location, used for diagnostics.
   ///
   /// \param Entity The name of the entity that involves the block pointer
   /// type, if known.
   ///
   /// \returns A suitable block pointer type, if there are no
   /// errors. Otherwise, returns a NULL type.
   QualType BuildBlockPointerType(QualType T, SourceLocation Loc,
                                  DeclarationName Entity);
 
   /// Build a paren type including \p T.
   QualType BuildParenType(QualType T);
   QualType BuildAtomicType(QualType T, SourceLocation Loc);
 
   /// Build a Read-only Pipe type.
   ///
   /// \param T The type to which we'll be building a Pipe.
   ///
   /// \param Loc We do not use it for now.
   ///
   /// \returns A suitable pipe type, if there are no errors. Otherwise, returns
   /// a NULL type.
   QualType BuildReadPipeType(QualType T, SourceLocation Loc);
 
   /// Build a Write-only Pipe type.
   ///
   /// \param T The type to which we'll be building a Pipe.
   ///
   /// \param Loc We do not use it for now.
   ///
   /// \returns A suitable pipe type, if there are no errors. Otherwise, returns
   /// a NULL type.
   QualType BuildWritePipeType(QualType T, SourceLocation Loc);
 
   /// Build a bit-precise integer type.
   ///
   /// \param IsUnsigned Boolean representing the signedness of the type.
   ///
   /// \param BitWidth Size of this int type in bits, or an expression
   /// representing that.
   ///
   /// \param Loc Location of the keyword.
   QualType BuildBitIntType(bool IsUnsigned, Expr *BitWidth, SourceLocation Loc);
 
   /// GetTypeForDeclarator - Convert the type for the specified
   /// declarator to Type instances.
   ///
   /// The result of this call will never be null, but the associated
   /// type may be a null type if there's an unrecoverable error.
   TypeSourceInfo *GetTypeForDeclarator(Declarator &D);
   TypeSourceInfo *GetTypeForDeclaratorCast(Declarator &D, QualType FromTy);
 
   /// Package the given type and TSI into a ParsedType.
   ParsedType CreateParsedType(QualType T, TypeSourceInfo *TInfo);
   static QualType GetTypeFromParser(ParsedType Ty,
                                     TypeSourceInfo **TInfo = nullptr);
 
   TypeResult ActOnTypeName(Declarator &D);
 
   // Check whether the size of array element of type \p EltTy is a multiple of
   // its alignment and return false if it isn't.
   bool checkArrayElementAlignment(QualType EltTy, SourceLocation Loc);
 
   void
   diagnoseIgnoredQualifiers(unsigned DiagID, unsigned Quals,
                             SourceLocation FallbackLoc,
                             SourceLocation ConstQualLoc = SourceLocation(),
                             SourceLocation VolatileQualLoc = SourceLocation(),
                             SourceLocation RestrictQualLoc = SourceLocation(),
                             SourceLocation AtomicQualLoc = SourceLocation(),
                             SourceLocation UnalignedQualLoc = SourceLocation());
 
   /// Retrieve the keyword associated
   IdentifierInfo *getNullabilityKeyword(NullabilityKind nullability);
 
   /// Adjust the calling convention of a method to be the ABI default if it
   /// wasn't specified explicitly.  This handles method types formed from
   /// function type typedefs and typename template arguments.
   void adjustMemberFunctionCC(QualType &T, bool HasThisPointer,
                               bool IsCtorOrDtor, SourceLocation Loc);
 
   // Check if there is an explicit attribute, but only look through parens.
   // The intent is to look for an attribute on the current declarator, but not
   // one that came from a typedef.
   bool hasExplicitCallingConv(QualType T);
 
   /// Check whether a nullability type specifier can be added to the given
   /// type through some means not written in source (e.g. API notes).
   ///
   /// \param Type The type to which the nullability specifier will be
   /// added. On success, this type will be updated appropriately.
   ///
   /// \param Nullability The nullability specifier to add.
   ///
   /// \param DiagLoc The location to use for diagnostics.
   ///
   /// \param AllowArrayTypes Whether to accept nullability specifiers on an
   /// array type (e.g., because it will decay to a pointer).
   ///
   /// \param OverrideExisting Whether to override an existing, locally-specified
   /// nullability specifier rather than complaining about the conflict.
   ///
   /// \returns true if nullability cannot be applied, false otherwise.
   bool CheckImplicitNullabilityTypeSpecifier(QualType &Type,
                                              NullabilityKind Nullability,
                                              SourceLocation DiagLoc,
                                              bool AllowArrayTypes,
                                              bool OverrideExisting);
 
   /// Get the type of expression E, triggering instantiation to complete the
   /// type if necessary -- that is, if the expression refers to a templated
   /// static data member of incomplete array type.
   ///
   /// May still return an incomplete type if instantiation was not possible or
   /// if the type is incomplete for a different reason. Use
   /// RequireCompleteExprType instead if a diagnostic is expected for an
   /// incomplete expression type.
   QualType getCompletedType(Expr *E);
 
   void completeExprArrayBound(Expr *E);
 
   /// Ensure that the type of the given expression is complete.
   ///
   /// This routine checks whether the expression \p E has a complete type. If
   /// the expression refers to an instantiable construct, that instantiation is
   /// performed as needed to complete its type. Furthermore
   /// Sema::RequireCompleteType is called for the expression's type (or in the
   /// case of a reference type, the referred-to type).
   ///
   /// \param E The expression whose type is required to be complete.
   /// \param Kind Selects which completeness rules should be applied.
   /// \param Diagnoser The object that will emit a diagnostic if the type is
   /// incomplete.
   ///
   /// \returns \c true if the type of \p E is incomplete and diagnosed, \c false
   /// otherwise.
   bool RequireCompleteExprType(Expr *E, CompleteTypeKind Kind,
                                TypeDiagnoser &Diagnoser);
   bool RequireCompleteExprType(Expr *E, unsigned DiagID);
 
   template <typename... Ts>
   bool RequireCompleteExprType(Expr *E, unsigned DiagID, const Ts &...Args) {
     BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireCompleteExprType(E, CompleteTypeKind::Default, Diagnoser);
   }
 
   /// Retrieve a version of the type 'T' that is elaborated by Keyword,
   /// qualified by the nested-name-specifier contained in SS, and that is
   /// (re)declared by OwnedTagDecl, which is nullptr if this is not a
   /// (re)declaration.
   QualType getElaboratedType(ElaboratedTypeKeyword Keyword,
                              const CXXScopeSpec &SS, QualType T,
                              TagDecl *OwnedTagDecl = nullptr);
 
   // Returns the underlying type of a decltype with the given expression.
   QualType getDecltypeForExpr(Expr *E);
 
   QualType BuildTypeofExprType(Expr *E, TypeOfKind Kind);
   /// If AsUnevaluated is false, E is treated as though it were an evaluated
   /// context, such as when building a type for decltype(auto).
   QualType BuildDecltypeType(Expr *E, bool AsUnevaluated = true);
 
   QualType ActOnPackIndexingType(QualType Pattern, Expr *IndexExpr,
                                  SourceLocation Loc,
                                  SourceLocation EllipsisLoc);
   QualType BuildPackIndexingType(QualType Pattern, Expr *IndexExpr,
                                  SourceLocation Loc, SourceLocation EllipsisLoc,
                                  bool FullySubstituted = false,
                                  ArrayRef<QualType> Expansions = {});
 
   using UTTKind = UnaryTransformType::UTTKind;
   QualType BuildUnaryTransformType(QualType BaseType, UTTKind UKind,
                                    SourceLocation Loc);
   QualType BuiltinEnumUnderlyingType(QualType BaseType, SourceLocation Loc);
   QualType BuiltinAddPointer(QualType BaseType, SourceLocation Loc);
   QualType BuiltinRemovePointer(QualType BaseType, SourceLocation Loc);
   QualType BuiltinDecay(QualType BaseType, SourceLocation Loc);
   QualType BuiltinAddReference(QualType BaseType, UTTKind UKind,
                                SourceLocation Loc);
   QualType BuiltinRemoveExtent(QualType BaseType, UTTKind UKind,
                                SourceLocation Loc);
   QualType BuiltinRemoveReference(QualType BaseType, UTTKind UKind,
                                   SourceLocation Loc);
   QualType BuiltinChangeCVRQualifiers(QualType BaseType, UTTKind UKind,
                                       SourceLocation Loc);
   QualType BuiltinChangeSignedness(QualType BaseType, UTTKind UKind,
                                    SourceLocation Loc);
 
   /// Ensure that the type T is a literal type.
   ///
   /// This routine checks whether the type @p T is a literal type. If @p T is an
   /// incomplete type, an attempt is made to complete it. If @p T is a literal
   /// type, or @p AllowIncompleteType is true and @p T is an incomplete type,
   /// returns false. Otherwise, this routine issues the diagnostic @p PD (giving
   /// it the type @p T), along with notes explaining why the type is not a
   /// literal type, and returns true.
   ///
   /// @param Loc  The location in the source that the non-literal type
   /// diagnostic should refer to.
   ///
   /// @param T  The type that this routine is examining for literalness.
   ///
   /// @param Diagnoser Emits a diagnostic if T is not a literal type.
   ///
   /// @returns @c true if @p T is not a literal type and a diagnostic was
   /// emitted, @c false otherwise.
   bool RequireLiteralType(SourceLocation Loc, QualType T,
                           TypeDiagnoser &Diagnoser);
   bool RequireLiteralType(SourceLocation Loc, QualType T, unsigned DiagID);
 
   template <typename... Ts>
   bool RequireLiteralType(SourceLocation Loc, QualType T, unsigned DiagID,
                           const Ts &...Args) {
     BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireLiteralType(Loc, T, Diagnoser);
   }
 
   bool isCompleteType(SourceLocation Loc, QualType T,
                       CompleteTypeKind Kind = CompleteTypeKind::Default) {
     return !RequireCompleteTypeImpl(Loc, T, Kind, nullptr);
   }
 
   /// Ensure that the type T is a complete type.
   ///
   /// This routine checks whether the type @p T is complete in any
   /// context where a complete type is required. If @p T is a complete
   /// type, returns false. If @p T is a class template specialization,
   /// this routine then attempts to perform class template
   /// instantiation. If instantiation fails, or if @p T is incomplete
   /// and cannot be completed, issues the diagnostic @p diag (giving it
   /// the type @p T) and returns true.
   ///
   /// @param Loc  The location in the source that the incomplete type
   /// diagnostic should refer to.
   ///
   /// @param T  The type that this routine is examining for completeness.
   ///
   /// @param Kind Selects which completeness rules should be applied.
   ///
   /// @returns @c true if @p T is incomplete and a diagnostic was emitted,
   /// @c false otherwise.
   bool RequireCompleteType(SourceLocation Loc, QualType T,
                            CompleteTypeKind Kind, TypeDiagnoser &Diagnoser);
   bool RequireCompleteType(SourceLocation Loc, QualType T,
                            CompleteTypeKind Kind, unsigned DiagID);
 
   bool RequireCompleteType(SourceLocation Loc, QualType T,
                            TypeDiagnoser &Diagnoser) {
     return RequireCompleteType(Loc, T, CompleteTypeKind::Default, Diagnoser);
   }
   bool RequireCompleteType(SourceLocation Loc, QualType T, unsigned DiagID) {
     return RequireCompleteType(Loc, T, CompleteTypeKind::Default, DiagID);
   }
 
   template <typename... Ts>
   bool RequireCompleteType(SourceLocation Loc, QualType T, unsigned DiagID,
                            const Ts &...Args) {
     BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireCompleteType(Loc, T, Diagnoser);
   }
 
   /// Determine whether a declaration is visible to name lookup.
   bool isVisible(const NamedDecl *D) {
     return D->isUnconditionallyVisible() ||
            isAcceptableSlow(D, AcceptableKind::Visible);
   }
 
   /// Determine whether a declaration is reachable.
   bool isReachable(const NamedDecl *D) {
     // All visible declarations are reachable.
     return D->isUnconditionallyVisible() ||
            isAcceptableSlow(D, AcceptableKind::Reachable);
   }
 
   /// Determine whether a declaration is acceptable (visible/reachable).
   bool isAcceptable(const NamedDecl *D, AcceptableKind Kind) {
     return Kind == AcceptableKind::Visible ? isVisible(D) : isReachable(D);
   }
 
   /// Determine if \p D and \p Suggested have a structurally compatible
   /// layout as described in C11 6.2.7/1.
   bool hasStructuralCompatLayout(Decl *D, Decl *Suggested);
 
   /// Determine if \p D has a visible definition. If not, suggest a declaration
   /// that should be made visible to expose the definition.
   bool hasVisibleDefinition(NamedDecl *D, NamedDecl **Suggested,
                             bool OnlyNeedComplete = false);
   bool hasVisibleDefinition(const NamedDecl *D) {
     NamedDecl *Hidden;
     return hasVisibleDefinition(const_cast<NamedDecl *>(D), &Hidden);
   }
 
   /// Determine if \p D has a reachable definition. If not, suggest a
   /// declaration that should be made reachable to expose the definition.
   bool hasReachableDefinition(NamedDecl *D, NamedDecl **Suggested,
                               bool OnlyNeedComplete = false);
   bool hasReachableDefinition(NamedDecl *D) {
     NamedDecl *Hidden;
     return hasReachableDefinition(D, &Hidden);
   }
 
   bool hasAcceptableDefinition(NamedDecl *D, NamedDecl **Suggested,
                                AcceptableKind Kind,
                                bool OnlyNeedComplete = false);
   bool hasAcceptableDefinition(NamedDecl *D, AcceptableKind Kind) {
     NamedDecl *Hidden;
     return hasAcceptableDefinition(D, &Hidden, Kind);
   }
 
 private:
   /// The implementation of RequireCompleteType
   bool RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
                                CompleteTypeKind Kind, TypeDiagnoser *Diagnoser);
 
   /// Nullability type specifiers.
   IdentifierInfo *Ident__Nonnull = nullptr;
   IdentifierInfo *Ident__Nullable = nullptr;
   IdentifierInfo *Ident__Nullable_result = nullptr;
   IdentifierInfo *Ident__Null_unspecified = nullptr;
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name FixIt Helpers
   /// Implementations are in SemaFixItUtils.cpp
   ///@{
 
 public:
   /// Get a string to suggest for zero-initialization of a type.
   std::string getFixItZeroInitializerForType(QualType T,
                                              SourceLocation Loc) const;
   std::string getFixItZeroLiteralForType(QualType T, SourceLocation Loc) const;
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name API Notes
   /// Implementations are in SemaAPINotes.cpp
   ///@{
 
 public:
   /// Map any API notes provided for this declaration to attributes on the
   /// declaration.
   ///
   /// Triggered by declaration-attribute processing.
   void ProcessAPINotes(Decl *D);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Bounds Safety
   /// Implementations are in SemaBoundsSafety.cpp
   ///@{
 public:
   /// Check if applying the specified attribute variant from the "counted by"
   /// family of attributes to FieldDecl \p FD is semantically valid. If
   /// semantically invalid diagnostics will be emitted explaining the problems.
   ///
   /// \param FD The FieldDecl to apply the attribute to
   /// \param E The count expression on the attribute
   /// \param[out] Decls If the attribute is semantically valid \p Decls
   ///             is populated with TypeCoupledDeclRefInfo objects, each
   ///             describing Decls referred to in \p E.
   /// \param CountInBytes If true the attribute is from the "sized_by" family of
   ///                     attributes. If the false the attribute is from
   ///                     "counted_by" family of attributes.
   /// \param OrNull If true the attribute is from the "_or_null" suffixed family
   ///               of attributes. If false the attribute does not have the
   ///               suffix.
   ///
   /// Together \p CountInBytes and \p OrNull decide the attribute variant. E.g.
   /// \p CountInBytes and \p OrNull both being true indicates the
   /// `counted_by_or_null` attribute.
   ///
   /// \returns false iff semantically valid.
   bool CheckCountedByAttrOnField(
       FieldDecl *FD, Expr *E,
       llvm::SmallVectorImpl<TypeCoupledDeclRefInfo> &Decls, bool CountInBytes,
       bool OrNull);
 
   ///@}
 };
 
 DeductionFailureInfo
 MakeDeductionFailureInfo(ASTContext &Context, TemplateDeductionResult TDK,
                          sema::TemplateDeductionInfo &Info);
 
 /// Contains a late templated function.
 /// Will be parsed at the end of the translation unit, used by Sema & Parser.
 struct LateParsedTemplate {
   CachedTokens Toks;
   /// The template function declaration to be late parsed.
   Decl *D;
   /// Floating-point options in the point of definition.
   FPOptions FPO;
 };
 
 template <>
 void Sema::PragmaStack<Sema::AlignPackInfo>::Act(SourceLocation PragmaLocation,
                                                  PragmaMsStackAction Action,
                                                  llvm::StringRef StackSlotLabel,
                                                  AlignPackInfo Value);
 } // end namespace clang
 
 #endif
diff --git a/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiate.cpp b/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiate.cpp
index a09e3be83c45..c2e8ed0c602e 100644
--- a/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1,4496 +1,4489 @@
 //===------- SemaTemplateInstantiate.cpp - C++ Template Instantiation ------===/
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //===----------------------------------------------------------------------===/
 //
 //  This file implements C++ template instantiation.
 //
 //===----------------------------------------------------------------------===/
 
 #include "TreeTransform.h"
 #include "clang/AST/ASTConcept.h"
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTLambda.h"
 #include "clang/AST/ASTMutationListener.h"
 #include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprConcepts.h"
 #include "clang/AST/PrettyDeclStackTrace.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/Type.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/AST/TypeVisitor.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/Stack.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Sema/DeclSpec.h"
 #include "clang/Sema/EnterExpressionEvaluationContext.h"
 #include "clang/Sema/Initialization.h"
 #include "clang/Sema/Lookup.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Sema/SemaConcept.h"
 #include "clang/Sema/SemaInternal.h"
 #include "clang/Sema/Template.h"
 #include "clang/Sema/TemplateDeduction.h"
 #include "clang/Sema/TemplateInstCallback.h"
 #include "llvm/ADT/STLForwardCompat.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TimeProfiler.h"
 #include <optional>
 
 using namespace clang;
 using namespace sema;
 
 //===----------------------------------------------------------------------===/
 // Template Instantiation Support
 //===----------------------------------------------------------------------===/
 
 namespace {
 namespace TemplateInstArgsHelpers {
 struct Response {
   const Decl *NextDecl = nullptr;
   bool IsDone = false;
   bool ClearRelativeToPrimary = true;
   static Response Done() {
     Response R;
     R.IsDone = true;
     return R;
   }
   static Response ChangeDecl(const Decl *ND) {
     Response R;
     R.NextDecl = ND;
     return R;
   }
   static Response ChangeDecl(const DeclContext *Ctx) {
     Response R;
     R.NextDecl = Decl::castFromDeclContext(Ctx);
     return R;
   }
 
   static Response UseNextDecl(const Decl *CurDecl) {
     return ChangeDecl(CurDecl->getDeclContext());
   }
 
   static Response DontClearRelativeToPrimaryNextDecl(const Decl *CurDecl) {
     Response R = Response::UseNextDecl(CurDecl);
     R.ClearRelativeToPrimary = false;
     return R;
   }
 };
 
 // Retrieve the primary template for a lambda call operator. It's
 // unfortunate that we only have the mappings of call operators rather
 // than lambda classes.
 const FunctionDecl *
 getPrimaryTemplateOfGenericLambda(const FunctionDecl *LambdaCallOperator) {
   if (!isLambdaCallOperator(LambdaCallOperator))
     return LambdaCallOperator;
   while (true) {
     if (auto *FTD = dyn_cast_if_present<FunctionTemplateDecl>(
             LambdaCallOperator->getDescribedTemplate());
         FTD && FTD->getInstantiatedFromMemberTemplate()) {
       LambdaCallOperator =
           FTD->getInstantiatedFromMemberTemplate()->getTemplatedDecl();
     } else if (LambdaCallOperator->getPrimaryTemplate()) {
       // Cases where the lambda operator is instantiated in
       // TemplateDeclInstantiator::VisitCXXMethodDecl.
       LambdaCallOperator =
           LambdaCallOperator->getPrimaryTemplate()->getTemplatedDecl();
     } else if (auto *Prev = cast<CXXMethodDecl>(LambdaCallOperator)
                                 ->getInstantiatedFromMemberFunction())
       LambdaCallOperator = Prev;
     else
       break;
   }
   return LambdaCallOperator;
 }
 
 struct EnclosingTypeAliasTemplateDetails {
   TypeAliasTemplateDecl *Template = nullptr;
   TypeAliasTemplateDecl *PrimaryTypeAliasDecl = nullptr;
   ArrayRef<TemplateArgument> AssociatedTemplateArguments;
 
   explicit operator bool() noexcept { return Template; }
 };
 
 // Find the enclosing type alias template Decl from CodeSynthesisContexts, as
 // well as its primary template and instantiating template arguments.
 EnclosingTypeAliasTemplateDetails
 getEnclosingTypeAliasTemplateDecl(Sema &SemaRef) {
   for (auto &CSC : llvm::reverse(SemaRef.CodeSynthesisContexts)) {
     if (CSC.Kind != Sema::CodeSynthesisContext::SynthesisKind::
                         TypeAliasTemplateInstantiation)
       continue;
     EnclosingTypeAliasTemplateDetails Result;
     auto *TATD = cast<TypeAliasTemplateDecl>(CSC.Entity),
          *Next = TATD->getInstantiatedFromMemberTemplate();
     Result = {
         /*Template=*/TATD,
         /*PrimaryTypeAliasDecl=*/TATD,
         /*AssociatedTemplateArguments=*/CSC.template_arguments(),
     };
     while (Next) {
       Result.PrimaryTypeAliasDecl = Next;
       Next = Next->getInstantiatedFromMemberTemplate();
     }
     return Result;
   }
   return {};
 }
 
 // Check if we are currently inside of a lambda expression that is
 // surrounded by a using alias declaration. e.g.
 //   template <class> using type = decltype([](auto) { ^ }());
 // We have to do so since a TypeAliasTemplateDecl (or a TypeAliasDecl) is never
 // a DeclContext, nor does it have an associated specialization Decl from which
 // we could collect these template arguments.
 bool isLambdaEnclosedByTypeAliasDecl(
     const FunctionDecl *LambdaCallOperator,
     const TypeAliasTemplateDecl *PrimaryTypeAliasDecl) {
   struct Visitor : RecursiveASTVisitor<Visitor> {
     Visitor(const FunctionDecl *CallOperator) : CallOperator(CallOperator) {}
     bool VisitLambdaExpr(const LambdaExpr *LE) {
       // Return true to bail out of the traversal, implying the Decl contains
       // the lambda.
       return getPrimaryTemplateOfGenericLambda(LE->getCallOperator()) !=
              CallOperator;
     }
     const FunctionDecl *CallOperator;
   };
 
   QualType Underlying =
       PrimaryTypeAliasDecl->getTemplatedDecl()->getUnderlyingType();
 
   return !Visitor(getPrimaryTemplateOfGenericLambda(LambdaCallOperator))
               .TraverseType(Underlying);
 }
 
 // Add template arguments from a variable template instantiation.
 Response
 HandleVarTemplateSpec(const VarTemplateSpecializationDecl *VarTemplSpec,
                       MultiLevelTemplateArgumentList &Result,
                       bool SkipForSpecialization) {
   // For a class-scope explicit specialization, there are no template arguments
   // at this level, but there may be enclosing template arguments.
   if (VarTemplSpec->isClassScopeExplicitSpecialization())
     return Response::DontClearRelativeToPrimaryNextDecl(VarTemplSpec);
 
   // We're done when we hit an explicit specialization.
   if (VarTemplSpec->getSpecializationKind() == TSK_ExplicitSpecialization &&
       !isa<VarTemplatePartialSpecializationDecl>(VarTemplSpec))
     return Response::Done();
 
   // If this variable template specialization was instantiated from a
   // specialized member that is a variable template, we're done.
   assert(VarTemplSpec->getSpecializedTemplate() && "No variable template?");
   llvm::PointerUnion<VarTemplateDecl *, VarTemplatePartialSpecializationDecl *>
       Specialized = VarTemplSpec->getSpecializedTemplateOrPartial();
   if (VarTemplatePartialSpecializationDecl *Partial =
           Specialized.dyn_cast<VarTemplatePartialSpecializationDecl *>()) {
     if (!SkipForSpecialization)
       Result.addOuterTemplateArguments(
           Partial, VarTemplSpec->getTemplateInstantiationArgs().asArray(),
           /*Final=*/false);
     if (Partial->isMemberSpecialization())
       return Response::Done();
   } else {
     VarTemplateDecl *Tmpl = Specialized.get<VarTemplateDecl *>();
     if (!SkipForSpecialization)
       Result.addOuterTemplateArguments(
           Tmpl, VarTemplSpec->getTemplateInstantiationArgs().asArray(),
           /*Final=*/false);
     if (Tmpl->isMemberSpecialization())
       return Response::Done();
   }
   return Response::DontClearRelativeToPrimaryNextDecl(VarTemplSpec);
 }
 
 // If we have a template template parameter with translation unit context,
 // then we're performing substitution into a default template argument of
 // this template template parameter before we've constructed the template
 // that will own this template template parameter. In this case, we
 // use empty template parameter lists for all of the outer templates
 // to avoid performing any substitutions.
 Response
 HandleDefaultTempArgIntoTempTempParam(const TemplateTemplateParmDecl *TTP,
                                       MultiLevelTemplateArgumentList &Result) {
   for (unsigned I = 0, N = TTP->getDepth() + 1; I != N; ++I)
     Result.addOuterTemplateArguments(std::nullopt);
   return Response::Done();
 }
 
 Response HandlePartialClassTemplateSpec(
     const ClassTemplatePartialSpecializationDecl *PartialClassTemplSpec,
     MultiLevelTemplateArgumentList &Result, bool SkipForSpecialization) {
   if (!SkipForSpecialization)
       Result.addOuterRetainedLevels(PartialClassTemplSpec->getTemplateDepth());
   return Response::Done();
 }
 
 // Add template arguments from a class template instantiation.
 Response
 HandleClassTemplateSpec(const ClassTemplateSpecializationDecl *ClassTemplSpec,
                         MultiLevelTemplateArgumentList &Result,
                         bool SkipForSpecialization) {
   if (!ClassTemplSpec->isClassScopeExplicitSpecialization()) {
     // We're done when we hit an explicit specialization.
     if (ClassTemplSpec->getSpecializationKind() == TSK_ExplicitSpecialization &&
         !isa<ClassTemplatePartialSpecializationDecl>(ClassTemplSpec))
       return Response::Done();
 
     if (!SkipForSpecialization)
       Result.addOuterTemplateArguments(
           const_cast<ClassTemplateSpecializationDecl *>(ClassTemplSpec),
           ClassTemplSpec->getTemplateInstantiationArgs().asArray(),
           /*Final=*/false);
 
     // If this class template specialization was instantiated from a
     // specialized member that is a class template, we're done.
     assert(ClassTemplSpec->getSpecializedTemplate() && "No class template?");
     if (ClassTemplSpec->getSpecializedTemplate()->isMemberSpecialization())
       return Response::Done();
 
     // If this was instantiated from a partial template specialization, we need
     // to get the next level of declaration context from the partial
     // specialization, as the ClassTemplateSpecializationDecl's
     // DeclContext/LexicalDeclContext will be for the primary template.
     if (auto *InstFromPartialTempl = ClassTemplSpec->getSpecializedTemplateOrPartial()
                       .dyn_cast<ClassTemplatePartialSpecializationDecl *>())
       return Response::ChangeDecl(InstFromPartialTempl->getLexicalDeclContext());
   }
   return Response::UseNextDecl(ClassTemplSpec);
 }
 
 Response HandleFunction(Sema &SemaRef, const FunctionDecl *Function,
                         MultiLevelTemplateArgumentList &Result,
                         const FunctionDecl *Pattern, bool RelativeToPrimary,
-                        bool ForConstraintInstantiation) {
+                        bool ForConstraintInstantiation,
+                        bool ForDefaultArgumentSubstitution) {
   // Add template arguments from a function template specialization.
   if (!RelativeToPrimary &&
       Function->getTemplateSpecializationKindForInstantiation() ==
           TSK_ExplicitSpecialization)
     return Response::Done();
 
   if (!RelativeToPrimary &&
       Function->getTemplateSpecializationKind() == TSK_ExplicitSpecialization) {
     // This is an implicit instantiation of an explicit specialization. We
     // don't get any template arguments from this function but might get
     // some from an enclosing template.
     return Response::UseNextDecl(Function);
   } else if (const TemplateArgumentList *TemplateArgs =
                  Function->getTemplateSpecializationArgs()) {
     // Add the template arguments for this specialization.
     Result.addOuterTemplateArguments(const_cast<FunctionDecl *>(Function),
                                      TemplateArgs->asArray(),
                                      /*Final=*/false);
 
     if (RelativeToPrimary &&
         (Function->getTemplateSpecializationKind() ==
              TSK_ExplicitSpecialization ||
          (Function->getFriendObjectKind() &&
           !Function->getPrimaryTemplate()->getFriendObjectKind())))
       return Response::UseNextDecl(Function);
 
     // If this function was instantiated from a specialized member that is
     // a function template, we're done.
     assert(Function->getPrimaryTemplate() && "No function template?");
-    if (Function->getPrimaryTemplate()->isMemberSpecialization())
+    if (!ForDefaultArgumentSubstitution &&
+        Function->getPrimaryTemplate()->isMemberSpecialization())
       return Response::Done();
 
     // If this function is a generic lambda specialization, we are done.
     if (!ForConstraintInstantiation &&
         isGenericLambdaCallOperatorOrStaticInvokerSpecialization(Function))
       return Response::Done();
 
   } else if (Function->getDescribedFunctionTemplate()) {
     assert(
         (ForConstraintInstantiation || Result.getNumSubstitutedLevels() == 0) &&
         "Outer template not instantiated?");
   }
   // If this is a friend or local declaration and it declares an entity at
   // namespace scope, take arguments from its lexical parent
   // instead of its semantic parent, unless of course the pattern we're
   // instantiating actually comes from the file's context!
   if ((Function->getFriendObjectKind() || Function->isLocalExternDecl()) &&
       Function->getNonTransparentDeclContext()->isFileContext() &&
       (!Pattern || !Pattern->getLexicalDeclContext()->isFileContext())) {
     return Response::ChangeDecl(Function->getLexicalDeclContext());
   }
 
   if (ForConstraintInstantiation && Function->getFriendObjectKind())
     return Response::ChangeDecl(Function->getLexicalDeclContext());
   return Response::UseNextDecl(Function);
 }
 
 Response HandleFunctionTemplateDecl(const FunctionTemplateDecl *FTD,
                                     MultiLevelTemplateArgumentList &Result) {
   if (!isa<ClassTemplateSpecializationDecl>(FTD->getDeclContext())) {
     Result.addOuterTemplateArguments(
         const_cast<FunctionTemplateDecl *>(FTD),
         const_cast<FunctionTemplateDecl *>(FTD)->getInjectedTemplateArgs(),
         /*Final=*/false);
 
     NestedNameSpecifier *NNS = FTD->getTemplatedDecl()->getQualifier();
 
     while (const Type *Ty = NNS ? NNS->getAsType() : nullptr) {
       if (NNS->isInstantiationDependent()) {
         if (const auto *TSTy = Ty->getAs<TemplateSpecializationType>()) {
           ArrayRef<TemplateArgument> Arguments = TSTy->template_arguments();
           // Prefer template arguments from the injected-class-type if possible.
           // For example,
           // ```cpp
           // template <class... Pack> struct S {
           //   template <class T> void foo();
           // };
           // template <class... Pack> template <class T>
           //           ^^^^^^^^^^^^^ InjectedTemplateArgs
           //           They're of kind TemplateArgument::Pack, not of
           //           TemplateArgument::Type.
           // void S<Pack...>::foo() {}
           //        ^^^^^^^
           //        TSTy->template_arguments() (which are of PackExpansionType)
           // ```
           // This meets the contract in
           // TreeTransform::TryExpandParameterPacks that the template arguments
           // for unexpanded parameters should be of a Pack kind.
           if (TSTy->isCurrentInstantiation()) {
             auto *RD = TSTy->getCanonicalTypeInternal()->getAsCXXRecordDecl();
             if (ClassTemplateDecl *CTD = RD->getDescribedClassTemplate())
               Arguments = CTD->getInjectedTemplateArgs();
             else if (auto *Specialization =
                          dyn_cast<ClassTemplateSpecializationDecl>(RD))
               Arguments =
                   Specialization->getTemplateInstantiationArgs().asArray();
           }
           Result.addOuterTemplateArguments(
               const_cast<FunctionTemplateDecl *>(FTD), Arguments,
               /*Final=*/false);
         }
       }
 
       NNS = NNS->getPrefix();
     }
   }
 
   return Response::ChangeDecl(FTD->getLexicalDeclContext());
 }
 
 Response HandleRecordDecl(Sema &SemaRef, const CXXRecordDecl *Rec,
                           MultiLevelTemplateArgumentList &Result,
                           ASTContext &Context,
                           bool ForConstraintInstantiation) {
   if (ClassTemplateDecl *ClassTemplate = Rec->getDescribedClassTemplate()) {
     assert(
         (ForConstraintInstantiation || Result.getNumSubstitutedLevels() == 0) &&
         "Outer template not instantiated?");
     if (ClassTemplate->isMemberSpecialization())
       return Response::Done();
     if (ForConstraintInstantiation)
       Result.addOuterTemplateArguments(const_cast<CXXRecordDecl *>(Rec),
                                        ClassTemplate->getInjectedTemplateArgs(),
                                        /*Final=*/false);
   }
 
   if (const MemberSpecializationInfo *MSInfo =
           Rec->getMemberSpecializationInfo())
     if (MSInfo->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
       return Response::Done();
 
   bool IsFriend = Rec->getFriendObjectKind() ||
                   (Rec->getDescribedClassTemplate() &&
                    Rec->getDescribedClassTemplate()->getFriendObjectKind());
   if (ForConstraintInstantiation && IsFriend &&
       Rec->getNonTransparentDeclContext()->isFileContext()) {
     return Response::ChangeDecl(Rec->getLexicalDeclContext());
   }
 
   // This is to make sure we pick up the VarTemplateSpecializationDecl or the
   // TypeAliasTemplateDecl that this lambda is defined inside of.
   if (Rec->isLambda()) {
     if (const Decl *LCD = Rec->getLambdaContextDecl())
       return Response::ChangeDecl(LCD);
     // Retrieve the template arguments for a using alias declaration.
     // This is necessary for constraint checking, since we always keep
     // constraints relative to the primary template.
     if (auto TypeAlias = getEnclosingTypeAliasTemplateDecl(SemaRef);
         ForConstraintInstantiation && TypeAlias) {
       if (isLambdaEnclosedByTypeAliasDecl(Rec->getLambdaCallOperator(),
                                           TypeAlias.PrimaryTypeAliasDecl)) {
         Result.addOuterTemplateArguments(TypeAlias.Template,
                                          TypeAlias.AssociatedTemplateArguments,
                                          /*Final=*/false);
         // Visit the parent of the current type alias declaration rather than
         // the lambda thereof.
         // E.g., in the following example:
         // struct S {
         //  template <class> using T = decltype([]<Concept> {} ());
         // };
         // void foo() {
         //   S::T var;
         // }
         // The instantiated lambda expression (which we're visiting at 'var')
         // has a function DeclContext 'foo' rather than the Record DeclContext
         // S. This seems to be an oversight to me that we may want to set a
         // Sema Context from the CXXScopeSpec before substituting into T.
         return Response::ChangeDecl(TypeAlias.Template->getDeclContext());
       }
     }
   }
 
   return Response::UseNextDecl(Rec);
 }
 
 Response HandleImplicitConceptSpecializationDecl(
     const ImplicitConceptSpecializationDecl *CSD,
     MultiLevelTemplateArgumentList &Result) {
   Result.addOuterTemplateArguments(
       const_cast<ImplicitConceptSpecializationDecl *>(CSD),
       CSD->getTemplateArguments(),
       /*Final=*/false);
   return Response::UseNextDecl(CSD);
 }
 
 Response HandleGenericDeclContext(const Decl *CurDecl) {
   return Response::UseNextDecl(CurDecl);
 }
 } // namespace TemplateInstArgsHelpers
 } // namespace
 
 MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
     const NamedDecl *ND, const DeclContext *DC, bool Final,
     std::optional<ArrayRef<TemplateArgument>> Innermost, bool RelativeToPrimary,
     const FunctionDecl *Pattern, bool ForConstraintInstantiation,
-    bool SkipForSpecialization) {
+    bool SkipForSpecialization, bool ForDefaultArgumentSubstitution) {
   assert((ND || DC) && "Can't find arguments for a decl if one isn't provided");
   // Accumulate the set of template argument lists in this structure.
   MultiLevelTemplateArgumentList Result;
 
   using namespace TemplateInstArgsHelpers;
   const Decl *CurDecl = ND;
 
   if (!CurDecl)
     CurDecl = Decl::castFromDeclContext(DC);
 
   if (Innermost) {
     Result.addOuterTemplateArguments(const_cast<NamedDecl *>(ND), *Innermost,
                                      Final);
     // Populate placeholder template arguments for TemplateTemplateParmDecls.
     // This is essential for the case e.g.
     //
     // template <class> concept Concept = false;
     // template <template <Concept C> class T> void foo(T<int>)
     //
     // where parameter C has a depth of 1 but the substituting argument `int`
     // has a depth of 0.
     if (const auto *TTP = dyn_cast<TemplateTemplateParmDecl>(CurDecl))
       HandleDefaultTempArgIntoTempTempParam(TTP, Result);
     CurDecl = Response::UseNextDecl(CurDecl).NextDecl;
   }
 
   while (!CurDecl->isFileContextDecl()) {
     Response R;
     if (const auto *VarTemplSpec =
             dyn_cast<VarTemplateSpecializationDecl>(CurDecl)) {
       R = HandleVarTemplateSpec(VarTemplSpec, Result, SkipForSpecialization);
     } else if (const auto *PartialClassTemplSpec =
                    dyn_cast<ClassTemplatePartialSpecializationDecl>(CurDecl)) {
       R = HandlePartialClassTemplateSpec(PartialClassTemplSpec, Result,
                                          SkipForSpecialization);
     } else if (const auto *ClassTemplSpec =
                    dyn_cast<ClassTemplateSpecializationDecl>(CurDecl)) {
       R = HandleClassTemplateSpec(ClassTemplSpec, Result,
                                   SkipForSpecialization);
     } else if (const auto *Function = dyn_cast<FunctionDecl>(CurDecl)) {
       R = HandleFunction(*this, Function, Result, Pattern, RelativeToPrimary,
-                         ForConstraintInstantiation);
+                         ForConstraintInstantiation,
+                         ForDefaultArgumentSubstitution);
     } else if (const auto *Rec = dyn_cast<CXXRecordDecl>(CurDecl)) {
       R = HandleRecordDecl(*this, Rec, Result, Context,
                            ForConstraintInstantiation);
     } else if (const auto *CSD =
                    dyn_cast<ImplicitConceptSpecializationDecl>(CurDecl)) {
       R = HandleImplicitConceptSpecializationDecl(CSD, Result);
     } else if (const auto *FTD = dyn_cast<FunctionTemplateDecl>(CurDecl)) {
       R = HandleFunctionTemplateDecl(FTD, Result);
     } else if (const auto *CTD = dyn_cast<ClassTemplateDecl>(CurDecl)) {
       R = Response::ChangeDecl(CTD->getLexicalDeclContext());
     } else if (!isa<DeclContext>(CurDecl)) {
       R = Response::DontClearRelativeToPrimaryNextDecl(CurDecl);
       if (const auto *TTP = dyn_cast<TemplateTemplateParmDecl>(CurDecl)) {
         R = HandleDefaultTempArgIntoTempTempParam(TTP, Result);
       }
     } else {
       R = HandleGenericDeclContext(CurDecl);
     }
 
     if (R.IsDone)
       return Result;
     if (R.ClearRelativeToPrimary)
       RelativeToPrimary = false;
     assert(R.NextDecl);
     CurDecl = R.NextDecl;
   }
 
   return Result;
 }
 
 bool Sema::CodeSynthesisContext::isInstantiationRecord() const {
   switch (Kind) {
   case TemplateInstantiation:
   case ExceptionSpecInstantiation:
   case DefaultTemplateArgumentInstantiation:
   case DefaultFunctionArgumentInstantiation:
   case ExplicitTemplateArgumentSubstitution:
   case DeducedTemplateArgumentSubstitution:
   case PriorTemplateArgumentSubstitution:
   case ConstraintsCheck:
   case NestedRequirementConstraintsCheck:
     return true;
 
   case RequirementInstantiation:
   case RequirementParameterInstantiation:
   case DefaultTemplateArgumentChecking:
   case DeclaringSpecialMember:
   case DeclaringImplicitEqualityComparison:
   case DefiningSynthesizedFunction:
   case ExceptionSpecEvaluation:
   case ConstraintSubstitution:
   case ParameterMappingSubstitution:
   case ConstraintNormalization:
   case RewritingOperatorAsSpaceship:
   case InitializingStructuredBinding:
   case MarkingClassDllexported:
   case BuildingBuiltinDumpStructCall:
   case LambdaExpressionSubstitution:
   case BuildingDeductionGuides:
   case TypeAliasTemplateInstantiation:
     return false;
 
   // This function should never be called when Kind's value is Memoization.
   case Memoization:
     break;
   }
 
   llvm_unreachable("Invalid SynthesisKind!");
 }
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, CodeSynthesisContext::SynthesisKind Kind,
     SourceLocation PointOfInstantiation, SourceRange InstantiationRange,
     Decl *Entity, NamedDecl *Template, ArrayRef<TemplateArgument> TemplateArgs,
     sema::TemplateDeductionInfo *DeductionInfo)
     : SemaRef(SemaRef) {
   // Don't allow further instantiation if a fatal error and an uncompilable
   // error have occurred. Any diagnostics we might have raised will not be
   // visible, and we do not need to construct a correct AST.
   if (SemaRef.Diags.hasFatalErrorOccurred() &&
       SemaRef.hasUncompilableErrorOccurred()) {
     Invalid = true;
     return;
   }
   Invalid = CheckInstantiationDepth(PointOfInstantiation, InstantiationRange);
   if (!Invalid) {
     CodeSynthesisContext Inst;
     Inst.Kind = Kind;
     Inst.PointOfInstantiation = PointOfInstantiation;
     Inst.Entity = Entity;
     Inst.Template = Template;
     Inst.TemplateArgs = TemplateArgs.data();
     Inst.NumTemplateArgs = TemplateArgs.size();
     Inst.DeductionInfo = DeductionInfo;
     Inst.InstantiationRange = InstantiationRange;
     SemaRef.pushCodeSynthesisContext(Inst);
 
     AlreadyInstantiating = !Inst.Entity ? false :
         !SemaRef.InstantiatingSpecializations
              .insert({Inst.Entity->getCanonicalDecl(), Inst.Kind})
              .second;
     atTemplateBegin(SemaRef.TemplateInstCallbacks, SemaRef, Inst);
   }
 }
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, Decl *Entity,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(SemaRef,
                             CodeSynthesisContext::TemplateInstantiation,
                             PointOfInstantiation, InstantiationRange, Entity) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, FunctionDecl *Entity,
     ExceptionSpecification, SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::ExceptionSpecInstantiation,
           PointOfInstantiation, InstantiationRange, Entity) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateParameter Param,
     TemplateDecl *Template, ArrayRef<TemplateArgument> TemplateArgs,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef,
           CodeSynthesisContext::DefaultTemplateArgumentInstantiation,
           PointOfInstantiation, InstantiationRange, getAsNamedDecl(Param),
           Template, TemplateArgs) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     FunctionTemplateDecl *FunctionTemplate,
     ArrayRef<TemplateArgument> TemplateArgs,
     CodeSynthesisContext::SynthesisKind Kind,
     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
     : InstantiatingTemplate(SemaRef, Kind, PointOfInstantiation,
                             InstantiationRange, FunctionTemplate, nullptr,
                             TemplateArgs, &DeductionInfo) {
   assert(Kind == CodeSynthesisContext::ExplicitTemplateArgumentSubstitution ||
          Kind == CodeSynthesisContext::DeducedTemplateArgumentSubstitution ||
          Kind == CodeSynthesisContext::BuildingDeductionGuides);
 }
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     TemplateDecl *Template,
     ArrayRef<TemplateArgument> TemplateArgs,
     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef,
           CodeSynthesisContext::DeducedTemplateArgumentSubstitution,
           PointOfInstantiation, InstantiationRange, Template, nullptr,
           TemplateArgs, &DeductionInfo) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     ClassTemplatePartialSpecializationDecl *PartialSpec,
     ArrayRef<TemplateArgument> TemplateArgs,
     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef,
           CodeSynthesisContext::DeducedTemplateArgumentSubstitution,
           PointOfInstantiation, InstantiationRange, PartialSpec, nullptr,
           TemplateArgs, &DeductionInfo) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     VarTemplatePartialSpecializationDecl *PartialSpec,
     ArrayRef<TemplateArgument> TemplateArgs,
     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef,
           CodeSynthesisContext::DeducedTemplateArgumentSubstitution,
           PointOfInstantiation, InstantiationRange, PartialSpec, nullptr,
           TemplateArgs, &DeductionInfo) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, ParmVarDecl *Param,
     ArrayRef<TemplateArgument> TemplateArgs, SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef,
           CodeSynthesisContext::DefaultFunctionArgumentInstantiation,
           PointOfInstantiation, InstantiationRange, Param, nullptr,
           TemplateArgs) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, NamedDecl *Template,
     NonTypeTemplateParmDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef,
           CodeSynthesisContext::PriorTemplateArgumentSubstitution,
           PointOfInstantiation, InstantiationRange, Param, Template,
           TemplateArgs) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, NamedDecl *Template,
     TemplateTemplateParmDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef,
           CodeSynthesisContext::PriorTemplateArgumentSubstitution,
           PointOfInstantiation, InstantiationRange, Param, Template,
           TemplateArgs) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     TypeAliasTemplateDecl *Entity, ArrayRef<TemplateArgument> TemplateArgs,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::TypeAliasTemplateInstantiation,
           PointOfInstantiation, InstantiationRange, /*Entity=*/Entity,
           /*Template=*/nullptr, TemplateArgs) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateDecl *Template,
     NamedDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::DefaultTemplateArgumentChecking,
           PointOfInstantiation, InstantiationRange, Param, Template,
           TemplateArgs) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     concepts::Requirement *Req, sema::TemplateDeductionInfo &DeductionInfo,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::RequirementInstantiation,
           PointOfInstantiation, InstantiationRange, /*Entity=*/nullptr,
           /*Template=*/nullptr, /*TemplateArgs=*/std::nullopt, &DeductionInfo) {
 }
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     concepts::NestedRequirement *Req, ConstraintsCheck,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::NestedRequirementConstraintsCheck,
           PointOfInstantiation, InstantiationRange, /*Entity=*/nullptr,
           /*Template=*/nullptr, /*TemplateArgs=*/std::nullopt) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, const RequiresExpr *RE,
     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::RequirementParameterInstantiation,
           PointOfInstantiation, InstantiationRange, /*Entity=*/nullptr,
           /*Template=*/nullptr, /*TemplateArgs=*/std::nullopt, &DeductionInfo) {
 }
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     ConstraintsCheck, NamedDecl *Template,
     ArrayRef<TemplateArgument> TemplateArgs, SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::ConstraintsCheck,
           PointOfInstantiation, InstantiationRange, Template, nullptr,
           TemplateArgs) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     ConstraintSubstitution, NamedDecl *Template,
     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::ConstraintSubstitution,
           PointOfInstantiation, InstantiationRange, Template, nullptr,
           {}, &DeductionInfo) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     ConstraintNormalization, NamedDecl *Template,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::ConstraintNormalization,
           PointOfInstantiation, InstantiationRange, Template) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation,
     ParameterMappingSubstitution, NamedDecl *Template,
     SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::ParameterMappingSubstitution,
           PointOfInstantiation, InstantiationRange, Template) {}
 
 Sema::InstantiatingTemplate::InstantiatingTemplate(
     Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateDecl *Entity,
     BuildingDeductionGuidesTag, SourceRange InstantiationRange)
     : InstantiatingTemplate(
           SemaRef, CodeSynthesisContext::BuildingDeductionGuides,
           PointOfInstantiation, InstantiationRange, Entity) {}
 
 
 void Sema::pushCodeSynthesisContext(CodeSynthesisContext Ctx) {
   Ctx.SavedInNonInstantiationSFINAEContext = InNonInstantiationSFINAEContext;
   InNonInstantiationSFINAEContext = false;
 
   CodeSynthesisContexts.push_back(Ctx);
 
   if (!Ctx.isInstantiationRecord())
     ++NonInstantiationEntries;
 
   // Check to see if we're low on stack space. We can't do anything about this
   // from here, but we can at least warn the user.
   if (isStackNearlyExhausted())
     warnStackExhausted(Ctx.PointOfInstantiation);
 }
 
 void Sema::popCodeSynthesisContext() {
   auto &Active = CodeSynthesisContexts.back();
   if (!Active.isInstantiationRecord()) {
     assert(NonInstantiationEntries > 0);
     --NonInstantiationEntries;
   }
 
   InNonInstantiationSFINAEContext = Active.SavedInNonInstantiationSFINAEContext;
 
   // Name lookup no longer looks in this template's defining module.
   assert(CodeSynthesisContexts.size() >=
              CodeSynthesisContextLookupModules.size() &&
          "forgot to remove a lookup module for a template instantiation");
   if (CodeSynthesisContexts.size() ==
       CodeSynthesisContextLookupModules.size()) {
     if (Module *M = CodeSynthesisContextLookupModules.back())
       LookupModulesCache.erase(M);
     CodeSynthesisContextLookupModules.pop_back();
   }
 
   // If we've left the code synthesis context for the current context stack,
   // stop remembering that we've emitted that stack.
   if (CodeSynthesisContexts.size() ==
       LastEmittedCodeSynthesisContextDepth)
     LastEmittedCodeSynthesisContextDepth = 0;
 
   CodeSynthesisContexts.pop_back();
 }
 
 void Sema::InstantiatingTemplate::Clear() {
   if (!Invalid) {
     if (!AlreadyInstantiating) {
       auto &Active = SemaRef.CodeSynthesisContexts.back();
       if (Active.Entity)
         SemaRef.InstantiatingSpecializations.erase(
             {Active.Entity->getCanonicalDecl(), Active.Kind});
     }
 
     atTemplateEnd(SemaRef.TemplateInstCallbacks, SemaRef,
                   SemaRef.CodeSynthesisContexts.back());
 
     SemaRef.popCodeSynthesisContext();
     Invalid = true;
   }
 }
 
 static std::string convertCallArgsToString(Sema &S,
                                            llvm::ArrayRef<const Expr *> Args) {
   std::string Result;
   llvm::raw_string_ostream OS(Result);
   llvm::ListSeparator Comma;
   for (const Expr *Arg : Args) {
     OS << Comma;
     Arg->IgnoreParens()->printPretty(OS, nullptr,
                                      S.Context.getPrintingPolicy());
   }
   return Result;
 }
 
 bool Sema::InstantiatingTemplate::CheckInstantiationDepth(
                                         SourceLocation PointOfInstantiation,
                                            SourceRange InstantiationRange) {
   assert(SemaRef.NonInstantiationEntries <=
          SemaRef.CodeSynthesisContexts.size());
   if ((SemaRef.CodeSynthesisContexts.size() -
           SemaRef.NonInstantiationEntries)
         <= SemaRef.getLangOpts().InstantiationDepth)
     return false;
 
   SemaRef.Diag(PointOfInstantiation,
                diag::err_template_recursion_depth_exceeded)
     << SemaRef.getLangOpts().InstantiationDepth
     << InstantiationRange;
   SemaRef.Diag(PointOfInstantiation, diag::note_template_recursion_depth)
     << SemaRef.getLangOpts().InstantiationDepth;
   return true;
 }
 
 void Sema::PrintInstantiationStack() {
   // Determine which template instantiations to skip, if any.
   unsigned SkipStart = CodeSynthesisContexts.size(), SkipEnd = SkipStart;
   unsigned Limit = Diags.getTemplateBacktraceLimit();
   if (Limit && Limit < CodeSynthesisContexts.size()) {
     SkipStart = Limit / 2 + Limit % 2;
     SkipEnd = CodeSynthesisContexts.size() - Limit / 2;
   }
 
   // FIXME: In all of these cases, we need to show the template arguments
   unsigned InstantiationIdx = 0;
   for (SmallVectorImpl<CodeSynthesisContext>::reverse_iterator
          Active = CodeSynthesisContexts.rbegin(),
          ActiveEnd = CodeSynthesisContexts.rend();
        Active != ActiveEnd;
        ++Active, ++InstantiationIdx) {
     // Skip this instantiation?
     if (InstantiationIdx >= SkipStart && InstantiationIdx < SkipEnd) {
       if (InstantiationIdx == SkipStart) {
         // Note that we're skipping instantiations.
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_instantiation_contexts_suppressed)
           << unsigned(CodeSynthesisContexts.size() - Limit);
       }
       continue;
     }
 
     switch (Active->Kind) {
     case CodeSynthesisContext::TemplateInstantiation: {
       Decl *D = Active->Entity;
       if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D)) {
         unsigned DiagID = diag::note_template_member_class_here;
         if (isa<ClassTemplateSpecializationDecl>(Record))
           DiagID = diag::note_template_class_instantiation_here;
         Diags.Report(Active->PointOfInstantiation, DiagID)
           << Record << Active->InstantiationRange;
       } else if (FunctionDecl *Function = dyn_cast<FunctionDecl>(D)) {
         unsigned DiagID;
         if (Function->getPrimaryTemplate())
           DiagID = diag::note_function_template_spec_here;
         else
           DiagID = diag::note_template_member_function_here;
         Diags.Report(Active->PointOfInstantiation, DiagID)
           << Function
           << Active->InstantiationRange;
       } else if (VarDecl *VD = dyn_cast<VarDecl>(D)) {
         Diags.Report(Active->PointOfInstantiation,
                      VD->isStaticDataMember()?
                        diag::note_template_static_data_member_def_here
                      : diag::note_template_variable_def_here)
           << VD
           << Active->InstantiationRange;
       } else if (EnumDecl *ED = dyn_cast<EnumDecl>(D)) {
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_template_enum_def_here)
           << ED
           << Active->InstantiationRange;
       } else if (FieldDecl *FD = dyn_cast<FieldDecl>(D)) {
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_template_nsdmi_here)
             << FD << Active->InstantiationRange;
       } else if (ClassTemplateDecl *CTD = dyn_cast<ClassTemplateDecl>(D)) {
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_template_class_instantiation_here)
             << CTD << Active->InstantiationRange;
       }
       break;
     }
 
     case CodeSynthesisContext::DefaultTemplateArgumentInstantiation: {
       TemplateDecl *Template = cast<TemplateDecl>(Active->Template);
       SmallString<128> TemplateArgsStr;
       llvm::raw_svector_ostream OS(TemplateArgsStr);
       Template->printName(OS, getPrintingPolicy());
       printTemplateArgumentList(OS, Active->template_arguments(),
                                 getPrintingPolicy());
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_default_arg_instantiation_here)
         << OS.str()
         << Active->InstantiationRange;
       break;
     }
 
     case CodeSynthesisContext::ExplicitTemplateArgumentSubstitution: {
       FunctionTemplateDecl *FnTmpl = cast<FunctionTemplateDecl>(Active->Entity);
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_explicit_template_arg_substitution_here)
         << FnTmpl
         << getTemplateArgumentBindingsText(FnTmpl->getTemplateParameters(),
                                            Active->TemplateArgs,
                                            Active->NumTemplateArgs)
         << Active->InstantiationRange;
       break;
     }
 
     case CodeSynthesisContext::DeducedTemplateArgumentSubstitution: {
       if (FunctionTemplateDecl *FnTmpl =
               dyn_cast<FunctionTemplateDecl>(Active->Entity)) {
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_function_template_deduction_instantiation_here)
           << FnTmpl
           << getTemplateArgumentBindingsText(FnTmpl->getTemplateParameters(),
                                              Active->TemplateArgs,
                                              Active->NumTemplateArgs)
           << Active->InstantiationRange;
       } else {
         bool IsVar = isa<VarTemplateDecl>(Active->Entity) ||
                      isa<VarTemplateSpecializationDecl>(Active->Entity);
         bool IsTemplate = false;
         TemplateParameterList *Params;
         if (auto *D = dyn_cast<TemplateDecl>(Active->Entity)) {
           IsTemplate = true;
           Params = D->getTemplateParameters();
         } else if (auto *D = dyn_cast<ClassTemplatePartialSpecializationDecl>(
                        Active->Entity)) {
           Params = D->getTemplateParameters();
         } else if (auto *D = dyn_cast<VarTemplatePartialSpecializationDecl>(
                        Active->Entity)) {
           Params = D->getTemplateParameters();
         } else {
           llvm_unreachable("unexpected template kind");
         }
 
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_deduced_template_arg_substitution_here)
           << IsVar << IsTemplate << cast<NamedDecl>(Active->Entity)
           << getTemplateArgumentBindingsText(Params, Active->TemplateArgs,
                                              Active->NumTemplateArgs)
           << Active->InstantiationRange;
       }
       break;
     }
 
     case CodeSynthesisContext::DefaultFunctionArgumentInstantiation: {
       ParmVarDecl *Param = cast<ParmVarDecl>(Active->Entity);
       FunctionDecl *FD = cast<FunctionDecl>(Param->getDeclContext());
 
       SmallString<128> TemplateArgsStr;
       llvm::raw_svector_ostream OS(TemplateArgsStr);
       FD->printName(OS, getPrintingPolicy());
       printTemplateArgumentList(OS, Active->template_arguments(),
                                 getPrintingPolicy());
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_default_function_arg_instantiation_here)
         << OS.str()
         << Active->InstantiationRange;
       break;
     }
 
     case CodeSynthesisContext::PriorTemplateArgumentSubstitution: {
       NamedDecl *Parm = cast<NamedDecl>(Active->Entity);
       std::string Name;
       if (!Parm->getName().empty())
         Name = std::string(" '") + Parm->getName().str() + "'";
 
       TemplateParameterList *TemplateParams = nullptr;
       if (TemplateDecl *Template = dyn_cast<TemplateDecl>(Active->Template))
         TemplateParams = Template->getTemplateParameters();
       else
         TemplateParams =
           cast<ClassTemplatePartialSpecializationDecl>(Active->Template)
                                                       ->getTemplateParameters();
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_prior_template_arg_substitution)
         << isa<TemplateTemplateParmDecl>(Parm)
         << Name
         << getTemplateArgumentBindingsText(TemplateParams,
                                            Active->TemplateArgs,
                                            Active->NumTemplateArgs)
         << Active->InstantiationRange;
       break;
     }
 
     case CodeSynthesisContext::DefaultTemplateArgumentChecking: {
       TemplateParameterList *TemplateParams = nullptr;
       if (TemplateDecl *Template = dyn_cast<TemplateDecl>(Active->Template))
         TemplateParams = Template->getTemplateParameters();
       else
         TemplateParams =
           cast<ClassTemplatePartialSpecializationDecl>(Active->Template)
                                                       ->getTemplateParameters();
 
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_template_default_arg_checking)
         << getTemplateArgumentBindingsText(TemplateParams,
                                            Active->TemplateArgs,
                                            Active->NumTemplateArgs)
         << Active->InstantiationRange;
       break;
     }
 
     case CodeSynthesisContext::ExceptionSpecEvaluation:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_evaluating_exception_spec_here)
           << cast<FunctionDecl>(Active->Entity);
       break;
 
     case CodeSynthesisContext::ExceptionSpecInstantiation:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_template_exception_spec_instantiation_here)
         << cast<FunctionDecl>(Active->Entity)
         << Active->InstantiationRange;
       break;
 
     case CodeSynthesisContext::RequirementInstantiation:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_template_requirement_instantiation_here)
         << Active->InstantiationRange;
       break;
     case CodeSynthesisContext::RequirementParameterInstantiation:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_template_requirement_params_instantiation_here)
           << Active->InstantiationRange;
       break;
 
     case CodeSynthesisContext::NestedRequirementConstraintsCheck:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_nested_requirement_here)
         << Active->InstantiationRange;
       break;
 
     case CodeSynthesisContext::DeclaringSpecialMember:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_in_declaration_of_implicit_special_member)
           << cast<CXXRecordDecl>(Active->Entity)
           << llvm::to_underlying(Active->SpecialMember);
       break;
 
     case CodeSynthesisContext::DeclaringImplicitEqualityComparison:
       Diags.Report(Active->Entity->getLocation(),
                    diag::note_in_declaration_of_implicit_equality_comparison);
       break;
 
     case CodeSynthesisContext::DefiningSynthesizedFunction: {
       // FIXME: For synthesized functions that are not defaulted,
       // produce a note.
       auto *FD = dyn_cast<FunctionDecl>(Active->Entity);
       DefaultedFunctionKind DFK =
           FD ? getDefaultedFunctionKind(FD) : DefaultedFunctionKind();
       if (DFK.isSpecialMember()) {
         auto *MD = cast<CXXMethodDecl>(FD);
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_member_synthesized_at)
             << MD->isExplicitlyDefaulted()
             << llvm::to_underlying(DFK.asSpecialMember())
             << Context.getTagDeclType(MD->getParent());
       } else if (DFK.isComparison()) {
         QualType RecordType = FD->getParamDecl(0)
                                   ->getType()
                                   .getNonReferenceType()
                                   .getUnqualifiedType();
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_comparison_synthesized_at)
             << (int)DFK.asComparison() << RecordType;
       }
       break;
     }
 
     case CodeSynthesisContext::RewritingOperatorAsSpaceship:
       Diags.Report(Active->Entity->getLocation(),
                    diag::note_rewriting_operator_as_spaceship);
       break;
 
     case CodeSynthesisContext::InitializingStructuredBinding:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_in_binding_decl_init)
           << cast<BindingDecl>(Active->Entity);
       break;
 
     case CodeSynthesisContext::MarkingClassDllexported:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_due_to_dllexported_class)
           << cast<CXXRecordDecl>(Active->Entity) << !getLangOpts().CPlusPlus11;
       break;
 
     case CodeSynthesisContext::BuildingBuiltinDumpStructCall:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_building_builtin_dump_struct_call)
           << convertCallArgsToString(
                  *this, llvm::ArrayRef(Active->CallArgs, Active->NumCallArgs));
       break;
 
     case CodeSynthesisContext::Memoization:
       break;
 
     case CodeSynthesisContext::LambdaExpressionSubstitution:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_lambda_substitution_here);
       break;
     case CodeSynthesisContext::ConstraintsCheck: {
       unsigned DiagID = 0;
       if (!Active->Entity) {
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_nested_requirement_here)
           << Active->InstantiationRange;
         break;
       }
       if (isa<ConceptDecl>(Active->Entity))
         DiagID = diag::note_concept_specialization_here;
       else if (isa<TemplateDecl>(Active->Entity))
         DiagID = diag::note_checking_constraints_for_template_id_here;
       else if (isa<VarTemplatePartialSpecializationDecl>(Active->Entity))
         DiagID = diag::note_checking_constraints_for_var_spec_id_here;
       else if (isa<ClassTemplatePartialSpecializationDecl>(Active->Entity))
         DiagID = diag::note_checking_constraints_for_class_spec_id_here;
       else {
         assert(isa<FunctionDecl>(Active->Entity));
         DiagID = diag::note_checking_constraints_for_function_here;
       }
       SmallString<128> TemplateArgsStr;
       llvm::raw_svector_ostream OS(TemplateArgsStr);
       cast<NamedDecl>(Active->Entity)->printName(OS, getPrintingPolicy());
       if (!isa<FunctionDecl>(Active->Entity)) {
         printTemplateArgumentList(OS, Active->template_arguments(),
                                   getPrintingPolicy());
       }
       Diags.Report(Active->PointOfInstantiation, DiagID) << OS.str()
         << Active->InstantiationRange;
       break;
     }
     case CodeSynthesisContext::ConstraintSubstitution:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_constraint_substitution_here)
           << Active->InstantiationRange;
       break;
     case CodeSynthesisContext::ConstraintNormalization:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_constraint_normalization_here)
           << cast<NamedDecl>(Active->Entity)->getName()
           << Active->InstantiationRange;
       break;
     case CodeSynthesisContext::ParameterMappingSubstitution:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_parameter_mapping_substitution_here)
           << Active->InstantiationRange;
       break;
     case CodeSynthesisContext::BuildingDeductionGuides:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_building_deduction_guide_here);
       break;
     case CodeSynthesisContext::TypeAliasTemplateInstantiation:
       Diags.Report(Active->PointOfInstantiation,
                    diag::note_template_type_alias_instantiation_here)
           << cast<TypeAliasTemplateDecl>(Active->Entity)
           << Active->InstantiationRange;
       break;
     }
   }
 }
 
 std::optional<TemplateDeductionInfo *> Sema::isSFINAEContext() const {
   if (InNonInstantiationSFINAEContext)
     return std::optional<TemplateDeductionInfo *>(nullptr);
 
   for (SmallVectorImpl<CodeSynthesisContext>::const_reverse_iterator
          Active = CodeSynthesisContexts.rbegin(),
          ActiveEnd = CodeSynthesisContexts.rend();
        Active != ActiveEnd;
        ++Active)
   {
     switch (Active->Kind) {
     case CodeSynthesisContext::TypeAliasTemplateInstantiation:
       // An instantiation of an alias template may or may not be a SFINAE
       // context, depending on what else is on the stack.
       if (isa<TypeAliasTemplateDecl>(Active->Entity))
         break;
       [[fallthrough]];
     case CodeSynthesisContext::TemplateInstantiation:
     case CodeSynthesisContext::DefaultFunctionArgumentInstantiation:
     case CodeSynthesisContext::ExceptionSpecInstantiation:
     case CodeSynthesisContext::ConstraintsCheck:
     case CodeSynthesisContext::ParameterMappingSubstitution:
     case CodeSynthesisContext::ConstraintNormalization:
     case CodeSynthesisContext::NestedRequirementConstraintsCheck:
       // This is a template instantiation, so there is no SFINAE.
       return std::nullopt;
     case CodeSynthesisContext::LambdaExpressionSubstitution:
       // [temp.deduct]p9
       // A lambda-expression appearing in a function type or a template
       // parameter is not considered part of the immediate context for the
       // purposes of template argument deduction.
       // CWG2672: A lambda-expression body is never in the immediate context.
       return std::nullopt;
 
     case CodeSynthesisContext::DefaultTemplateArgumentInstantiation:
     case CodeSynthesisContext::PriorTemplateArgumentSubstitution:
     case CodeSynthesisContext::DefaultTemplateArgumentChecking:
     case CodeSynthesisContext::RewritingOperatorAsSpaceship:
       // A default template argument instantiation and substitution into
       // template parameters with arguments for prior parameters may or may
       // not be a SFINAE context; look further up the stack.
       break;
 
     case CodeSynthesisContext::ExplicitTemplateArgumentSubstitution:
     case CodeSynthesisContext::DeducedTemplateArgumentSubstitution:
       // We're either substituting explicitly-specified template arguments,
       // deduced template arguments. SFINAE applies unless we are in a lambda
       // body, see [temp.deduct]p9.
     case CodeSynthesisContext::ConstraintSubstitution:
     case CodeSynthesisContext::RequirementInstantiation:
     case CodeSynthesisContext::RequirementParameterInstantiation:
       // SFINAE always applies in a constraint expression or a requirement
       // in a requires expression.
       assert(Active->DeductionInfo && "Missing deduction info pointer");
       return Active->DeductionInfo;
 
     case CodeSynthesisContext::DeclaringSpecialMember:
     case CodeSynthesisContext::DeclaringImplicitEqualityComparison:
     case CodeSynthesisContext::DefiningSynthesizedFunction:
     case CodeSynthesisContext::InitializingStructuredBinding:
     case CodeSynthesisContext::MarkingClassDllexported:
     case CodeSynthesisContext::BuildingBuiltinDumpStructCall:
     case CodeSynthesisContext::BuildingDeductionGuides:
       // This happens in a context unrelated to template instantiation, so
       // there is no SFINAE.
       return std::nullopt;
 
     case CodeSynthesisContext::ExceptionSpecEvaluation:
       // FIXME: This should not be treated as a SFINAE context, because
       // we will cache an incorrect exception specification. However, clang
       // bootstrap relies this! See PR31692.
       break;
 
     case CodeSynthesisContext::Memoization:
       break;
     }
 
     // The inner context was transparent for SFINAE. If it occurred within a
     // non-instantiation SFINAE context, then SFINAE applies.
     if (Active->SavedInNonInstantiationSFINAEContext)
       return std::optional<TemplateDeductionInfo *>(nullptr);
   }
 
   return std::nullopt;
 }
 
 //===----------------------------------------------------------------------===/
 // Template Instantiation for Types
 //===----------------------------------------------------------------------===/
 namespace {
   class TemplateInstantiator : public TreeTransform<TemplateInstantiator> {
     const MultiLevelTemplateArgumentList &TemplateArgs;
     SourceLocation Loc;
     DeclarationName Entity;
     // Whether to evaluate the C++20 constraints or simply substitute into them.
     bool EvaluateConstraints = true;
 
   public:
     typedef TreeTransform<TemplateInstantiator> inherited;
 
     TemplateInstantiator(Sema &SemaRef,
                          const MultiLevelTemplateArgumentList &TemplateArgs,
                          SourceLocation Loc, DeclarationName Entity)
         : inherited(SemaRef), TemplateArgs(TemplateArgs), Loc(Loc),
           Entity(Entity) {}
 
     void setEvaluateConstraints(bool B) {
       EvaluateConstraints = B;
     }
     bool getEvaluateConstraints() {
       return EvaluateConstraints;
     }
 
     /// Determine whether the given type \p T has already been
     /// transformed.
     ///
     /// For the purposes of template instantiation, a type has already been
     /// transformed if it is NULL or if it is not dependent.
     bool AlreadyTransformed(QualType T);
 
     /// Returns the location of the entity being instantiated, if known.
     SourceLocation getBaseLocation() { return Loc; }
 
     /// Returns the name of the entity being instantiated, if any.
     DeclarationName getBaseEntity() { return Entity; }
 
     /// Sets the "base" location and entity when that
     /// information is known based on another transformation.
     void setBase(SourceLocation Loc, DeclarationName Entity) {
       this->Loc = Loc;
       this->Entity = Entity;
     }
 
     unsigned TransformTemplateDepth(unsigned Depth) {
       return TemplateArgs.getNewDepth(Depth);
     }
 
     std::optional<unsigned> getPackIndex(TemplateArgument Pack) {
       int Index = getSema().ArgumentPackSubstitutionIndex;
       if (Index == -1)
         return std::nullopt;
       return Pack.pack_size() - 1 - Index;
     }
 
     bool TryExpandParameterPacks(SourceLocation EllipsisLoc,
                                  SourceRange PatternRange,
                                  ArrayRef<UnexpandedParameterPack> Unexpanded,
                                  bool &ShouldExpand, bool &RetainExpansion,
                                  std::optional<unsigned> &NumExpansions) {
       return getSema().CheckParameterPacksForExpansion(EllipsisLoc,
                                                        PatternRange, Unexpanded,
                                                        TemplateArgs,
                                                        ShouldExpand,
                                                        RetainExpansion,
                                                        NumExpansions);
     }
 
     void ExpandingFunctionParameterPack(ParmVarDecl *Pack) {
       SemaRef.CurrentInstantiationScope->MakeInstantiatedLocalArgPack(Pack);
     }
 
     TemplateArgument ForgetPartiallySubstitutedPack() {
       TemplateArgument Result;
       if (NamedDecl *PartialPack
             = SemaRef.CurrentInstantiationScope->getPartiallySubstitutedPack()){
         MultiLevelTemplateArgumentList &TemplateArgs
           = const_cast<MultiLevelTemplateArgumentList &>(this->TemplateArgs);
         unsigned Depth, Index;
         std::tie(Depth, Index) = getDepthAndIndex(PartialPack);
         if (TemplateArgs.hasTemplateArgument(Depth, Index)) {
           Result = TemplateArgs(Depth, Index);
           TemplateArgs.setArgument(Depth, Index, TemplateArgument());
         }
       }
 
       return Result;
     }
 
     void RememberPartiallySubstitutedPack(TemplateArgument Arg) {
       if (Arg.isNull())
         return;
 
       if (NamedDecl *PartialPack
             = SemaRef.CurrentInstantiationScope->getPartiallySubstitutedPack()){
         MultiLevelTemplateArgumentList &TemplateArgs
         = const_cast<MultiLevelTemplateArgumentList &>(this->TemplateArgs);
         unsigned Depth, Index;
         std::tie(Depth, Index) = getDepthAndIndex(PartialPack);
         TemplateArgs.setArgument(Depth, Index, Arg);
       }
     }
 
     /// Transform the given declaration by instantiating a reference to
     /// this declaration.
     Decl *TransformDecl(SourceLocation Loc, Decl *D);
 
     void transformAttrs(Decl *Old, Decl *New) {
       SemaRef.InstantiateAttrs(TemplateArgs, Old, New);
     }
 
     void transformedLocalDecl(Decl *Old, ArrayRef<Decl *> NewDecls) {
       if (Old->isParameterPack()) {
         SemaRef.CurrentInstantiationScope->MakeInstantiatedLocalArgPack(Old);
         for (auto *New : NewDecls)
           SemaRef.CurrentInstantiationScope->InstantiatedLocalPackArg(
               Old, cast<VarDecl>(New));
         return;
       }
 
       assert(NewDecls.size() == 1 &&
              "should only have multiple expansions for a pack");
       Decl *New = NewDecls.front();
 
       // If we've instantiated the call operator of a lambda or the call
       // operator template of a generic lambda, update the "instantiation of"
       // information.
       auto *NewMD = dyn_cast<CXXMethodDecl>(New);
       if (NewMD && isLambdaCallOperator(NewMD)) {
         auto *OldMD = dyn_cast<CXXMethodDecl>(Old);
         if (auto *NewTD = NewMD->getDescribedFunctionTemplate())
           NewTD->setInstantiatedFromMemberTemplate(
               OldMD->getDescribedFunctionTemplate());
         else
           NewMD->setInstantiationOfMemberFunction(OldMD,
                                                   TSK_ImplicitInstantiation);
       }
 
       SemaRef.CurrentInstantiationScope->InstantiatedLocal(Old, New);
 
       // We recreated a local declaration, but not by instantiating it. There
       // may be pending dependent diagnostics to produce.
       if (auto *DC = dyn_cast<DeclContext>(Old);
           DC && DC->isDependentContext() && DC->isFunctionOrMethod())
         SemaRef.PerformDependentDiagnostics(DC, TemplateArgs);
     }
 
     /// Transform the definition of the given declaration by
     /// instantiating it.
     Decl *TransformDefinition(SourceLocation Loc, Decl *D);
 
     /// Transform the first qualifier within a scope by instantiating the
     /// declaration.
     NamedDecl *TransformFirstQualifierInScope(NamedDecl *D, SourceLocation Loc);
 
     bool TransformExceptionSpec(SourceLocation Loc,
                                 FunctionProtoType::ExceptionSpecInfo &ESI,
                                 SmallVectorImpl<QualType> &Exceptions,
                                 bool &Changed);
 
     /// Rebuild the exception declaration and register the declaration
     /// as an instantiated local.
     VarDecl *RebuildExceptionDecl(VarDecl *ExceptionDecl,
                                   TypeSourceInfo *Declarator,
                                   SourceLocation StartLoc,
                                   SourceLocation NameLoc,
                                   IdentifierInfo *Name);
 
     /// Rebuild the Objective-C exception declaration and register the
     /// declaration as an instantiated local.
     VarDecl *RebuildObjCExceptionDecl(VarDecl *ExceptionDecl,
                                       TypeSourceInfo *TSInfo, QualType T);
 
     /// Check for tag mismatches when instantiating an
     /// elaborated type.
     QualType RebuildElaboratedType(SourceLocation KeywordLoc,
                                    ElaboratedTypeKeyword Keyword,
                                    NestedNameSpecifierLoc QualifierLoc,
                                    QualType T);
 
     TemplateName
     TransformTemplateName(CXXScopeSpec &SS, TemplateName Name,
                           SourceLocation NameLoc,
                           QualType ObjectType = QualType(),
                           NamedDecl *FirstQualifierInScope = nullptr,
                           bool AllowInjectedClassName = false);
 
     const CXXAssumeAttr *TransformCXXAssumeAttr(const CXXAssumeAttr *AA);
     const LoopHintAttr *TransformLoopHintAttr(const LoopHintAttr *LH);
     const NoInlineAttr *TransformStmtNoInlineAttr(const Stmt *OrigS,
                                                   const Stmt *InstS,
                                                   const NoInlineAttr *A);
     const AlwaysInlineAttr *
     TransformStmtAlwaysInlineAttr(const Stmt *OrigS, const Stmt *InstS,
                                   const AlwaysInlineAttr *A);
     const CodeAlignAttr *TransformCodeAlignAttr(const CodeAlignAttr *CA);
     ExprResult TransformPredefinedExpr(PredefinedExpr *E);
     ExprResult TransformDeclRefExpr(DeclRefExpr *E);
     ExprResult TransformCXXDefaultArgExpr(CXXDefaultArgExpr *E);
 
     ExprResult TransformTemplateParmRefExpr(DeclRefExpr *E,
                                             NonTypeTemplateParmDecl *D);
     ExprResult TransformSubstNonTypeTemplateParmPackExpr(
                                            SubstNonTypeTemplateParmPackExpr *E);
     ExprResult TransformSubstNonTypeTemplateParmExpr(
                                            SubstNonTypeTemplateParmExpr *E);
 
     /// Rebuild a DeclRefExpr for a VarDecl reference.
     ExprResult RebuildVarDeclRefExpr(VarDecl *PD, SourceLocation Loc);
 
     /// Transform a reference to a function or init-capture parameter pack.
     ExprResult TransformFunctionParmPackRefExpr(DeclRefExpr *E, VarDecl *PD);
 
     /// Transform a FunctionParmPackExpr which was built when we couldn't
     /// expand a function parameter pack reference which refers to an expanded
     /// pack.
     ExprResult TransformFunctionParmPackExpr(FunctionParmPackExpr *E);
 
     QualType TransformFunctionProtoType(TypeLocBuilder &TLB,
                                         FunctionProtoTypeLoc TL) {
       // Call the base version; it will forward to our overridden version below.
       return inherited::TransformFunctionProtoType(TLB, TL);
     }
 
     QualType TransformInjectedClassNameType(TypeLocBuilder &TLB,
                                             InjectedClassNameTypeLoc TL) {
       auto Type = inherited::TransformInjectedClassNameType(TLB, TL);
       // Special case for transforming a deduction guide, we return a
       // transformed TemplateSpecializationType.
       if (Type.isNull() &&
           SemaRef.CodeSynthesisContexts.back().Kind ==
               Sema::CodeSynthesisContext::BuildingDeductionGuides) {
         // Return a TemplateSpecializationType for transforming a deduction
         // guide.
         if (auto *ICT = TL.getType()->getAs<InjectedClassNameType>()) {
           auto Type =
               inherited::TransformType(ICT->getInjectedSpecializationType());
           TLB.pushTrivial(SemaRef.Context, Type, TL.getNameLoc());
           return Type;
         }
       }
       return Type;
     }
     // Override the default version to handle a rewrite-template-arg-pack case
     // for building a deduction guide.
     bool TransformTemplateArgument(const TemplateArgumentLoc &Input,
                                    TemplateArgumentLoc &Output,
                                    bool Uneval = false) {
       const TemplateArgument &Arg = Input.getArgument();
       std::vector<TemplateArgument> TArgs;
       switch (Arg.getKind()) {
       case TemplateArgument::Pack:
         // Literally rewrite the template argument pack, instead of unpacking
         // it.
         for (auto &pack : Arg.getPackAsArray()) {
           TemplateArgumentLoc Input = SemaRef.getTrivialTemplateArgumentLoc(
               pack, QualType(), SourceLocation{});
           TemplateArgumentLoc Output;
           if (SemaRef.SubstTemplateArgument(Input, TemplateArgs, Output))
             return true; // fails
           TArgs.push_back(Output.getArgument());
         }
         Output = SemaRef.getTrivialTemplateArgumentLoc(
             TemplateArgument(llvm::ArrayRef(TArgs).copy(SemaRef.Context)),
             QualType(), SourceLocation{});
         return false;
       default:
         break;
       }
       return inherited::TransformTemplateArgument(Input, Output, Uneval);
     }
 
     template<typename Fn>
     QualType TransformFunctionProtoType(TypeLocBuilder &TLB,
                                         FunctionProtoTypeLoc TL,
                                         CXXRecordDecl *ThisContext,
                                         Qualifiers ThisTypeQuals,
                                         Fn TransformExceptionSpec);
 
     ParmVarDecl *
     TransformFunctionTypeParam(ParmVarDecl *OldParm, int indexAdjustment,
                                std::optional<unsigned> NumExpansions,
                                bool ExpectParameterPack);
 
     using inherited::TransformTemplateTypeParmType;
     /// Transforms a template type parameter type by performing
     /// substitution of the corresponding template type argument.
     QualType TransformTemplateTypeParmType(TypeLocBuilder &TLB,
                                            TemplateTypeParmTypeLoc TL,
                                            bool SuppressObjCLifetime);
 
     QualType BuildSubstTemplateTypeParmType(
         TypeLocBuilder &TLB, bool SuppressObjCLifetime, bool Final,
         Decl *AssociatedDecl, unsigned Index, std::optional<unsigned> PackIndex,
         TemplateArgument Arg, SourceLocation NameLoc);
 
     /// Transforms an already-substituted template type parameter pack
     /// into either itself (if we aren't substituting into its pack expansion)
     /// or the appropriate substituted argument.
     using inherited::TransformSubstTemplateTypeParmPackType;
     QualType
     TransformSubstTemplateTypeParmPackType(TypeLocBuilder &TLB,
                                            SubstTemplateTypeParmPackTypeLoc TL,
                                            bool SuppressObjCLifetime);
 
     CXXRecordDecl::LambdaDependencyKind
     ComputeLambdaDependency(LambdaScopeInfo *LSI) {
       if (auto TypeAlias =
               TemplateInstArgsHelpers::getEnclosingTypeAliasTemplateDecl(
                   getSema());
           TypeAlias && TemplateInstArgsHelpers::isLambdaEnclosedByTypeAliasDecl(
                            LSI->CallOperator, TypeAlias.PrimaryTypeAliasDecl)) {
         unsigned TypeAliasDeclDepth = TypeAlias.Template->getTemplateDepth();
         if (TypeAliasDeclDepth >= TemplateArgs.getNumSubstitutedLevels())
           return CXXRecordDecl::LambdaDependencyKind::LDK_AlwaysDependent;
         for (const TemplateArgument &TA : TypeAlias.AssociatedTemplateArguments)
           if (TA.isDependent())
             return CXXRecordDecl::LambdaDependencyKind::LDK_AlwaysDependent;
       }
       return inherited::ComputeLambdaDependency(LSI);
     }
 
     ExprResult TransformLambdaExpr(LambdaExpr *E) {
       LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
       Sema::ConstraintEvalRAII<TemplateInstantiator> RAII(*this);
 
       ExprResult Result = inherited::TransformLambdaExpr(E);
       if (Result.isInvalid())
         return Result;
 
       CXXMethodDecl *MD = Result.getAs<LambdaExpr>()->getCallOperator();
       for (ParmVarDecl *PVD : MD->parameters()) {
         assert(PVD && "null in a parameter list");
         if (!PVD->hasDefaultArg())
           continue;
         Expr *UninstExpr = PVD->getUninstantiatedDefaultArg();
         // FIXME: Obtain the source location for the '=' token.
         SourceLocation EqualLoc = UninstExpr->getBeginLoc();
         if (SemaRef.SubstDefaultArgument(EqualLoc, PVD, TemplateArgs)) {
           // If substitution fails, the default argument is set to a
           // RecoveryExpr that wraps the uninstantiated default argument so
           // that downstream diagnostics are omitted.
           ExprResult ErrorResult = SemaRef.CreateRecoveryExpr(
               UninstExpr->getBeginLoc(), UninstExpr->getEndLoc(),
               { UninstExpr }, UninstExpr->getType());
           if (ErrorResult.isUsable())
             PVD->setDefaultArg(ErrorResult.get());
         }
       }
 
       return Result;
     }
 
     StmtResult TransformLambdaBody(LambdaExpr *E, Stmt *Body) {
       // Currently, we instantiate the body when instantiating the lambda
       // expression. However, `EvaluateConstraints` is disabled during the
       // instantiation of the lambda expression, causing the instantiation
       // failure of the return type requirement in the body. If p0588r1 is fully
       // implemented, the body will be lazily instantiated, and this problem
       // will not occur. Here, `EvaluateConstraints` is temporarily set to
       // `true` to temporarily fix this issue.
       // FIXME: This temporary fix can be removed after fully implementing
       // p0588r1.
       bool Prev = EvaluateConstraints;
       EvaluateConstraints = true;
       StmtResult Stmt = inherited::TransformLambdaBody(E, Body);
       EvaluateConstraints = Prev;
       return Stmt;
     }
 
     ExprResult TransformRequiresExpr(RequiresExpr *E) {
       LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
       ExprResult TransReq = inherited::TransformRequiresExpr(E);
       if (TransReq.isInvalid())
         return TransReq;
       assert(TransReq.get() != E &&
              "Do not change value of isSatisfied for the existing expression. "
              "Create a new expression instead.");
       if (E->getBody()->isDependentContext()) {
         Sema::SFINAETrap Trap(SemaRef);
         // We recreate the RequiresExpr body, but not by instantiating it.
         // Produce pending diagnostics for dependent access check.
         SemaRef.PerformDependentDiagnostics(E->getBody(), TemplateArgs);
         // FIXME: Store SFINAE diagnostics in RequiresExpr for diagnosis.
         if (Trap.hasErrorOccurred())
           TransReq.getAs<RequiresExpr>()->setSatisfied(false);
       }
       return TransReq;
     }
 
     bool TransformRequiresExprRequirements(
         ArrayRef<concepts::Requirement *> Reqs,
         SmallVectorImpl<concepts::Requirement *> &Transformed) {
       bool SatisfactionDetermined = false;
       for (concepts::Requirement *Req : Reqs) {
         concepts::Requirement *TransReq = nullptr;
         if (!SatisfactionDetermined) {
           if (auto *TypeReq = dyn_cast<concepts::TypeRequirement>(Req))
             TransReq = TransformTypeRequirement(TypeReq);
           else if (auto *ExprReq = dyn_cast<concepts::ExprRequirement>(Req))
             TransReq = TransformExprRequirement(ExprReq);
           else
             TransReq = TransformNestedRequirement(
                 cast<concepts::NestedRequirement>(Req));
           if (!TransReq)
             return true;
           if (!TransReq->isDependent() && !TransReq->isSatisfied())
             // [expr.prim.req]p6
             //   [...]  The substitution and semantic constraint checking
             //   proceeds in lexical order and stops when a condition that
             //   determines the result of the requires-expression is
             //   encountered. [..]
             SatisfactionDetermined = true;
         } else
           TransReq = Req;
         Transformed.push_back(TransReq);
       }
       return false;
     }
 
     TemplateParameterList *TransformTemplateParameterList(
                               TemplateParameterList *OrigTPL)  {
       if (!OrigTPL || !OrigTPL->size()) return OrigTPL;
 
       DeclContext *Owner = OrigTPL->getParam(0)->getDeclContext();
       TemplateDeclInstantiator  DeclInstantiator(getSema(),
                         /* DeclContext *Owner */ Owner, TemplateArgs);
       DeclInstantiator.setEvaluateConstraints(EvaluateConstraints);
       return DeclInstantiator.SubstTemplateParams(OrigTPL);
     }
 
     concepts::TypeRequirement *
     TransformTypeRequirement(concepts::TypeRequirement *Req);
     concepts::ExprRequirement *
     TransformExprRequirement(concepts::ExprRequirement *Req);
     concepts::NestedRequirement *
     TransformNestedRequirement(concepts::NestedRequirement *Req);
     ExprResult TransformRequiresTypeParams(
         SourceLocation KWLoc, SourceLocation RBraceLoc, const RequiresExpr *RE,
         RequiresExprBodyDecl *Body, ArrayRef<ParmVarDecl *> Params,
         SmallVectorImpl<QualType> &PTypes,
         SmallVectorImpl<ParmVarDecl *> &TransParams,
         Sema::ExtParameterInfoBuilder &PInfos);
 
   private:
     ExprResult
     transformNonTypeTemplateParmRef(Decl *AssociatedDecl,
                                     const NonTypeTemplateParmDecl *parm,
                                     SourceLocation loc, TemplateArgument arg,
                                     std::optional<unsigned> PackIndex);
   };
 }
 
 bool TemplateInstantiator::AlreadyTransformed(QualType T) {
   if (T.isNull())
     return true;
 
   if (T->isInstantiationDependentType() || T->isVariablyModifiedType())
     return false;
 
   getSema().MarkDeclarationsReferencedInType(Loc, T);
   return true;
 }
 
 static TemplateArgument
 getPackSubstitutedTemplateArgument(Sema &S, TemplateArgument Arg) {
   assert(S.ArgumentPackSubstitutionIndex >= 0);
   assert(S.ArgumentPackSubstitutionIndex < (int)Arg.pack_size());
   Arg = Arg.pack_begin()[S.ArgumentPackSubstitutionIndex];
   if (Arg.isPackExpansion())
     Arg = Arg.getPackExpansionPattern();
   return Arg;
 }
 
 Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
   if (!D)
     return nullptr;
 
   if (TemplateTemplateParmDecl *TTP = dyn_cast<TemplateTemplateParmDecl>(D)) {
     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
       // If the corresponding template argument is NULL or non-existent, it's
       // because we are performing instantiation from explicitly-specified
       // template arguments in a function template, but there were some
       // arguments left unspecified.
       if (!TemplateArgs.hasTemplateArgument(TTP->getDepth(),
                                             TTP->getPosition()))
         return D;
 
       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getPosition());
 
       if (TTP->isParameterPack()) {
         assert(Arg.getKind() == TemplateArgument::Pack &&
                "Missing argument pack");
         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
       }
 
       TemplateName Template = Arg.getAsTemplate();
       assert(!Template.isNull() && Template.getAsTemplateDecl() &&
              "Wrong kind of template template argument");
       return Template.getAsTemplateDecl();
     }
 
     // Fall through to find the instantiated declaration for this template
     // template parameter.
   }
 
   return SemaRef.FindInstantiatedDecl(Loc, cast<NamedDecl>(D), TemplateArgs);
 }
 
 Decl *TemplateInstantiator::TransformDefinition(SourceLocation Loc, Decl *D) {
   Decl *Inst = getSema().SubstDecl(D, getSema().CurContext, TemplateArgs);
   if (!Inst)
     return nullptr;
 
   getSema().CurrentInstantiationScope->InstantiatedLocal(D, Inst);
   return Inst;
 }
 
 bool TemplateInstantiator::TransformExceptionSpec(
     SourceLocation Loc, FunctionProtoType::ExceptionSpecInfo &ESI,
     SmallVectorImpl<QualType> &Exceptions, bool &Changed) {
   if (ESI.Type == EST_Uninstantiated) {
     ESI.instantiate();
     Changed = true;
   }
   return inherited::TransformExceptionSpec(Loc, ESI, Exceptions, Changed);
 }
 
 NamedDecl *
 TemplateInstantiator::TransformFirstQualifierInScope(NamedDecl *D,
                                                      SourceLocation Loc) {
   // If the first part of the nested-name-specifier was a template type
   // parameter, instantiate that type parameter down to a tag type.
   if (TemplateTypeParmDecl *TTPD = dyn_cast_or_null<TemplateTypeParmDecl>(D)) {
     const TemplateTypeParmType *TTP
       = cast<TemplateTypeParmType>(getSema().Context.getTypeDeclType(TTPD));
 
     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
       // FIXME: This needs testing w/ member access expressions.
       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getIndex());
 
       if (TTP->isParameterPack()) {
         assert(Arg.getKind() == TemplateArgument::Pack &&
                "Missing argument pack");
 
         if (getSema().ArgumentPackSubstitutionIndex == -1)
           return nullptr;
 
         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
       }
 
       QualType T = Arg.getAsType();
       if (T.isNull())
         return cast_or_null<NamedDecl>(TransformDecl(Loc, D));
 
       if (const TagType *Tag = T->getAs<TagType>())
         return Tag->getDecl();
 
       // The resulting type is not a tag; complain.
       getSema().Diag(Loc, diag::err_nested_name_spec_non_tag) << T;
       return nullptr;
     }
   }
 
   return cast_or_null<NamedDecl>(TransformDecl(Loc, D));
 }
 
 VarDecl *
 TemplateInstantiator::RebuildExceptionDecl(VarDecl *ExceptionDecl,
                                            TypeSourceInfo *Declarator,
                                            SourceLocation StartLoc,
                                            SourceLocation NameLoc,
                                            IdentifierInfo *Name) {
   VarDecl *Var = inherited::RebuildExceptionDecl(ExceptionDecl, Declarator,
                                                  StartLoc, NameLoc, Name);
   if (Var)
     getSema().CurrentInstantiationScope->InstantiatedLocal(ExceptionDecl, Var);
   return Var;
 }
 
 VarDecl *TemplateInstantiator::RebuildObjCExceptionDecl(VarDecl *ExceptionDecl,
                                                         TypeSourceInfo *TSInfo,
                                                         QualType T) {
   VarDecl *Var = inherited::RebuildObjCExceptionDecl(ExceptionDecl, TSInfo, T);
   if (Var)
     getSema().CurrentInstantiationScope->InstantiatedLocal(ExceptionDecl, Var);
   return Var;
 }
 
 QualType
 TemplateInstantiator::RebuildElaboratedType(SourceLocation KeywordLoc,
                                             ElaboratedTypeKeyword Keyword,
                                             NestedNameSpecifierLoc QualifierLoc,
                                             QualType T) {
   if (const TagType *TT = T->getAs<TagType>()) {
     TagDecl* TD = TT->getDecl();
 
     SourceLocation TagLocation = KeywordLoc;
 
     IdentifierInfo *Id = TD->getIdentifier();
 
     // TODO: should we even warn on struct/class mismatches for this?  Seems
     // like it's likely to produce a lot of spurious errors.
     if (Id && Keyword != ElaboratedTypeKeyword::None &&
         Keyword != ElaboratedTypeKeyword::Typename) {
       TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForKeyword(Keyword);
       if (!SemaRef.isAcceptableTagRedeclaration(TD, Kind, /*isDefinition*/false,
                                                 TagLocation, Id)) {
         SemaRef.Diag(TagLocation, diag::err_use_with_wrong_tag)
           << Id
           << FixItHint::CreateReplacement(SourceRange(TagLocation),
                                           TD->getKindName());
         SemaRef.Diag(TD->getLocation(), diag::note_previous_use);
       }
     }
   }
 
   return inherited::RebuildElaboratedType(KeywordLoc, Keyword, QualifierLoc, T);
 }
 
 TemplateName TemplateInstantiator::TransformTemplateName(
     CXXScopeSpec &SS, TemplateName Name, SourceLocation NameLoc,
     QualType ObjectType, NamedDecl *FirstQualifierInScope,
     bool AllowInjectedClassName) {
   if (TemplateTemplateParmDecl *TTP
        = dyn_cast_or_null<TemplateTemplateParmDecl>(Name.getAsTemplateDecl())) {
     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
       // If the corresponding template argument is NULL or non-existent, it's
       // because we are performing instantiation from explicitly-specified
       // template arguments in a function template, but there were some
       // arguments left unspecified.
       if (!TemplateArgs.hasTemplateArgument(TTP->getDepth(),
                                             TTP->getPosition()))
         return Name;
 
       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getPosition());
 
       if (TemplateArgs.isRewrite()) {
         // We're rewriting the template parameter as a reference to another
         // template parameter.
         if (Arg.getKind() == TemplateArgument::Pack) {
           assert(Arg.pack_size() == 1 && Arg.pack_begin()->isPackExpansion() &&
                  "unexpected pack arguments in template rewrite");
           Arg = Arg.pack_begin()->getPackExpansionPattern();
         }
         assert(Arg.getKind() == TemplateArgument::Template &&
                "unexpected nontype template argument kind in template rewrite");
         return Arg.getAsTemplate();
       }
 
       auto [AssociatedDecl, Final] =
           TemplateArgs.getAssociatedDecl(TTP->getDepth());
       std::optional<unsigned> PackIndex;
       if (TTP->isParameterPack()) {
         assert(Arg.getKind() == TemplateArgument::Pack &&
                "Missing argument pack");
 
         if (getSema().ArgumentPackSubstitutionIndex == -1) {
           // We have the template argument pack to substitute, but we're not
           // actually expanding the enclosing pack expansion yet. So, just
           // keep the entire argument pack.
           return getSema().Context.getSubstTemplateTemplateParmPack(
               Arg, AssociatedDecl, TTP->getIndex(), Final);
         }
 
         PackIndex = getPackIndex(Arg);
         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
       }
 
       TemplateName Template = Arg.getAsTemplate();
       assert(!Template.isNull() && "Null template template argument");
 
       if (Final)
         return Template;
       return getSema().Context.getSubstTemplateTemplateParm(
           Template, AssociatedDecl, TTP->getIndex(), PackIndex);
     }
   }
 
   if (SubstTemplateTemplateParmPackStorage *SubstPack
       = Name.getAsSubstTemplateTemplateParmPack()) {
     if (getSema().ArgumentPackSubstitutionIndex == -1)
       return Name;
 
     TemplateArgument Pack = SubstPack->getArgumentPack();
     TemplateName Template =
         getPackSubstitutedTemplateArgument(getSema(), Pack).getAsTemplate();
     if (SubstPack->getFinal())
       return Template;
     return getSema().Context.getSubstTemplateTemplateParm(
         Template, SubstPack->getAssociatedDecl(), SubstPack->getIndex(),
         getPackIndex(Pack));
   }
 
   return inherited::TransformTemplateName(SS, Name, NameLoc, ObjectType,
                                           FirstQualifierInScope,
                                           AllowInjectedClassName);
 }
 
 ExprResult
 TemplateInstantiator::TransformPredefinedExpr(PredefinedExpr *E) {
   if (!E->isTypeDependent())
     return E;
 
   return getSema().BuildPredefinedExpr(E->getLocation(), E->getIdentKind());
 }
 
 ExprResult
 TemplateInstantiator::TransformTemplateParmRefExpr(DeclRefExpr *E,
                                                NonTypeTemplateParmDecl *NTTP) {
   // If the corresponding template argument is NULL or non-existent, it's
   // because we are performing instantiation from explicitly-specified
   // template arguments in a function template, but there were some
   // arguments left unspecified.
   if (!TemplateArgs.hasTemplateArgument(NTTP->getDepth(),
                                         NTTP->getPosition()))
     return E;
 
   TemplateArgument Arg = TemplateArgs(NTTP->getDepth(), NTTP->getPosition());
 
   if (TemplateArgs.isRewrite()) {
     // We're rewriting the template parameter as a reference to another
     // template parameter.
     if (Arg.getKind() == TemplateArgument::Pack) {
       assert(Arg.pack_size() == 1 && Arg.pack_begin()->isPackExpansion() &&
              "unexpected pack arguments in template rewrite");
       Arg = Arg.pack_begin()->getPackExpansionPattern();
     }
     assert(Arg.getKind() == TemplateArgument::Expression &&
            "unexpected nontype template argument kind in template rewrite");
     // FIXME: This can lead to the same subexpression appearing multiple times
     // in a complete expression.
     return Arg.getAsExpr();
   }
 
   auto [AssociatedDecl, _] = TemplateArgs.getAssociatedDecl(NTTP->getDepth());
   std::optional<unsigned> PackIndex;
   if (NTTP->isParameterPack()) {
     assert(Arg.getKind() == TemplateArgument::Pack &&
            "Missing argument pack");
 
     if (getSema().ArgumentPackSubstitutionIndex == -1) {
       // We have an argument pack, but we can't select a particular argument
       // out of it yet. Therefore, we'll build an expression to hold on to that
       // argument pack.
       QualType TargetType = SemaRef.SubstType(NTTP->getType(), TemplateArgs,
                                               E->getLocation(),
                                               NTTP->getDeclName());
       if (TargetType.isNull())
         return ExprError();
 
       QualType ExprType = TargetType.getNonLValueExprType(SemaRef.Context);
       if (TargetType->isRecordType())
         ExprType.addConst();
       // FIXME: Pass in Final.
       return new (SemaRef.Context) SubstNonTypeTemplateParmPackExpr(
           ExprType, TargetType->isReferenceType() ? VK_LValue : VK_PRValue,
           E->getLocation(), Arg, AssociatedDecl, NTTP->getPosition());
     }
     PackIndex = getPackIndex(Arg);
     Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
   }
   // FIXME: Don't put subst node on Final replacement.
   return transformNonTypeTemplateParmRef(AssociatedDecl, NTTP, E->getLocation(),
                                          Arg, PackIndex);
 }
 
 const CXXAssumeAttr *
 TemplateInstantiator::TransformCXXAssumeAttr(const CXXAssumeAttr *AA) {
   ExprResult Res = getDerived().TransformExpr(AA->getAssumption());
   if (!Res.isUsable())
     return AA;
 
   Res = getSema().BuildCXXAssumeExpr(Res.get(), AA->getAttrName(),
                                      AA->getRange());
   if (!Res.isUsable())
     return AA;
 
   return CXXAssumeAttr::CreateImplicit(getSema().Context, Res.get(),
                                        AA->getRange());
 }
 
 const LoopHintAttr *
 TemplateInstantiator::TransformLoopHintAttr(const LoopHintAttr *LH) {
   Expr *TransformedExpr = getDerived().TransformExpr(LH->getValue()).get();
 
   if (TransformedExpr == LH->getValue())
     return LH;
 
   // Generate error if there is a problem with the value.
   if (getSema().CheckLoopHintExpr(TransformedExpr, LH->getLocation(),
                                   LH->getSemanticSpelling() ==
                                       LoopHintAttr::Pragma_unroll))
     return LH;
 
   LoopHintAttr::OptionType Option = LH->getOption();
   LoopHintAttr::LoopHintState State = LH->getState();
 
   llvm::APSInt ValueAPS =
       TransformedExpr->EvaluateKnownConstInt(getSema().getASTContext());
   // The values of 0 and 1 block any unrolling of the loop.
   if (ValueAPS.isZero() || ValueAPS.isOne()) {
     Option = LoopHintAttr::Unroll;
     State = LoopHintAttr::Disable;
   }
 
   // Create new LoopHintValueAttr with integral expression in place of the
   // non-type template parameter.
   return LoopHintAttr::CreateImplicit(getSema().Context, Option, State,
                                       TransformedExpr, *LH);
 }
 const NoInlineAttr *TemplateInstantiator::TransformStmtNoInlineAttr(
     const Stmt *OrigS, const Stmt *InstS, const NoInlineAttr *A) {
   if (!A || getSema().CheckNoInlineAttr(OrigS, InstS, *A))
     return nullptr;
 
   return A;
 }
 const AlwaysInlineAttr *TemplateInstantiator::TransformStmtAlwaysInlineAttr(
     const Stmt *OrigS, const Stmt *InstS, const AlwaysInlineAttr *A) {
   if (!A || getSema().CheckAlwaysInlineAttr(OrigS, InstS, *A))
     return nullptr;
 
   return A;
 }
 
 const CodeAlignAttr *
 TemplateInstantiator::TransformCodeAlignAttr(const CodeAlignAttr *CA) {
   Expr *TransformedExpr = getDerived().TransformExpr(CA->getAlignment()).get();
   return getSema().BuildCodeAlignAttr(*CA, TransformedExpr);
 }
 
 ExprResult TemplateInstantiator::transformNonTypeTemplateParmRef(
     Decl *AssociatedDecl, const NonTypeTemplateParmDecl *parm,
     SourceLocation loc, TemplateArgument arg,
     std::optional<unsigned> PackIndex) {
   ExprResult result;
 
   // Determine the substituted parameter type. We can usually infer this from
   // the template argument, but not always.
   auto SubstParamType = [&] {
     QualType T;
     if (parm->isExpandedParameterPack())
       T = parm->getExpansionType(SemaRef.ArgumentPackSubstitutionIndex);
     else
       T = parm->getType();
     if (parm->isParameterPack() && isa<PackExpansionType>(T))
       T = cast<PackExpansionType>(T)->getPattern();
     return SemaRef.SubstType(T, TemplateArgs, loc, parm->getDeclName());
   };
 
   bool refParam = false;
 
   // The template argument itself might be an expression, in which case we just
   // return that expression. This happens when substituting into an alias
   // template.
   if (arg.getKind() == TemplateArgument::Expression) {
     Expr *argExpr = arg.getAsExpr();
     result = argExpr;
     if (argExpr->isLValue()) {
       if (argExpr->getType()->isRecordType()) {
         // Check whether the parameter was actually a reference.
         QualType paramType = SubstParamType();
         if (paramType.isNull())
           return ExprError();
         refParam = paramType->isReferenceType();
       } else {
         refParam = true;
       }
     }
   } else if (arg.getKind() == TemplateArgument::Declaration ||
              arg.getKind() == TemplateArgument::NullPtr) {
     if (arg.getKind() == TemplateArgument::Declaration) {
       ValueDecl *VD = arg.getAsDecl();
 
       // Find the instantiation of the template argument.  This is
       // required for nested templates.
       VD = cast_or_null<ValueDecl>(
              getSema().FindInstantiatedDecl(loc, VD, TemplateArgs));
       if (!VD)
         return ExprError();
     }
 
     QualType paramType = arg.getNonTypeTemplateArgumentType();
     assert(!paramType.isNull() && "type substitution failed for param type");
     assert(!paramType->isDependentType() && "param type still dependent");
     result = SemaRef.BuildExpressionFromDeclTemplateArgument(arg, paramType, loc);
     refParam = paramType->isReferenceType();
   } else {
     QualType paramType = arg.getNonTypeTemplateArgumentType();
     result = SemaRef.BuildExpressionFromNonTypeTemplateArgument(arg, loc);
     refParam = paramType->isReferenceType();
     assert(result.isInvalid() ||
            SemaRef.Context.hasSameType(result.get()->getType(),
                                        paramType.getNonReferenceType()));
   }
 
   if (result.isInvalid())
     return ExprError();
 
   Expr *resultExpr = result.get();
   // FIXME: Don't put subst node on final replacement.
   return new (SemaRef.Context) SubstNonTypeTemplateParmExpr(
       resultExpr->getType(), resultExpr->getValueKind(), loc, resultExpr,
       AssociatedDecl, parm->getIndex(), PackIndex, refParam);
 }
 
 ExprResult
 TemplateInstantiator::TransformSubstNonTypeTemplateParmPackExpr(
                                           SubstNonTypeTemplateParmPackExpr *E) {
   if (getSema().ArgumentPackSubstitutionIndex == -1) {
     // We aren't expanding the parameter pack, so just return ourselves.
     return E;
   }
 
   TemplateArgument Pack = E->getArgumentPack();
   TemplateArgument Arg = getPackSubstitutedTemplateArgument(getSema(), Pack);
   // FIXME: Don't put subst node on final replacement.
   return transformNonTypeTemplateParmRef(
       E->getAssociatedDecl(), E->getParameterPack(),
       E->getParameterPackLocation(), Arg, getPackIndex(Pack));
 }
 
 ExprResult
 TemplateInstantiator::TransformSubstNonTypeTemplateParmExpr(
                                           SubstNonTypeTemplateParmExpr *E) {
   ExprResult SubstReplacement = E->getReplacement();
   if (!isa<ConstantExpr>(SubstReplacement.get()))
     SubstReplacement = TransformExpr(E->getReplacement());
   if (SubstReplacement.isInvalid())
     return true;
   QualType SubstType = TransformType(E->getParameterType(getSema().Context));
   if (SubstType.isNull())
     return true;
   // The type may have been previously dependent and not now, which means we
   // might have to implicit cast the argument to the new type, for example:
   // template<auto T, decltype(T) U>
   // concept C = sizeof(U) == 4;
   // void foo() requires C<2, 'a'> { }
   // When normalizing foo(), we first form the normalized constraints of C:
   // AtomicExpr(sizeof(U) == 4,
   //            U=SubstNonTypeTemplateParmExpr(Param=U,
   //                                           Expr=DeclRef(U),
   //                                           Type=decltype(T)))
   // Then we substitute T = 2, U = 'a' into the parameter mapping, and need to
   // produce:
   // AtomicExpr(sizeof(U) == 4,
   //            U=SubstNonTypeTemplateParmExpr(Param=U,
   //                                           Expr=ImpCast(
   //                                               decltype(2),
   //                                               SubstNTTPE(Param=U, Expr='a',
   //                                                          Type=char)),
   //                                           Type=decltype(2)))
   // The call to CheckTemplateArgument here produces the ImpCast.
   TemplateArgument SugaredConverted, CanonicalConverted;
   if (SemaRef
           .CheckTemplateArgument(E->getParameter(), SubstType,
                                  SubstReplacement.get(), SugaredConverted,
                                  CanonicalConverted, Sema::CTAK_Specified)
           .isInvalid())
     return true;
   return transformNonTypeTemplateParmRef(E->getAssociatedDecl(),
                                          E->getParameter(), E->getExprLoc(),
                                          SugaredConverted, E->getPackIndex());
 }
 
 ExprResult TemplateInstantiator::RebuildVarDeclRefExpr(VarDecl *PD,
                                                        SourceLocation Loc) {
   DeclarationNameInfo NameInfo(PD->getDeclName(), Loc);
   return getSema().BuildDeclarationNameExpr(CXXScopeSpec(), NameInfo, PD);
 }
 
 ExprResult
 TemplateInstantiator::TransformFunctionParmPackExpr(FunctionParmPackExpr *E) {
   if (getSema().ArgumentPackSubstitutionIndex != -1) {
     // We can expand this parameter pack now.
     VarDecl *D = E->getExpansion(getSema().ArgumentPackSubstitutionIndex);
     VarDecl *VD = cast_or_null<VarDecl>(TransformDecl(E->getExprLoc(), D));
     if (!VD)
       return ExprError();
     return RebuildVarDeclRefExpr(VD, E->getExprLoc());
   }
 
   QualType T = TransformType(E->getType());
   if (T.isNull())
     return ExprError();
 
   // Transform each of the parameter expansions into the corresponding
   // parameters in the instantiation of the function decl.
   SmallVector<VarDecl *, 8> Vars;
   Vars.reserve(E->getNumExpansions());
   for (FunctionParmPackExpr::iterator I = E->begin(), End = E->end();
        I != End; ++I) {
     VarDecl *D = cast_or_null<VarDecl>(TransformDecl(E->getExprLoc(), *I));
     if (!D)
       return ExprError();
     Vars.push_back(D);
   }
 
   auto *PackExpr =
       FunctionParmPackExpr::Create(getSema().Context, T, E->getParameterPack(),
                                    E->getParameterPackLocation(), Vars);
   getSema().MarkFunctionParmPackReferenced(PackExpr);
   return PackExpr;
 }
 
 ExprResult
 TemplateInstantiator::TransformFunctionParmPackRefExpr(DeclRefExpr *E,
                                                        VarDecl *PD) {
   typedef LocalInstantiationScope::DeclArgumentPack DeclArgumentPack;
   llvm::PointerUnion<Decl *, DeclArgumentPack *> *Found
     = getSema().CurrentInstantiationScope->findInstantiationOf(PD);
   assert(Found && "no instantiation for parameter pack");
 
   Decl *TransformedDecl;
   if (DeclArgumentPack *Pack = Found->dyn_cast<DeclArgumentPack *>()) {
     // If this is a reference to a function parameter pack which we can
     // substitute but can't yet expand, build a FunctionParmPackExpr for it.
     if (getSema().ArgumentPackSubstitutionIndex == -1) {
       QualType T = TransformType(E->getType());
       if (T.isNull())
         return ExprError();
       auto *PackExpr = FunctionParmPackExpr::Create(getSema().Context, T, PD,
                                                     E->getExprLoc(), *Pack);
       getSema().MarkFunctionParmPackReferenced(PackExpr);
       return PackExpr;
     }
 
     TransformedDecl = (*Pack)[getSema().ArgumentPackSubstitutionIndex];
   } else {
     TransformedDecl = Found->get<Decl*>();
   }
 
   // We have either an unexpanded pack or a specific expansion.
   return RebuildVarDeclRefExpr(cast<VarDecl>(TransformedDecl), E->getExprLoc());
 }
 
 ExprResult
 TemplateInstantiator::TransformDeclRefExpr(DeclRefExpr *E) {
   NamedDecl *D = E->getDecl();
 
   // Handle references to non-type template parameters and non-type template
   // parameter packs.
   if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(D)) {
     if (NTTP->getDepth() < TemplateArgs.getNumLevels())
       return TransformTemplateParmRefExpr(E, NTTP);
 
     // We have a non-type template parameter that isn't fully substituted;
     // FindInstantiatedDecl will find it in the local instantiation scope.
   }
 
   // Handle references to function parameter packs.
   if (VarDecl *PD = dyn_cast<VarDecl>(D))
     if (PD->isParameterPack())
       return TransformFunctionParmPackRefExpr(E, PD);
 
   return inherited::TransformDeclRefExpr(E);
 }
 
 ExprResult TemplateInstantiator::TransformCXXDefaultArgExpr(
     CXXDefaultArgExpr *E) {
   assert(!cast<FunctionDecl>(E->getParam()->getDeclContext())->
              getDescribedFunctionTemplate() &&
          "Default arg expressions are never formed in dependent cases.");
   return SemaRef.BuildCXXDefaultArgExpr(
       E->getUsedLocation(), cast<FunctionDecl>(E->getParam()->getDeclContext()),
       E->getParam());
 }
 
 template<typename Fn>
 QualType TemplateInstantiator::TransformFunctionProtoType(TypeLocBuilder &TLB,
                                  FunctionProtoTypeLoc TL,
                                  CXXRecordDecl *ThisContext,
                                  Qualifiers ThisTypeQuals,
                                  Fn TransformExceptionSpec) {
   // We need a local instantiation scope for this function prototype.
   LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
   return inherited::TransformFunctionProtoType(
       TLB, TL, ThisContext, ThisTypeQuals, TransformExceptionSpec);
 }
 
 ParmVarDecl *TemplateInstantiator::TransformFunctionTypeParam(
     ParmVarDecl *OldParm, int indexAdjustment,
     std::optional<unsigned> NumExpansions, bool ExpectParameterPack) {
   auto NewParm = SemaRef.SubstParmVarDecl(
       OldParm, TemplateArgs, indexAdjustment, NumExpansions,
       ExpectParameterPack, EvaluateConstraints);
   if (NewParm && SemaRef.getLangOpts().OpenCL)
     SemaRef.deduceOpenCLAddressSpace(NewParm);
   return NewParm;
 }
 
 QualType TemplateInstantiator::BuildSubstTemplateTypeParmType(
     TypeLocBuilder &TLB, bool SuppressObjCLifetime, bool Final,
     Decl *AssociatedDecl, unsigned Index, std::optional<unsigned> PackIndex,
     TemplateArgument Arg, SourceLocation NameLoc) {
   QualType Replacement = Arg.getAsType();
 
   // If the template parameter had ObjC lifetime qualifiers,
   // then any such qualifiers on the replacement type are ignored.
   if (SuppressObjCLifetime) {
     Qualifiers RQs;
     RQs = Replacement.getQualifiers();
     RQs.removeObjCLifetime();
     Replacement =
         SemaRef.Context.getQualifiedType(Replacement.getUnqualifiedType(), RQs);
   }
 
   if (Final) {
     TLB.pushTrivial(SemaRef.Context, Replacement, NameLoc);
     return Replacement;
   }
   // TODO: only do this uniquing once, at the start of instantiation.
   QualType Result = getSema().Context.getSubstTemplateTypeParmType(
       Replacement, AssociatedDecl, Index, PackIndex);
   SubstTemplateTypeParmTypeLoc NewTL =
       TLB.push<SubstTemplateTypeParmTypeLoc>(Result);
   NewTL.setNameLoc(NameLoc);
   return Result;
 }
 
 QualType
 TemplateInstantiator::TransformTemplateTypeParmType(TypeLocBuilder &TLB,
                                                     TemplateTypeParmTypeLoc TL,
                                                     bool SuppressObjCLifetime) {
   const TemplateTypeParmType *T = TL.getTypePtr();
   if (T->getDepth() < TemplateArgs.getNumLevels()) {
     // Replace the template type parameter with its corresponding
     // template argument.
 
     // If the corresponding template argument is NULL or doesn't exist, it's
     // because we are performing instantiation from explicitly-specified
     // template arguments in a function template class, but there were some
     // arguments left unspecified.
     if (!TemplateArgs.hasTemplateArgument(T->getDepth(), T->getIndex())) {
       TemplateTypeParmTypeLoc NewTL
         = TLB.push<TemplateTypeParmTypeLoc>(TL.getType());
       NewTL.setNameLoc(TL.getNameLoc());
       return TL.getType();
     }
 
     TemplateArgument Arg = TemplateArgs(T->getDepth(), T->getIndex());
 
     if (TemplateArgs.isRewrite()) {
       // We're rewriting the template parameter as a reference to another
       // template parameter.
       if (Arg.getKind() == TemplateArgument::Pack) {
         assert(Arg.pack_size() == 1 && Arg.pack_begin()->isPackExpansion() &&
                "unexpected pack arguments in template rewrite");
         Arg = Arg.pack_begin()->getPackExpansionPattern();
       }
       assert(Arg.getKind() == TemplateArgument::Type &&
              "unexpected nontype template argument kind in template rewrite");
       QualType NewT = Arg.getAsType();
       TLB.pushTrivial(SemaRef.Context, NewT, TL.getNameLoc());
       return NewT;
     }
 
     auto [AssociatedDecl, Final] =
         TemplateArgs.getAssociatedDecl(T->getDepth());
     std::optional<unsigned> PackIndex;
     if (T->isParameterPack()) {
       assert(Arg.getKind() == TemplateArgument::Pack &&
              "Missing argument pack");
 
       if (getSema().ArgumentPackSubstitutionIndex == -1) {
         // We have the template argument pack, but we're not expanding the
         // enclosing pack expansion yet. Just save the template argument
         // pack for later substitution.
         QualType Result = getSema().Context.getSubstTemplateTypeParmPackType(
             AssociatedDecl, T->getIndex(), Final, Arg);
         SubstTemplateTypeParmPackTypeLoc NewTL
           = TLB.push<SubstTemplateTypeParmPackTypeLoc>(Result);
         NewTL.setNameLoc(TL.getNameLoc());
         return Result;
       }
 
       // PackIndex starts from last element.
       PackIndex = getPackIndex(Arg);
       Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
     }
 
     assert(Arg.getKind() == TemplateArgument::Type &&
            "Template argument kind mismatch");
 
     return BuildSubstTemplateTypeParmType(TLB, SuppressObjCLifetime, Final,
                                           AssociatedDecl, T->getIndex(),
                                           PackIndex, Arg, TL.getNameLoc());
   }
 
   // The template type parameter comes from an inner template (e.g.,
   // the template parameter list of a member template inside the
   // template we are instantiating). Create a new template type
   // parameter with the template "level" reduced by one.
   TemplateTypeParmDecl *NewTTPDecl = nullptr;
   if (TemplateTypeParmDecl *OldTTPDecl = T->getDecl())
     NewTTPDecl = cast_or_null<TemplateTypeParmDecl>(
         TransformDecl(TL.getNameLoc(), OldTTPDecl));
   QualType Result = getSema().Context.getTemplateTypeParmType(
       T->getDepth() - TemplateArgs.getNumSubstitutedLevels(), T->getIndex(),
       T->isParameterPack(), NewTTPDecl);
   TemplateTypeParmTypeLoc NewTL = TLB.push<TemplateTypeParmTypeLoc>(Result);
   NewTL.setNameLoc(TL.getNameLoc());
   return Result;
 }
 
 QualType TemplateInstantiator::TransformSubstTemplateTypeParmPackType(
     TypeLocBuilder &TLB, SubstTemplateTypeParmPackTypeLoc TL,
     bool SuppressObjCLifetime) {
   const SubstTemplateTypeParmPackType *T = TL.getTypePtr();
 
   Decl *NewReplaced = TransformDecl(TL.getNameLoc(), T->getAssociatedDecl());
 
   if (getSema().ArgumentPackSubstitutionIndex == -1) {
     // We aren't expanding the parameter pack, so just return ourselves.
     QualType Result = TL.getType();
     if (NewReplaced != T->getAssociatedDecl())
       Result = getSema().Context.getSubstTemplateTypeParmPackType(
           NewReplaced, T->getIndex(), T->getFinal(), T->getArgumentPack());
     SubstTemplateTypeParmPackTypeLoc NewTL =
         TLB.push<SubstTemplateTypeParmPackTypeLoc>(Result);
     NewTL.setNameLoc(TL.getNameLoc());
     return Result;
   }
 
   TemplateArgument Pack = T->getArgumentPack();
   TemplateArgument Arg = getPackSubstitutedTemplateArgument(getSema(), Pack);
   return BuildSubstTemplateTypeParmType(
       TLB, SuppressObjCLifetime, T->getFinal(), NewReplaced, T->getIndex(),
       getPackIndex(Pack), Arg, TL.getNameLoc());
 }
 
 static concepts::Requirement::SubstitutionDiagnostic *
 createSubstDiag(Sema &S, TemplateDeductionInfo &Info,
                 concepts::EntityPrinter Printer) {
   SmallString<128> Message;
   SourceLocation ErrorLoc;
   if (Info.hasSFINAEDiagnostic()) {
     PartialDiagnosticAt PDA(SourceLocation(),
                             PartialDiagnostic::NullDiagnostic{});
     Info.takeSFINAEDiagnostic(PDA);
     PDA.second.EmitToString(S.getDiagnostics(), Message);
     ErrorLoc = PDA.first;
   } else {
     ErrorLoc = Info.getLocation();
   }
   SmallString<128> Entity;
   llvm::raw_svector_ostream OS(Entity);
   Printer(OS);
   const ASTContext &C = S.Context;
   return new (C) concepts::Requirement::SubstitutionDiagnostic{
       C.backupStr(Entity), ErrorLoc, C.backupStr(Message)};
 }
 
 concepts::Requirement::SubstitutionDiagnostic *
 concepts::createSubstDiagAt(Sema &S, SourceLocation Location,
                             EntityPrinter Printer) {
   SmallString<128> Entity;
   llvm::raw_svector_ostream OS(Entity);
   Printer(OS);
   const ASTContext &C = S.Context;
   return new (C) concepts::Requirement::SubstitutionDiagnostic{
       /*SubstitutedEntity=*/C.backupStr(Entity),
       /*DiagLoc=*/Location, /*DiagMessage=*/StringRef()};
 }
 
 ExprResult TemplateInstantiator::TransformRequiresTypeParams(
     SourceLocation KWLoc, SourceLocation RBraceLoc, const RequiresExpr *RE,
     RequiresExprBodyDecl *Body, ArrayRef<ParmVarDecl *> Params,
     SmallVectorImpl<QualType> &PTypes,
     SmallVectorImpl<ParmVarDecl *> &TransParams,
     Sema::ExtParameterInfoBuilder &PInfos) {
 
   TemplateDeductionInfo Info(KWLoc);
   Sema::InstantiatingTemplate TypeInst(SemaRef, KWLoc,
                                        RE, Info,
                                        SourceRange{KWLoc, RBraceLoc});
   Sema::SFINAETrap Trap(SemaRef);
 
   unsigned ErrorIdx;
   if (getDerived().TransformFunctionTypeParams(
           KWLoc, Params, /*ParamTypes=*/nullptr, /*ParamInfos=*/nullptr, PTypes,
           &TransParams, PInfos, &ErrorIdx) ||
       Trap.hasErrorOccurred()) {
     SmallVector<concepts::Requirement *, 4> TransReqs;
     ParmVarDecl *FailedDecl = Params[ErrorIdx];
     // Add a 'failed' Requirement to contain the error that caused the failure
     // here.
     TransReqs.push_back(RebuildTypeRequirement(createSubstDiag(
         SemaRef, Info, [&](llvm::raw_ostream &OS) { OS << *FailedDecl; })));
     return getDerived().RebuildRequiresExpr(KWLoc, Body, RE->getLParenLoc(),
                                             TransParams, RE->getRParenLoc(),
                                             TransReqs, RBraceLoc);
   }
 
   return ExprResult{};
 }
 
 concepts::TypeRequirement *
 TemplateInstantiator::TransformTypeRequirement(concepts::TypeRequirement *Req) {
   if (!Req->isDependent() && !AlwaysRebuild())
     return Req;
   if (Req->isSubstitutionFailure()) {
     if (AlwaysRebuild())
       return RebuildTypeRequirement(
               Req->getSubstitutionDiagnostic());
     return Req;
   }
 
   Sema::SFINAETrap Trap(SemaRef);
   TemplateDeductionInfo Info(Req->getType()->getTypeLoc().getBeginLoc());
   Sema::InstantiatingTemplate TypeInst(SemaRef,
       Req->getType()->getTypeLoc().getBeginLoc(), Req, Info,
       Req->getType()->getTypeLoc().getSourceRange());
   if (TypeInst.isInvalid())
     return nullptr;
   TypeSourceInfo *TransType = TransformType(Req->getType());
   if (!TransType || Trap.hasErrorOccurred())
     return RebuildTypeRequirement(createSubstDiag(SemaRef, Info,
         [&] (llvm::raw_ostream& OS) {
             Req->getType()->getType().print(OS, SemaRef.getPrintingPolicy());
         }));
   return RebuildTypeRequirement(TransType);
 }
 
 concepts::ExprRequirement *
 TemplateInstantiator::TransformExprRequirement(concepts::ExprRequirement *Req) {
   if (!Req->isDependent() && !AlwaysRebuild())
     return Req;
 
   Sema::SFINAETrap Trap(SemaRef);
 
   llvm::PointerUnion<Expr *, concepts::Requirement::SubstitutionDiagnostic *>
       TransExpr;
   if (Req->isExprSubstitutionFailure())
     TransExpr = Req->getExprSubstitutionDiagnostic();
   else {
     Expr *E = Req->getExpr();
     TemplateDeductionInfo Info(E->getBeginLoc());
     Sema::InstantiatingTemplate ExprInst(SemaRef, E->getBeginLoc(), Req, Info,
                                          E->getSourceRange());
     if (ExprInst.isInvalid())
       return nullptr;
     ExprResult TransExprRes = TransformExpr(E);
     if (!TransExprRes.isInvalid() && !Trap.hasErrorOccurred() &&
         TransExprRes.get()->hasPlaceholderType())
       TransExprRes = SemaRef.CheckPlaceholderExpr(TransExprRes.get());
     if (TransExprRes.isInvalid() || Trap.hasErrorOccurred())
       TransExpr = createSubstDiag(SemaRef, Info, [&](llvm::raw_ostream &OS) {
         E->printPretty(OS, nullptr, SemaRef.getPrintingPolicy());
       });
     else
       TransExpr = TransExprRes.get();
   }
 
   std::optional<concepts::ExprRequirement::ReturnTypeRequirement> TransRetReq;
   const auto &RetReq = Req->getReturnTypeRequirement();
   if (RetReq.isEmpty())
     TransRetReq.emplace();
   else if (RetReq.isSubstitutionFailure())
     TransRetReq.emplace(RetReq.getSubstitutionDiagnostic());
   else if (RetReq.isTypeConstraint()) {
     TemplateParameterList *OrigTPL =
         RetReq.getTypeConstraintTemplateParameterList();
     TemplateDeductionInfo Info(OrigTPL->getTemplateLoc());
     Sema::InstantiatingTemplate TPLInst(SemaRef, OrigTPL->getTemplateLoc(),
                                         Req, Info, OrigTPL->getSourceRange());
     if (TPLInst.isInvalid())
       return nullptr;
     TemplateParameterList *TPL = TransformTemplateParameterList(OrigTPL);
     if (!TPL || Trap.hasErrorOccurred())
       TransRetReq.emplace(createSubstDiag(SemaRef, Info,
           [&] (llvm::raw_ostream& OS) {
               RetReq.getTypeConstraint()->getImmediatelyDeclaredConstraint()
                   ->printPretty(OS, nullptr, SemaRef.getPrintingPolicy());
           }));
     else {
       TPLInst.Clear();
       TransRetReq.emplace(TPL);
     }
   }
   assert(TransRetReq && "All code paths leading here must set TransRetReq");
   if (Expr *E = TransExpr.dyn_cast<Expr *>())
     return RebuildExprRequirement(E, Req->isSimple(), Req->getNoexceptLoc(),
                                   std::move(*TransRetReq));
   return RebuildExprRequirement(
       TransExpr.get<concepts::Requirement::SubstitutionDiagnostic *>(),
       Req->isSimple(), Req->getNoexceptLoc(), std::move(*TransRetReq));
 }
 
 concepts::NestedRequirement *
 TemplateInstantiator::TransformNestedRequirement(
     concepts::NestedRequirement *Req) {
   if (!Req->isDependent() && !AlwaysRebuild())
     return Req;
   if (Req->hasInvalidConstraint()) {
     if (AlwaysRebuild())
       return RebuildNestedRequirement(Req->getInvalidConstraintEntity(),
                                       Req->getConstraintSatisfaction());
     return Req;
   }
   Sema::InstantiatingTemplate ReqInst(SemaRef,
       Req->getConstraintExpr()->getBeginLoc(), Req,
       Sema::InstantiatingTemplate::ConstraintsCheck{},
       Req->getConstraintExpr()->getSourceRange());
   if (!getEvaluateConstraints()) {
     ExprResult TransConstraint = TransformExpr(Req->getConstraintExpr());
     if (TransConstraint.isInvalid() || !TransConstraint.get())
       return nullptr;
     if (TransConstraint.get()->isInstantiationDependent())
       return new (SemaRef.Context)
           concepts::NestedRequirement(TransConstraint.get());
     ConstraintSatisfaction Satisfaction;
     return new (SemaRef.Context) concepts::NestedRequirement(
         SemaRef.Context, TransConstraint.get(), Satisfaction);
   }
 
   ExprResult TransConstraint;
   ConstraintSatisfaction Satisfaction;
   TemplateDeductionInfo Info(Req->getConstraintExpr()->getBeginLoc());
   {
     EnterExpressionEvaluationContext ContextRAII(
         SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     Sema::SFINAETrap Trap(SemaRef);
     Sema::InstantiatingTemplate ConstrInst(SemaRef,
         Req->getConstraintExpr()->getBeginLoc(), Req, Info,
         Req->getConstraintExpr()->getSourceRange());
     if (ConstrInst.isInvalid())
       return nullptr;
     llvm::SmallVector<Expr *> Result;
     if (!SemaRef.CheckConstraintSatisfaction(
             nullptr, {Req->getConstraintExpr()}, Result, TemplateArgs,
             Req->getConstraintExpr()->getSourceRange(), Satisfaction) &&
         !Result.empty())
       TransConstraint = Result[0];
     assert(!Trap.hasErrorOccurred() && "Substitution failures must be handled "
                                        "by CheckConstraintSatisfaction.");
   }
   ASTContext &C = SemaRef.Context;
   if (TransConstraint.isUsable() &&
       TransConstraint.get()->isInstantiationDependent())
     return new (C) concepts::NestedRequirement(TransConstraint.get());
   if (TransConstraint.isInvalid() || !TransConstraint.get() ||
       Satisfaction.HasSubstitutionFailure()) {
     SmallString<128> Entity;
     llvm::raw_svector_ostream OS(Entity);
     Req->getConstraintExpr()->printPretty(OS, nullptr,
                                           SemaRef.getPrintingPolicy());
     return new (C) concepts::NestedRequirement(
         SemaRef.Context, C.backupStr(Entity), Satisfaction);
   }
   return new (C)
       concepts::NestedRequirement(C, TransConstraint.get(), Satisfaction);
 }
 
 TypeSourceInfo *Sema::SubstType(TypeSourceInfo *T,
                                 const MultiLevelTemplateArgumentList &Args,
                                 SourceLocation Loc,
                                 DeclarationName Entity,
                                 bool AllowDeducedTST) {
   assert(!CodeSynthesisContexts.empty() &&
          "Cannot perform an instantiation without some context on the "
          "instantiation stack");
 
   if (!T->getType()->isInstantiationDependentType() &&
       !T->getType()->isVariablyModifiedType())
     return T;
 
   TemplateInstantiator Instantiator(*this, Args, Loc, Entity);
   return AllowDeducedTST ? Instantiator.TransformTypeWithDeducedTST(T)
                          : Instantiator.TransformType(T);
 }
 
 TypeSourceInfo *Sema::SubstType(TypeLoc TL,
                                 const MultiLevelTemplateArgumentList &Args,
                                 SourceLocation Loc,
                                 DeclarationName Entity) {
   assert(!CodeSynthesisContexts.empty() &&
          "Cannot perform an instantiation without some context on the "
          "instantiation stack");
 
   if (TL.getType().isNull())
     return nullptr;
 
   if (!TL.getType()->isInstantiationDependentType() &&
       !TL.getType()->isVariablyModifiedType()) {
     // FIXME: Make a copy of the TypeLoc data here, so that we can
     // return a new TypeSourceInfo. Inefficient!
     TypeLocBuilder TLB;
     TLB.pushFullCopy(TL);
     return TLB.getTypeSourceInfo(Context, TL.getType());
   }
 
   TemplateInstantiator Instantiator(*this, Args, Loc, Entity);
   TypeLocBuilder TLB;
   TLB.reserve(TL.getFullDataSize());
   QualType Result = Instantiator.TransformType(TLB, TL);
   if (Result.isNull())
     return nullptr;
 
   return TLB.getTypeSourceInfo(Context, Result);
 }
 
 /// Deprecated form of the above.
 QualType Sema::SubstType(QualType T,
                          const MultiLevelTemplateArgumentList &TemplateArgs,
                          SourceLocation Loc, DeclarationName Entity) {
   assert(!CodeSynthesisContexts.empty() &&
          "Cannot perform an instantiation without some context on the "
          "instantiation stack");
 
   // If T is not a dependent type or a variably-modified type, there
   // is nothing to do.
   if (!T->isInstantiationDependentType() && !T->isVariablyModifiedType())
     return T;
 
   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc, Entity);
   return Instantiator.TransformType(T);
 }
 
 static bool NeedsInstantiationAsFunctionType(TypeSourceInfo *T) {
   if (T->getType()->isInstantiationDependentType() ||
       T->getType()->isVariablyModifiedType())
     return true;
 
   TypeLoc TL = T->getTypeLoc().IgnoreParens();
   if (!TL.getAs<FunctionProtoTypeLoc>())
     return false;
 
   FunctionProtoTypeLoc FP = TL.castAs<FunctionProtoTypeLoc>();
   for (ParmVarDecl *P : FP.getParams()) {
     // This must be synthesized from a typedef.
     if (!P) continue;
 
     // If there are any parameters, a new TypeSourceInfo that refers to the
     // instantiated parameters must be built.
     return true;
   }
 
   return false;
 }
 
 TypeSourceInfo *Sema::SubstFunctionDeclType(TypeSourceInfo *T,
                                 const MultiLevelTemplateArgumentList &Args,
                                 SourceLocation Loc,
                                 DeclarationName Entity,
                                 CXXRecordDecl *ThisContext,
                                 Qualifiers ThisTypeQuals,
                                 bool EvaluateConstraints) {
   assert(!CodeSynthesisContexts.empty() &&
          "Cannot perform an instantiation without some context on the "
          "instantiation stack");
 
   if (!NeedsInstantiationAsFunctionType(T))
     return T;
 
   TemplateInstantiator Instantiator(*this, Args, Loc, Entity);
   Instantiator.setEvaluateConstraints(EvaluateConstraints);
 
   TypeLocBuilder TLB;
 
   TypeLoc TL = T->getTypeLoc();
   TLB.reserve(TL.getFullDataSize());
 
   QualType Result;
 
   if (FunctionProtoTypeLoc Proto =
           TL.IgnoreParens().getAs<FunctionProtoTypeLoc>()) {
     // Instantiate the type, other than its exception specification. The
     // exception specification is instantiated in InitFunctionInstantiation
     // once we've built the FunctionDecl.
     // FIXME: Set the exception specification to EST_Uninstantiated here,
     // instead of rebuilding the function type again later.
     Result = Instantiator.TransformFunctionProtoType(
         TLB, Proto, ThisContext, ThisTypeQuals,
         [](FunctionProtoType::ExceptionSpecInfo &ESI,
            bool &Changed) { return false; });
   } else {
     Result = Instantiator.TransformType(TLB, TL);
   }
   // When there are errors resolving types, clang may use IntTy as a fallback,
   // breaking our assumption that function declarations have function types.
   if (Result.isNull() || !Result->isFunctionType())
     return nullptr;
 
   return TLB.getTypeSourceInfo(Context, Result);
 }
 
 bool Sema::SubstExceptionSpec(SourceLocation Loc,
                               FunctionProtoType::ExceptionSpecInfo &ESI,
                               SmallVectorImpl<QualType> &ExceptionStorage,
                               const MultiLevelTemplateArgumentList &Args) {
   bool Changed = false;
   TemplateInstantiator Instantiator(*this, Args, Loc, DeclarationName());
   return Instantiator.TransformExceptionSpec(Loc, ESI, ExceptionStorage,
                                              Changed);
 }
 
 void Sema::SubstExceptionSpec(FunctionDecl *New, const FunctionProtoType *Proto,
                               const MultiLevelTemplateArgumentList &Args) {
   FunctionProtoType::ExceptionSpecInfo ESI =
       Proto->getExtProtoInfo().ExceptionSpec;
 
   SmallVector<QualType, 4> ExceptionStorage;
   if (SubstExceptionSpec(New->getTypeSourceInfo()->getTypeLoc().getEndLoc(),
                          ESI, ExceptionStorage, Args))
     // On error, recover by dropping the exception specification.
     ESI.Type = EST_None;
 
   UpdateExceptionSpec(New, ESI);
 }
 
 namespace {
 
   struct GetContainedInventedTypeParmVisitor :
     public TypeVisitor<GetContainedInventedTypeParmVisitor,
                        TemplateTypeParmDecl *> {
     using TypeVisitor<GetContainedInventedTypeParmVisitor,
                       TemplateTypeParmDecl *>::Visit;
 
     TemplateTypeParmDecl *Visit(QualType T) {
       if (T.isNull())
         return nullptr;
       return Visit(T.getTypePtr());
     }
     // The deduced type itself.
     TemplateTypeParmDecl *VisitTemplateTypeParmType(
         const TemplateTypeParmType *T) {
       if (!T->getDecl() || !T->getDecl()->isImplicit())
         return nullptr;
       return T->getDecl();
     }
 
     // Only these types can contain 'auto' types, and subsequently be replaced
     // by references to invented parameters.
 
     TemplateTypeParmDecl *VisitElaboratedType(const ElaboratedType *T) {
       return Visit(T->getNamedType());
     }
 
     TemplateTypeParmDecl *VisitPointerType(const PointerType *T) {
       return Visit(T->getPointeeType());
     }
 
     TemplateTypeParmDecl *VisitBlockPointerType(const BlockPointerType *T) {
       return Visit(T->getPointeeType());
     }
 
     TemplateTypeParmDecl *VisitReferenceType(const ReferenceType *T) {
       return Visit(T->getPointeeTypeAsWritten());
     }
 
     TemplateTypeParmDecl *VisitMemberPointerType(const MemberPointerType *T) {
       return Visit(T->getPointeeType());
     }
 
     TemplateTypeParmDecl *VisitArrayType(const ArrayType *T) {
       return Visit(T->getElementType());
     }
 
     TemplateTypeParmDecl *VisitDependentSizedExtVectorType(
       const DependentSizedExtVectorType *T) {
       return Visit(T->getElementType());
     }
 
     TemplateTypeParmDecl *VisitVectorType(const VectorType *T) {
       return Visit(T->getElementType());
     }
 
     TemplateTypeParmDecl *VisitFunctionProtoType(const FunctionProtoType *T) {
       return VisitFunctionType(T);
     }
 
     TemplateTypeParmDecl *VisitFunctionType(const FunctionType *T) {
       return Visit(T->getReturnType());
     }
 
     TemplateTypeParmDecl *VisitParenType(const ParenType *T) {
       return Visit(T->getInnerType());
     }
 
     TemplateTypeParmDecl *VisitAttributedType(const AttributedType *T) {
       return Visit(T->getModifiedType());
     }
 
     TemplateTypeParmDecl *VisitMacroQualifiedType(const MacroQualifiedType *T) {
       return Visit(T->getUnderlyingType());
     }
 
     TemplateTypeParmDecl *VisitAdjustedType(const AdjustedType *T) {
       return Visit(T->getOriginalType());
     }
 
     TemplateTypeParmDecl *VisitPackExpansionType(const PackExpansionType *T) {
       return Visit(T->getPattern());
     }
   };
 
 } // namespace
 
 bool Sema::SubstTypeConstraint(
     TemplateTypeParmDecl *Inst, const TypeConstraint *TC,
     const MultiLevelTemplateArgumentList &TemplateArgs,
     bool EvaluateConstraints) {
   const ASTTemplateArgumentListInfo *TemplArgInfo =
       TC->getTemplateArgsAsWritten();
 
   if (!EvaluateConstraints) {
       Inst->setTypeConstraint(TC->getConceptReference(),
                               TC->getImmediatelyDeclaredConstraint());
       return false;
   }
 
   TemplateArgumentListInfo InstArgs;
 
   if (TemplArgInfo) {
     InstArgs.setLAngleLoc(TemplArgInfo->LAngleLoc);
     InstArgs.setRAngleLoc(TemplArgInfo->RAngleLoc);
     if (SubstTemplateArguments(TemplArgInfo->arguments(), TemplateArgs,
                                InstArgs))
       return true;
   }
   return AttachTypeConstraint(
       TC->getNestedNameSpecifierLoc(), TC->getConceptNameInfo(),
       TC->getNamedConcept(),
       /*FoundDecl=*/TC->getConceptReference()->getFoundDecl(), &InstArgs, Inst,
       Inst->isParameterPack()
           ? cast<CXXFoldExpr>(TC->getImmediatelyDeclaredConstraint())
                 ->getEllipsisLoc()
           : SourceLocation());
 }
 
 ParmVarDecl *Sema::SubstParmVarDecl(
     ParmVarDecl *OldParm, const MultiLevelTemplateArgumentList &TemplateArgs,
     int indexAdjustment, std::optional<unsigned> NumExpansions,
     bool ExpectParameterPack, bool EvaluateConstraint) {
   TypeSourceInfo *OldDI = OldParm->getTypeSourceInfo();
   TypeSourceInfo *NewDI = nullptr;
 
   TypeLoc OldTL = OldDI->getTypeLoc();
   if (PackExpansionTypeLoc ExpansionTL = OldTL.getAs<PackExpansionTypeLoc>()) {
 
     // We have a function parameter pack. Substitute into the pattern of the
     // expansion.
     NewDI = SubstType(ExpansionTL.getPatternLoc(), TemplateArgs,
                       OldParm->getLocation(), OldParm->getDeclName());
     if (!NewDI)
       return nullptr;
 
     if (NewDI->getType()->containsUnexpandedParameterPack()) {
       // We still have unexpanded parameter packs, which means that
       // our function parameter is still a function parameter pack.
       // Therefore, make its type a pack expansion type.
       NewDI = CheckPackExpansion(NewDI, ExpansionTL.getEllipsisLoc(),
                                  NumExpansions);
     } else if (ExpectParameterPack) {
       // We expected to get a parameter pack but didn't (because the type
       // itself is not a pack expansion type), so complain. This can occur when
       // the substitution goes through an alias template that "loses" the
       // pack expansion.
       Diag(OldParm->getLocation(),
            diag::err_function_parameter_pack_without_parameter_packs)
         << NewDI->getType();
       return nullptr;
     }
   } else {
     NewDI = SubstType(OldDI, TemplateArgs, OldParm->getLocation(),
                       OldParm->getDeclName());
   }
 
   if (!NewDI)
     return nullptr;
 
   if (NewDI->getType()->isVoidType()) {
     Diag(OldParm->getLocation(), diag::err_param_with_void_type);
     return nullptr;
   }
 
   // In abbreviated templates, TemplateTypeParmDecls with possible
   // TypeConstraints are created when the parameter list is originally parsed.
   // The TypeConstraints can therefore reference other functions parameters in
   // the abbreviated function template, which is why we must instantiate them
   // here, when the instantiated versions of those referenced parameters are in
   // scope.
   if (TemplateTypeParmDecl *TTP =
           GetContainedInventedTypeParmVisitor().Visit(OldDI->getType())) {
     if (const TypeConstraint *TC = TTP->getTypeConstraint()) {
       auto *Inst = cast_or_null<TemplateTypeParmDecl>(
           FindInstantiatedDecl(TTP->getLocation(), TTP, TemplateArgs));
       // We will first get here when instantiating the abbreviated function
       // template's described function, but we might also get here later.
       // Make sure we do not instantiate the TypeConstraint more than once.
       if (Inst && !Inst->getTypeConstraint()) {
         if (SubstTypeConstraint(Inst, TC, TemplateArgs, EvaluateConstraint))
           return nullptr;
       }
     }
   }
 
   ParmVarDecl *NewParm = CheckParameter(Context.getTranslationUnitDecl(),
                                         OldParm->getInnerLocStart(),
                                         OldParm->getLocation(),
                                         OldParm->getIdentifier(),
                                         NewDI->getType(), NewDI,
                                         OldParm->getStorageClass());
   if (!NewParm)
     return nullptr;
 
   // Mark the (new) default argument as uninstantiated (if any).
   if (OldParm->hasUninstantiatedDefaultArg()) {
     Expr *Arg = OldParm->getUninstantiatedDefaultArg();
     NewParm->setUninstantiatedDefaultArg(Arg);
   } else if (OldParm->hasUnparsedDefaultArg()) {
     NewParm->setUnparsedDefaultArg();
     UnparsedDefaultArgInstantiations[OldParm].push_back(NewParm);
   } else if (Expr *Arg = OldParm->getDefaultArg()) {
     // Default arguments cannot be substituted until the declaration context
     // for the associated function or lambda capture class is available.
     // This is necessary for cases like the following where construction of
     // the lambda capture class for the outer lambda is dependent on the
     // parameter types but where the default argument is dependent on the
     // outer lambda's declaration context.
     //   template <typename T>
     //   auto f() {
     //     return [](T = []{ return T{}; }()) { return 0; };
     //   }
     NewParm->setUninstantiatedDefaultArg(Arg);
   }
 
   NewParm->setExplicitObjectParameterLoc(
       OldParm->getExplicitObjectParamThisLoc());
   NewParm->setHasInheritedDefaultArg(OldParm->hasInheritedDefaultArg());
 
   if (OldParm->isParameterPack() && !NewParm->isParameterPack()) {
     // Add the new parameter to the instantiated parameter pack.
     CurrentInstantiationScope->InstantiatedLocalPackArg(OldParm, NewParm);
   } else {
     // Introduce an Old -> New mapping
     CurrentInstantiationScope->InstantiatedLocal(OldParm, NewParm);
   }
 
   // FIXME: OldParm may come from a FunctionProtoType, in which case CurContext
   // can be anything, is this right ?
   NewParm->setDeclContext(CurContext);
 
   NewParm->setScopeInfo(OldParm->getFunctionScopeDepth(),
                         OldParm->getFunctionScopeIndex() + indexAdjustment);
 
   InstantiateAttrs(TemplateArgs, OldParm, NewParm);
 
   return NewParm;
 }
 
 bool Sema::SubstParmTypes(
     SourceLocation Loc, ArrayRef<ParmVarDecl *> Params,
     const FunctionProtoType::ExtParameterInfo *ExtParamInfos,
     const MultiLevelTemplateArgumentList &TemplateArgs,
     SmallVectorImpl<QualType> &ParamTypes,
     SmallVectorImpl<ParmVarDecl *> *OutParams,
     ExtParameterInfoBuilder &ParamInfos) {
   assert(!CodeSynthesisContexts.empty() &&
          "Cannot perform an instantiation without some context on the "
          "instantiation stack");
 
   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc,
                                     DeclarationName());
   return Instantiator.TransformFunctionTypeParams(
       Loc, Params, nullptr, ExtParamInfos, ParamTypes, OutParams, ParamInfos);
 }
 
 bool Sema::SubstDefaultArgument(
     SourceLocation Loc,
     ParmVarDecl *Param,
     const MultiLevelTemplateArgumentList &TemplateArgs,
     bool ForCallExpr) {
   FunctionDecl *FD = cast<FunctionDecl>(Param->getDeclContext());
   Expr *PatternExpr = Param->getUninstantiatedDefaultArg();
 
   EnterExpressionEvaluationContext EvalContext(
       *this, ExpressionEvaluationContext::PotentiallyEvaluated, Param);
 
   InstantiatingTemplate Inst(*this, Loc, Param, TemplateArgs.getInnermost());
   if (Inst.isInvalid())
     return true;
   if (Inst.isAlreadyInstantiating()) {
     Diag(Param->getBeginLoc(), diag::err_recursive_default_argument) << FD;
     Param->setInvalidDecl();
     return true;
   }
 
   ExprResult Result;
   {
     // C++ [dcl.fct.default]p5:
     //   The names in the [default argument] expression are bound, and
     //   the semantic constraints are checked, at the point where the
     //   default argument expression appears.
     ContextRAII SavedContext(*this, FD);
     std::unique_ptr<LocalInstantiationScope> LIS;
-    MultiLevelTemplateArgumentList NewTemplateArgs = TemplateArgs;
 
     if (ForCallExpr) {
       // When instantiating a default argument due to use in a call expression,
       // an instantiation scope that includes the parameters of the callee is
       // required to satisfy references from the default argument. For example:
       //   template<typename T> void f(T a, int = decltype(a)());
       //   void g() { f(0); }
       LIS = std::make_unique<LocalInstantiationScope>(*this);
       FunctionDecl *PatternFD = FD->getTemplateInstantiationPattern(
           /*ForDefinition*/ false);
       if (addInstantiatedParametersToScope(FD, PatternFD, *LIS, TemplateArgs))
         return true;
-      const FunctionTemplateDecl *PrimaryTemplate = FD->getPrimaryTemplate();
-      if (PrimaryTemplate && PrimaryTemplate->isOutOfLine()) {
-        TemplateArgumentList *CurrentTemplateArgumentList =
-            TemplateArgumentList::CreateCopy(getASTContext(),
-                                             TemplateArgs.getInnermost());
-        NewTemplateArgs = getTemplateInstantiationArgs(
-            FD, FD->getDeclContext(), /*Final=*/false,
-            CurrentTemplateArgumentList->asArray(), /*RelativeToPrimary=*/true);
-      }
     }
 
     runWithSufficientStackSpace(Loc, [&] {
-      Result = SubstInitializer(PatternExpr, NewTemplateArgs,
+      Result = SubstInitializer(PatternExpr, TemplateArgs,
                                 /*DirectInit*/ false);
     });
   }
   if (Result.isInvalid())
     return true;
 
   if (ForCallExpr) {
     // Check the expression as an initializer for the parameter.
     InitializedEntity Entity
       = InitializedEntity::InitializeParameter(Context, Param);
     InitializationKind Kind = InitializationKind::CreateCopy(
         Param->getLocation(),
         /*FIXME:EqualLoc*/ PatternExpr->getBeginLoc());
     Expr *ResultE = Result.getAs<Expr>();
 
     InitializationSequence InitSeq(*this, Entity, Kind, ResultE);
     Result = InitSeq.Perform(*this, Entity, Kind, ResultE);
     if (Result.isInvalid())
       return true;
 
     Result =
         ActOnFinishFullExpr(Result.getAs<Expr>(), Param->getOuterLocStart(),
                             /*DiscardedValue*/ false);
   } else {
     // FIXME: Obtain the source location for the '=' token.
     SourceLocation EqualLoc = PatternExpr->getBeginLoc();
     Result = ConvertParamDefaultArgument(Param, Result.getAs<Expr>(), EqualLoc);
   }
   if (Result.isInvalid())
       return true;
 
   // Remember the instantiated default argument.
   Param->setDefaultArg(Result.getAs<Expr>());
 
   return false;
 }
 
 bool
 Sema::SubstBaseSpecifiers(CXXRecordDecl *Instantiation,
                           CXXRecordDecl *Pattern,
                           const MultiLevelTemplateArgumentList &TemplateArgs) {
   bool Invalid = false;
   SmallVector<CXXBaseSpecifier*, 4> InstantiatedBases;
   for (const auto &Base : Pattern->bases()) {
     if (!Base.getType()->isDependentType()) {
       if (const CXXRecordDecl *RD = Base.getType()->getAsCXXRecordDecl()) {
         if (RD->isInvalidDecl())
           Instantiation->setInvalidDecl();
       }
       InstantiatedBases.push_back(new (Context) CXXBaseSpecifier(Base));
       continue;
     }
 
     SourceLocation EllipsisLoc;
     TypeSourceInfo *BaseTypeLoc;
     if (Base.isPackExpansion()) {
       // This is a pack expansion. See whether we should expand it now, or
       // wait until later.
       SmallVector<UnexpandedParameterPack, 2> Unexpanded;
       collectUnexpandedParameterPacks(Base.getTypeSourceInfo()->getTypeLoc(),
                                       Unexpanded);
       bool ShouldExpand = false;
       bool RetainExpansion = false;
       std::optional<unsigned> NumExpansions;
       if (CheckParameterPacksForExpansion(Base.getEllipsisLoc(),
                                           Base.getSourceRange(),
                                           Unexpanded,
                                           TemplateArgs, ShouldExpand,
                                           RetainExpansion,
                                           NumExpansions)) {
         Invalid = true;
         continue;
       }
 
       // If we should expand this pack expansion now, do so.
       if (ShouldExpand) {
         for (unsigned I = 0; I != *NumExpansions; ++I) {
             Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this, I);
 
           TypeSourceInfo *BaseTypeLoc = SubstType(Base.getTypeSourceInfo(),
                                                   TemplateArgs,
                                               Base.getSourceRange().getBegin(),
                                                   DeclarationName());
           if (!BaseTypeLoc) {
             Invalid = true;
             continue;
           }
 
           if (CXXBaseSpecifier *InstantiatedBase
                 = CheckBaseSpecifier(Instantiation,
                                      Base.getSourceRange(),
                                      Base.isVirtual(),
                                      Base.getAccessSpecifierAsWritten(),
                                      BaseTypeLoc,
                                      SourceLocation()))
             InstantiatedBases.push_back(InstantiatedBase);
           else
             Invalid = true;
         }
 
         continue;
       }
 
       // The resulting base specifier will (still) be a pack expansion.
       EllipsisLoc = Base.getEllipsisLoc();
       Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this, -1);
       BaseTypeLoc = SubstType(Base.getTypeSourceInfo(),
                               TemplateArgs,
                               Base.getSourceRange().getBegin(),
                               DeclarationName());
     } else {
       BaseTypeLoc = SubstType(Base.getTypeSourceInfo(),
                               TemplateArgs,
                               Base.getSourceRange().getBegin(),
                               DeclarationName());
     }
 
     if (!BaseTypeLoc) {
       Invalid = true;
       continue;
     }
 
     if (CXXBaseSpecifier *InstantiatedBase
           = CheckBaseSpecifier(Instantiation,
                                Base.getSourceRange(),
                                Base.isVirtual(),
                                Base.getAccessSpecifierAsWritten(),
                                BaseTypeLoc,
                                EllipsisLoc))
       InstantiatedBases.push_back(InstantiatedBase);
     else
       Invalid = true;
   }
 
   if (!Invalid && AttachBaseSpecifiers(Instantiation, InstantiatedBases))
     Invalid = true;
 
   return Invalid;
 }
 
 // Defined via #include from SemaTemplateInstantiateDecl.cpp
 namespace clang {
   namespace sema {
     Attr *instantiateTemplateAttribute(const Attr *At, ASTContext &C, Sema &S,
                             const MultiLevelTemplateArgumentList &TemplateArgs);
     Attr *instantiateTemplateAttributeForDecl(
         const Attr *At, ASTContext &C, Sema &S,
         const MultiLevelTemplateArgumentList &TemplateArgs);
   }
 }
 
 bool
 Sema::InstantiateClass(SourceLocation PointOfInstantiation,
                        CXXRecordDecl *Instantiation, CXXRecordDecl *Pattern,
                        const MultiLevelTemplateArgumentList &TemplateArgs,
                        TemplateSpecializationKind TSK,
                        bool Complain) {
   CXXRecordDecl *PatternDef
     = cast_or_null<CXXRecordDecl>(Pattern->getDefinition());
   if (DiagnoseUninstantiableTemplate(PointOfInstantiation, Instantiation,
                                 Instantiation->getInstantiatedFromMemberClass(),
                                      Pattern, PatternDef, TSK, Complain))
     return true;
 
   llvm::TimeTraceScope TimeScope("InstantiateClass", [&]() {
     llvm::TimeTraceMetadata M;
     llvm::raw_string_ostream OS(M.Detail);
     Instantiation->getNameForDiagnostic(OS, getPrintingPolicy(),
                                         /*Qualified=*/true);
     if (llvm::isTimeTraceVerbose()) {
       auto Loc = SourceMgr.getExpansionLoc(Instantiation->getLocation());
       M.File = SourceMgr.getFilename(Loc);
       M.Line = SourceMgr.getExpansionLineNumber(Loc);
     }
     return M;
   });
 
   Pattern = PatternDef;
 
   // Record the point of instantiation.
   if (MemberSpecializationInfo *MSInfo
         = Instantiation->getMemberSpecializationInfo()) {
     MSInfo->setTemplateSpecializationKind(TSK);
     MSInfo->setPointOfInstantiation(PointOfInstantiation);
   } else if (ClassTemplateSpecializationDecl *Spec
         = dyn_cast<ClassTemplateSpecializationDecl>(Instantiation)) {
     Spec->setTemplateSpecializationKind(TSK);
     Spec->setPointOfInstantiation(PointOfInstantiation);
   }
 
   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
   if (Inst.isInvalid())
     return true;
   assert(!Inst.isAlreadyInstantiating() && "should have been caught by caller");
   PrettyDeclStackTraceEntry CrashInfo(Context, Instantiation, SourceLocation(),
                                       "instantiating class definition");
 
   // Enter the scope of this instantiation. We don't use
   // PushDeclContext because we don't have a scope.
   ContextRAII SavedContext(*this, Instantiation);
   EnterExpressionEvaluationContext EvalContext(
       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
 
   // If this is an instantiation of a local class, merge this local
   // instantiation scope with the enclosing scope. Otherwise, every
   // instantiation of a class has its own local instantiation scope.
   bool MergeWithParentScope = !Instantiation->isDefinedOutsideFunctionOrMethod();
   LocalInstantiationScope Scope(*this, MergeWithParentScope);
 
   // Some class state isn't processed immediately but delayed till class
   // instantiation completes. We may not be ready to handle any delayed state
   // already on the stack as it might correspond to a different class, so save
   // it now and put it back later.
   SavePendingParsedClassStateRAII SavedPendingParsedClassState(*this);
 
   // Pull attributes from the pattern onto the instantiation.
   InstantiateAttrs(TemplateArgs, Pattern, Instantiation);
 
   // Start the definition of this instantiation.
   Instantiation->startDefinition();
 
   // The instantiation is visible here, even if it was first declared in an
   // unimported module.
   Instantiation->setVisibleDespiteOwningModule();
 
   // FIXME: This loses the as-written tag kind for an explicit instantiation.
   Instantiation->setTagKind(Pattern->getTagKind());
 
   // Do substitution on the base class specifiers.
   if (SubstBaseSpecifiers(Instantiation, Pattern, TemplateArgs))
     Instantiation->setInvalidDecl();
 
   TemplateDeclInstantiator Instantiator(*this, Instantiation, TemplateArgs);
   Instantiator.setEvaluateConstraints(false);
   SmallVector<Decl*, 4> Fields;
   // Delay instantiation of late parsed attributes.
   LateInstantiatedAttrVec LateAttrs;
   Instantiator.enableLateAttributeInstantiation(&LateAttrs);
 
   bool MightHaveConstexprVirtualFunctions = false;
   for (auto *Member : Pattern->decls()) {
     // Don't instantiate members not belonging in this semantic context.
     // e.g. for:
     // @code
     //    template <int i> class A {
     //      class B *g;
     //    };
     // @endcode
     // 'class B' has the template as lexical context but semantically it is
     // introduced in namespace scope.
     if (Member->getDeclContext() != Pattern)
       continue;
 
     // BlockDecls can appear in a default-member-initializer. They must be the
     // child of a BlockExpr, so we only know how to instantiate them from there.
     // Similarly, lambda closure types are recreated when instantiating the
     // corresponding LambdaExpr.
     if (isa<BlockDecl>(Member) ||
         (isa<CXXRecordDecl>(Member) && cast<CXXRecordDecl>(Member)->isLambda()))
       continue;
 
     if (Member->isInvalidDecl()) {
       Instantiation->setInvalidDecl();
       continue;
     }
 
     Decl *NewMember = Instantiator.Visit(Member);
     if (NewMember) {
       if (FieldDecl *Field = dyn_cast<FieldDecl>(NewMember)) {
         Fields.push_back(Field);
       } else if (EnumDecl *Enum = dyn_cast<EnumDecl>(NewMember)) {
         // C++11 [temp.inst]p1: The implicit instantiation of a class template
         // specialization causes the implicit instantiation of the definitions
         // of unscoped member enumerations.
         // Record a point of instantiation for this implicit instantiation.
         if (TSK == TSK_ImplicitInstantiation && !Enum->isScoped() &&
             Enum->isCompleteDefinition()) {
           MemberSpecializationInfo *MSInfo =Enum->getMemberSpecializationInfo();
           assert(MSInfo && "no spec info for member enum specialization");
           MSInfo->setTemplateSpecializationKind(TSK_ImplicitInstantiation);
           MSInfo->setPointOfInstantiation(PointOfInstantiation);
         }
       } else if (StaticAssertDecl *SA = dyn_cast<StaticAssertDecl>(NewMember)) {
         if (SA->isFailed()) {
           // A static_assert failed. Bail out; instantiating this
           // class is probably not meaningful.
           Instantiation->setInvalidDecl();
           break;
         }
       } else if (CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(NewMember)) {
         if (MD->isConstexpr() && !MD->getFriendObjectKind() &&
             (MD->isVirtualAsWritten() || Instantiation->getNumBases()))
           MightHaveConstexprVirtualFunctions = true;
       }
 
       if (NewMember->isInvalidDecl())
         Instantiation->setInvalidDecl();
     } else {
       // FIXME: Eventually, a NULL return will mean that one of the
       // instantiations was a semantic disaster, and we'll want to mark the
       // declaration invalid.
       // For now, we expect to skip some members that we can't yet handle.
     }
   }
 
   // Finish checking fields.
   ActOnFields(nullptr, Instantiation->getLocation(), Instantiation, Fields,
               SourceLocation(), SourceLocation(), ParsedAttributesView());
   CheckCompletedCXXClass(nullptr, Instantiation);
 
   // Default arguments are parsed, if not instantiated. We can go instantiate
   // default arg exprs for default constructors if necessary now. Unless we're
   // parsing a class, in which case wait until that's finished.
   if (ParsingClassDepth == 0)
     ActOnFinishCXXNonNestedClass();
 
   // Instantiate late parsed attributes, and attach them to their decls.
   // See Sema::InstantiateAttrs
   for (LateInstantiatedAttrVec::iterator I = LateAttrs.begin(),
        E = LateAttrs.end(); I != E; ++I) {
     assert(CurrentInstantiationScope == Instantiator.getStartingScope());
     CurrentInstantiationScope = I->Scope;
 
     // Allow 'this' within late-parsed attributes.
     auto *ND = cast<NamedDecl>(I->NewDecl);
     auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(ND->getDeclContext());
     CXXThisScopeRAII ThisScope(*this, ThisContext, Qualifiers(),
                                ND->isCXXInstanceMember());
 
     Attr *NewAttr =
       instantiateTemplateAttribute(I->TmplAttr, Context, *this, TemplateArgs);
     if (NewAttr)
       I->NewDecl->addAttr(NewAttr);
     LocalInstantiationScope::deleteScopes(I->Scope,
                                           Instantiator.getStartingScope());
   }
   Instantiator.disableLateAttributeInstantiation();
   LateAttrs.clear();
 
   ActOnFinishDelayedMemberInitializers(Instantiation);
 
   // FIXME: We should do something similar for explicit instantiations so they
   // end up in the right module.
   if (TSK == TSK_ImplicitInstantiation) {
     Instantiation->setLocation(Pattern->getLocation());
     Instantiation->setLocStart(Pattern->getInnerLocStart());
     Instantiation->setBraceRange(Pattern->getBraceRange());
   }
 
   if (!Instantiation->isInvalidDecl()) {
     // Perform any dependent diagnostics from the pattern.
     if (Pattern->isDependentContext())
       PerformDependentDiagnostics(Pattern, TemplateArgs);
 
     // Instantiate any out-of-line class template partial
     // specializations now.
     for (TemplateDeclInstantiator::delayed_partial_spec_iterator
               P = Instantiator.delayed_partial_spec_begin(),
            PEnd = Instantiator.delayed_partial_spec_end();
          P != PEnd; ++P) {
       if (!Instantiator.InstantiateClassTemplatePartialSpecialization(
               P->first, P->second)) {
         Instantiation->setInvalidDecl();
         break;
       }
     }
 
     // Instantiate any out-of-line variable template partial
     // specializations now.
     for (TemplateDeclInstantiator::delayed_var_partial_spec_iterator
               P = Instantiator.delayed_var_partial_spec_begin(),
            PEnd = Instantiator.delayed_var_partial_spec_end();
          P != PEnd; ++P) {
       if (!Instantiator.InstantiateVarTemplatePartialSpecialization(
               P->first, P->second)) {
         Instantiation->setInvalidDecl();
         break;
       }
     }
   }
 
   // Exit the scope of this instantiation.
   SavedContext.pop();
 
   if (!Instantiation->isInvalidDecl()) {
     // Always emit the vtable for an explicit instantiation definition
     // of a polymorphic class template specialization. Otherwise, eagerly
     // instantiate only constexpr virtual functions in preparation for their use
     // in constant evaluation.
     if (TSK == TSK_ExplicitInstantiationDefinition)
       MarkVTableUsed(PointOfInstantiation, Instantiation, true);
     else if (MightHaveConstexprVirtualFunctions)
       MarkVirtualMembersReferenced(PointOfInstantiation, Instantiation,
                                    /*ConstexprOnly*/ true);
   }
 
   Consumer.HandleTagDeclDefinition(Instantiation);
 
   return Instantiation->isInvalidDecl();
 }
 
 bool Sema::InstantiateEnum(SourceLocation PointOfInstantiation,
                            EnumDecl *Instantiation, EnumDecl *Pattern,
                            const MultiLevelTemplateArgumentList &TemplateArgs,
                            TemplateSpecializationKind TSK) {
   EnumDecl *PatternDef = Pattern->getDefinition();
   if (DiagnoseUninstantiableTemplate(PointOfInstantiation, Instantiation,
                                  Instantiation->getInstantiatedFromMemberEnum(),
                                      Pattern, PatternDef, TSK,/*Complain*/true))
     return true;
   Pattern = PatternDef;
 
   // Record the point of instantiation.
   if (MemberSpecializationInfo *MSInfo
         = Instantiation->getMemberSpecializationInfo()) {
     MSInfo->setTemplateSpecializationKind(TSK);
     MSInfo->setPointOfInstantiation(PointOfInstantiation);
   }
 
   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
   if (Inst.isInvalid())
     return true;
   if (Inst.isAlreadyInstantiating())
     return false;
   PrettyDeclStackTraceEntry CrashInfo(Context, Instantiation, SourceLocation(),
                                       "instantiating enum definition");
 
   // The instantiation is visible here, even if it was first declared in an
   // unimported module.
   Instantiation->setVisibleDespiteOwningModule();
 
   // Enter the scope of this instantiation. We don't use
   // PushDeclContext because we don't have a scope.
   ContextRAII SavedContext(*this, Instantiation);
   EnterExpressionEvaluationContext EvalContext(
       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
 
   LocalInstantiationScope Scope(*this, /*MergeWithParentScope*/true);
 
   // Pull attributes from the pattern onto the instantiation.
   InstantiateAttrs(TemplateArgs, Pattern, Instantiation);
 
   TemplateDeclInstantiator Instantiator(*this, Instantiation, TemplateArgs);
   Instantiator.InstantiateEnumDefinition(Instantiation, Pattern);
 
   // Exit the scope of this instantiation.
   SavedContext.pop();
 
   return Instantiation->isInvalidDecl();
 }
 
 bool Sema::InstantiateInClassInitializer(
     SourceLocation PointOfInstantiation, FieldDecl *Instantiation,
     FieldDecl *Pattern, const MultiLevelTemplateArgumentList &TemplateArgs) {
   // If there is no initializer, we don't need to do anything.
   if (!Pattern->hasInClassInitializer())
     return false;
 
   assert(Instantiation->getInClassInitStyle() ==
              Pattern->getInClassInitStyle() &&
          "pattern and instantiation disagree about init style");
 
   // Error out if we haven't parsed the initializer of the pattern yet because
   // we are waiting for the closing brace of the outer class.
   Expr *OldInit = Pattern->getInClassInitializer();
   if (!OldInit) {
     RecordDecl *PatternRD = Pattern->getParent();
     RecordDecl *OutermostClass = PatternRD->getOuterLexicalRecordContext();
     Diag(PointOfInstantiation,
          diag::err_default_member_initializer_not_yet_parsed)
         << OutermostClass << Pattern;
     Diag(Pattern->getEndLoc(),
          diag::note_default_member_initializer_not_yet_parsed);
     Instantiation->setInvalidDecl();
     return true;
   }
 
   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
   if (Inst.isInvalid())
     return true;
   if (Inst.isAlreadyInstantiating()) {
     // Error out if we hit an instantiation cycle for this initializer.
     Diag(PointOfInstantiation, diag::err_default_member_initializer_cycle)
       << Instantiation;
     return true;
   }
   PrettyDeclStackTraceEntry CrashInfo(Context, Instantiation, SourceLocation(),
                                       "instantiating default member init");
 
   // Enter the scope of this instantiation. We don't use PushDeclContext because
   // we don't have a scope.
   ContextRAII SavedContext(*this, Instantiation->getParent());
   EnterExpressionEvaluationContext EvalContext(
       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
   ExprEvalContexts.back().DelayedDefaultInitializationContext = {
       PointOfInstantiation, Instantiation, CurContext};
 
   LocalInstantiationScope Scope(*this, true);
 
   // Instantiate the initializer.
   ActOnStartCXXInClassMemberInitializer();
   CXXThisScopeRAII ThisScope(*this, Instantiation->getParent(), Qualifiers());
 
   ExprResult NewInit = SubstInitializer(OldInit, TemplateArgs,
                                         /*CXXDirectInit=*/false);
   Expr *Init = NewInit.get();
   assert((!Init || !isa<ParenListExpr>(Init)) && "call-style init in class");
   ActOnFinishCXXInClassMemberInitializer(
       Instantiation, Init ? Init->getBeginLoc() : SourceLocation(), Init);
 
   if (auto *L = getASTMutationListener())
     L->DefaultMemberInitializerInstantiated(Instantiation);
 
   // Return true if the in-class initializer is still missing.
   return !Instantiation->getInClassInitializer();
 }
 
 namespace {
   /// A partial specialization whose template arguments have matched
   /// a given template-id.
   struct PartialSpecMatchResult {
     ClassTemplatePartialSpecializationDecl *Partial;
     TemplateArgumentList *Args;
   };
 }
 
 bool Sema::usesPartialOrExplicitSpecialization(
     SourceLocation Loc, ClassTemplateSpecializationDecl *ClassTemplateSpec) {
   if (ClassTemplateSpec->getTemplateSpecializationKind() ==
       TSK_ExplicitSpecialization)
     return true;
 
   SmallVector<ClassTemplatePartialSpecializationDecl *, 4> PartialSpecs;
   ClassTemplateSpec->getSpecializedTemplate()
                    ->getPartialSpecializations(PartialSpecs);
   for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I) {
     TemplateDeductionInfo Info(Loc);
     if (DeduceTemplateArguments(PartialSpecs[I],
                                 ClassTemplateSpec->getTemplateArgs().asArray(),
                                 Info) == TemplateDeductionResult::Success)
       return true;
   }
 
   return false;
 }
 
 /// Get the instantiation pattern to use to instantiate the definition of a
 /// given ClassTemplateSpecializationDecl (either the pattern of the primary
 /// template or of a partial specialization).
 static ActionResult<CXXRecordDecl *>
 getPatternForClassTemplateSpecialization(
     Sema &S, SourceLocation PointOfInstantiation,
     ClassTemplateSpecializationDecl *ClassTemplateSpec,
     TemplateSpecializationKind TSK) {
   Sema::InstantiatingTemplate Inst(S, PointOfInstantiation, ClassTemplateSpec);
   if (Inst.isInvalid())
     return {/*Invalid=*/true};
   if (Inst.isAlreadyInstantiating())
     return {/*Invalid=*/false};
 
   llvm::PointerUnion<ClassTemplateDecl *,
                      ClassTemplatePartialSpecializationDecl *>
       Specialized = ClassTemplateSpec->getSpecializedTemplateOrPartial();
   if (!Specialized.is<ClassTemplatePartialSpecializationDecl *>()) {
     // Find best matching specialization.
     ClassTemplateDecl *Template = ClassTemplateSpec->getSpecializedTemplate();
 
     // C++ [temp.class.spec.match]p1:
     //   When a class template is used in a context that requires an
     //   instantiation of the class, it is necessary to determine
     //   whether the instantiation is to be generated using the primary
     //   template or one of the partial specializations. This is done by
     //   matching the template arguments of the class template
     //   specialization with the template argument lists of the partial
     //   specializations.
     typedef PartialSpecMatchResult MatchResult;
     SmallVector<MatchResult, 4> Matched;
     SmallVector<ClassTemplatePartialSpecializationDecl *, 4> PartialSpecs;
     Template->getPartialSpecializations(PartialSpecs);
     TemplateSpecCandidateSet FailedCandidates(PointOfInstantiation);
     for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I) {
       ClassTemplatePartialSpecializationDecl *Partial = PartialSpecs[I];
       TemplateDeductionInfo Info(FailedCandidates.getLocation());
       if (TemplateDeductionResult Result = S.DeduceTemplateArguments(
               Partial, ClassTemplateSpec->getTemplateArgs().asArray(), Info);
           Result != TemplateDeductionResult::Success) {
         // Store the failed-deduction information for use in diagnostics, later.
         // TODO: Actually use the failed-deduction info?
         FailedCandidates.addCandidate().set(
             DeclAccessPair::make(Template, AS_public), Partial,
             MakeDeductionFailureInfo(S.Context, Result, Info));
         (void)Result;
       } else {
         Matched.push_back(PartialSpecMatchResult());
         Matched.back().Partial = Partial;
         Matched.back().Args = Info.takeCanonical();
       }
     }
 
     // If we're dealing with a member template where the template parameters
     // have been instantiated, this provides the original template parameters
     // from which the member template's parameters were instantiated.
 
     if (Matched.size() >= 1) {
       SmallVectorImpl<MatchResult>::iterator Best = Matched.begin();
       if (Matched.size() == 1) {
         //   -- If exactly one matching specialization is found, the
         //      instantiation is generated from that specialization.
         // We don't need to do anything for this.
       } else {
         //   -- If more than one matching specialization is found, the
         //      partial order rules (14.5.4.2) are used to determine
         //      whether one of the specializations is more specialized
         //      than the others. If none of the specializations is more
         //      specialized than all of the other matching
         //      specializations, then the use of the class template is
         //      ambiguous and the program is ill-formed.
         for (SmallVectorImpl<MatchResult>::iterator P = Best + 1,
                                                  PEnd = Matched.end();
              P != PEnd; ++P) {
           if (S.getMoreSpecializedPartialSpecialization(
                   P->Partial, Best->Partial, PointOfInstantiation) ==
               P->Partial)
             Best = P;
         }
 
         // Determine if the best partial specialization is more specialized than
         // the others.
         bool Ambiguous = false;
         for (SmallVectorImpl<MatchResult>::iterator P = Matched.begin(),
                                                  PEnd = Matched.end();
              P != PEnd; ++P) {
           if (P != Best && S.getMoreSpecializedPartialSpecialization(
                                P->Partial, Best->Partial,
                                PointOfInstantiation) != Best->Partial) {
             Ambiguous = true;
             break;
           }
         }
 
         if (Ambiguous) {
           // Partial ordering did not produce a clear winner. Complain.
           Inst.Clear();
           ClassTemplateSpec->setInvalidDecl();
           S.Diag(PointOfInstantiation,
                  diag::err_partial_spec_ordering_ambiguous)
               << ClassTemplateSpec;
 
           // Print the matching partial specializations.
           for (SmallVectorImpl<MatchResult>::iterator P = Matched.begin(),
                                                    PEnd = Matched.end();
                P != PEnd; ++P)
             S.Diag(P->Partial->getLocation(), diag::note_partial_spec_match)
                 << S.getTemplateArgumentBindingsText(
                        P->Partial->getTemplateParameters(), *P->Args);
 
           return {/*Invalid=*/true};
         }
       }
 
       ClassTemplateSpec->setInstantiationOf(Best->Partial, Best->Args);
     } else {
       //   -- If no matches are found, the instantiation is generated
       //      from the primary template.
     }
   }
 
   CXXRecordDecl *Pattern = nullptr;
   Specialized = ClassTemplateSpec->getSpecializedTemplateOrPartial();
   if (auto *PartialSpec =
           Specialized.dyn_cast<ClassTemplatePartialSpecializationDecl *>()) {
     // Instantiate using the best class template partial specialization.
     while (PartialSpec->getInstantiatedFromMember()) {
       // If we've found an explicit specialization of this class template,
       // stop here and use that as the pattern.
       if (PartialSpec->isMemberSpecialization())
         break;
 
       PartialSpec = PartialSpec->getInstantiatedFromMember();
     }
     Pattern = PartialSpec;
   } else {
     ClassTemplateDecl *Template = ClassTemplateSpec->getSpecializedTemplate();
     while (Template->getInstantiatedFromMemberTemplate()) {
       // If we've found an explicit specialization of this class template,
       // stop here and use that as the pattern.
       if (Template->isMemberSpecialization())
         break;
 
       Template = Template->getInstantiatedFromMemberTemplate();
     }
     Pattern = Template->getTemplatedDecl();
   }
 
   return Pattern;
 }
 
 bool Sema::InstantiateClassTemplateSpecialization(
     SourceLocation PointOfInstantiation,
     ClassTemplateSpecializationDecl *ClassTemplateSpec,
     TemplateSpecializationKind TSK, bool Complain) {
   // Perform the actual instantiation on the canonical declaration.
   ClassTemplateSpec = cast<ClassTemplateSpecializationDecl>(
       ClassTemplateSpec->getCanonicalDecl());
   if (ClassTemplateSpec->isInvalidDecl())
     return true;
 
   ActionResult<CXXRecordDecl *> Pattern =
       getPatternForClassTemplateSpecialization(*this, PointOfInstantiation,
                                                ClassTemplateSpec, TSK);
   if (!Pattern.isUsable())
     return Pattern.isInvalid();
 
   return InstantiateClass(
       PointOfInstantiation, ClassTemplateSpec, Pattern.get(),
       getTemplateInstantiationArgs(ClassTemplateSpec), TSK, Complain);
 }
 
 void
 Sema::InstantiateClassMembers(SourceLocation PointOfInstantiation,
                               CXXRecordDecl *Instantiation,
                         const MultiLevelTemplateArgumentList &TemplateArgs,
                               TemplateSpecializationKind TSK) {
   // FIXME: We need to notify the ASTMutationListener that we did all of these
   // things, in case we have an explicit instantiation definition in a PCM, a
   // module, or preamble, and the declaration is in an imported AST.
   assert(
       (TSK == TSK_ExplicitInstantiationDefinition ||
        TSK == TSK_ExplicitInstantiationDeclaration ||
        (TSK == TSK_ImplicitInstantiation && Instantiation->isLocalClass())) &&
       "Unexpected template specialization kind!");
   for (auto *D : Instantiation->decls()) {
     bool SuppressNew = false;
     if (auto *Function = dyn_cast<FunctionDecl>(D)) {
       if (FunctionDecl *Pattern =
               Function->getInstantiatedFromMemberFunction()) {
 
         if (Function->isIneligibleOrNotSelected())
           continue;
 
         if (Function->getTrailingRequiresClause()) {
           ConstraintSatisfaction Satisfaction;
           if (CheckFunctionConstraints(Function, Satisfaction) ||
               !Satisfaction.IsSatisfied) {
             continue;
           }
         }
 
         if (Function->hasAttr<ExcludeFromExplicitInstantiationAttr>())
           continue;
 
         MemberSpecializationInfo *MSInfo =
             Function->getMemberSpecializationInfo();
         assert(MSInfo && "No member specialization information?");
         if (MSInfo->getTemplateSpecializationKind()
                                                  == TSK_ExplicitSpecialization)
           continue;
 
         if (CheckSpecializationInstantiationRedecl(PointOfInstantiation, TSK,
                                                    Function,
                                         MSInfo->getTemplateSpecializationKind(),
                                               MSInfo->getPointOfInstantiation(),
                                                    SuppressNew) ||
             SuppressNew)
           continue;
 
         // C++11 [temp.explicit]p8:
         //   An explicit instantiation definition that names a class template
         //   specialization explicitly instantiates the class template
         //   specialization and is only an explicit instantiation definition
         //   of members whose definition is visible at the point of
         //   instantiation.
         if (TSK == TSK_ExplicitInstantiationDefinition && !Pattern->isDefined())
           continue;
 
         Function->setTemplateSpecializationKind(TSK, PointOfInstantiation);
 
         if (Function->isDefined()) {
           // Let the ASTConsumer know that this function has been explicitly
           // instantiated now, and its linkage might have changed.
           Consumer.HandleTopLevelDecl(DeclGroupRef(Function));
         } else if (TSK == TSK_ExplicitInstantiationDefinition) {
           InstantiateFunctionDefinition(PointOfInstantiation, Function);
         } else if (TSK == TSK_ImplicitInstantiation) {
           PendingLocalImplicitInstantiations.push_back(
               std::make_pair(Function, PointOfInstantiation));
         }
       }
     } else if (auto *Var = dyn_cast<VarDecl>(D)) {
       if (isa<VarTemplateSpecializationDecl>(Var))
         continue;
 
       if (Var->isStaticDataMember()) {
         if (Var->hasAttr<ExcludeFromExplicitInstantiationAttr>())
           continue;
 
         MemberSpecializationInfo *MSInfo = Var->getMemberSpecializationInfo();
         assert(MSInfo && "No member specialization information?");
         if (MSInfo->getTemplateSpecializationKind()
                                                  == TSK_ExplicitSpecialization)
           continue;
 
         if (CheckSpecializationInstantiationRedecl(PointOfInstantiation, TSK,
                                                    Var,
                                         MSInfo->getTemplateSpecializationKind(),
                                               MSInfo->getPointOfInstantiation(),
                                                    SuppressNew) ||
             SuppressNew)
           continue;
 
         if (TSK == TSK_ExplicitInstantiationDefinition) {
           // C++0x [temp.explicit]p8:
           //   An explicit instantiation definition that names a class template
           //   specialization explicitly instantiates the class template
           //   specialization and is only an explicit instantiation definition
           //   of members whose definition is visible at the point of
           //   instantiation.
           if (!Var->getInstantiatedFromStaticDataMember()->getDefinition())
             continue;
 
           Var->setTemplateSpecializationKind(TSK, PointOfInstantiation);
           InstantiateVariableDefinition(PointOfInstantiation, Var);
         } else {
           Var->setTemplateSpecializationKind(TSK, PointOfInstantiation);
         }
       }
     } else if (auto *Record = dyn_cast<CXXRecordDecl>(D)) {
       if (Record->hasAttr<ExcludeFromExplicitInstantiationAttr>())
         continue;
 
       // Always skip the injected-class-name, along with any
       // redeclarations of nested classes, since both would cause us
       // to try to instantiate the members of a class twice.
       // Skip closure types; they'll get instantiated when we instantiate
       // the corresponding lambda-expression.
       if (Record->isInjectedClassName() || Record->getPreviousDecl() ||
           Record->isLambda())
         continue;
 
       MemberSpecializationInfo *MSInfo = Record->getMemberSpecializationInfo();
       assert(MSInfo && "No member specialization information?");
 
       if (MSInfo->getTemplateSpecializationKind()
                                                 == TSK_ExplicitSpecialization)
         continue;
 
       if (Context.getTargetInfo().getTriple().isOSWindows() &&
           TSK == TSK_ExplicitInstantiationDeclaration) {
         // On Windows, explicit instantiation decl of the outer class doesn't
         // affect the inner class. Typically extern template declarations are
         // used in combination with dll import/export annotations, but those
         // are not propagated from the outer class templates to inner classes.
         // Therefore, do not instantiate inner classes on this platform, so
         // that users don't end up with undefined symbols during linking.
         continue;
       }
 
       if (CheckSpecializationInstantiationRedecl(PointOfInstantiation, TSK,
                                                  Record,
                                         MSInfo->getTemplateSpecializationKind(),
                                               MSInfo->getPointOfInstantiation(),
                                                  SuppressNew) ||
           SuppressNew)
         continue;
 
       CXXRecordDecl *Pattern = Record->getInstantiatedFromMemberClass();
       assert(Pattern && "Missing instantiated-from-template information");
 
       if (!Record->getDefinition()) {
         if (!Pattern->getDefinition()) {
           // C++0x [temp.explicit]p8:
           //   An explicit instantiation definition that names a class template
           //   specialization explicitly instantiates the class template
           //   specialization and is only an explicit instantiation definition
           //   of members whose definition is visible at the point of
           //   instantiation.
           if (TSK == TSK_ExplicitInstantiationDeclaration) {
             MSInfo->setTemplateSpecializationKind(TSK);
             MSInfo->setPointOfInstantiation(PointOfInstantiation);
           }
 
           continue;
         }
 
         InstantiateClass(PointOfInstantiation, Record, Pattern,
                          TemplateArgs,
                          TSK);
       } else {
         if (TSK == TSK_ExplicitInstantiationDefinition &&
             Record->getTemplateSpecializationKind() ==
                 TSK_ExplicitInstantiationDeclaration) {
           Record->setTemplateSpecializationKind(TSK);
           MarkVTableUsed(PointOfInstantiation, Record, true);
         }
       }
 
       Pattern = cast_or_null<CXXRecordDecl>(Record->getDefinition());
       if (Pattern)
         InstantiateClassMembers(PointOfInstantiation, Pattern, TemplateArgs,
                                 TSK);
     } else if (auto *Enum = dyn_cast<EnumDecl>(D)) {
       MemberSpecializationInfo *MSInfo = Enum->getMemberSpecializationInfo();
       assert(MSInfo && "No member specialization information?");
 
       if (MSInfo->getTemplateSpecializationKind()
             == TSK_ExplicitSpecialization)
         continue;
 
       if (CheckSpecializationInstantiationRedecl(
             PointOfInstantiation, TSK, Enum,
             MSInfo->getTemplateSpecializationKind(),
             MSInfo->getPointOfInstantiation(), SuppressNew) ||
           SuppressNew)
         continue;
 
       if (Enum->getDefinition())
         continue;
 
       EnumDecl *Pattern = Enum->getTemplateInstantiationPattern();
       assert(Pattern && "Missing instantiated-from-template information");
 
       if (TSK == TSK_ExplicitInstantiationDefinition) {
         if (!Pattern->getDefinition())
           continue;
 
         InstantiateEnum(PointOfInstantiation, Enum, Pattern, TemplateArgs, TSK);
       } else {
         MSInfo->setTemplateSpecializationKind(TSK);
         MSInfo->setPointOfInstantiation(PointOfInstantiation);
       }
     } else if (auto *Field = dyn_cast<FieldDecl>(D)) {
       // No need to instantiate in-class initializers during explicit
       // instantiation.
       if (Field->hasInClassInitializer() && TSK == TSK_ImplicitInstantiation) {
         CXXRecordDecl *ClassPattern =
             Instantiation->getTemplateInstantiationPattern();
         DeclContext::lookup_result Lookup =
             ClassPattern->lookup(Field->getDeclName());
         FieldDecl *Pattern = Lookup.find_first<FieldDecl>();
         assert(Pattern);
         InstantiateInClassInitializer(PointOfInstantiation, Field, Pattern,
                                       TemplateArgs);
       }
     }
   }
 }
 
 void
 Sema::InstantiateClassTemplateSpecializationMembers(
                                            SourceLocation PointOfInstantiation,
                             ClassTemplateSpecializationDecl *ClassTemplateSpec,
                                                TemplateSpecializationKind TSK) {
   // C++0x [temp.explicit]p7:
   //   An explicit instantiation that names a class template
   //   specialization is an explicit instantion of the same kind
   //   (declaration or definition) of each of its members (not
   //   including members inherited from base classes) that has not
   //   been previously explicitly specialized in the translation unit
   //   containing the explicit instantiation, except as described
   //   below.
   InstantiateClassMembers(PointOfInstantiation, ClassTemplateSpec,
                           getTemplateInstantiationArgs(ClassTemplateSpec),
                           TSK);
 }
 
 StmtResult
 Sema::SubstStmt(Stmt *S, const MultiLevelTemplateArgumentList &TemplateArgs) {
   if (!S)
     return S;
 
   TemplateInstantiator Instantiator(*this, TemplateArgs,
                                     SourceLocation(),
                                     DeclarationName());
   return Instantiator.TransformStmt(S);
 }
 
 bool Sema::SubstTemplateArgument(
     const TemplateArgumentLoc &Input,
     const MultiLevelTemplateArgumentList &TemplateArgs,
     TemplateArgumentLoc &Output, SourceLocation Loc,
     const DeclarationName &Entity) {
   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc, Entity);
   return Instantiator.TransformTemplateArgument(Input, Output);
 }
 
 bool Sema::SubstTemplateArguments(
     ArrayRef<TemplateArgumentLoc> Args,
     const MultiLevelTemplateArgumentList &TemplateArgs,
     TemplateArgumentListInfo &Out) {
   TemplateInstantiator Instantiator(*this, TemplateArgs, SourceLocation(),
                                     DeclarationName());
   return Instantiator.TransformTemplateArguments(Args.begin(), Args.end(), Out);
 }
 
 ExprResult
 Sema::SubstExpr(Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs) {
   if (!E)
     return E;
 
   TemplateInstantiator Instantiator(*this, TemplateArgs,
                                     SourceLocation(),
                                     DeclarationName());
   return Instantiator.TransformExpr(E);
 }
 
 ExprResult
 Sema::SubstConstraintExpr(Expr *E,
                           const MultiLevelTemplateArgumentList &TemplateArgs) {
   // FIXME: should call SubstExpr directly if this function is equivalent or
   //        should it be different?
   return SubstExpr(E, TemplateArgs);
 }
 
 ExprResult Sema::SubstConstraintExprWithoutSatisfaction(
     Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs) {
   if (!E)
     return E;
 
   TemplateInstantiator Instantiator(*this, TemplateArgs, SourceLocation(),
                                     DeclarationName());
   Instantiator.setEvaluateConstraints(false);
   return Instantiator.TransformExpr(E);
 }
 
 ExprResult Sema::SubstInitializer(Expr *Init,
                           const MultiLevelTemplateArgumentList &TemplateArgs,
                           bool CXXDirectInit) {
   TemplateInstantiator Instantiator(*this, TemplateArgs, SourceLocation(),
                                     DeclarationName());
   return Instantiator.TransformInitializer(Init, CXXDirectInit);
 }
 
 bool Sema::SubstExprs(ArrayRef<Expr *> Exprs, bool IsCall,
                       const MultiLevelTemplateArgumentList &TemplateArgs,
                       SmallVectorImpl<Expr *> &Outputs) {
   if (Exprs.empty())
     return false;
 
   TemplateInstantiator Instantiator(*this, TemplateArgs,
                                     SourceLocation(),
                                     DeclarationName());
   return Instantiator.TransformExprs(Exprs.data(), Exprs.size(),
                                      IsCall, Outputs);
 }
 
 NestedNameSpecifierLoc
 Sema::SubstNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS,
                         const MultiLevelTemplateArgumentList &TemplateArgs) {
   if (!NNS)
     return NestedNameSpecifierLoc();
 
   TemplateInstantiator Instantiator(*this, TemplateArgs, NNS.getBeginLoc(),
                                     DeclarationName());
   return Instantiator.TransformNestedNameSpecifierLoc(NNS);
 }
 
 DeclarationNameInfo
 Sema::SubstDeclarationNameInfo(const DeclarationNameInfo &NameInfo,
                          const MultiLevelTemplateArgumentList &TemplateArgs) {
   TemplateInstantiator Instantiator(*this, TemplateArgs, NameInfo.getLoc(),
                                     NameInfo.getName());
   return Instantiator.TransformDeclarationNameInfo(NameInfo);
 }
 
 TemplateName
 Sema::SubstTemplateName(NestedNameSpecifierLoc QualifierLoc,
                         TemplateName Name, SourceLocation Loc,
                         const MultiLevelTemplateArgumentList &TemplateArgs) {
   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc,
                                     DeclarationName());
   CXXScopeSpec SS;
   SS.Adopt(QualifierLoc);
   return Instantiator.TransformTemplateName(SS, Name, Loc);
 }
 
 static const Decl *getCanonicalParmVarDecl(const Decl *D) {
   // When storing ParmVarDecls in the local instantiation scope, we always
   // want to use the ParmVarDecl from the canonical function declaration,
   // since the map is then valid for any redeclaration or definition of that
   // function.
   if (const ParmVarDecl *PV = dyn_cast<ParmVarDecl>(D)) {
     if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(PV->getDeclContext())) {
       unsigned i = PV->getFunctionScopeIndex();
       // This parameter might be from a freestanding function type within the
       // function and isn't necessarily referring to one of FD's parameters.
       if (i < FD->getNumParams() && FD->getParamDecl(i) == PV)
         return FD->getCanonicalDecl()->getParamDecl(i);
     }
   }
   return D;
 }
 
 
 llvm::PointerUnion<Decl *, LocalInstantiationScope::DeclArgumentPack *> *
 LocalInstantiationScope::findInstantiationOf(const Decl *D) {
   D = getCanonicalParmVarDecl(D);
   for (LocalInstantiationScope *Current = this; Current;
        Current = Current->Outer) {
 
     // Check if we found something within this scope.
     const Decl *CheckD = D;
     do {
       LocalDeclsMap::iterator Found = Current->LocalDecls.find(CheckD);
       if (Found != Current->LocalDecls.end())
         return &Found->second;
 
       // If this is a tag declaration, it's possible that we need to look for
       // a previous declaration.
       if (const TagDecl *Tag = dyn_cast<TagDecl>(CheckD))
         CheckD = Tag->getPreviousDecl();
       else
         CheckD = nullptr;
     } while (CheckD);
 
     // If we aren't combined with our outer scope, we're done.
     if (!Current->CombineWithOuterScope)
       break;
   }
 
   // If we're performing a partial substitution during template argument
   // deduction, we may not have values for template parameters yet.
   if (isa<NonTypeTemplateParmDecl>(D) || isa<TemplateTypeParmDecl>(D) ||
       isa<TemplateTemplateParmDecl>(D))
     return nullptr;
 
   // Local types referenced prior to definition may require instantiation.
   if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D))
     if (RD->isLocalClass())
       return nullptr;
 
   // Enumeration types referenced prior to definition may appear as a result of
   // error recovery.
   if (isa<EnumDecl>(D))
     return nullptr;
 
   // Materialized typedefs/type alias for implicit deduction guides may require
   // instantiation.
   if (isa<TypedefNameDecl>(D) &&
       isa<CXXDeductionGuideDecl>(D->getDeclContext()))
     return nullptr;
 
   // If we didn't find the decl, then we either have a sema bug, or we have a
   // forward reference to a label declaration.  Return null to indicate that
   // we have an uninstantiated label.
   assert(isa<LabelDecl>(D) && "declaration not instantiated in this scope");
   return nullptr;
 }
 
 void LocalInstantiationScope::InstantiatedLocal(const Decl *D, Decl *Inst) {
   D = getCanonicalParmVarDecl(D);
   llvm::PointerUnion<Decl *, DeclArgumentPack *> &Stored = LocalDecls[D];
   if (Stored.isNull()) {
 #ifndef NDEBUG
     // It should not be present in any surrounding scope either.
     LocalInstantiationScope *Current = this;
     while (Current->CombineWithOuterScope && Current->Outer) {
       Current = Current->Outer;
       assert(!Current->LocalDecls.contains(D) &&
              "Instantiated local in inner and outer scopes");
     }
 #endif
     Stored = Inst;
   } else if (DeclArgumentPack *Pack = Stored.dyn_cast<DeclArgumentPack *>()) {
     Pack->push_back(cast<VarDecl>(Inst));
   } else {
     assert(Stored.get<Decl *>() == Inst && "Already instantiated this local");
   }
 }
 
 void LocalInstantiationScope::InstantiatedLocalPackArg(const Decl *D,
                                                        VarDecl *Inst) {
   D = getCanonicalParmVarDecl(D);
   DeclArgumentPack *Pack = LocalDecls[D].get<DeclArgumentPack *>();
   Pack->push_back(Inst);
 }
 
 void LocalInstantiationScope::MakeInstantiatedLocalArgPack(const Decl *D) {
 #ifndef NDEBUG
   // This should be the first time we've been told about this decl.
   for (LocalInstantiationScope *Current = this;
        Current && Current->CombineWithOuterScope; Current = Current->Outer)
     assert(!Current->LocalDecls.contains(D) &&
            "Creating local pack after instantiation of local");
 #endif
 
   D = getCanonicalParmVarDecl(D);
   llvm::PointerUnion<Decl *, DeclArgumentPack *> &Stored = LocalDecls[D];
   DeclArgumentPack *Pack = new DeclArgumentPack;
   Stored = Pack;
   ArgumentPacks.push_back(Pack);
 }
 
 bool LocalInstantiationScope::isLocalPackExpansion(const Decl *D) {
   for (DeclArgumentPack *Pack : ArgumentPacks)
     if (llvm::is_contained(*Pack, D))
       return true;
   return false;
 }
 
 void LocalInstantiationScope::SetPartiallySubstitutedPack(NamedDecl *Pack,
                                           const TemplateArgument *ExplicitArgs,
                                                     unsigned NumExplicitArgs) {
   assert((!PartiallySubstitutedPack || PartiallySubstitutedPack == Pack) &&
          "Already have a partially-substituted pack");
   assert((!PartiallySubstitutedPack
           || NumArgsInPartiallySubstitutedPack == NumExplicitArgs) &&
          "Wrong number of arguments in partially-substituted pack");
   PartiallySubstitutedPack = Pack;
   ArgsInPartiallySubstitutedPack = ExplicitArgs;
   NumArgsInPartiallySubstitutedPack = NumExplicitArgs;
 }
 
 NamedDecl *LocalInstantiationScope::getPartiallySubstitutedPack(
                                          const TemplateArgument **ExplicitArgs,
                                               unsigned *NumExplicitArgs) const {
   if (ExplicitArgs)
     *ExplicitArgs = nullptr;
   if (NumExplicitArgs)
     *NumExplicitArgs = 0;
 
   for (const LocalInstantiationScope *Current = this; Current;
        Current = Current->Outer) {
     if (Current->PartiallySubstitutedPack) {
       if (ExplicitArgs)
         *ExplicitArgs = Current->ArgsInPartiallySubstitutedPack;
       if (NumExplicitArgs)
         *NumExplicitArgs = Current->NumArgsInPartiallySubstitutedPack;
 
       return Current->PartiallySubstitutedPack;
     }
 
     if (!Current->CombineWithOuterScope)
       break;
   }
 
   return nullptr;
 }
diff --git a/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index a12d2eff1d2c..614e6ea12541 100644
--- a/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1,6477 +1,6479 @@
 //===--- SemaTemplateInstantiateDecl.cpp - C++ Template Decl Instantiation ===/
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //===----------------------------------------------------------------------===/
 //
 //  This file implements C++ template instantiation for declarations.
 //
 //===----------------------------------------------------------------------===/
 
 #include "TreeTransform.h"
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTMutationListener.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/DeclVisitor.h"
 #include "clang/AST/DependentDiagnostic.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/PrettyDeclStackTrace.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Sema/EnterExpressionEvaluationContext.h"
 #include "clang/Sema/Initialization.h"
 #include "clang/Sema/Lookup.h"
 #include "clang/Sema/ScopeInfo.h"
 #include "clang/Sema/SemaAMDGPU.h"
 #include "clang/Sema/SemaCUDA.h"
 #include "clang/Sema/SemaInternal.h"
 #include "clang/Sema/SemaObjC.h"
 #include "clang/Sema/SemaOpenMP.h"
 #include "clang/Sema/SemaSwift.h"
 #include "clang/Sema/Template.h"
 #include "clang/Sema/TemplateInstCallback.h"
 #include "llvm/Support/TimeProfiler.h"
 #include <optional>
 
 using namespace clang;
 
 static bool isDeclWithinFunction(const Decl *D) {
   const DeclContext *DC = D->getDeclContext();
   if (DC->isFunctionOrMethod())
     return true;
 
   if (DC->isRecord())
     return cast<CXXRecordDecl>(DC)->isLocalClass();
 
   return false;
 }
 
 template<typename DeclT>
 static bool SubstQualifier(Sema &SemaRef, const DeclT *OldDecl, DeclT *NewDecl,
                            const MultiLevelTemplateArgumentList &TemplateArgs) {
   if (!OldDecl->getQualifierLoc())
     return false;
 
   assert((NewDecl->getFriendObjectKind() ||
           !OldDecl->getLexicalDeclContext()->isDependentContext()) &&
          "non-friend with qualified name defined in dependent context");
   Sema::ContextRAII SavedContext(
       SemaRef,
       const_cast<DeclContext *>(NewDecl->getFriendObjectKind()
                                     ? NewDecl->getLexicalDeclContext()
                                     : OldDecl->getLexicalDeclContext()));
 
   NestedNameSpecifierLoc NewQualifierLoc
       = SemaRef.SubstNestedNameSpecifierLoc(OldDecl->getQualifierLoc(),
                                             TemplateArgs);
 
   if (!NewQualifierLoc)
     return true;
 
   NewDecl->setQualifierInfo(NewQualifierLoc);
   return false;
 }
 
 bool TemplateDeclInstantiator::SubstQualifier(const DeclaratorDecl *OldDecl,
                                               DeclaratorDecl *NewDecl) {
   return ::SubstQualifier(SemaRef, OldDecl, NewDecl, TemplateArgs);
 }
 
 bool TemplateDeclInstantiator::SubstQualifier(const TagDecl *OldDecl,
                                               TagDecl *NewDecl) {
   return ::SubstQualifier(SemaRef, OldDecl, NewDecl, TemplateArgs);
 }
 
 // Include attribute instantiation code.
 #include "clang/Sema/AttrTemplateInstantiate.inc"
 
 static void instantiateDependentAlignedAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const AlignedAttr *Aligned, Decl *New, bool IsPackExpansion) {
   if (Aligned->isAlignmentExpr()) {
     // The alignment expression is a constant expression.
     EnterExpressionEvaluationContext Unevaluated(
         S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     ExprResult Result = S.SubstExpr(Aligned->getAlignmentExpr(), TemplateArgs);
     if (!Result.isInvalid())
       S.AddAlignedAttr(New, *Aligned, Result.getAs<Expr>(), IsPackExpansion);
   } else {
     if (TypeSourceInfo *Result =
             S.SubstType(Aligned->getAlignmentType(), TemplateArgs,
                         Aligned->getLocation(), DeclarationName())) {
       if (!S.CheckAlignasTypeArgument(Aligned->getSpelling(), Result,
                                       Aligned->getLocation(),
                                       Result->getTypeLoc().getSourceRange()))
         S.AddAlignedAttr(New, *Aligned, Result, IsPackExpansion);
     }
   }
 }
 
 static void instantiateDependentAlignedAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const AlignedAttr *Aligned, Decl *New) {
   if (!Aligned->isPackExpansion()) {
     instantiateDependentAlignedAttr(S, TemplateArgs, Aligned, New, false);
     return;
   }
 
   SmallVector<UnexpandedParameterPack, 2> Unexpanded;
   if (Aligned->isAlignmentExpr())
     S.collectUnexpandedParameterPacks(Aligned->getAlignmentExpr(),
                                       Unexpanded);
   else
     S.collectUnexpandedParameterPacks(Aligned->getAlignmentType()->getTypeLoc(),
                                       Unexpanded);
   assert(!Unexpanded.empty() && "Pack expansion without parameter packs?");
 
   // Determine whether we can expand this attribute pack yet.
   bool Expand = true, RetainExpansion = false;
   std::optional<unsigned> NumExpansions;
   // FIXME: Use the actual location of the ellipsis.
   SourceLocation EllipsisLoc = Aligned->getLocation();
   if (S.CheckParameterPacksForExpansion(EllipsisLoc, Aligned->getRange(),
                                         Unexpanded, TemplateArgs, Expand,
                                         RetainExpansion, NumExpansions))
     return;
 
   if (!Expand) {
     Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(S, -1);
     instantiateDependentAlignedAttr(S, TemplateArgs, Aligned, New, true);
   } else {
     for (unsigned I = 0; I != *NumExpansions; ++I) {
       Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(S, I);
       instantiateDependentAlignedAttr(S, TemplateArgs, Aligned, New, false);
     }
   }
 }
 
 static void instantiateDependentAssumeAlignedAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const AssumeAlignedAttr *Aligned, Decl *New) {
   // The alignment expression is a constant expression.
   EnterExpressionEvaluationContext Unevaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
   Expr *E, *OE = nullptr;
   ExprResult Result = S.SubstExpr(Aligned->getAlignment(), TemplateArgs);
   if (Result.isInvalid())
     return;
   E = Result.getAs<Expr>();
 
   if (Aligned->getOffset()) {
     Result = S.SubstExpr(Aligned->getOffset(), TemplateArgs);
     if (Result.isInvalid())
       return;
     OE = Result.getAs<Expr>();
   }
 
   S.AddAssumeAlignedAttr(New, *Aligned, E, OE);
 }
 
 static void instantiateDependentAlignValueAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const AlignValueAttr *Aligned, Decl *New) {
   // The alignment expression is a constant expression.
   EnterExpressionEvaluationContext Unevaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
   ExprResult Result = S.SubstExpr(Aligned->getAlignment(), TemplateArgs);
   if (!Result.isInvalid())
     S.AddAlignValueAttr(New, *Aligned, Result.getAs<Expr>());
 }
 
 static void instantiateDependentAllocAlignAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const AllocAlignAttr *Align, Decl *New) {
   Expr *Param = IntegerLiteral::Create(
       S.getASTContext(),
       llvm::APInt(64, Align->getParamIndex().getSourceIndex()),
       S.getASTContext().UnsignedLongLongTy, Align->getLocation());
   S.AddAllocAlignAttr(New, *Align, Param);
 }
 
 static void instantiateDependentAnnotationAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const AnnotateAttr *Attr, Decl *New) {
   EnterExpressionEvaluationContext Unevaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
   // If the attribute has delayed arguments it will have to instantiate those
   // and handle them as new arguments for the attribute.
   bool HasDelayedArgs = Attr->delayedArgs_size();
 
   ArrayRef<Expr *> ArgsToInstantiate =
       HasDelayedArgs
           ? ArrayRef<Expr *>{Attr->delayedArgs_begin(), Attr->delayedArgs_end()}
           : ArrayRef<Expr *>{Attr->args_begin(), Attr->args_end()};
 
   SmallVector<Expr *, 4> Args;
   if (S.SubstExprs(ArgsToInstantiate,
                    /*IsCall=*/false, TemplateArgs, Args))
     return;
 
   StringRef Str = Attr->getAnnotation();
   if (HasDelayedArgs) {
     if (Args.size() < 1) {
       S.Diag(Attr->getLoc(), diag::err_attribute_too_few_arguments)
           << Attr << 1;
       return;
     }
 
     if (!S.checkStringLiteralArgumentAttr(*Attr, Args[0], Str))
       return;
 
     llvm::SmallVector<Expr *, 4> ActualArgs;
     ActualArgs.insert(ActualArgs.begin(), Args.begin() + 1, Args.end());
     std::swap(Args, ActualArgs);
   }
   S.AddAnnotationAttr(New, *Attr, Str, Args);
 }
 
 static Expr *instantiateDependentFunctionAttrCondition(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const Attr *A, Expr *OldCond, const Decl *Tmpl, FunctionDecl *New) {
   Expr *Cond = nullptr;
   {
     Sema::ContextRAII SwitchContext(S, New);
     EnterExpressionEvaluationContext Unevaluated(
         S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     ExprResult Result = S.SubstExpr(OldCond, TemplateArgs);
     if (Result.isInvalid())
       return nullptr;
     Cond = Result.getAs<Expr>();
   }
   if (!Cond->isTypeDependent()) {
     ExprResult Converted = S.PerformContextuallyConvertToBool(Cond);
     if (Converted.isInvalid())
       return nullptr;
     Cond = Converted.get();
   }
 
   SmallVector<PartialDiagnosticAt, 8> Diags;
   if (OldCond->isValueDependent() && !Cond->isValueDependent() &&
       !Expr::isPotentialConstantExprUnevaluated(Cond, New, Diags)) {
     S.Diag(A->getLocation(), diag::err_attr_cond_never_constant_expr) << A;
     for (const auto &P : Diags)
       S.Diag(P.first, P.second);
     return nullptr;
   }
   return Cond;
 }
 
 static void instantiateDependentEnableIfAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const EnableIfAttr *EIA, const Decl *Tmpl, FunctionDecl *New) {
   Expr *Cond = instantiateDependentFunctionAttrCondition(
       S, TemplateArgs, EIA, EIA->getCond(), Tmpl, New);
 
   if (Cond)
     New->addAttr(new (S.getASTContext()) EnableIfAttr(S.getASTContext(), *EIA,
                                                       Cond, EIA->getMessage()));
 }
 
 static void instantiateDependentDiagnoseIfAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const DiagnoseIfAttr *DIA, const Decl *Tmpl, FunctionDecl *New) {
   Expr *Cond = instantiateDependentFunctionAttrCondition(
       S, TemplateArgs, DIA, DIA->getCond(), Tmpl, New);
 
   if (Cond)
     New->addAttr(new (S.getASTContext()) DiagnoseIfAttr(
         S.getASTContext(), *DIA, Cond, DIA->getMessage(),
         DIA->getDiagnosticType(), DIA->getArgDependent(), New));
 }
 
 // Constructs and adds to New a new instance of CUDALaunchBoundsAttr using
 // template A as the base and arguments from TemplateArgs.
 static void instantiateDependentCUDALaunchBoundsAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const CUDALaunchBoundsAttr &Attr, Decl *New) {
   // The alignment expression is a constant expression.
   EnterExpressionEvaluationContext Unevaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
   ExprResult Result = S.SubstExpr(Attr.getMaxThreads(), TemplateArgs);
   if (Result.isInvalid())
     return;
   Expr *MaxThreads = Result.getAs<Expr>();
 
   Expr *MinBlocks = nullptr;
   if (Attr.getMinBlocks()) {
     Result = S.SubstExpr(Attr.getMinBlocks(), TemplateArgs);
     if (Result.isInvalid())
       return;
     MinBlocks = Result.getAs<Expr>();
   }
 
   Expr *MaxBlocks = nullptr;
   if (Attr.getMaxBlocks()) {
     Result = S.SubstExpr(Attr.getMaxBlocks(), TemplateArgs);
     if (Result.isInvalid())
       return;
     MaxBlocks = Result.getAs<Expr>();
   }
 
   S.AddLaunchBoundsAttr(New, Attr, MaxThreads, MinBlocks, MaxBlocks);
 }
 
 static void
 instantiateDependentModeAttr(Sema &S,
                              const MultiLevelTemplateArgumentList &TemplateArgs,
                              const ModeAttr &Attr, Decl *New) {
   S.AddModeAttr(New, Attr, Attr.getMode(),
                 /*InInstantiation=*/true);
 }
 
 /// Instantiation of 'declare simd' attribute and its arguments.
 static void instantiateOMPDeclareSimdDeclAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const OMPDeclareSimdDeclAttr &Attr, Decl *New) {
   // Allow 'this' in clauses with varlists.
   if (auto *FTD = dyn_cast<FunctionTemplateDecl>(New))
     New = FTD->getTemplatedDecl();
   auto *FD = cast<FunctionDecl>(New);
   auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(FD->getDeclContext());
   SmallVector<Expr *, 4> Uniforms, Aligneds, Alignments, Linears, Steps;
   SmallVector<unsigned, 4> LinModifiers;
 
   auto SubstExpr = [&](Expr *E) -> ExprResult {
     if (auto *DRE = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts()))
       if (auto *PVD = dyn_cast<ParmVarDecl>(DRE->getDecl())) {
         Sema::ContextRAII SavedContext(S, FD);
         LocalInstantiationScope Local(S);
         if (FD->getNumParams() > PVD->getFunctionScopeIndex())
           Local.InstantiatedLocal(
               PVD, FD->getParamDecl(PVD->getFunctionScopeIndex()));
         return S.SubstExpr(E, TemplateArgs);
       }
     Sema::CXXThisScopeRAII ThisScope(S, ThisContext, Qualifiers(),
                                      FD->isCXXInstanceMember());
     return S.SubstExpr(E, TemplateArgs);
   };
 
   // Substitute a single OpenMP clause, which is a potentially-evaluated
   // full-expression.
   auto Subst = [&](Expr *E) -> ExprResult {
     EnterExpressionEvaluationContext Evaluated(
         S, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
     ExprResult Res = SubstExpr(E);
     if (Res.isInvalid())
       return Res;
     return S.ActOnFinishFullExpr(Res.get(), false);
   };
 
   ExprResult Simdlen;
   if (auto *E = Attr.getSimdlen())
     Simdlen = Subst(E);
 
   if (Attr.uniforms_size() > 0) {
     for(auto *E : Attr.uniforms()) {
       ExprResult Inst = Subst(E);
       if (Inst.isInvalid())
         continue;
       Uniforms.push_back(Inst.get());
     }
   }
 
   auto AI = Attr.alignments_begin();
   for (auto *E : Attr.aligneds()) {
     ExprResult Inst = Subst(E);
     if (Inst.isInvalid())
       continue;
     Aligneds.push_back(Inst.get());
     Inst = ExprEmpty();
     if (*AI)
       Inst = S.SubstExpr(*AI, TemplateArgs);
     Alignments.push_back(Inst.get());
     ++AI;
   }
 
   auto SI = Attr.steps_begin();
   for (auto *E : Attr.linears()) {
     ExprResult Inst = Subst(E);
     if (Inst.isInvalid())
       continue;
     Linears.push_back(Inst.get());
     Inst = ExprEmpty();
     if (*SI)
       Inst = S.SubstExpr(*SI, TemplateArgs);
     Steps.push_back(Inst.get());
     ++SI;
   }
   LinModifiers.append(Attr.modifiers_begin(), Attr.modifiers_end());
   (void)S.OpenMP().ActOnOpenMPDeclareSimdDirective(
       S.ConvertDeclToDeclGroup(New), Attr.getBranchState(), Simdlen.get(),
       Uniforms, Aligneds, Alignments, Linears, LinModifiers, Steps,
       Attr.getRange());
 }
 
 /// Instantiation of 'declare variant' attribute and its arguments.
 static void instantiateOMPDeclareVariantAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const OMPDeclareVariantAttr &Attr, Decl *New) {
   // Allow 'this' in clauses with varlists.
   if (auto *FTD = dyn_cast<FunctionTemplateDecl>(New))
     New = FTD->getTemplatedDecl();
   auto *FD = cast<FunctionDecl>(New);
   auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(FD->getDeclContext());
 
   auto &&SubstExpr = [FD, ThisContext, &S, &TemplateArgs](Expr *E) {
     if (auto *DRE = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts()))
       if (auto *PVD = dyn_cast<ParmVarDecl>(DRE->getDecl())) {
         Sema::ContextRAII SavedContext(S, FD);
         LocalInstantiationScope Local(S);
         if (FD->getNumParams() > PVD->getFunctionScopeIndex())
           Local.InstantiatedLocal(
               PVD, FD->getParamDecl(PVD->getFunctionScopeIndex()));
         return S.SubstExpr(E, TemplateArgs);
       }
     Sema::CXXThisScopeRAII ThisScope(S, ThisContext, Qualifiers(),
                                      FD->isCXXInstanceMember());
     return S.SubstExpr(E, TemplateArgs);
   };
 
   // Substitute a single OpenMP clause, which is a potentially-evaluated
   // full-expression.
   auto &&Subst = [&SubstExpr, &S](Expr *E) {
     EnterExpressionEvaluationContext Evaluated(
         S, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
     ExprResult Res = SubstExpr(E);
     if (Res.isInvalid())
       return Res;
     return S.ActOnFinishFullExpr(Res.get(), false);
   };
 
   ExprResult VariantFuncRef;
   if (Expr *E = Attr.getVariantFuncRef()) {
     // Do not mark function as is used to prevent its emission if this is the
     // only place where it is used.
     EnterExpressionEvaluationContext Unevaluated(
         S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     VariantFuncRef = Subst(E);
   }
 
   // Copy the template version of the OMPTraitInfo and run substitute on all
   // score and condition expressiosn.
   OMPTraitInfo &TI = S.getASTContext().getNewOMPTraitInfo();
   TI = *Attr.getTraitInfos();
 
   // Try to substitute template parameters in score and condition expressions.
   auto SubstScoreOrConditionExpr = [&S, Subst](Expr *&E, bool) {
     if (E) {
       EnterExpressionEvaluationContext Unevaluated(
           S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
       ExprResult ER = Subst(E);
       if (ER.isUsable())
         E = ER.get();
       else
         return true;
     }
     return false;
   };
   if (TI.anyScoreOrCondition(SubstScoreOrConditionExpr))
     return;
 
   Expr *E = VariantFuncRef.get();
 
   // Check function/variant ref for `omp declare variant` but not for `omp
   // begin declare variant` (which use implicit attributes).
   std::optional<std::pair<FunctionDecl *, Expr *>> DeclVarData =
       S.OpenMP().checkOpenMPDeclareVariantFunction(
           S.ConvertDeclToDeclGroup(New), E, TI, Attr.appendArgs_size(),
           Attr.getRange());
 
   if (!DeclVarData)
     return;
 
   E = DeclVarData->second;
   FD = DeclVarData->first;
 
   if (auto *VariantDRE = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts())) {
     if (auto *VariantFD = dyn_cast<FunctionDecl>(VariantDRE->getDecl())) {
       if (auto *VariantFTD = VariantFD->getDescribedFunctionTemplate()) {
         if (!VariantFTD->isThisDeclarationADefinition())
           return;
         Sema::TentativeAnalysisScope Trap(S);
         const TemplateArgumentList *TAL = TemplateArgumentList::CreateCopy(
             S.Context, TemplateArgs.getInnermost());
 
         auto *SubstFD = S.InstantiateFunctionDeclaration(VariantFTD, TAL,
                                                          New->getLocation());
         if (!SubstFD)
           return;
         QualType NewType = S.Context.mergeFunctionTypes(
             SubstFD->getType(), FD->getType(),
             /* OfBlockPointer */ false,
             /* Unqualified */ false, /* AllowCXX */ true);
         if (NewType.isNull())
           return;
         S.InstantiateFunctionDefinition(
             New->getLocation(), SubstFD, /* Recursive */ true,
             /* DefinitionRequired */ false, /* AtEndOfTU */ false);
         SubstFD->setInstantiationIsPending(!SubstFD->isDefined());
         E = DeclRefExpr::Create(S.Context, NestedNameSpecifierLoc(),
                                 SourceLocation(), SubstFD,
                                 /* RefersToEnclosingVariableOrCapture */ false,
                                 /* NameLoc */ SubstFD->getLocation(),
                                 SubstFD->getType(), ExprValueKind::VK_PRValue);
       }
     }
   }
 
   SmallVector<Expr *, 8> NothingExprs;
   SmallVector<Expr *, 8> NeedDevicePtrExprs;
   SmallVector<OMPInteropInfo, 4> AppendArgs;
 
   for (Expr *E : Attr.adjustArgsNothing()) {
     ExprResult ER = Subst(E);
     if (ER.isInvalid())
       continue;
     NothingExprs.push_back(ER.get());
   }
   for (Expr *E : Attr.adjustArgsNeedDevicePtr()) {
     ExprResult ER = Subst(E);
     if (ER.isInvalid())
       continue;
     NeedDevicePtrExprs.push_back(ER.get());
   }
   for (OMPInteropInfo &II : Attr.appendArgs()) {
     // When prefer_type is implemented for append_args handle them here too.
     AppendArgs.emplace_back(II.IsTarget, II.IsTargetSync);
   }
 
   S.OpenMP().ActOnOpenMPDeclareVariantDirective(
       FD, E, TI, NothingExprs, NeedDevicePtrExprs, AppendArgs, SourceLocation(),
       SourceLocation(), Attr.getRange());
 }
 
 static void instantiateDependentAMDGPUFlatWorkGroupSizeAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const AMDGPUFlatWorkGroupSizeAttr &Attr, Decl *New) {
   // Both min and max expression are constant expressions.
   EnterExpressionEvaluationContext Unevaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
   ExprResult Result = S.SubstExpr(Attr.getMin(), TemplateArgs);
   if (Result.isInvalid())
     return;
   Expr *MinExpr = Result.getAs<Expr>();
 
   Result = S.SubstExpr(Attr.getMax(), TemplateArgs);
   if (Result.isInvalid())
     return;
   Expr *MaxExpr = Result.getAs<Expr>();
 
   S.AMDGPU().addAMDGPUFlatWorkGroupSizeAttr(New, Attr, MinExpr, MaxExpr);
 }
 
 ExplicitSpecifier Sema::instantiateExplicitSpecifier(
     const MultiLevelTemplateArgumentList &TemplateArgs, ExplicitSpecifier ES) {
   if (!ES.getExpr())
     return ES;
   Expr *OldCond = ES.getExpr();
   Expr *Cond = nullptr;
   {
     EnterExpressionEvaluationContext Unevaluated(
         *this, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     ExprResult SubstResult = SubstExpr(OldCond, TemplateArgs);
     if (SubstResult.isInvalid()) {
       return ExplicitSpecifier::Invalid();
     }
     Cond = SubstResult.get();
   }
   ExplicitSpecifier Result(Cond, ES.getKind());
   if (!Cond->isTypeDependent())
     tryResolveExplicitSpecifier(Result);
   return Result;
 }
 
 static void instantiateDependentAMDGPUWavesPerEUAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const AMDGPUWavesPerEUAttr &Attr, Decl *New) {
   // Both min and max expression are constant expressions.
   EnterExpressionEvaluationContext Unevaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
   ExprResult Result = S.SubstExpr(Attr.getMin(), TemplateArgs);
   if (Result.isInvalid())
     return;
   Expr *MinExpr = Result.getAs<Expr>();
 
   Expr *MaxExpr = nullptr;
   if (auto Max = Attr.getMax()) {
     Result = S.SubstExpr(Max, TemplateArgs);
     if (Result.isInvalid())
       return;
     MaxExpr = Result.getAs<Expr>();
   }
 
   S.AMDGPU().addAMDGPUWavesPerEUAttr(New, Attr, MinExpr, MaxExpr);
 }
 
 static void instantiateDependentAMDGPUMaxNumWorkGroupsAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const AMDGPUMaxNumWorkGroupsAttr &Attr, Decl *New) {
   EnterExpressionEvaluationContext Unevaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
   ExprResult ResultX = S.SubstExpr(Attr.getMaxNumWorkGroupsX(), TemplateArgs);
   if (!ResultX.isUsable())
     return;
   ExprResult ResultY = S.SubstExpr(Attr.getMaxNumWorkGroupsY(), TemplateArgs);
   if (!ResultY.isUsable())
     return;
   ExprResult ResultZ = S.SubstExpr(Attr.getMaxNumWorkGroupsZ(), TemplateArgs);
   if (!ResultZ.isUsable())
     return;
 
   Expr *XExpr = ResultX.getAs<Expr>();
   Expr *YExpr = ResultY.getAs<Expr>();
   Expr *ZExpr = ResultZ.getAs<Expr>();
 
   S.AMDGPU().addAMDGPUMaxNumWorkGroupsAttr(New, Attr, XExpr, YExpr, ZExpr);
 }
 
 // This doesn't take any template parameters, but we have a custom action that
 // needs to happen when the kernel itself is instantiated. We need to run the
 // ItaniumMangler to mark the names required to name this kernel.
 static void instantiateDependentSYCLKernelAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const SYCLKernelAttr &Attr, Decl *New) {
   New->addAttr(Attr.clone(S.getASTContext()));
 }
 
 /// Determine whether the attribute A might be relevant to the declaration D.
 /// If not, we can skip instantiating it. The attribute may or may not have
 /// been instantiated yet.
 static bool isRelevantAttr(Sema &S, const Decl *D, const Attr *A) {
   // 'preferred_name' is only relevant to the matching specialization of the
   // template.
   if (const auto *PNA = dyn_cast<PreferredNameAttr>(A)) {
     QualType T = PNA->getTypedefType();
     const auto *RD = cast<CXXRecordDecl>(D);
     if (!T->isDependentType() && !RD->isDependentContext() &&
         !declaresSameEntity(T->getAsCXXRecordDecl(), RD))
       return false;
     for (const auto *ExistingPNA : D->specific_attrs<PreferredNameAttr>())
       if (S.Context.hasSameType(ExistingPNA->getTypedefType(),
                                 PNA->getTypedefType()))
         return false;
     return true;
   }
 
   if (const auto *BA = dyn_cast<BuiltinAttr>(A)) {
     const FunctionDecl *FD = dyn_cast<FunctionDecl>(D);
     switch (BA->getID()) {
     case Builtin::BIforward:
       // Do not treat 'std::forward' as a builtin if it takes an rvalue reference
       // type and returns an lvalue reference type. The library implementation
       // will produce an error in this case; don't get in its way.
       if (FD && FD->getNumParams() >= 1 &&
           FD->getParamDecl(0)->getType()->isRValueReferenceType() &&
           FD->getReturnType()->isLValueReferenceType()) {
         return false;
       }
       [[fallthrough]];
     case Builtin::BImove:
     case Builtin::BImove_if_noexcept:
       // HACK: Super-old versions of libc++ (3.1 and earlier) provide
       // std::forward and std::move overloads that sometimes return by value
       // instead of by reference when building in C++98 mode. Don't treat such
       // cases as builtins.
       if (FD && !FD->getReturnType()->isReferenceType())
         return false;
       break;
     }
   }
 
   return true;
 }
 
 static void instantiateDependentHLSLParamModifierAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const HLSLParamModifierAttr *Attr, Decl *New) {
   ParmVarDecl *P = cast<ParmVarDecl>(New);
   P->addAttr(Attr->clone(S.getASTContext()));
   P->setType(S.getASTContext().getLValueReferenceType(P->getType()));
 }
 
 void Sema::InstantiateAttrsForDecl(
     const MultiLevelTemplateArgumentList &TemplateArgs, const Decl *Tmpl,
     Decl *New, LateInstantiatedAttrVec *LateAttrs,
     LocalInstantiationScope *OuterMostScope) {
   if (NamedDecl *ND = dyn_cast<NamedDecl>(New)) {
     // FIXME: This function is called multiple times for the same template
     // specialization. We should only instantiate attributes that were added
     // since the previous instantiation.
     for (const auto *TmplAttr : Tmpl->attrs()) {
       if (!isRelevantAttr(*this, New, TmplAttr))
         continue;
 
       // FIXME: If any of the special case versions from InstantiateAttrs become
       // applicable to template declaration, we'll need to add them here.
       CXXThisScopeRAII ThisScope(
           *this, dyn_cast_or_null<CXXRecordDecl>(ND->getDeclContext()),
           Qualifiers(), ND->isCXXInstanceMember());
 
       Attr *NewAttr = sema::instantiateTemplateAttributeForDecl(
           TmplAttr, Context, *this, TemplateArgs);
       if (NewAttr && isRelevantAttr(*this, New, NewAttr))
         New->addAttr(NewAttr);
     }
   }
 }
 
 static Sema::RetainOwnershipKind
 attrToRetainOwnershipKind(const Attr *A) {
   switch (A->getKind()) {
   case clang::attr::CFConsumed:
     return Sema::RetainOwnershipKind::CF;
   case clang::attr::OSConsumed:
     return Sema::RetainOwnershipKind::OS;
   case clang::attr::NSConsumed:
     return Sema::RetainOwnershipKind::NS;
   default:
     llvm_unreachable("Wrong argument supplied");
   }
 }
 
 void Sema::InstantiateAttrs(const MultiLevelTemplateArgumentList &TemplateArgs,
                             const Decl *Tmpl, Decl *New,
                             LateInstantiatedAttrVec *LateAttrs,
                             LocalInstantiationScope *OuterMostScope) {
   for (const auto *TmplAttr : Tmpl->attrs()) {
     if (!isRelevantAttr(*this, New, TmplAttr))
       continue;
 
     // FIXME: This should be generalized to more than just the AlignedAttr.
     const AlignedAttr *Aligned = dyn_cast<AlignedAttr>(TmplAttr);
     if (Aligned && Aligned->isAlignmentDependent()) {
       instantiateDependentAlignedAttr(*this, TemplateArgs, Aligned, New);
       continue;
     }
 
     if (const auto *AssumeAligned = dyn_cast<AssumeAlignedAttr>(TmplAttr)) {
       instantiateDependentAssumeAlignedAttr(*this, TemplateArgs, AssumeAligned, New);
       continue;
     }
 
     if (const auto *AlignValue = dyn_cast<AlignValueAttr>(TmplAttr)) {
       instantiateDependentAlignValueAttr(*this, TemplateArgs, AlignValue, New);
       continue;
     }
 
     if (const auto *AllocAlign = dyn_cast<AllocAlignAttr>(TmplAttr)) {
       instantiateDependentAllocAlignAttr(*this, TemplateArgs, AllocAlign, New);
       continue;
     }
 
     if (const auto *Annotate = dyn_cast<AnnotateAttr>(TmplAttr)) {
       instantiateDependentAnnotationAttr(*this, TemplateArgs, Annotate, New);
       continue;
     }
 
     if (const auto *EnableIf = dyn_cast<EnableIfAttr>(TmplAttr)) {
       instantiateDependentEnableIfAttr(*this, TemplateArgs, EnableIf, Tmpl,
                                        cast<FunctionDecl>(New));
       continue;
     }
 
     if (const auto *DiagnoseIf = dyn_cast<DiagnoseIfAttr>(TmplAttr)) {
       instantiateDependentDiagnoseIfAttr(*this, TemplateArgs, DiagnoseIf, Tmpl,
                                          cast<FunctionDecl>(New));
       continue;
     }
 
     if (const auto *CUDALaunchBounds =
             dyn_cast<CUDALaunchBoundsAttr>(TmplAttr)) {
       instantiateDependentCUDALaunchBoundsAttr(*this, TemplateArgs,
                                                *CUDALaunchBounds, New);
       continue;
     }
 
     if (const auto *Mode = dyn_cast<ModeAttr>(TmplAttr)) {
       instantiateDependentModeAttr(*this, TemplateArgs, *Mode, New);
       continue;
     }
 
     if (const auto *OMPAttr = dyn_cast<OMPDeclareSimdDeclAttr>(TmplAttr)) {
       instantiateOMPDeclareSimdDeclAttr(*this, TemplateArgs, *OMPAttr, New);
       continue;
     }
 
     if (const auto *OMPAttr = dyn_cast<OMPDeclareVariantAttr>(TmplAttr)) {
       instantiateOMPDeclareVariantAttr(*this, TemplateArgs, *OMPAttr, New);
       continue;
     }
 
     if (const auto *AMDGPUFlatWorkGroupSize =
             dyn_cast<AMDGPUFlatWorkGroupSizeAttr>(TmplAttr)) {
       instantiateDependentAMDGPUFlatWorkGroupSizeAttr(
           *this, TemplateArgs, *AMDGPUFlatWorkGroupSize, New);
     }
 
     if (const auto *AMDGPUFlatWorkGroupSize =
             dyn_cast<AMDGPUWavesPerEUAttr>(TmplAttr)) {
       instantiateDependentAMDGPUWavesPerEUAttr(*this, TemplateArgs,
                                                *AMDGPUFlatWorkGroupSize, New);
     }
 
     if (const auto *AMDGPUMaxNumWorkGroups =
             dyn_cast<AMDGPUMaxNumWorkGroupsAttr>(TmplAttr)) {
       instantiateDependentAMDGPUMaxNumWorkGroupsAttr(
           *this, TemplateArgs, *AMDGPUMaxNumWorkGroups, New);
     }
 
     if (const auto *ParamAttr = dyn_cast<HLSLParamModifierAttr>(TmplAttr)) {
       instantiateDependentHLSLParamModifierAttr(*this, TemplateArgs, ParamAttr,
                                                 New);
       continue;
     }
 
     // Existing DLL attribute on the instantiation takes precedence.
     if (TmplAttr->getKind() == attr::DLLExport ||
         TmplAttr->getKind() == attr::DLLImport) {
       if (New->hasAttr<DLLExportAttr>() || New->hasAttr<DLLImportAttr>()) {
         continue;
       }
     }
 
     if (const auto *ABIAttr = dyn_cast<ParameterABIAttr>(TmplAttr)) {
       Swift().AddParameterABIAttr(New, *ABIAttr, ABIAttr->getABI());
       continue;
     }
 
     if (isa<NSConsumedAttr>(TmplAttr) || isa<OSConsumedAttr>(TmplAttr) ||
         isa<CFConsumedAttr>(TmplAttr)) {
       ObjC().AddXConsumedAttr(New, *TmplAttr,
                               attrToRetainOwnershipKind(TmplAttr),
                               /*template instantiation=*/true);
       continue;
     }
 
     if (auto *A = dyn_cast<PointerAttr>(TmplAttr)) {
       if (!New->hasAttr<PointerAttr>())
         New->addAttr(A->clone(Context));
       continue;
     }
 
     if (auto *A = dyn_cast<OwnerAttr>(TmplAttr)) {
       if (!New->hasAttr<OwnerAttr>())
         New->addAttr(A->clone(Context));
       continue;
     }
 
     if (auto *A = dyn_cast<SYCLKernelAttr>(TmplAttr)) {
       instantiateDependentSYCLKernelAttr(*this, TemplateArgs, *A, New);
       continue;
     }
 
     assert(!TmplAttr->isPackExpansion());
     if (TmplAttr->isLateParsed() && LateAttrs) {
       // Late parsed attributes must be instantiated and attached after the
       // enclosing class has been instantiated.  See Sema::InstantiateClass.
       LocalInstantiationScope *Saved = nullptr;
       if (CurrentInstantiationScope)
         Saved = CurrentInstantiationScope->cloneScopes(OuterMostScope);
       LateAttrs->push_back(LateInstantiatedAttribute(TmplAttr, Saved, New));
     } else {
       // Allow 'this' within late-parsed attributes.
       auto *ND = cast<NamedDecl>(New);
       auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(ND->getDeclContext());
       CXXThisScopeRAII ThisScope(*this, ThisContext, Qualifiers(),
                                  ND->isCXXInstanceMember());
 
       Attr *NewAttr = sema::instantiateTemplateAttribute(TmplAttr, Context,
                                                          *this, TemplateArgs);
       if (NewAttr && isRelevantAttr(*this, New, TmplAttr))
         New->addAttr(NewAttr);
     }
   }
 }
 
 void Sema::updateAttrsForLateParsedTemplate(const Decl *Pattern, Decl *Inst) {
   for (const auto *Attr : Pattern->attrs()) {
     if (auto *A = dyn_cast<StrictFPAttr>(Attr)) {
       if (!Inst->hasAttr<StrictFPAttr>())
         Inst->addAttr(A->clone(getASTContext()));
       continue;
     }
   }
 }
 
 void Sema::InstantiateDefaultCtorDefaultArgs(CXXConstructorDecl *Ctor) {
   assert(Context.getTargetInfo().getCXXABI().isMicrosoft() &&
          Ctor->isDefaultConstructor());
   unsigned NumParams = Ctor->getNumParams();
   if (NumParams == 0)
     return;
   DLLExportAttr *Attr = Ctor->getAttr<DLLExportAttr>();
   if (!Attr)
     return;
   for (unsigned I = 0; I != NumParams; ++I) {
     (void)CheckCXXDefaultArgExpr(Attr->getLocation(), Ctor,
                                    Ctor->getParamDecl(I));
     CleanupVarDeclMarking();
   }
 }
 
 /// Get the previous declaration of a declaration for the purposes of template
 /// instantiation. If this finds a previous declaration, then the previous
 /// declaration of the instantiation of D should be an instantiation of the
 /// result of this function.
 template<typename DeclT>
 static DeclT *getPreviousDeclForInstantiation(DeclT *D) {
   DeclT *Result = D->getPreviousDecl();
 
   // If the declaration is within a class, and the previous declaration was
   // merged from a different definition of that class, then we don't have a
   // previous declaration for the purpose of template instantiation.
   if (Result && isa<CXXRecordDecl>(D->getDeclContext()) &&
       D->getLexicalDeclContext() != Result->getLexicalDeclContext())
     return nullptr;
 
   return Result;
 }
 
 Decl *
 TemplateDeclInstantiator::VisitTranslationUnitDecl(TranslationUnitDecl *D) {
   llvm_unreachable("Translation units cannot be instantiated");
 }
 
 Decl *TemplateDeclInstantiator::VisitHLSLBufferDecl(HLSLBufferDecl *Decl) {
   llvm_unreachable("HLSL buffer declarations cannot be instantiated");
 }
 
 Decl *
 TemplateDeclInstantiator::VisitPragmaCommentDecl(PragmaCommentDecl *D) {
   llvm_unreachable("pragma comment cannot be instantiated");
 }
 
 Decl *TemplateDeclInstantiator::VisitPragmaDetectMismatchDecl(
     PragmaDetectMismatchDecl *D) {
   llvm_unreachable("pragma comment cannot be instantiated");
 }
 
 Decl *
 TemplateDeclInstantiator::VisitExternCContextDecl(ExternCContextDecl *D) {
   llvm_unreachable("extern \"C\" context cannot be instantiated");
 }
 
 Decl *TemplateDeclInstantiator::VisitMSGuidDecl(MSGuidDecl *D) {
   llvm_unreachable("GUID declaration cannot be instantiated");
 }
 
 Decl *TemplateDeclInstantiator::VisitUnnamedGlobalConstantDecl(
     UnnamedGlobalConstantDecl *D) {
   llvm_unreachable("UnnamedGlobalConstantDecl cannot be instantiated");
 }
 
 Decl *TemplateDeclInstantiator::VisitTemplateParamObjectDecl(
     TemplateParamObjectDecl *D) {
   llvm_unreachable("template parameter objects cannot be instantiated");
 }
 
 Decl *
 TemplateDeclInstantiator::VisitLabelDecl(LabelDecl *D) {
   LabelDecl *Inst = LabelDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                       D->getIdentifier());
   Owner->addDecl(Inst);
   return Inst;
 }
 
 Decl *
 TemplateDeclInstantiator::VisitNamespaceDecl(NamespaceDecl *D) {
   llvm_unreachable("Namespaces cannot be instantiated");
 }
 
 Decl *
 TemplateDeclInstantiator::VisitNamespaceAliasDecl(NamespaceAliasDecl *D) {
   NamespaceAliasDecl *Inst
     = NamespaceAliasDecl::Create(SemaRef.Context, Owner,
                                  D->getNamespaceLoc(),
                                  D->getAliasLoc(),
                                  D->getIdentifier(),
                                  D->getQualifierLoc(),
                                  D->getTargetNameLoc(),
                                  D->getNamespace());
   Owner->addDecl(Inst);
   return Inst;
 }
 
 Decl *TemplateDeclInstantiator::InstantiateTypedefNameDecl(TypedefNameDecl *D,
                                                            bool IsTypeAlias) {
   bool Invalid = false;
   TypeSourceInfo *DI = D->getTypeSourceInfo();
   if (DI->getType()->isInstantiationDependentType() ||
       DI->getType()->isVariablyModifiedType()) {
     DI = SemaRef.SubstType(DI, TemplateArgs,
                            D->getLocation(), D->getDeclName());
     if (!DI) {
       Invalid = true;
       DI = SemaRef.Context.getTrivialTypeSourceInfo(SemaRef.Context.IntTy);
     }
   } else {
     SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
   }
 
   // HACK: 2012-10-23 g++ has a bug where it gets the value kind of ?: wrong.
   // libstdc++ relies upon this bug in its implementation of common_type.  If we
   // happen to be processing that implementation, fake up the g++ ?:
   // semantics. See LWG issue 2141 for more information on the bug.  The bugs
   // are fixed in g++ and libstdc++ 4.9.0 (2014-04-22).
   const DecltypeType *DT = DI->getType()->getAs<DecltypeType>();
   CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D->getDeclContext());
   if (DT && RD && isa<ConditionalOperator>(DT->getUnderlyingExpr()) &&
       DT->isReferenceType() &&
       RD->getEnclosingNamespaceContext() == SemaRef.getStdNamespace() &&
       RD->getIdentifier() && RD->getIdentifier()->isStr("common_type") &&
       D->getIdentifier() && D->getIdentifier()->isStr("type") &&
       SemaRef.getSourceManager().isInSystemHeader(D->getBeginLoc()))
     // Fold it to the (non-reference) type which g++ would have produced.
     DI = SemaRef.Context.getTrivialTypeSourceInfo(
       DI->getType().getNonReferenceType());
 
   // Create the new typedef
   TypedefNameDecl *Typedef;
   if (IsTypeAlias)
     Typedef = TypeAliasDecl::Create(SemaRef.Context, Owner, D->getBeginLoc(),
                                     D->getLocation(), D->getIdentifier(), DI);
   else
     Typedef = TypedefDecl::Create(SemaRef.Context, Owner, D->getBeginLoc(),
                                   D->getLocation(), D->getIdentifier(), DI);
   if (Invalid)
     Typedef->setInvalidDecl();
 
   // If the old typedef was the name for linkage purposes of an anonymous
   // tag decl, re-establish that relationship for the new typedef.
   if (const TagType *oldTagType = D->getUnderlyingType()->getAs<TagType>()) {
     TagDecl *oldTag = oldTagType->getDecl();
     if (oldTag->getTypedefNameForAnonDecl() == D && !Invalid) {
       TagDecl *newTag = DI->getType()->castAs<TagType>()->getDecl();
       assert(!newTag->hasNameForLinkage());
       newTag->setTypedefNameForAnonDecl(Typedef);
     }
   }
 
   if (TypedefNameDecl *Prev = getPreviousDeclForInstantiation(D)) {
     NamedDecl *InstPrev = SemaRef.FindInstantiatedDecl(D->getLocation(), Prev,
                                                        TemplateArgs);
     if (!InstPrev)
       return nullptr;
 
     TypedefNameDecl *InstPrevTypedef = cast<TypedefNameDecl>(InstPrev);
 
     // If the typedef types are not identical, reject them.
     SemaRef.isIncompatibleTypedef(InstPrevTypedef, Typedef);
 
     Typedef->setPreviousDecl(InstPrevTypedef);
   }
 
   SemaRef.InstantiateAttrs(TemplateArgs, D, Typedef);
 
   if (D->getUnderlyingType()->getAs<DependentNameType>())
     SemaRef.inferGslPointerAttribute(Typedef);
 
   Typedef->setAccess(D->getAccess());
   Typedef->setReferenced(D->isReferenced());
 
   return Typedef;
 }
 
 Decl *TemplateDeclInstantiator::VisitTypedefDecl(TypedefDecl *D) {
   Decl *Typedef = InstantiateTypedefNameDecl(D, /*IsTypeAlias=*/false);
   if (Typedef)
     Owner->addDecl(Typedef);
   return Typedef;
 }
 
 Decl *TemplateDeclInstantiator::VisitTypeAliasDecl(TypeAliasDecl *D) {
   Decl *Typedef = InstantiateTypedefNameDecl(D, /*IsTypeAlias=*/true);
   if (Typedef)
     Owner->addDecl(Typedef);
   return Typedef;
 }
 
 Decl *TemplateDeclInstantiator::InstantiateTypeAliasTemplateDecl(
     TypeAliasTemplateDecl *D) {
   // Create a local instantiation scope for this type alias template, which
   // will contain the instantiations of the template parameters.
   LocalInstantiationScope Scope(SemaRef);
 
   TemplateParameterList *TempParams = D->getTemplateParameters();
   TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
   if (!InstParams)
     return nullptr;
 
   TypeAliasDecl *Pattern = D->getTemplatedDecl();
   Sema::InstantiatingTemplate InstTemplate(
       SemaRef, D->getBeginLoc(), D,
       D->getTemplateDepth() >= TemplateArgs.getNumLevels()
           ? ArrayRef<TemplateArgument>()
           : (TemplateArgs.begin() + TemplateArgs.getNumLevels() - 1 -
              D->getTemplateDepth())
                 ->Args);
   if (InstTemplate.isInvalid())
     return nullptr;
 
   TypeAliasTemplateDecl *PrevAliasTemplate = nullptr;
   if (getPreviousDeclForInstantiation<TypedefNameDecl>(Pattern)) {
     DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName());
     if (!Found.empty()) {
       PrevAliasTemplate = dyn_cast<TypeAliasTemplateDecl>(Found.front());
     }
   }
 
   TypeAliasDecl *AliasInst = cast_or_null<TypeAliasDecl>(
     InstantiateTypedefNameDecl(Pattern, /*IsTypeAlias=*/true));
   if (!AliasInst)
     return nullptr;
 
   TypeAliasTemplateDecl *Inst
     = TypeAliasTemplateDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                     D->getDeclName(), InstParams, AliasInst);
   AliasInst->setDescribedAliasTemplate(Inst);
   if (PrevAliasTemplate)
     Inst->setPreviousDecl(PrevAliasTemplate);
 
   Inst->setAccess(D->getAccess());
 
   if (!PrevAliasTemplate)
     Inst->setInstantiatedFromMemberTemplate(D);
 
   return Inst;
 }
 
 Decl *
 TemplateDeclInstantiator::VisitTypeAliasTemplateDecl(TypeAliasTemplateDecl *D) {
   Decl *Inst = InstantiateTypeAliasTemplateDecl(D);
   if (Inst)
     Owner->addDecl(Inst);
 
   return Inst;
 }
 
 Decl *TemplateDeclInstantiator::VisitBindingDecl(BindingDecl *D) {
   auto *NewBD = BindingDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                     D->getIdentifier());
   NewBD->setReferenced(D->isReferenced());
   SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewBD);
   return NewBD;
 }
 
 Decl *TemplateDeclInstantiator::VisitDecompositionDecl(DecompositionDecl *D) {
   // Transform the bindings first.
   SmallVector<BindingDecl*, 16> NewBindings;
   for (auto *OldBD : D->bindings())
     NewBindings.push_back(cast<BindingDecl>(VisitBindingDecl(OldBD)));
   ArrayRef<BindingDecl*> NewBindingArray = NewBindings;
 
   auto *NewDD = cast_or_null<DecompositionDecl>(
       VisitVarDecl(D, /*InstantiatingVarTemplate=*/false, &NewBindingArray));
 
   if (!NewDD || NewDD->isInvalidDecl())
     for (auto *NewBD : NewBindings)
       NewBD->setInvalidDecl();
 
   return NewDD;
 }
 
 Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D) {
   return VisitVarDecl(D, /*InstantiatingVarTemplate=*/false);
 }
 
 Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D,
                                              bool InstantiatingVarTemplate,
                                              ArrayRef<BindingDecl*> *Bindings) {
 
   // Do substitution on the type of the declaration
   TypeSourceInfo *DI = SemaRef.SubstType(
       D->getTypeSourceInfo(), TemplateArgs, D->getTypeSpecStartLoc(),
       D->getDeclName(), /*AllowDeducedTST*/true);
   if (!DI)
     return nullptr;
 
   if (DI->getType()->isFunctionType()) {
     SemaRef.Diag(D->getLocation(), diag::err_variable_instantiates_to_function)
       << D->isStaticDataMember() << DI->getType();
     return nullptr;
   }
 
   DeclContext *DC = Owner;
   if (D->isLocalExternDecl())
     SemaRef.adjustContextForLocalExternDecl(DC);
 
   // Build the instantiated declaration.
   VarDecl *Var;
   if (Bindings)
     Var = DecompositionDecl::Create(SemaRef.Context, DC, D->getInnerLocStart(),
                                     D->getLocation(), DI->getType(), DI,
                                     D->getStorageClass(), *Bindings);
   else
     Var = VarDecl::Create(SemaRef.Context, DC, D->getInnerLocStart(),
                           D->getLocation(), D->getIdentifier(), DI->getType(),
                           DI, D->getStorageClass());
 
   // In ARC, infer 'retaining' for variables of retainable type.
   if (SemaRef.getLangOpts().ObjCAutoRefCount &&
       SemaRef.ObjC().inferObjCARCLifetime(Var))
     Var->setInvalidDecl();
 
   if (SemaRef.getLangOpts().OpenCL)
     SemaRef.deduceOpenCLAddressSpace(Var);
 
   // Substitute the nested name specifier, if any.
   if (SubstQualifier(D, Var))
     return nullptr;
 
   SemaRef.BuildVariableInstantiation(Var, D, TemplateArgs, LateAttrs, Owner,
                                      StartingScope, InstantiatingVarTemplate);
   if (D->isNRVOVariable() && !Var->isInvalidDecl()) {
     QualType RT;
     if (auto *F = dyn_cast<FunctionDecl>(DC))
       RT = F->getReturnType();
     else if (isa<BlockDecl>(DC))
       RT = cast<FunctionType>(SemaRef.getCurBlock()->FunctionType)
                ->getReturnType();
     else
       llvm_unreachable("Unknown context type");
 
     // This is the last chance we have of checking copy elision eligibility
     // for functions in dependent contexts. The sema actions for building
     // the return statement during template instantiation will have no effect
     // regarding copy elision, since NRVO propagation runs on the scope exit
     // actions, and these are not run on instantiation.
     // This might run through some VarDecls which were returned from non-taken
     // 'if constexpr' branches, and these will end up being constructed on the
     // return slot even if they will never be returned, as a sort of accidental
     // 'optimization'. Notably, functions with 'auto' return types won't have it
     // deduced by this point. Coupled with the limitation described
     // previously, this makes it very hard to support copy elision for these.
     Sema::NamedReturnInfo Info = SemaRef.getNamedReturnInfo(Var);
     bool NRVO = SemaRef.getCopyElisionCandidate(Info, RT) != nullptr;
     Var->setNRVOVariable(NRVO);
   }
 
   Var->setImplicit(D->isImplicit());
 
   if (Var->isStaticLocal())
     SemaRef.CheckStaticLocalForDllExport(Var);
 
   if (Var->getTLSKind())
     SemaRef.CheckThreadLocalForLargeAlignment(Var);
 
   return Var;
 }
 
 Decl *TemplateDeclInstantiator::VisitAccessSpecDecl(AccessSpecDecl *D) {
   AccessSpecDecl* AD
     = AccessSpecDecl::Create(SemaRef.Context, D->getAccess(), Owner,
                              D->getAccessSpecifierLoc(), D->getColonLoc());
   Owner->addHiddenDecl(AD);
   return AD;
 }
 
 Decl *TemplateDeclInstantiator::VisitFieldDecl(FieldDecl *D) {
   bool Invalid = false;
   TypeSourceInfo *DI = D->getTypeSourceInfo();
   if (DI->getType()->isInstantiationDependentType() ||
       DI->getType()->isVariablyModifiedType())  {
     DI = SemaRef.SubstType(DI, TemplateArgs,
                            D->getLocation(), D->getDeclName());
     if (!DI) {
       DI = D->getTypeSourceInfo();
       Invalid = true;
     } else if (DI->getType()->isFunctionType()) {
       // C++ [temp.arg.type]p3:
       //   If a declaration acquires a function type through a type
       //   dependent on a template-parameter and this causes a
       //   declaration that does not use the syntactic form of a
       //   function declarator to have function type, the program is
       //   ill-formed.
       SemaRef.Diag(D->getLocation(), diag::err_field_instantiates_to_function)
         << DI->getType();
       Invalid = true;
     }
   } else {
     SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
   }
 
   Expr *BitWidth = D->getBitWidth();
   if (Invalid)
     BitWidth = nullptr;
   else if (BitWidth) {
     // The bit-width expression is a constant expression.
     EnterExpressionEvaluationContext Unevaluated(
         SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
     ExprResult InstantiatedBitWidth
       = SemaRef.SubstExpr(BitWidth, TemplateArgs);
     if (InstantiatedBitWidth.isInvalid()) {
       Invalid = true;
       BitWidth = nullptr;
     } else
       BitWidth = InstantiatedBitWidth.getAs<Expr>();
   }
 
   FieldDecl *Field = SemaRef.CheckFieldDecl(D->getDeclName(),
                                             DI->getType(), DI,
                                             cast<RecordDecl>(Owner),
                                             D->getLocation(),
                                             D->isMutable(),
                                             BitWidth,
                                             D->getInClassInitStyle(),
                                             D->getInnerLocStart(),
                                             D->getAccess(),
                                             nullptr);
   if (!Field) {
     cast<Decl>(Owner)->setInvalidDecl();
     return nullptr;
   }
 
   SemaRef.InstantiateAttrs(TemplateArgs, D, Field, LateAttrs, StartingScope);
 
   if (Field->hasAttrs())
     SemaRef.CheckAlignasUnderalignment(Field);
 
   if (Invalid)
     Field->setInvalidDecl();
 
   if (!Field->getDeclName()) {
     // Keep track of where this decl came from.
     SemaRef.Context.setInstantiatedFromUnnamedFieldDecl(Field, D);
   }
   if (CXXRecordDecl *Parent= dyn_cast<CXXRecordDecl>(Field->getDeclContext())) {
     if (Parent->isAnonymousStructOrUnion() &&
         Parent->getRedeclContext()->isFunctionOrMethod())
       SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Field);
   }
 
   Field->setImplicit(D->isImplicit());
   Field->setAccess(D->getAccess());
   Owner->addDecl(Field);
 
   return Field;
 }
 
 Decl *TemplateDeclInstantiator::VisitMSPropertyDecl(MSPropertyDecl *D) {
   bool Invalid = false;
   TypeSourceInfo *DI = D->getTypeSourceInfo();
 
   if (DI->getType()->isVariablyModifiedType()) {
     SemaRef.Diag(D->getLocation(), diag::err_property_is_variably_modified)
       << D;
     Invalid = true;
   } else if (DI->getType()->isInstantiationDependentType())  {
     DI = SemaRef.SubstType(DI, TemplateArgs,
                            D->getLocation(), D->getDeclName());
     if (!DI) {
       DI = D->getTypeSourceInfo();
       Invalid = true;
     } else if (DI->getType()->isFunctionType()) {
       // C++ [temp.arg.type]p3:
       //   If a declaration acquires a function type through a type
       //   dependent on a template-parameter and this causes a
       //   declaration that does not use the syntactic form of a
       //   function declarator to have function type, the program is
       //   ill-formed.
       SemaRef.Diag(D->getLocation(), diag::err_field_instantiates_to_function)
       << DI->getType();
       Invalid = true;
     }
   } else {
     SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
   }
 
   MSPropertyDecl *Property = MSPropertyDecl::Create(
       SemaRef.Context, Owner, D->getLocation(), D->getDeclName(), DI->getType(),
       DI, D->getBeginLoc(), D->getGetterId(), D->getSetterId());
 
   SemaRef.InstantiateAttrs(TemplateArgs, D, Property, LateAttrs,
                            StartingScope);
 
   if (Invalid)
     Property->setInvalidDecl();
 
   Property->setAccess(D->getAccess());
   Owner->addDecl(Property);
 
   return Property;
 }
 
 Decl *TemplateDeclInstantiator::VisitIndirectFieldDecl(IndirectFieldDecl *D) {
   NamedDecl **NamedChain =
     new (SemaRef.Context)NamedDecl*[D->getChainingSize()];
 
   int i = 0;
   for (auto *PI : D->chain()) {
     NamedDecl *Next = SemaRef.FindInstantiatedDecl(D->getLocation(), PI,
                                               TemplateArgs);
     if (!Next)
       return nullptr;
 
     NamedChain[i++] = Next;
   }
 
   QualType T = cast<FieldDecl>(NamedChain[i-1])->getType();
   IndirectFieldDecl *IndirectField = IndirectFieldDecl::Create(
       SemaRef.Context, Owner, D->getLocation(), D->getIdentifier(), T,
       {NamedChain, D->getChainingSize()});
 
   for (const auto *Attr : D->attrs())
     IndirectField->addAttr(Attr->clone(SemaRef.Context));
 
   IndirectField->setImplicit(D->isImplicit());
   IndirectField->setAccess(D->getAccess());
   Owner->addDecl(IndirectField);
   return IndirectField;
 }
 
 Decl *TemplateDeclInstantiator::VisitFriendDecl(FriendDecl *D) {
   // Handle friend type expressions by simply substituting template
   // parameters into the pattern type and checking the result.
   if (TypeSourceInfo *Ty = D->getFriendType()) {
     TypeSourceInfo *InstTy;
     // If this is an unsupported friend, don't bother substituting template
     // arguments into it. The actual type referred to won't be used by any
     // parts of Clang, and may not be valid for instantiating. Just use the
     // same info for the instantiated friend.
     if (D->isUnsupportedFriend()) {
       InstTy = Ty;
     } else {
       InstTy = SemaRef.SubstType(Ty, TemplateArgs,
                                  D->getLocation(), DeclarationName());
     }
     if (!InstTy)
       return nullptr;
 
     FriendDecl *FD = FriendDecl::Create(
         SemaRef.Context, Owner, D->getLocation(), InstTy, D->getFriendLoc());
     FD->setAccess(AS_public);
     FD->setUnsupportedFriend(D->isUnsupportedFriend());
     Owner->addDecl(FD);
     return FD;
   }
 
   NamedDecl *ND = D->getFriendDecl();
   assert(ND && "friend decl must be a decl or a type!");
 
   // All of the Visit implementations for the various potential friend
   // declarations have to be carefully written to work for friend
   // objects, with the most important detail being that the target
   // decl should almost certainly not be placed in Owner.
   Decl *NewND = Visit(ND);
   if (!NewND) return nullptr;
 
   FriendDecl *FD =
     FriendDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                        cast<NamedDecl>(NewND), D->getFriendLoc());
   FD->setAccess(AS_public);
   FD->setUnsupportedFriend(D->isUnsupportedFriend());
   Owner->addDecl(FD);
   return FD;
 }
 
 Decl *TemplateDeclInstantiator::VisitStaticAssertDecl(StaticAssertDecl *D) {
   Expr *AssertExpr = D->getAssertExpr();
 
   // The expression in a static assertion is a constant expression.
   EnterExpressionEvaluationContext Unevaluated(
       SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
   ExprResult InstantiatedAssertExpr
     = SemaRef.SubstExpr(AssertExpr, TemplateArgs);
   if (InstantiatedAssertExpr.isInvalid())
     return nullptr;
 
   ExprResult InstantiatedMessageExpr =
       SemaRef.SubstExpr(D->getMessage(), TemplateArgs);
   if (InstantiatedMessageExpr.isInvalid())
     return nullptr;
 
   return SemaRef.BuildStaticAssertDeclaration(
       D->getLocation(), InstantiatedAssertExpr.get(),
       InstantiatedMessageExpr.get(), D->getRParenLoc(), D->isFailed());
 }
 
 Decl *TemplateDeclInstantiator::VisitEnumDecl(EnumDecl *D) {
   EnumDecl *PrevDecl = nullptr;
   if (EnumDecl *PatternPrev = getPreviousDeclForInstantiation(D)) {
     NamedDecl *Prev = SemaRef.FindInstantiatedDecl(D->getLocation(),
                                                    PatternPrev,
                                                    TemplateArgs);
     if (!Prev) return nullptr;
     PrevDecl = cast<EnumDecl>(Prev);
   }
 
   EnumDecl *Enum =
       EnumDecl::Create(SemaRef.Context, Owner, D->getBeginLoc(),
                        D->getLocation(), D->getIdentifier(), PrevDecl,
                        D->isScoped(), D->isScopedUsingClassTag(), D->isFixed());
   if (D->isFixed()) {
     if (TypeSourceInfo *TI = D->getIntegerTypeSourceInfo()) {
       // If we have type source information for the underlying type, it means it
       // has been explicitly set by the user. Perform substitution on it before
       // moving on.
       SourceLocation UnderlyingLoc = TI->getTypeLoc().getBeginLoc();
       TypeSourceInfo *NewTI = SemaRef.SubstType(TI, TemplateArgs, UnderlyingLoc,
                                                 DeclarationName());
       if (!NewTI || SemaRef.CheckEnumUnderlyingType(NewTI))
         Enum->setIntegerType(SemaRef.Context.IntTy);
       else
         Enum->setIntegerTypeSourceInfo(NewTI);
     } else {
       assert(!D->getIntegerType()->isDependentType()
              && "Dependent type without type source info");
       Enum->setIntegerType(D->getIntegerType());
     }
   }
 
   SemaRef.InstantiateAttrs(TemplateArgs, D, Enum);
 
   Enum->setInstantiationOfMemberEnum(D, TSK_ImplicitInstantiation);
   Enum->setAccess(D->getAccess());
   // Forward the mangling number from the template to the instantiated decl.
   SemaRef.Context.setManglingNumber(Enum, SemaRef.Context.getManglingNumber(D));
   // See if the old tag was defined along with a declarator.
   // If it did, mark the new tag as being associated with that declarator.
   if (DeclaratorDecl *DD = SemaRef.Context.getDeclaratorForUnnamedTagDecl(D))
     SemaRef.Context.addDeclaratorForUnnamedTagDecl(Enum, DD);
   // See if the old tag was defined along with a typedef.
   // If it did, mark the new tag as being associated with that typedef.
   if (TypedefNameDecl *TND = SemaRef.Context.getTypedefNameForUnnamedTagDecl(D))
     SemaRef.Context.addTypedefNameForUnnamedTagDecl(Enum, TND);
   if (SubstQualifier(D, Enum)) return nullptr;
   Owner->addDecl(Enum);
 
   EnumDecl *Def = D->getDefinition();
   if (Def && Def != D) {
     // If this is an out-of-line definition of an enum member template, check
     // that the underlying types match in the instantiation of both
     // declarations.
     if (TypeSourceInfo *TI = Def->getIntegerTypeSourceInfo()) {
       SourceLocation UnderlyingLoc = TI->getTypeLoc().getBeginLoc();
       QualType DefnUnderlying =
         SemaRef.SubstType(TI->getType(), TemplateArgs,
                           UnderlyingLoc, DeclarationName());
       SemaRef.CheckEnumRedeclaration(Def->getLocation(), Def->isScoped(),
                                      DefnUnderlying, /*IsFixed=*/true, Enum);
     }
   }
 
   // C++11 [temp.inst]p1: The implicit instantiation of a class template
   // specialization causes the implicit instantiation of the declarations, but
   // not the definitions of scoped member enumerations.
   //
   // DR1484 clarifies that enumeration definitions inside of a template
   // declaration aren't considered entities that can be separately instantiated
   // from the rest of the entity they are declared inside of.
   if (isDeclWithinFunction(D) ? D == Def : Def && !Enum->isScoped()) {
     SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Enum);
     InstantiateEnumDefinition(Enum, Def);
   }
 
   return Enum;
 }
 
 void TemplateDeclInstantiator::InstantiateEnumDefinition(
     EnumDecl *Enum, EnumDecl *Pattern) {
   Enum->startDefinition();
 
   // Update the location to refer to the definition.
   Enum->setLocation(Pattern->getLocation());
 
   SmallVector<Decl*, 4> Enumerators;
 
   EnumConstantDecl *LastEnumConst = nullptr;
   for (auto *EC : Pattern->enumerators()) {
     // The specified value for the enumerator.
     ExprResult Value((Expr *)nullptr);
     if (Expr *UninstValue = EC->getInitExpr()) {
       // The enumerator's value expression is a constant expression.
       EnterExpressionEvaluationContext Unevaluated(
           SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
       Value = SemaRef.SubstExpr(UninstValue, TemplateArgs);
     }
 
     // Drop the initial value and continue.
     bool isInvalid = false;
     if (Value.isInvalid()) {
       Value = nullptr;
       isInvalid = true;
     }
 
     EnumConstantDecl *EnumConst
       = SemaRef.CheckEnumConstant(Enum, LastEnumConst,
                                   EC->getLocation(), EC->getIdentifier(),
                                   Value.get());
 
     if (isInvalid) {
       if (EnumConst)
         EnumConst->setInvalidDecl();
       Enum->setInvalidDecl();
     }
 
     if (EnumConst) {
       SemaRef.InstantiateAttrs(TemplateArgs, EC, EnumConst);
 
       EnumConst->setAccess(Enum->getAccess());
       Enum->addDecl(EnumConst);
       Enumerators.push_back(EnumConst);
       LastEnumConst = EnumConst;
 
       if (Pattern->getDeclContext()->isFunctionOrMethod() &&
           !Enum->isScoped()) {
         // If the enumeration is within a function or method, record the enum
         // constant as a local.
         SemaRef.CurrentInstantiationScope->InstantiatedLocal(EC, EnumConst);
       }
     }
   }
 
   SemaRef.ActOnEnumBody(Enum->getLocation(), Enum->getBraceRange(), Enum,
                         Enumerators, nullptr, ParsedAttributesView());
 }
 
 Decl *TemplateDeclInstantiator::VisitEnumConstantDecl(EnumConstantDecl *D) {
   llvm_unreachable("EnumConstantDecls can only occur within EnumDecls.");
 }
 
 Decl *
 TemplateDeclInstantiator::VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D) {
   llvm_unreachable("BuiltinTemplateDecls cannot be instantiated.");
 }
 
 Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
   bool isFriend = (D->getFriendObjectKind() != Decl::FOK_None);
 
   // Create a local instantiation scope for this class template, which
   // will contain the instantiations of the template parameters.
   LocalInstantiationScope Scope(SemaRef);
   TemplateParameterList *TempParams = D->getTemplateParameters();
   TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
   if (!InstParams)
     return nullptr;
 
   CXXRecordDecl *Pattern = D->getTemplatedDecl();
 
   // Instantiate the qualifier.  We have to do this first in case
   // we're a friend declaration, because if we are then we need to put
   // the new declaration in the appropriate context.
   NestedNameSpecifierLoc QualifierLoc = Pattern->getQualifierLoc();
   if (QualifierLoc) {
     QualifierLoc = SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc,
                                                        TemplateArgs);
     if (!QualifierLoc)
       return nullptr;
   }
 
   CXXRecordDecl *PrevDecl = nullptr;
   ClassTemplateDecl *PrevClassTemplate = nullptr;
 
   if (!isFriend && getPreviousDeclForInstantiation(Pattern)) {
     DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName());
     if (!Found.empty()) {
       PrevClassTemplate = dyn_cast<ClassTemplateDecl>(Found.front());
       if (PrevClassTemplate)
         PrevDecl = PrevClassTemplate->getTemplatedDecl();
     }
   }
 
   // If this isn't a friend, then it's a member template, in which
   // case we just want to build the instantiation in the
   // specialization.  If it is a friend, we want to build it in
   // the appropriate context.
   DeclContext *DC = Owner;
   if (isFriend) {
     if (QualifierLoc) {
       CXXScopeSpec SS;
       SS.Adopt(QualifierLoc);
       DC = SemaRef.computeDeclContext(SS);
       if (!DC) return nullptr;
     } else {
       DC = SemaRef.FindInstantiatedContext(Pattern->getLocation(),
                                            Pattern->getDeclContext(),
                                            TemplateArgs);
     }
 
     // Look for a previous declaration of the template in the owning
     // context.
     LookupResult R(SemaRef, Pattern->getDeclName(), Pattern->getLocation(),
                    Sema::LookupOrdinaryName,
                    SemaRef.forRedeclarationInCurContext());
     SemaRef.LookupQualifiedName(R, DC);
 
     if (R.isSingleResult()) {
       PrevClassTemplate = R.getAsSingle<ClassTemplateDecl>();
       if (PrevClassTemplate)
         PrevDecl = PrevClassTemplate->getTemplatedDecl();
     }
 
     if (!PrevClassTemplate && QualifierLoc) {
       SemaRef.Diag(Pattern->getLocation(), diag::err_not_tag_in_scope)
           << llvm::to_underlying(D->getTemplatedDecl()->getTagKind())
           << Pattern->getDeclName() << DC << QualifierLoc.getSourceRange();
       return nullptr;
     }
   }
 
   CXXRecordDecl *RecordInst = CXXRecordDecl::Create(
       SemaRef.Context, Pattern->getTagKind(), DC, Pattern->getBeginLoc(),
       Pattern->getLocation(), Pattern->getIdentifier(), PrevDecl,
       /*DelayTypeCreation=*/true);
   if (QualifierLoc)
     RecordInst->setQualifierInfo(QualifierLoc);
 
   SemaRef.InstantiateAttrsForDecl(TemplateArgs, Pattern, RecordInst, LateAttrs,
                                                               StartingScope);
 
   ClassTemplateDecl *Inst
     = ClassTemplateDecl::Create(SemaRef.Context, DC, D->getLocation(),
                                 D->getIdentifier(), InstParams, RecordInst);
   RecordInst->setDescribedClassTemplate(Inst);
 
   if (isFriend) {
     assert(!Owner->isDependentContext());
     Inst->setLexicalDeclContext(Owner);
     RecordInst->setLexicalDeclContext(Owner);
     Inst->setObjectOfFriendDecl();
 
     if (PrevClassTemplate) {
       Inst->setCommonPtr(PrevClassTemplate->getCommonPtr());
       RecordInst->setTypeForDecl(
           PrevClassTemplate->getTemplatedDecl()->getTypeForDecl());
       const ClassTemplateDecl *MostRecentPrevCT =
           PrevClassTemplate->getMostRecentDecl();
       TemplateParameterList *PrevParams =
           MostRecentPrevCT->getTemplateParameters();
 
       // Make sure the parameter lists match.
       if (!SemaRef.TemplateParameterListsAreEqual(
               RecordInst, InstParams, MostRecentPrevCT->getTemplatedDecl(),
               PrevParams, true, Sema::TPL_TemplateMatch))
         return nullptr;
 
       // Do some additional validation, then merge default arguments
       // from the existing declarations.
       if (SemaRef.CheckTemplateParameterList(InstParams, PrevParams,
                                              Sema::TPC_ClassTemplate))
         return nullptr;
 
       Inst->setAccess(PrevClassTemplate->getAccess());
     } else {
       Inst->setAccess(D->getAccess());
     }
 
     Inst->setObjectOfFriendDecl();
     // TODO: do we want to track the instantiation progeny of this
     // friend target decl?
   } else {
     Inst->setAccess(D->getAccess());
     if (!PrevClassTemplate)
       Inst->setInstantiatedFromMemberTemplate(D);
   }
 
   Inst->setPreviousDecl(PrevClassTemplate);
 
   // Trigger creation of the type for the instantiation.
   SemaRef.Context.getInjectedClassNameType(
       RecordInst, Inst->getInjectedClassNameSpecialization());
 
   // Finish handling of friends.
   if (isFriend) {
     DC->makeDeclVisibleInContext(Inst);
     return Inst;
   }
 
   if (D->isOutOfLine()) {
     Inst->setLexicalDeclContext(D->getLexicalDeclContext());
     RecordInst->setLexicalDeclContext(D->getLexicalDeclContext());
   }
 
   Owner->addDecl(Inst);
 
   if (!PrevClassTemplate) {
     // Queue up any out-of-line partial specializations of this member
     // class template; the client will force their instantiation once
     // the enclosing class has been instantiated.
     SmallVector<ClassTemplatePartialSpecializationDecl *, 4> PartialSpecs;
     D->getPartialSpecializations(PartialSpecs);
     for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I)
       if (PartialSpecs[I]->getFirstDecl()->isOutOfLine())
         OutOfLinePartialSpecs.push_back(std::make_pair(Inst, PartialSpecs[I]));
   }
 
   return Inst;
 }
 
 Decl *
 TemplateDeclInstantiator::VisitClassTemplatePartialSpecializationDecl(
                                    ClassTemplatePartialSpecializationDecl *D) {
   ClassTemplateDecl *ClassTemplate = D->getSpecializedTemplate();
 
   // Lookup the already-instantiated declaration in the instantiation
   // of the class template and return that.
   DeclContext::lookup_result Found
     = Owner->lookup(ClassTemplate->getDeclName());
   if (Found.empty())
     return nullptr;
 
   ClassTemplateDecl *InstClassTemplate
     = dyn_cast<ClassTemplateDecl>(Found.front());
   if (!InstClassTemplate)
     return nullptr;
 
   if (ClassTemplatePartialSpecializationDecl *Result
         = InstClassTemplate->findPartialSpecInstantiatedFromMember(D))
     return Result;
 
   return InstantiateClassTemplatePartialSpecialization(InstClassTemplate, D);
 }
 
 Decl *TemplateDeclInstantiator::VisitVarTemplateDecl(VarTemplateDecl *D) {
   assert(D->getTemplatedDecl()->isStaticDataMember() &&
          "Only static data member templates are allowed.");
 
   // Create a local instantiation scope for this variable template, which
   // will contain the instantiations of the template parameters.
   LocalInstantiationScope Scope(SemaRef);
   TemplateParameterList *TempParams = D->getTemplateParameters();
   TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
   if (!InstParams)
     return nullptr;
 
   VarDecl *Pattern = D->getTemplatedDecl();
   VarTemplateDecl *PrevVarTemplate = nullptr;
 
   if (getPreviousDeclForInstantiation(Pattern)) {
     DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName());
     if (!Found.empty())
       PrevVarTemplate = dyn_cast<VarTemplateDecl>(Found.front());
   }
 
   VarDecl *VarInst =
       cast_or_null<VarDecl>(VisitVarDecl(Pattern,
                                          /*InstantiatingVarTemplate=*/true));
   if (!VarInst) return nullptr;
 
   DeclContext *DC = Owner;
 
   VarTemplateDecl *Inst = VarTemplateDecl::Create(
       SemaRef.Context, DC, D->getLocation(), D->getIdentifier(), InstParams,
       VarInst);
   VarInst->setDescribedVarTemplate(Inst);
   Inst->setPreviousDecl(PrevVarTemplate);
 
   Inst->setAccess(D->getAccess());
   if (!PrevVarTemplate)
     Inst->setInstantiatedFromMemberTemplate(D);
 
   if (D->isOutOfLine()) {
     Inst->setLexicalDeclContext(D->getLexicalDeclContext());
     VarInst->setLexicalDeclContext(D->getLexicalDeclContext());
   }
 
   Owner->addDecl(Inst);
 
   if (!PrevVarTemplate) {
     // Queue up any out-of-line partial specializations of this member
     // variable template; the client will force their instantiation once
     // the enclosing class has been instantiated.
     SmallVector<VarTemplatePartialSpecializationDecl *, 4> PartialSpecs;
     D->getPartialSpecializations(PartialSpecs);
     for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I)
       if (PartialSpecs[I]->getFirstDecl()->isOutOfLine())
         OutOfLineVarPartialSpecs.push_back(
             std::make_pair(Inst, PartialSpecs[I]));
   }
 
   return Inst;
 }
 
 Decl *TemplateDeclInstantiator::VisitVarTemplatePartialSpecializationDecl(
     VarTemplatePartialSpecializationDecl *D) {
   assert(D->isStaticDataMember() &&
          "Only static data member templates are allowed.");
 
   VarTemplateDecl *VarTemplate = D->getSpecializedTemplate();
 
   // Lookup the already-instantiated declaration and return that.
   DeclContext::lookup_result Found = Owner->lookup(VarTemplate->getDeclName());
   assert(!Found.empty() && "Instantiation found nothing?");
 
   VarTemplateDecl *InstVarTemplate = dyn_cast<VarTemplateDecl>(Found.front());
   assert(InstVarTemplate && "Instantiation did not find a variable template?");
 
   if (VarTemplatePartialSpecializationDecl *Result =
           InstVarTemplate->findPartialSpecInstantiatedFromMember(D))
     return Result;
 
   return InstantiateVarTemplatePartialSpecialization(InstVarTemplate, D);
 }
 
 Decl *
 TemplateDeclInstantiator::VisitFunctionTemplateDecl(FunctionTemplateDecl *D) {
   // Create a local instantiation scope for this function template, which
   // will contain the instantiations of the template parameters and then get
   // merged with the local instantiation scope for the function template
   // itself.
   LocalInstantiationScope Scope(SemaRef);
   Sema::ConstraintEvalRAII<TemplateDeclInstantiator> RAII(*this);
 
   TemplateParameterList *TempParams = D->getTemplateParameters();
   TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
   if (!InstParams)
     return nullptr;
 
   FunctionDecl *Instantiated = nullptr;
   if (CXXMethodDecl *DMethod = dyn_cast<CXXMethodDecl>(D->getTemplatedDecl()))
     Instantiated = cast_or_null<FunctionDecl>(VisitCXXMethodDecl(DMethod,
                                                                  InstParams));
   else
     Instantiated = cast_or_null<FunctionDecl>(VisitFunctionDecl(
                                                           D->getTemplatedDecl(),
                                                                 InstParams));
 
   if (!Instantiated)
     return nullptr;
 
   // Link the instantiated function template declaration to the function
   // template from which it was instantiated.
   FunctionTemplateDecl *InstTemplate
     = Instantiated->getDescribedFunctionTemplate();
   InstTemplate->setAccess(D->getAccess());
   assert(InstTemplate &&
          "VisitFunctionDecl/CXXMethodDecl didn't create a template!");
 
   bool isFriend = (InstTemplate->getFriendObjectKind() != Decl::FOK_None);
 
   // Link the instantiation back to the pattern *unless* this is a
   // non-definition friend declaration.
   if (!InstTemplate->getInstantiatedFromMemberTemplate() &&
       !(isFriend && !D->getTemplatedDecl()->isThisDeclarationADefinition()))
     InstTemplate->setInstantiatedFromMemberTemplate(D);
 
   // Make declarations visible in the appropriate context.
   if (!isFriend) {
     Owner->addDecl(InstTemplate);
   } else if (InstTemplate->getDeclContext()->isRecord() &&
              !getPreviousDeclForInstantiation(D)) {
     SemaRef.CheckFriendAccess(InstTemplate);
   }
 
   return InstTemplate;
 }
 
 Decl *TemplateDeclInstantiator::VisitCXXRecordDecl(CXXRecordDecl *D) {
   CXXRecordDecl *PrevDecl = nullptr;
   if (CXXRecordDecl *PatternPrev = getPreviousDeclForInstantiation(D)) {
     NamedDecl *Prev = SemaRef.FindInstantiatedDecl(D->getLocation(),
                                                    PatternPrev,
                                                    TemplateArgs);
     if (!Prev) return nullptr;
     PrevDecl = cast<CXXRecordDecl>(Prev);
   }
 
   CXXRecordDecl *Record = nullptr;
   bool IsInjectedClassName = D->isInjectedClassName();
   if (D->isLambda())
     Record = CXXRecordDecl::CreateLambda(
         SemaRef.Context, Owner, D->getLambdaTypeInfo(), D->getLocation(),
         D->getLambdaDependencyKind(), D->isGenericLambda(),
         D->getLambdaCaptureDefault());
   else
     Record = CXXRecordDecl::Create(SemaRef.Context, D->getTagKind(), Owner,
                                    D->getBeginLoc(), D->getLocation(),
                                    D->getIdentifier(), PrevDecl,
                                    /*DelayTypeCreation=*/IsInjectedClassName);
   // Link the type of the injected-class-name to that of the outer class.
   if (IsInjectedClassName)
     (void)SemaRef.Context.getTypeDeclType(Record, cast<CXXRecordDecl>(Owner));
 
   // Substitute the nested name specifier, if any.
   if (SubstQualifier(D, Record))
     return nullptr;
 
   SemaRef.InstantiateAttrsForDecl(TemplateArgs, D, Record, LateAttrs,
                                                               StartingScope);
 
   Record->setImplicit(D->isImplicit());
   // FIXME: Check against AS_none is an ugly hack to work around the issue that
   // the tag decls introduced by friend class declarations don't have an access
   // specifier. Remove once this area of the code gets sorted out.
   if (D->getAccess() != AS_none)
     Record->setAccess(D->getAccess());
   if (!IsInjectedClassName)
     Record->setInstantiationOfMemberClass(D, TSK_ImplicitInstantiation);
 
   // If the original function was part of a friend declaration,
   // inherit its namespace state.
   if (D->getFriendObjectKind())
     Record->setObjectOfFriendDecl();
 
   // Make sure that anonymous structs and unions are recorded.
   if (D->isAnonymousStructOrUnion())
     Record->setAnonymousStructOrUnion(true);
 
   if (D->isLocalClass())
     SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Record);
 
   // Forward the mangling number from the template to the instantiated decl.
   SemaRef.Context.setManglingNumber(Record,
                                     SemaRef.Context.getManglingNumber(D));
 
   // See if the old tag was defined along with a declarator.
   // If it did, mark the new tag as being associated with that declarator.
   if (DeclaratorDecl *DD = SemaRef.Context.getDeclaratorForUnnamedTagDecl(D))
     SemaRef.Context.addDeclaratorForUnnamedTagDecl(Record, DD);
 
   // See if the old tag was defined along with a typedef.
   // If it did, mark the new tag as being associated with that typedef.
   if (TypedefNameDecl *TND = SemaRef.Context.getTypedefNameForUnnamedTagDecl(D))
     SemaRef.Context.addTypedefNameForUnnamedTagDecl(Record, TND);
 
   Owner->addDecl(Record);
 
   // DR1484 clarifies that the members of a local class are instantiated as part
   // of the instantiation of their enclosing entity.
   if (D->isCompleteDefinition() && D->isLocalClass()) {
     Sema::LocalEagerInstantiationScope LocalInstantiations(SemaRef);
 
     SemaRef.InstantiateClass(D->getLocation(), Record, D, TemplateArgs,
                              TSK_ImplicitInstantiation,
                              /*Complain=*/true);
 
     // For nested local classes, we will instantiate the members when we
     // reach the end of the outermost (non-nested) local class.
     if (!D->isCXXClassMember())
       SemaRef.InstantiateClassMembers(D->getLocation(), Record, TemplateArgs,
                                       TSK_ImplicitInstantiation);
 
     // This class may have local implicit instantiations that need to be
     // performed within this scope.
     LocalInstantiations.perform();
   }
 
   SemaRef.DiagnoseUnusedNestedTypedefs(Record);
 
   if (IsInjectedClassName)
     assert(Record->isInjectedClassName() && "Broken injected-class-name");
 
   return Record;
 }
 
 /// Adjust the given function type for an instantiation of the
 /// given declaration, to cope with modifications to the function's type that
 /// aren't reflected in the type-source information.
 ///
 /// \param D The declaration we're instantiating.
 /// \param TInfo The already-instantiated type.
 static QualType adjustFunctionTypeForInstantiation(ASTContext &Context,
                                                    FunctionDecl *D,
                                                    TypeSourceInfo *TInfo) {
   const FunctionProtoType *OrigFunc
     = D->getType()->castAs<FunctionProtoType>();
   const FunctionProtoType *NewFunc
     = TInfo->getType()->castAs<FunctionProtoType>();
   if (OrigFunc->getExtInfo() == NewFunc->getExtInfo())
     return TInfo->getType();
 
   FunctionProtoType::ExtProtoInfo NewEPI = NewFunc->getExtProtoInfo();
   NewEPI.ExtInfo = OrigFunc->getExtInfo();
   return Context.getFunctionType(NewFunc->getReturnType(),
                                  NewFunc->getParamTypes(), NewEPI);
 }
 
 /// Normal class members are of more specific types and therefore
 /// don't make it here.  This function serves three purposes:
 ///   1) instantiating function templates
 ///   2) substituting friend and local function declarations
 ///   3) substituting deduction guide declarations for nested class templates
 Decl *TemplateDeclInstantiator::VisitFunctionDecl(
     FunctionDecl *D, TemplateParameterList *TemplateParams,
     RewriteKind FunctionRewriteKind) {
   // Check whether there is already a function template specialization for
   // this declaration.
   FunctionTemplateDecl *FunctionTemplate = D->getDescribedFunctionTemplate();
   if (FunctionTemplate && !TemplateParams) {
     ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
 
     void *InsertPos = nullptr;
     FunctionDecl *SpecFunc
       = FunctionTemplate->findSpecialization(Innermost, InsertPos);
 
     // If we already have a function template specialization, return it.
     if (SpecFunc)
       return SpecFunc;
   }
 
   bool isFriend;
   if (FunctionTemplate)
     isFriend = (FunctionTemplate->getFriendObjectKind() != Decl::FOK_None);
   else
     isFriend = (D->getFriendObjectKind() != Decl::FOK_None);
 
   bool MergeWithParentScope = (TemplateParams != nullptr) ||
     Owner->isFunctionOrMethod() ||
     !(isa<Decl>(Owner) &&
       cast<Decl>(Owner)->isDefinedOutsideFunctionOrMethod());
   LocalInstantiationScope Scope(SemaRef, MergeWithParentScope);
 
   ExplicitSpecifier InstantiatedExplicitSpecifier;
   if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D)) {
     InstantiatedExplicitSpecifier = SemaRef.instantiateExplicitSpecifier(
         TemplateArgs, DGuide->getExplicitSpecifier());
     if (InstantiatedExplicitSpecifier.isInvalid())
       return nullptr;
   }
 
   SmallVector<ParmVarDecl *, 4> Params;
   TypeSourceInfo *TInfo = SubstFunctionType(D, Params);
   if (!TInfo)
     return nullptr;
   QualType T = adjustFunctionTypeForInstantiation(SemaRef.Context, D, TInfo);
 
   if (TemplateParams && TemplateParams->size()) {
     auto *LastParam =
         dyn_cast<TemplateTypeParmDecl>(TemplateParams->asArray().back());
     if (LastParam && LastParam->isImplicit() &&
         LastParam->hasTypeConstraint()) {
       // In abbreviated templates, the type-constraints of invented template
       // type parameters are instantiated with the function type, invalidating
       // the TemplateParameterList which relied on the template type parameter
       // not having a type constraint. Recreate the TemplateParameterList with
       // the updated parameter list.
       TemplateParams = TemplateParameterList::Create(
           SemaRef.Context, TemplateParams->getTemplateLoc(),
           TemplateParams->getLAngleLoc(), TemplateParams->asArray(),
           TemplateParams->getRAngleLoc(), TemplateParams->getRequiresClause());
     }
   }
 
   NestedNameSpecifierLoc QualifierLoc = D->getQualifierLoc();
   if (QualifierLoc) {
     QualifierLoc = SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc,
                                                        TemplateArgs);
     if (!QualifierLoc)
       return nullptr;
   }
 
   Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
 
   // If we're instantiating a local function declaration, put the result
   // in the enclosing namespace; otherwise we need to find the instantiated
   // context.
   DeclContext *DC;
   if (D->isLocalExternDecl()) {
     DC = Owner;
     SemaRef.adjustContextForLocalExternDecl(DC);
   } else if (isFriend && QualifierLoc) {
     CXXScopeSpec SS;
     SS.Adopt(QualifierLoc);
     DC = SemaRef.computeDeclContext(SS);
     if (!DC) return nullptr;
   } else {
     DC = SemaRef.FindInstantiatedContext(D->getLocation(), D->getDeclContext(),
                                          TemplateArgs);
   }
 
   DeclarationNameInfo NameInfo
     = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
 
   if (FunctionRewriteKind != RewriteKind::None)
     adjustForRewrite(FunctionRewriteKind, D, T, TInfo, NameInfo);
 
   FunctionDecl *Function;
   if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D)) {
     Function = CXXDeductionGuideDecl::Create(
         SemaRef.Context, DC, D->getInnerLocStart(),
         InstantiatedExplicitSpecifier, NameInfo, T, TInfo,
         D->getSourceRange().getEnd(), DGuide->getCorrespondingConstructor(),
         DGuide->getDeductionCandidateKind());
     Function->setAccess(D->getAccess());
   } else {
     Function = FunctionDecl::Create(
         SemaRef.Context, DC, D->getInnerLocStart(), NameInfo, T, TInfo,
         D->getCanonicalDecl()->getStorageClass(), D->UsesFPIntrin(),
         D->isInlineSpecified(), D->hasWrittenPrototype(), D->getConstexprKind(),
         TrailingRequiresClause);
     Function->setFriendConstraintRefersToEnclosingTemplate(
         D->FriendConstraintRefersToEnclosingTemplate());
     Function->setRangeEnd(D->getSourceRange().getEnd());
   }
 
   if (D->isInlined())
     Function->setImplicitlyInline();
 
   if (QualifierLoc)
     Function->setQualifierInfo(QualifierLoc);
 
   if (D->isLocalExternDecl())
     Function->setLocalExternDecl();
 
   DeclContext *LexicalDC = Owner;
   if (!isFriend && D->isOutOfLine() && !D->isLocalExternDecl()) {
     assert(D->getDeclContext()->isFileContext());
     LexicalDC = D->getDeclContext();
   }
   else if (D->isLocalExternDecl()) {
     LexicalDC = SemaRef.CurContext;
   }
 
   Function->setLexicalDeclContext(LexicalDC);
 
   // Attach the parameters
   for (unsigned P = 0; P < Params.size(); ++P)
     if (Params[P])
       Params[P]->setOwningFunction(Function);
   Function->setParams(Params);
 
   if (TrailingRequiresClause)
     Function->setTrailingRequiresClause(TrailingRequiresClause);
 
   if (TemplateParams) {
     // Our resulting instantiation is actually a function template, since we
     // are substituting only the outer template parameters. For example, given
     //
     //   template<typename T>
     //   struct X {
     //     template<typename U> friend void f(T, U);
     //   };
     //
     //   X<int> x;
     //
     // We are instantiating the friend function template "f" within X<int>,
     // which means substituting int for T, but leaving "f" as a friend function
     // template.
     // Build the function template itself.
     FunctionTemplate = FunctionTemplateDecl::Create(SemaRef.Context, DC,
                                                     Function->getLocation(),
                                                     Function->getDeclName(),
                                                     TemplateParams, Function);
     Function->setDescribedFunctionTemplate(FunctionTemplate);
 
     FunctionTemplate->setLexicalDeclContext(LexicalDC);
 
     if (isFriend && D->isThisDeclarationADefinition()) {
       FunctionTemplate->setInstantiatedFromMemberTemplate(
                                            D->getDescribedFunctionTemplate());
     }
   } else if (FunctionTemplate &&
              SemaRef.CodeSynthesisContexts.back().Kind !=
                  Sema::CodeSynthesisContext::BuildingDeductionGuides) {
     // Record this function template specialization.
     ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
     Function->setFunctionTemplateSpecialization(FunctionTemplate,
                             TemplateArgumentList::CreateCopy(SemaRef.Context,
                                                              Innermost),
                                                 /*InsertPos=*/nullptr);
   } else if (FunctionRewriteKind == RewriteKind::None) {
     if (isFriend && D->isThisDeclarationADefinition()) {
       // Do not connect the friend to the template unless it's actually a
       // definition. We don't want non-template functions to be marked as being
       // template instantiations.
       Function->setInstantiationOfMemberFunction(D, TSK_ImplicitInstantiation);
     } else if (!isFriend) {
       // If this is not a function template, and this is not a friend (that is,
       // this is a locally declared function), save the instantiation
       // relationship for the purposes of constraint instantiation.
       Function->setInstantiatedFromDecl(D);
     }
   }
 
   if (isFriend) {
     Function->setObjectOfFriendDecl();
     if (FunctionTemplateDecl *FT = Function->getDescribedFunctionTemplate())
       FT->setObjectOfFriendDecl();
   }
 
   if (InitFunctionInstantiation(Function, D))
     Function->setInvalidDecl();
 
   bool IsExplicitSpecialization = false;
 
   LookupResult Previous(
       SemaRef, Function->getDeclName(), SourceLocation(),
       D->isLocalExternDecl() ? Sema::LookupRedeclarationWithLinkage
                              : Sema::LookupOrdinaryName,
       D->isLocalExternDecl() ? RedeclarationKind::ForExternalRedeclaration
                              : SemaRef.forRedeclarationInCurContext());
 
   if (DependentFunctionTemplateSpecializationInfo *DFTSI =
           D->getDependentSpecializationInfo()) {
     assert(isFriend && "dependent specialization info on "
                        "non-member non-friend function?");
 
     // Instantiate the explicit template arguments.
     TemplateArgumentListInfo ExplicitArgs;
     if (const auto *ArgsWritten = DFTSI->TemplateArgumentsAsWritten) {
       ExplicitArgs.setLAngleLoc(ArgsWritten->getLAngleLoc());
       ExplicitArgs.setRAngleLoc(ArgsWritten->getRAngleLoc());
       if (SemaRef.SubstTemplateArguments(ArgsWritten->arguments(), TemplateArgs,
                                          ExplicitArgs))
         return nullptr;
     }
 
     // Map the candidates for the primary template to their instantiations.
     for (FunctionTemplateDecl *FTD : DFTSI->getCandidates()) {
       if (NamedDecl *ND =
               SemaRef.FindInstantiatedDecl(D->getLocation(), FTD, TemplateArgs))
         Previous.addDecl(ND);
       else
         return nullptr;
     }
 
     if (SemaRef.CheckFunctionTemplateSpecialization(
             Function,
             DFTSI->TemplateArgumentsAsWritten ? &ExplicitArgs : nullptr,
             Previous))
       Function->setInvalidDecl();
 
     IsExplicitSpecialization = true;
   } else if (const ASTTemplateArgumentListInfo *ArgsWritten =
                  D->getTemplateSpecializationArgsAsWritten()) {
     // The name of this function was written as a template-id.
     SemaRef.LookupQualifiedName(Previous, DC);
 
     // Instantiate the explicit template arguments.
     TemplateArgumentListInfo ExplicitArgs(ArgsWritten->getLAngleLoc(),
                                           ArgsWritten->getRAngleLoc());
     if (SemaRef.SubstTemplateArguments(ArgsWritten->arguments(), TemplateArgs,
                                        ExplicitArgs))
       return nullptr;
 
     if (SemaRef.CheckFunctionTemplateSpecialization(Function,
                                                     &ExplicitArgs,
                                                     Previous))
       Function->setInvalidDecl();
 
     IsExplicitSpecialization = true;
   } else if (TemplateParams || !FunctionTemplate) {
     // Look only into the namespace where the friend would be declared to
     // find a previous declaration. This is the innermost enclosing namespace,
     // as described in ActOnFriendFunctionDecl.
     SemaRef.LookupQualifiedName(Previous, DC->getRedeclContext());
 
     // In C++, the previous declaration we find might be a tag type
     // (class or enum). In this case, the new declaration will hide the
     // tag type. Note that this does not apply if we're declaring a
     // typedef (C++ [dcl.typedef]p4).
     if (Previous.isSingleTagDecl())
       Previous.clear();
 
     // Filter out previous declarations that don't match the scope. The only
     // effect this has is to remove declarations found in inline namespaces
     // for friend declarations with unqualified names.
     if (isFriend && !QualifierLoc) {
       SemaRef.FilterLookupForScope(Previous, DC, /*Scope=*/ nullptr,
                                    /*ConsiderLinkage=*/ true,
                                    QualifierLoc.hasQualifier());
     }
   }
 
   // Per [temp.inst], default arguments in function declarations at local scope
   // are instantiated along with the enclosing declaration. For example:
   //
   //   template<typename T>
   //   void ft() {
   //     void f(int = []{ return T::value; }());
   //   }
   //   template void ft<int>(); // error: type 'int' cannot be used prior
   //                                      to '::' because it has no members
   //
   // The error is issued during instantiation of ft<int>() because substitution
   // into the default argument fails; the default argument is instantiated even
   // though it is never used.
   if (Function->isLocalExternDecl()) {
     for (ParmVarDecl *PVD : Function->parameters()) {
       if (!PVD->hasDefaultArg())
         continue;
       if (SemaRef.SubstDefaultArgument(D->getInnerLocStart(), PVD, TemplateArgs)) {
         // If substitution fails, the default argument is set to a
         // RecoveryExpr that wraps the uninstantiated default argument so
         // that downstream diagnostics are omitted.
         Expr *UninstExpr = PVD->getUninstantiatedDefaultArg();
         ExprResult ErrorResult = SemaRef.CreateRecoveryExpr(
             UninstExpr->getBeginLoc(), UninstExpr->getEndLoc(),
             { UninstExpr }, UninstExpr->getType());
         if (ErrorResult.isUsable())
           PVD->setDefaultArg(ErrorResult.get());
       }
     }
   }
 
   SemaRef.CheckFunctionDeclaration(/*Scope*/ nullptr, Function, Previous,
                                    IsExplicitSpecialization,
                                    Function->isThisDeclarationADefinition());
 
   // Check the template parameter list against the previous declaration. The
   // goal here is to pick up default arguments added since the friend was
   // declared; we know the template parameter lists match, since otherwise
   // we would not have picked this template as the previous declaration.
   if (isFriend && TemplateParams && FunctionTemplate->getPreviousDecl()) {
     SemaRef.CheckTemplateParameterList(
         TemplateParams,
         FunctionTemplate->getPreviousDecl()->getTemplateParameters(),
         Function->isThisDeclarationADefinition()
             ? Sema::TPC_FriendFunctionTemplateDefinition
             : Sema::TPC_FriendFunctionTemplate);
   }
 
   // If we're introducing a friend definition after the first use, trigger
   // instantiation.
   // FIXME: If this is a friend function template definition, we should check
   // to see if any specializations have been used.
   if (isFriend && D->isThisDeclarationADefinition() && Function->isUsed(false)) {
     if (MemberSpecializationInfo *MSInfo =
             Function->getMemberSpecializationInfo()) {
       if (MSInfo->getPointOfInstantiation().isInvalid()) {
         SourceLocation Loc = D->getLocation(); // FIXME
         MSInfo->setPointOfInstantiation(Loc);
         SemaRef.PendingLocalImplicitInstantiations.push_back(
             std::make_pair(Function, Loc));
       }
     }
   }
 
   if (D->isExplicitlyDefaulted()) {
     if (SubstDefaultedFunction(Function, D))
       return nullptr;
   }
   if (D->isDeleted())
     SemaRef.SetDeclDeleted(Function, D->getLocation(), D->getDeletedMessage());
 
   NamedDecl *PrincipalDecl =
       (TemplateParams ? cast<NamedDecl>(FunctionTemplate) : Function);
 
   // If this declaration lives in a different context from its lexical context,
   // add it to the corresponding lookup table.
   if (isFriend ||
       (Function->isLocalExternDecl() && !Function->getPreviousDecl()))
     DC->makeDeclVisibleInContext(PrincipalDecl);
 
   if (Function->isOverloadedOperator() && !DC->isRecord() &&
       PrincipalDecl->isInIdentifierNamespace(Decl::IDNS_Ordinary))
     PrincipalDecl->setNonMemberOperator();
 
   return Function;
 }
 
 Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
     CXXMethodDecl *D, TemplateParameterList *TemplateParams,
     RewriteKind FunctionRewriteKind) {
   FunctionTemplateDecl *FunctionTemplate = D->getDescribedFunctionTemplate();
   if (FunctionTemplate && !TemplateParams) {
     // We are creating a function template specialization from a function
     // template. Check whether there is already a function template
     // specialization for this particular set of template arguments.
     ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
 
     void *InsertPos = nullptr;
     FunctionDecl *SpecFunc
       = FunctionTemplate->findSpecialization(Innermost, InsertPos);
 
     // If we already have a function template specialization, return it.
     if (SpecFunc)
       return SpecFunc;
   }
 
   bool isFriend;
   if (FunctionTemplate)
     isFriend = (FunctionTemplate->getFriendObjectKind() != Decl::FOK_None);
   else
     isFriend = (D->getFriendObjectKind() != Decl::FOK_None);
 
   bool MergeWithParentScope = (TemplateParams != nullptr) ||
     !(isa<Decl>(Owner) &&
       cast<Decl>(Owner)->isDefinedOutsideFunctionOrMethod());
   LocalInstantiationScope Scope(SemaRef, MergeWithParentScope);
 
   Sema::LambdaScopeForCallOperatorInstantiationRAII LambdaScope(
       SemaRef, const_cast<CXXMethodDecl *>(D), TemplateArgs, Scope);
 
   // Instantiate enclosing template arguments for friends.
   SmallVector<TemplateParameterList *, 4> TempParamLists;
   unsigned NumTempParamLists = 0;
   if (isFriend && (NumTempParamLists = D->getNumTemplateParameterLists())) {
     TempParamLists.resize(NumTempParamLists);
     for (unsigned I = 0; I != NumTempParamLists; ++I) {
       TemplateParameterList *TempParams = D->getTemplateParameterList(I);
       TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
       if (!InstParams)
         return nullptr;
       TempParamLists[I] = InstParams;
     }
   }
 
   auto InstantiatedExplicitSpecifier = ExplicitSpecifier::getFromDecl(D);
   // deduction guides need this
   const bool CouldInstantiate =
       InstantiatedExplicitSpecifier.getExpr() == nullptr ||
       !InstantiatedExplicitSpecifier.getExpr()->isValueDependent();
 
   // Delay the instantiation of the explicit-specifier until after the
   // constraints are checked during template argument deduction.
   if (CouldInstantiate ||
       SemaRef.CodeSynthesisContexts.back().Kind !=
           Sema::CodeSynthesisContext::DeducedTemplateArgumentSubstitution) {
     InstantiatedExplicitSpecifier = SemaRef.instantiateExplicitSpecifier(
         TemplateArgs, InstantiatedExplicitSpecifier);
 
     if (InstantiatedExplicitSpecifier.isInvalid())
       return nullptr;
   } else {
     InstantiatedExplicitSpecifier.setKind(ExplicitSpecKind::Unresolved);
   }
 
   // Implicit destructors/constructors created for local classes in
   // DeclareImplicit* (see SemaDeclCXX.cpp) might not have an associated TSI.
   // Unfortunately there isn't enough context in those functions to
   // conditionally populate the TSI without breaking non-template related use
   // cases. Populate TSIs prior to calling SubstFunctionType to make sure we get
   // a proper transformation.
   if (cast<CXXRecordDecl>(D->getParent())->isLambda() &&
       !D->getTypeSourceInfo() &&
       isa<CXXConstructorDecl, CXXDestructorDecl>(D)) {
     TypeSourceInfo *TSI =
         SemaRef.Context.getTrivialTypeSourceInfo(D->getType());
     D->setTypeSourceInfo(TSI);
   }
 
   SmallVector<ParmVarDecl *, 4> Params;
   TypeSourceInfo *TInfo = SubstFunctionType(D, Params);
   if (!TInfo)
     return nullptr;
   QualType T = adjustFunctionTypeForInstantiation(SemaRef.Context, D, TInfo);
 
   if (TemplateParams && TemplateParams->size()) {
     auto *LastParam =
         dyn_cast<TemplateTypeParmDecl>(TemplateParams->asArray().back());
     if (LastParam && LastParam->isImplicit() &&
         LastParam->hasTypeConstraint()) {
       // In abbreviated templates, the type-constraints of invented template
       // type parameters are instantiated with the function type, invalidating
       // the TemplateParameterList which relied on the template type parameter
       // not having a type constraint. Recreate the TemplateParameterList with
       // the updated parameter list.
       TemplateParams = TemplateParameterList::Create(
           SemaRef.Context, TemplateParams->getTemplateLoc(),
           TemplateParams->getLAngleLoc(), TemplateParams->asArray(),
           TemplateParams->getRAngleLoc(), TemplateParams->getRequiresClause());
     }
   }
 
   NestedNameSpecifierLoc QualifierLoc = D->getQualifierLoc();
   if (QualifierLoc) {
     QualifierLoc = SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc,
                                                  TemplateArgs);
     if (!QualifierLoc)
       return nullptr;
   }
 
   DeclContext *DC = Owner;
   if (isFriend) {
     if (QualifierLoc) {
       CXXScopeSpec SS;
       SS.Adopt(QualifierLoc);
       DC = SemaRef.computeDeclContext(SS);
 
       if (DC && SemaRef.RequireCompleteDeclContext(SS, DC))
         return nullptr;
     } else {
       DC = SemaRef.FindInstantiatedContext(D->getLocation(),
                                            D->getDeclContext(),
                                            TemplateArgs);
     }
     if (!DC) return nullptr;
   }
 
   CXXRecordDecl *Record = cast<CXXRecordDecl>(DC);
   Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
 
   DeclarationNameInfo NameInfo
     = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
 
   if (FunctionRewriteKind != RewriteKind::None)
     adjustForRewrite(FunctionRewriteKind, D, T, TInfo, NameInfo);
 
   // Build the instantiated method declaration.
   CXXMethodDecl *Method = nullptr;
 
   SourceLocation StartLoc = D->getInnerLocStart();
   if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(D)) {
     Method = CXXConstructorDecl::Create(
         SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
         InstantiatedExplicitSpecifier, Constructor->UsesFPIntrin(),
         Constructor->isInlineSpecified(), false,
         Constructor->getConstexprKind(), InheritedConstructor(),
         TrailingRequiresClause);
     Method->setRangeEnd(Constructor->getEndLoc());
   } else if (CXXDestructorDecl *Destructor = dyn_cast<CXXDestructorDecl>(D)) {
     Method = CXXDestructorDecl::Create(
         SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
         Destructor->UsesFPIntrin(), Destructor->isInlineSpecified(), false,
         Destructor->getConstexprKind(), TrailingRequiresClause);
     Method->setIneligibleOrNotSelected(true);
     Method->setRangeEnd(Destructor->getEndLoc());
     Method->setDeclName(SemaRef.Context.DeclarationNames.getCXXDestructorName(
         SemaRef.Context.getCanonicalType(
             SemaRef.Context.getTypeDeclType(Record))));
   } else if (CXXConversionDecl *Conversion = dyn_cast<CXXConversionDecl>(D)) {
     Method = CXXConversionDecl::Create(
         SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
         Conversion->UsesFPIntrin(), Conversion->isInlineSpecified(),
         InstantiatedExplicitSpecifier, Conversion->getConstexprKind(),
         Conversion->getEndLoc(), TrailingRequiresClause);
   } else {
     StorageClass SC = D->isStatic() ? SC_Static : SC_None;
     Method = CXXMethodDecl::Create(
         SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo, SC,
         D->UsesFPIntrin(), D->isInlineSpecified(), D->getConstexprKind(),
         D->getEndLoc(), TrailingRequiresClause);
   }
 
   if (D->isInlined())
     Method->setImplicitlyInline();
 
   if (QualifierLoc)
     Method->setQualifierInfo(QualifierLoc);
 
   if (TemplateParams) {
     // Our resulting instantiation is actually a function template, since we
     // are substituting only the outer template parameters. For example, given
     //
     //   template<typename T>
     //   struct X {
     //     template<typename U> void f(T, U);
     //   };
     //
     //   X<int> x;
     //
     // We are instantiating the member template "f" within X<int>, which means
     // substituting int for T, but leaving "f" as a member function template.
     // Build the function template itself.
     FunctionTemplate = FunctionTemplateDecl::Create(SemaRef.Context, Record,
                                                     Method->getLocation(),
                                                     Method->getDeclName(),
                                                     TemplateParams, Method);
     if (isFriend) {
       FunctionTemplate->setLexicalDeclContext(Owner);
       FunctionTemplate->setObjectOfFriendDecl();
     } else if (D->isOutOfLine())
       FunctionTemplate->setLexicalDeclContext(D->getLexicalDeclContext());
     Method->setDescribedFunctionTemplate(FunctionTemplate);
   } else if (FunctionTemplate) {
     // Record this function template specialization.
     ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
     Method->setFunctionTemplateSpecialization(FunctionTemplate,
                          TemplateArgumentList::CreateCopy(SemaRef.Context,
                                                           Innermost),
                                               /*InsertPos=*/nullptr);
   } else if (!isFriend && FunctionRewriteKind == RewriteKind::None) {
     // Record that this is an instantiation of a member function.
     Method->setInstantiationOfMemberFunction(D, TSK_ImplicitInstantiation);
   }
 
   // If we are instantiating a member function defined
   // out-of-line, the instantiation will have the same lexical
   // context (which will be a namespace scope) as the template.
   if (isFriend) {
     if (NumTempParamLists)
       Method->setTemplateParameterListsInfo(
           SemaRef.Context,
           llvm::ArrayRef(TempParamLists.data(), NumTempParamLists));
 
     Method->setLexicalDeclContext(Owner);
     Method->setObjectOfFriendDecl();
   } else if (D->isOutOfLine())
     Method->setLexicalDeclContext(D->getLexicalDeclContext());
 
   // Attach the parameters
   for (unsigned P = 0; P < Params.size(); ++P)
     Params[P]->setOwningFunction(Method);
   Method->setParams(Params);
 
   if (InitMethodInstantiation(Method, D))
     Method->setInvalidDecl();
 
   LookupResult Previous(SemaRef, NameInfo, Sema::LookupOrdinaryName,
                         RedeclarationKind::ForExternalRedeclaration);
 
   bool IsExplicitSpecialization = false;
 
   // If the name of this function was written as a template-id, instantiate
   // the explicit template arguments.
   if (DependentFunctionTemplateSpecializationInfo *DFTSI =
           D->getDependentSpecializationInfo()) {
     // Instantiate the explicit template arguments.
     TemplateArgumentListInfo ExplicitArgs;
     if (const auto *ArgsWritten = DFTSI->TemplateArgumentsAsWritten) {
       ExplicitArgs.setLAngleLoc(ArgsWritten->getLAngleLoc());
       ExplicitArgs.setRAngleLoc(ArgsWritten->getRAngleLoc());
       if (SemaRef.SubstTemplateArguments(ArgsWritten->arguments(), TemplateArgs,
                                          ExplicitArgs))
         return nullptr;
     }
 
     // Map the candidates for the primary template to their instantiations.
     for (FunctionTemplateDecl *FTD : DFTSI->getCandidates()) {
       if (NamedDecl *ND =
               SemaRef.FindInstantiatedDecl(D->getLocation(), FTD, TemplateArgs))
         Previous.addDecl(ND);
       else
         return nullptr;
     }
 
     if (SemaRef.CheckFunctionTemplateSpecialization(
             Method, DFTSI->TemplateArgumentsAsWritten ? &ExplicitArgs : nullptr,
             Previous))
       Method->setInvalidDecl();
 
     IsExplicitSpecialization = true;
   } else if (const ASTTemplateArgumentListInfo *ArgsWritten =
                  D->getTemplateSpecializationArgsAsWritten()) {
     SemaRef.LookupQualifiedName(Previous, DC);
 
     TemplateArgumentListInfo ExplicitArgs(ArgsWritten->getLAngleLoc(),
                                           ArgsWritten->getRAngleLoc());
 
     if (SemaRef.SubstTemplateArguments(ArgsWritten->arguments(), TemplateArgs,
                                        ExplicitArgs))
       return nullptr;
 
     if (SemaRef.CheckFunctionTemplateSpecialization(Method,
                                                     &ExplicitArgs,
                                                     Previous))
       Method->setInvalidDecl();
 
     IsExplicitSpecialization = true;
   } else if (!FunctionTemplate || TemplateParams || isFriend) {
     SemaRef.LookupQualifiedName(Previous, Record);
 
     // In C++, the previous declaration we find might be a tag type
     // (class or enum). In this case, the new declaration will hide the
     // tag type. Note that this does not apply if we're declaring a
     // typedef (C++ [dcl.typedef]p4).
     if (Previous.isSingleTagDecl())
       Previous.clear();
   }
 
   // Per [temp.inst], default arguments in member functions of local classes
   // are instantiated along with the member function declaration. For example:
   //
   //   template<typename T>
   //   void ft() {
   //     struct lc {
   //       int operator()(int p = []{ return T::value; }());
   //     };
   //   }
   //   template void ft<int>(); // error: type 'int' cannot be used prior
   //                                      to '::'because it has no members
   //
   // The error is issued during instantiation of ft<int>()::lc::operator()
   // because substitution into the default argument fails; the default argument
   // is instantiated even though it is never used.
   if (D->isInLocalScopeForInstantiation()) {
     for (unsigned P = 0; P < Params.size(); ++P) {
       if (!Params[P]->hasDefaultArg())
         continue;
       if (SemaRef.SubstDefaultArgument(StartLoc, Params[P], TemplateArgs)) {
         // If substitution fails, the default argument is set to a
         // RecoveryExpr that wraps the uninstantiated default argument so
         // that downstream diagnostics are omitted.
         Expr *UninstExpr = Params[P]->getUninstantiatedDefaultArg();
         ExprResult ErrorResult = SemaRef.CreateRecoveryExpr(
             UninstExpr->getBeginLoc(), UninstExpr->getEndLoc(),
             { UninstExpr }, UninstExpr->getType());
         if (ErrorResult.isUsable())
           Params[P]->setDefaultArg(ErrorResult.get());
       }
     }
   }
 
   SemaRef.CheckFunctionDeclaration(nullptr, Method, Previous,
                                    IsExplicitSpecialization,
                                    Method->isThisDeclarationADefinition());
 
   if (D->isPureVirtual())
     SemaRef.CheckPureMethod(Method, SourceRange());
 
   // Propagate access.  For a non-friend declaration, the access is
   // whatever we're propagating from.  For a friend, it should be the
   // previous declaration we just found.
   if (isFriend && Method->getPreviousDecl())
     Method->setAccess(Method->getPreviousDecl()->getAccess());
   else
     Method->setAccess(D->getAccess());
   if (FunctionTemplate)
     FunctionTemplate->setAccess(Method->getAccess());
 
   SemaRef.CheckOverrideControl(Method);
 
   // If a function is defined as defaulted or deleted, mark it as such now.
   if (D->isExplicitlyDefaulted()) {
     if (SubstDefaultedFunction(Method, D))
       return nullptr;
   }
   if (D->isDeletedAsWritten())
     SemaRef.SetDeclDeleted(Method, Method->getLocation(),
                            D->getDeletedMessage());
 
   // If this is an explicit specialization, mark the implicitly-instantiated
   // template specialization as being an explicit specialization too.
   // FIXME: Is this necessary?
   if (IsExplicitSpecialization && !isFriend)
     SemaRef.CompleteMemberSpecialization(Method, Previous);
 
   // If the method is a special member function, we need to mark it as
   // ineligible so that Owner->addDecl() won't mark the class as non trivial.
   // At the end of the class instantiation, we calculate eligibility again and
   // then we adjust trivility if needed.
   // We need this check to happen only after the method parameters are set,
   // because being e.g. a copy constructor depends on the instantiated
   // arguments.
   if (auto *Constructor = dyn_cast<CXXConstructorDecl>(Method)) {
     if (Constructor->isDefaultConstructor() ||
         Constructor->isCopyOrMoveConstructor())
       Method->setIneligibleOrNotSelected(true);
   } else if (Method->isCopyAssignmentOperator() ||
              Method->isMoveAssignmentOperator()) {
     Method->setIneligibleOrNotSelected(true);
   }
 
   // If there's a function template, let our caller handle it.
   if (FunctionTemplate) {
     // do nothing
 
   // Don't hide a (potentially) valid declaration with an invalid one.
   } else if (Method->isInvalidDecl() && !Previous.empty()) {
     // do nothing
 
   // Otherwise, check access to friends and make them visible.
   } else if (isFriend) {
     // We only need to re-check access for methods which we didn't
     // manage to match during parsing.
     if (!D->getPreviousDecl())
       SemaRef.CheckFriendAccess(Method);
 
     Record->makeDeclVisibleInContext(Method);
 
   // Otherwise, add the declaration.  We don't need to do this for
   // class-scope specializations because we'll have matched them with
   // the appropriate template.
   } else {
     Owner->addDecl(Method);
   }
 
   // PR17480: Honor the used attribute to instantiate member function
   // definitions
   if (Method->hasAttr<UsedAttr>()) {
     if (const auto *A = dyn_cast<CXXRecordDecl>(Owner)) {
       SourceLocation Loc;
       if (const MemberSpecializationInfo *MSInfo =
               A->getMemberSpecializationInfo())
         Loc = MSInfo->getPointOfInstantiation();
       else if (const auto *Spec = dyn_cast<ClassTemplateSpecializationDecl>(A))
         Loc = Spec->getPointOfInstantiation();
       SemaRef.MarkFunctionReferenced(Loc, Method);
     }
   }
 
   return Method;
 }
 
 Decl *TemplateDeclInstantiator::VisitCXXConstructorDecl(CXXConstructorDecl *D) {
   return VisitCXXMethodDecl(D);
 }
 
 Decl *TemplateDeclInstantiator::VisitCXXDestructorDecl(CXXDestructorDecl *D) {
   return VisitCXXMethodDecl(D);
 }
 
 Decl *TemplateDeclInstantiator::VisitCXXConversionDecl(CXXConversionDecl *D) {
   return VisitCXXMethodDecl(D);
 }
 
 Decl *TemplateDeclInstantiator::VisitParmVarDecl(ParmVarDecl *D) {
   return SemaRef.SubstParmVarDecl(D, TemplateArgs, /*indexAdjustment*/ 0,
                                   std::nullopt,
                                   /*ExpectParameterPack=*/false);
 }
 
 Decl *TemplateDeclInstantiator::VisitTemplateTypeParmDecl(
                                                     TemplateTypeParmDecl *D) {
   assert(D->getTypeForDecl()->isTemplateTypeParmType());
 
   std::optional<unsigned> NumExpanded;
 
   if (const TypeConstraint *TC = D->getTypeConstraint()) {
     if (D->isPackExpansion() && !D->isExpandedParameterPack()) {
       assert(TC->getTemplateArgsAsWritten() &&
              "type parameter can only be an expansion when explicit arguments "
              "are specified");
       // The template type parameter pack's type is a pack expansion of types.
       // Determine whether we need to expand this parameter pack into separate
       // types.
       SmallVector<UnexpandedParameterPack, 2> Unexpanded;
       for (auto &ArgLoc : TC->getTemplateArgsAsWritten()->arguments())
         SemaRef.collectUnexpandedParameterPacks(ArgLoc, Unexpanded);
 
       // Determine whether the set of unexpanded parameter packs can and should
       // be expanded.
       bool Expand = true;
       bool RetainExpansion = false;
       if (SemaRef.CheckParameterPacksForExpansion(
               cast<CXXFoldExpr>(TC->getImmediatelyDeclaredConstraint())
                   ->getEllipsisLoc(),
               SourceRange(TC->getConceptNameLoc(),
                           TC->hasExplicitTemplateArgs() ?
                           TC->getTemplateArgsAsWritten()->getRAngleLoc() :
                           TC->getConceptNameInfo().getEndLoc()),
               Unexpanded, TemplateArgs, Expand, RetainExpansion, NumExpanded))
         return nullptr;
     }
   }
 
   TemplateTypeParmDecl *Inst = TemplateTypeParmDecl::Create(
       SemaRef.Context, Owner, D->getBeginLoc(), D->getLocation(),
       D->getDepth() - TemplateArgs.getNumSubstitutedLevels(), D->getIndex(),
       D->getIdentifier(), D->wasDeclaredWithTypename(), D->isParameterPack(),
       D->hasTypeConstraint(), NumExpanded);
 
   Inst->setAccess(AS_public);
   Inst->setImplicit(D->isImplicit());
   if (auto *TC = D->getTypeConstraint()) {
     if (!D->isImplicit()) {
       // Invented template parameter type constraints will be instantiated
       // with the corresponding auto-typed parameter as it might reference
       // other parameters.
       if (SemaRef.SubstTypeConstraint(Inst, TC, TemplateArgs,
                                       EvaluateConstraints))
         return nullptr;
     }
   }
   if (D->hasDefaultArgument() && !D->defaultArgumentWasInherited()) {
     TemplateArgumentLoc Output;
     if (!SemaRef.SubstTemplateArgument(D->getDefaultArgument(), TemplateArgs,
                                        Output))
       Inst->setDefaultArgument(SemaRef.getASTContext(), Output);
   }
 
   // Introduce this template parameter's instantiation into the instantiation
   // scope.
   SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Inst);
 
   return Inst;
 }
 
 Decl *TemplateDeclInstantiator::VisitNonTypeTemplateParmDecl(
                                                  NonTypeTemplateParmDecl *D) {
   // Substitute into the type of the non-type template parameter.
   TypeLoc TL = D->getTypeSourceInfo()->getTypeLoc();
   SmallVector<TypeSourceInfo *, 4> ExpandedParameterPackTypesAsWritten;
   SmallVector<QualType, 4> ExpandedParameterPackTypes;
   bool IsExpandedParameterPack = false;
   TypeSourceInfo *DI;
   QualType T;
   bool Invalid = false;
 
   if (D->isExpandedParameterPack()) {
     // The non-type template parameter pack is an already-expanded pack
     // expansion of types. Substitute into each of the expanded types.
     ExpandedParameterPackTypes.reserve(D->getNumExpansionTypes());
     ExpandedParameterPackTypesAsWritten.reserve(D->getNumExpansionTypes());
     for (unsigned I = 0, N = D->getNumExpansionTypes(); I != N; ++I) {
       TypeSourceInfo *NewDI =
           SemaRef.SubstType(D->getExpansionTypeSourceInfo(I), TemplateArgs,
                             D->getLocation(), D->getDeclName());
       if (!NewDI)
         return nullptr;
 
       QualType NewT =
           SemaRef.CheckNonTypeTemplateParameterType(NewDI, D->getLocation());
       if (NewT.isNull())
         return nullptr;
 
       ExpandedParameterPackTypesAsWritten.push_back(NewDI);
       ExpandedParameterPackTypes.push_back(NewT);
     }
 
     IsExpandedParameterPack = true;
     DI = D->getTypeSourceInfo();
     T = DI->getType();
   } else if (D->isPackExpansion()) {
     // The non-type template parameter pack's type is a pack expansion of types.
     // Determine whether we need to expand this parameter pack into separate
     // types.
     PackExpansionTypeLoc Expansion = TL.castAs<PackExpansionTypeLoc>();
     TypeLoc Pattern = Expansion.getPatternLoc();
     SmallVector<UnexpandedParameterPack, 2> Unexpanded;
     SemaRef.collectUnexpandedParameterPacks(Pattern, Unexpanded);
 
     // Determine whether the set of unexpanded parameter packs can and should
     // be expanded.
     bool Expand = true;
     bool RetainExpansion = false;
     std::optional<unsigned> OrigNumExpansions =
         Expansion.getTypePtr()->getNumExpansions();
     std::optional<unsigned> NumExpansions = OrigNumExpansions;
     if (SemaRef.CheckParameterPacksForExpansion(Expansion.getEllipsisLoc(),
                                                 Pattern.getSourceRange(),
                                                 Unexpanded,
                                                 TemplateArgs,
                                                 Expand, RetainExpansion,
                                                 NumExpansions))
       return nullptr;
 
     if (Expand) {
       for (unsigned I = 0; I != *NumExpansions; ++I) {
         Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, I);
         TypeSourceInfo *NewDI = SemaRef.SubstType(Pattern, TemplateArgs,
                                                   D->getLocation(),
                                                   D->getDeclName());
         if (!NewDI)
           return nullptr;
 
         QualType NewT =
             SemaRef.CheckNonTypeTemplateParameterType(NewDI, D->getLocation());
         if (NewT.isNull())
           return nullptr;
 
         ExpandedParameterPackTypesAsWritten.push_back(NewDI);
         ExpandedParameterPackTypes.push_back(NewT);
       }
 
       // Note that we have an expanded parameter pack. The "type" of this
       // expanded parameter pack is the original expansion type, but callers
       // will end up using the expanded parameter pack types for type-checking.
       IsExpandedParameterPack = true;
       DI = D->getTypeSourceInfo();
       T = DI->getType();
     } else {
       // We cannot fully expand the pack expansion now, so substitute into the
       // pattern and create a new pack expansion type.
       Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, -1);
       TypeSourceInfo *NewPattern = SemaRef.SubstType(Pattern, TemplateArgs,
                                                      D->getLocation(),
                                                      D->getDeclName());
       if (!NewPattern)
         return nullptr;
 
       SemaRef.CheckNonTypeTemplateParameterType(NewPattern, D->getLocation());
       DI = SemaRef.CheckPackExpansion(NewPattern, Expansion.getEllipsisLoc(),
                                       NumExpansions);
       if (!DI)
         return nullptr;
 
       T = DI->getType();
     }
   } else {
     // Simple case: substitution into a parameter that is not a parameter pack.
     DI = SemaRef.SubstType(D->getTypeSourceInfo(), TemplateArgs,
                            D->getLocation(), D->getDeclName());
     if (!DI)
       return nullptr;
 
     // Check that this type is acceptable for a non-type template parameter.
     T = SemaRef.CheckNonTypeTemplateParameterType(DI, D->getLocation());
     if (T.isNull()) {
       T = SemaRef.Context.IntTy;
       Invalid = true;
     }
   }
 
   NonTypeTemplateParmDecl *Param;
   if (IsExpandedParameterPack)
     Param = NonTypeTemplateParmDecl::Create(
         SemaRef.Context, Owner, D->getInnerLocStart(), D->getLocation(),
         D->getDepth() - TemplateArgs.getNumSubstitutedLevels(),
         D->getPosition(), D->getIdentifier(), T, DI, ExpandedParameterPackTypes,
         ExpandedParameterPackTypesAsWritten);
   else
     Param = NonTypeTemplateParmDecl::Create(
         SemaRef.Context, Owner, D->getInnerLocStart(), D->getLocation(),
         D->getDepth() - TemplateArgs.getNumSubstitutedLevels(),
         D->getPosition(), D->getIdentifier(), T, D->isParameterPack(), DI);
 
   if (AutoTypeLoc AutoLoc = DI->getTypeLoc().getContainedAutoTypeLoc())
     if (AutoLoc.isConstrained()) {
       SourceLocation EllipsisLoc;
       if (IsExpandedParameterPack)
         EllipsisLoc =
             DI->getTypeLoc().getAs<PackExpansionTypeLoc>().getEllipsisLoc();
       else if (auto *Constraint = dyn_cast_if_present<CXXFoldExpr>(
                    D->getPlaceholderTypeConstraint()))
         EllipsisLoc = Constraint->getEllipsisLoc();
       // Note: We attach the uninstantiated constriant here, so that it can be
       // instantiated relative to the top level, like all our other
       // constraints.
       if (SemaRef.AttachTypeConstraint(AutoLoc, /*NewConstrainedParm=*/Param,
                                        /*OrigConstrainedParm=*/D, EllipsisLoc))
         Invalid = true;
     }
 
   Param->setAccess(AS_public);
   Param->setImplicit(D->isImplicit());
   if (Invalid)
     Param->setInvalidDecl();
 
   if (D->hasDefaultArgument() && !D->defaultArgumentWasInherited()) {
     EnterExpressionEvaluationContext ConstantEvaluated(
         SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     TemplateArgumentLoc Result;
     if (!SemaRef.SubstTemplateArgument(D->getDefaultArgument(), TemplateArgs,
                                        Result))
       Param->setDefaultArgument(SemaRef.Context, Result);
   }
 
   // Introduce this template parameter's instantiation into the instantiation
   // scope.
   SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Param);
   return Param;
 }
 
 static void collectUnexpandedParameterPacks(
     Sema &S,
     TemplateParameterList *Params,
     SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
   for (const auto &P : *Params) {
     if (P->isTemplateParameterPack())
       continue;
     if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(P))
       S.collectUnexpandedParameterPacks(NTTP->getTypeSourceInfo()->getTypeLoc(),
                                         Unexpanded);
     if (TemplateTemplateParmDecl *TTP = dyn_cast<TemplateTemplateParmDecl>(P))
       collectUnexpandedParameterPacks(S, TTP->getTemplateParameters(),
                                       Unexpanded);
   }
 }
 
 Decl *
 TemplateDeclInstantiator::VisitTemplateTemplateParmDecl(
                                                   TemplateTemplateParmDecl *D) {
   // Instantiate the template parameter list of the template template parameter.
   TemplateParameterList *TempParams = D->getTemplateParameters();
   TemplateParameterList *InstParams;
   SmallVector<TemplateParameterList*, 8> ExpandedParams;
 
   bool IsExpandedParameterPack = false;
 
   if (D->isExpandedParameterPack()) {
     // The template template parameter pack is an already-expanded pack
     // expansion of template parameters. Substitute into each of the expanded
     // parameters.
     ExpandedParams.reserve(D->getNumExpansionTemplateParameters());
     for (unsigned I = 0, N = D->getNumExpansionTemplateParameters();
          I != N; ++I) {
       LocalInstantiationScope Scope(SemaRef);
       TemplateParameterList *Expansion =
         SubstTemplateParams(D->getExpansionTemplateParameters(I));
       if (!Expansion)
         return nullptr;
       ExpandedParams.push_back(Expansion);
     }
 
     IsExpandedParameterPack = true;
     InstParams = TempParams;
   } else if (D->isPackExpansion()) {
     // The template template parameter pack expands to a pack of template
     // template parameters. Determine whether we need to expand this parameter
     // pack into separate parameters.
     SmallVector<UnexpandedParameterPack, 2> Unexpanded;
     collectUnexpandedParameterPacks(SemaRef, D->getTemplateParameters(),
                                     Unexpanded);
 
     // Determine whether the set of unexpanded parameter packs can and should
     // be expanded.
     bool Expand = true;
     bool RetainExpansion = false;
     std::optional<unsigned> NumExpansions;
     if (SemaRef.CheckParameterPacksForExpansion(D->getLocation(),
                                                 TempParams->getSourceRange(),
                                                 Unexpanded,
                                                 TemplateArgs,
                                                 Expand, RetainExpansion,
                                                 NumExpansions))
       return nullptr;
 
     if (Expand) {
       for (unsigned I = 0; I != *NumExpansions; ++I) {
         Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, I);
         LocalInstantiationScope Scope(SemaRef);
         TemplateParameterList *Expansion = SubstTemplateParams(TempParams);
         if (!Expansion)
           return nullptr;
         ExpandedParams.push_back(Expansion);
       }
 
       // Note that we have an expanded parameter pack. The "type" of this
       // expanded parameter pack is the original expansion type, but callers
       // will end up using the expanded parameter pack types for type-checking.
       IsExpandedParameterPack = true;
       InstParams = TempParams;
     } else {
       // We cannot fully expand the pack expansion now, so just substitute
       // into the pattern.
       Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, -1);
 
       LocalInstantiationScope Scope(SemaRef);
       InstParams = SubstTemplateParams(TempParams);
       if (!InstParams)
         return nullptr;
     }
   } else {
     // Perform the actual substitution of template parameters within a new,
     // local instantiation scope.
     LocalInstantiationScope Scope(SemaRef);
     InstParams = SubstTemplateParams(TempParams);
     if (!InstParams)
       return nullptr;
   }
 
   // Build the template template parameter.
   TemplateTemplateParmDecl *Param;
   if (IsExpandedParameterPack)
     Param = TemplateTemplateParmDecl::Create(
         SemaRef.Context, Owner, D->getLocation(),
         D->getDepth() - TemplateArgs.getNumSubstitutedLevels(),
         D->getPosition(), D->getIdentifier(), D->wasDeclaredWithTypename(),
         InstParams, ExpandedParams);
   else
     Param = TemplateTemplateParmDecl::Create(
         SemaRef.Context, Owner, D->getLocation(),
         D->getDepth() - TemplateArgs.getNumSubstitutedLevels(),
         D->getPosition(), D->isParameterPack(), D->getIdentifier(),
         D->wasDeclaredWithTypename(), InstParams);
   if (D->hasDefaultArgument() && !D->defaultArgumentWasInherited()) {
     NestedNameSpecifierLoc QualifierLoc =
         D->getDefaultArgument().getTemplateQualifierLoc();
     QualifierLoc =
         SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc, TemplateArgs);
     TemplateName TName = SemaRef.SubstTemplateName(
         QualifierLoc, D->getDefaultArgument().getArgument().getAsTemplate(),
         D->getDefaultArgument().getTemplateNameLoc(), TemplateArgs);
     if (!TName.isNull())
       Param->setDefaultArgument(
           SemaRef.Context,
           TemplateArgumentLoc(SemaRef.Context, TemplateArgument(TName),
                               D->getDefaultArgument().getTemplateQualifierLoc(),
                               D->getDefaultArgument().getTemplateNameLoc()));
   }
   Param->setAccess(AS_public);
   Param->setImplicit(D->isImplicit());
 
   // Introduce this template parameter's instantiation into the instantiation
   // scope.
   SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Param);
 
   return Param;
 }
 
 Decl *TemplateDeclInstantiator::VisitUsingDirectiveDecl(UsingDirectiveDecl *D) {
   // Using directives are never dependent (and never contain any types or
   // expressions), so they require no explicit instantiation work.
 
   UsingDirectiveDecl *Inst
     = UsingDirectiveDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                  D->getNamespaceKeyLocation(),
                                  D->getQualifierLoc(),
                                  D->getIdentLocation(),
                                  D->getNominatedNamespace(),
                                  D->getCommonAncestor());
 
   // Add the using directive to its declaration context
   // only if this is not a function or method.
   if (!Owner->isFunctionOrMethod())
     Owner->addDecl(Inst);
 
   return Inst;
 }
 
 Decl *TemplateDeclInstantiator::VisitBaseUsingDecls(BaseUsingDecl *D,
                                                     BaseUsingDecl *Inst,
                                                     LookupResult *Lookup) {
 
   bool isFunctionScope = Owner->isFunctionOrMethod();
 
   for (auto *Shadow : D->shadows()) {
     // FIXME: UsingShadowDecl doesn't preserve its immediate target, so
     // reconstruct it in the case where it matters. Hm, can we extract it from
     // the DeclSpec when parsing and save it in the UsingDecl itself?
     NamedDecl *OldTarget = Shadow->getTargetDecl();
     if (auto *CUSD = dyn_cast<ConstructorUsingShadowDecl>(Shadow))
       if (auto *BaseShadow = CUSD->getNominatedBaseClassShadowDecl())
         OldTarget = BaseShadow;
 
     NamedDecl *InstTarget = nullptr;
     if (auto *EmptyD =
             dyn_cast<UnresolvedUsingIfExistsDecl>(Shadow->getTargetDecl())) {
       InstTarget = UnresolvedUsingIfExistsDecl::Create(
           SemaRef.Context, Owner, EmptyD->getLocation(), EmptyD->getDeclName());
     } else {
       InstTarget = cast_or_null<NamedDecl>(SemaRef.FindInstantiatedDecl(
           Shadow->getLocation(), OldTarget, TemplateArgs));
     }
     if (!InstTarget)
       return nullptr;
 
     UsingShadowDecl *PrevDecl = nullptr;
     if (Lookup &&
         SemaRef.CheckUsingShadowDecl(Inst, InstTarget, *Lookup, PrevDecl))
       continue;
 
     if (UsingShadowDecl *OldPrev = getPreviousDeclForInstantiation(Shadow))
       PrevDecl = cast_or_null<UsingShadowDecl>(SemaRef.FindInstantiatedDecl(
           Shadow->getLocation(), OldPrev, TemplateArgs));
 
     UsingShadowDecl *InstShadow = SemaRef.BuildUsingShadowDecl(
         /*Scope*/ nullptr, Inst, InstTarget, PrevDecl);
     SemaRef.Context.setInstantiatedFromUsingShadowDecl(InstShadow, Shadow);
 
     if (isFunctionScope)
       SemaRef.CurrentInstantiationScope->InstantiatedLocal(Shadow, InstShadow);
   }
 
   return Inst;
 }
 
 Decl *TemplateDeclInstantiator::VisitUsingDecl(UsingDecl *D) {
 
   // The nested name specifier may be dependent, for example
   //     template <typename T> struct t {
   //       struct s1 { T f1(); };
   //       struct s2 : s1 { using s1::f1; };
   //     };
   //     template struct t<int>;
   // Here, in using s1::f1, s1 refers to t<T>::s1;
   // we need to substitute for t<int>::s1.
   NestedNameSpecifierLoc QualifierLoc
     = SemaRef.SubstNestedNameSpecifierLoc(D->getQualifierLoc(),
                                           TemplateArgs);
   if (!QualifierLoc)
     return nullptr;
 
   // For an inheriting constructor declaration, the name of the using
   // declaration is the name of a constructor in this class, not in the
   // base class.
   DeclarationNameInfo NameInfo = D->getNameInfo();
   if (NameInfo.getName().getNameKind() == DeclarationName::CXXConstructorName)
     if (auto *RD = dyn_cast<CXXRecordDecl>(SemaRef.CurContext))
       NameInfo.setName(SemaRef.Context.DeclarationNames.getCXXConstructorName(
           SemaRef.Context.getCanonicalType(SemaRef.Context.getRecordType(RD))));
 
   // We only need to do redeclaration lookups if we're in a class scope (in
   // fact, it's not really even possible in non-class scopes).
   bool CheckRedeclaration = Owner->isRecord();
   LookupResult Prev(SemaRef, NameInfo, Sema::LookupUsingDeclName,
                     RedeclarationKind::ForVisibleRedeclaration);
 
   UsingDecl *NewUD = UsingDecl::Create(SemaRef.Context, Owner,
                                        D->getUsingLoc(),
                                        QualifierLoc,
                                        NameInfo,
                                        D->hasTypename());
 
   CXXScopeSpec SS;
   SS.Adopt(QualifierLoc);
   if (CheckRedeclaration) {
     Prev.setHideTags(false);
     SemaRef.LookupQualifiedName(Prev, Owner);
 
     // Check for invalid redeclarations.
     if (SemaRef.CheckUsingDeclRedeclaration(D->getUsingLoc(),
                                             D->hasTypename(), SS,
                                             D->getLocation(), Prev))
       NewUD->setInvalidDecl();
   }
 
   if (!NewUD->isInvalidDecl() &&
       SemaRef.CheckUsingDeclQualifier(D->getUsingLoc(), D->hasTypename(), SS,
                                       NameInfo, D->getLocation(), nullptr, D))
     NewUD->setInvalidDecl();
 
   SemaRef.Context.setInstantiatedFromUsingDecl(NewUD, D);
   NewUD->setAccess(D->getAccess());
   Owner->addDecl(NewUD);
 
   // Don't process the shadow decls for an invalid decl.
   if (NewUD->isInvalidDecl())
     return NewUD;
 
   // If the using scope was dependent, or we had dependent bases, we need to
   // recheck the inheritance
   if (NameInfo.getName().getNameKind() == DeclarationName::CXXConstructorName)
     SemaRef.CheckInheritingConstructorUsingDecl(NewUD);
 
   return VisitBaseUsingDecls(D, NewUD, CheckRedeclaration ? &Prev : nullptr);
 }
 
 Decl *TemplateDeclInstantiator::VisitUsingEnumDecl(UsingEnumDecl *D) {
   // Cannot be a dependent type, but still could be an instantiation
   EnumDecl *EnumD = cast_or_null<EnumDecl>(SemaRef.FindInstantiatedDecl(
       D->getLocation(), D->getEnumDecl(), TemplateArgs));
 
   if (SemaRef.RequireCompleteEnumDecl(EnumD, EnumD->getLocation()))
     return nullptr;
 
   TypeSourceInfo *TSI = SemaRef.SubstType(D->getEnumType(), TemplateArgs,
                                           D->getLocation(), D->getDeclName());
 
   if (!TSI)
     return nullptr;
 
   UsingEnumDecl *NewUD =
       UsingEnumDecl::Create(SemaRef.Context, Owner, D->getUsingLoc(),
                             D->getEnumLoc(), D->getLocation(), TSI);
 
   SemaRef.Context.setInstantiatedFromUsingEnumDecl(NewUD, D);
   NewUD->setAccess(D->getAccess());
   Owner->addDecl(NewUD);
 
   // Don't process the shadow decls for an invalid decl.
   if (NewUD->isInvalidDecl())
     return NewUD;
 
   // We don't have to recheck for duplication of the UsingEnumDecl itself, as it
   // cannot be dependent, and will therefore have been checked during template
   // definition.
 
   return VisitBaseUsingDecls(D, NewUD, nullptr);
 }
 
 Decl *TemplateDeclInstantiator::VisitUsingShadowDecl(UsingShadowDecl *D) {
   // Ignore these;  we handle them in bulk when processing the UsingDecl.
   return nullptr;
 }
 
 Decl *TemplateDeclInstantiator::VisitConstructorUsingShadowDecl(
     ConstructorUsingShadowDecl *D) {
   // Ignore these;  we handle them in bulk when processing the UsingDecl.
   return nullptr;
 }
 
 template <typename T>
 Decl *TemplateDeclInstantiator::instantiateUnresolvedUsingDecl(
     T *D, bool InstantiatingPackElement) {
   // If this is a pack expansion, expand it now.
   if (D->isPackExpansion() && !InstantiatingPackElement) {
     SmallVector<UnexpandedParameterPack, 2> Unexpanded;
     SemaRef.collectUnexpandedParameterPacks(D->getQualifierLoc(), Unexpanded);
     SemaRef.collectUnexpandedParameterPacks(D->getNameInfo(), Unexpanded);
 
     // Determine whether the set of unexpanded parameter packs can and should
     // be expanded.
     bool Expand = true;
     bool RetainExpansion = false;
     std::optional<unsigned> NumExpansions;
     if (SemaRef.CheckParameterPacksForExpansion(
           D->getEllipsisLoc(), D->getSourceRange(), Unexpanded, TemplateArgs,
             Expand, RetainExpansion, NumExpansions))
       return nullptr;
 
     // This declaration cannot appear within a function template signature,
     // so we can't have a partial argument list for a parameter pack.
     assert(!RetainExpansion &&
            "should never need to retain an expansion for UsingPackDecl");
 
     if (!Expand) {
       // We cannot fully expand the pack expansion now, so substitute into the
       // pattern and create a new pack expansion.
       Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, -1);
       return instantiateUnresolvedUsingDecl(D, true);
     }
 
     // Within a function, we don't have any normal way to check for conflicts
     // between shadow declarations from different using declarations in the
     // same pack expansion, but this is always ill-formed because all expansions
     // must produce (conflicting) enumerators.
     //
     // Sadly we can't just reject this in the template definition because it
     // could be valid if the pack is empty or has exactly one expansion.
     if (D->getDeclContext()->isFunctionOrMethod() && *NumExpansions > 1) {
       SemaRef.Diag(D->getEllipsisLoc(),
                    diag::err_using_decl_redeclaration_expansion);
       return nullptr;
     }
 
     // Instantiate the slices of this pack and build a UsingPackDecl.
     SmallVector<NamedDecl*, 8> Expansions;
     for (unsigned I = 0; I != *NumExpansions; ++I) {
       Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, I);
       Decl *Slice = instantiateUnresolvedUsingDecl(D, true);
       if (!Slice)
         return nullptr;
       // Note that we can still get unresolved using declarations here, if we
       // had arguments for all packs but the pattern also contained other
       // template arguments (this only happens during partial substitution, eg
       // into the body of a generic lambda in a function template).
       Expansions.push_back(cast<NamedDecl>(Slice));
     }
 
     auto *NewD = SemaRef.BuildUsingPackDecl(D, Expansions);
     if (isDeclWithinFunction(D))
       SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewD);
     return NewD;
   }
 
   UnresolvedUsingTypenameDecl *TD = dyn_cast<UnresolvedUsingTypenameDecl>(D);
   SourceLocation TypenameLoc = TD ? TD->getTypenameLoc() : SourceLocation();
 
   NestedNameSpecifierLoc QualifierLoc
     = SemaRef.SubstNestedNameSpecifierLoc(D->getQualifierLoc(),
                                           TemplateArgs);
   if (!QualifierLoc)
     return nullptr;
 
   CXXScopeSpec SS;
   SS.Adopt(QualifierLoc);
 
   DeclarationNameInfo NameInfo
     = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
 
   // Produce a pack expansion only if we're not instantiating a particular
   // slice of a pack expansion.
   bool InstantiatingSlice = D->getEllipsisLoc().isValid() &&
                             SemaRef.ArgumentPackSubstitutionIndex != -1;
   SourceLocation EllipsisLoc =
       InstantiatingSlice ? SourceLocation() : D->getEllipsisLoc();
 
   bool IsUsingIfExists = D->template hasAttr<UsingIfExistsAttr>();
   NamedDecl *UD = SemaRef.BuildUsingDeclaration(
       /*Scope*/ nullptr, D->getAccess(), D->getUsingLoc(),
       /*HasTypename*/ TD, TypenameLoc, SS, NameInfo, EllipsisLoc,
       ParsedAttributesView(),
       /*IsInstantiation*/ true, IsUsingIfExists);
   if (UD) {
     SemaRef.InstantiateAttrs(TemplateArgs, D, UD);
     SemaRef.Context.setInstantiatedFromUsingDecl(UD, D);
   }
 
   return UD;
 }
 
 Decl *TemplateDeclInstantiator::VisitUnresolvedUsingTypenameDecl(
     UnresolvedUsingTypenameDecl *D) {
   return instantiateUnresolvedUsingDecl(D);
 }
 
 Decl *TemplateDeclInstantiator::VisitUnresolvedUsingValueDecl(
     UnresolvedUsingValueDecl *D) {
   return instantiateUnresolvedUsingDecl(D);
 }
 
 Decl *TemplateDeclInstantiator::VisitUnresolvedUsingIfExistsDecl(
     UnresolvedUsingIfExistsDecl *D) {
   llvm_unreachable("referring to unresolved decl out of UsingShadowDecl");
 }
 
 Decl *TemplateDeclInstantiator::VisitUsingPackDecl(UsingPackDecl *D) {
   SmallVector<NamedDecl*, 8> Expansions;
   for (auto *UD : D->expansions()) {
     if (NamedDecl *NewUD =
             SemaRef.FindInstantiatedDecl(D->getLocation(), UD, TemplateArgs))
       Expansions.push_back(NewUD);
     else
       return nullptr;
   }
 
   auto *NewD = SemaRef.BuildUsingPackDecl(D, Expansions);
   if (isDeclWithinFunction(D))
     SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewD);
   return NewD;
 }
 
 Decl *TemplateDeclInstantiator::VisitOMPThreadPrivateDecl(
                                      OMPThreadPrivateDecl *D) {
   SmallVector<Expr *, 5> Vars;
   for (auto *I : D->varlists()) {
     Expr *Var = SemaRef.SubstExpr(I, TemplateArgs).get();
     assert(isa<DeclRefExpr>(Var) && "threadprivate arg is not a DeclRefExpr");
     Vars.push_back(Var);
   }
 
   OMPThreadPrivateDecl *TD =
       SemaRef.OpenMP().CheckOMPThreadPrivateDecl(D->getLocation(), Vars);
 
   TD->setAccess(AS_public);
   Owner->addDecl(TD);
 
   return TD;
 }
 
 Decl *TemplateDeclInstantiator::VisitOMPAllocateDecl(OMPAllocateDecl *D) {
   SmallVector<Expr *, 5> Vars;
   for (auto *I : D->varlists()) {
     Expr *Var = SemaRef.SubstExpr(I, TemplateArgs).get();
     assert(isa<DeclRefExpr>(Var) && "allocate arg is not a DeclRefExpr");
     Vars.push_back(Var);
   }
   SmallVector<OMPClause *, 4> Clauses;
   // Copy map clauses from the original mapper.
   for (OMPClause *C : D->clauselists()) {
     OMPClause *IC = nullptr;
     if (auto *AC = dyn_cast<OMPAllocatorClause>(C)) {
       ExprResult NewE = SemaRef.SubstExpr(AC->getAllocator(), TemplateArgs);
       if (!NewE.isUsable())
         continue;
       IC = SemaRef.OpenMP().ActOnOpenMPAllocatorClause(
           NewE.get(), AC->getBeginLoc(), AC->getLParenLoc(), AC->getEndLoc());
     } else if (auto *AC = dyn_cast<OMPAlignClause>(C)) {
       ExprResult NewE = SemaRef.SubstExpr(AC->getAlignment(), TemplateArgs);
       if (!NewE.isUsable())
         continue;
       IC = SemaRef.OpenMP().ActOnOpenMPAlignClause(
           NewE.get(), AC->getBeginLoc(), AC->getLParenLoc(), AC->getEndLoc());
       // If align clause value ends up being invalid, this can end up null.
       if (!IC)
         continue;
     }
     Clauses.push_back(IC);
   }
 
   Sema::DeclGroupPtrTy Res = SemaRef.OpenMP().ActOnOpenMPAllocateDirective(
       D->getLocation(), Vars, Clauses, Owner);
   if (Res.get().isNull())
     return nullptr;
   return Res.get().getSingleDecl();
 }
 
 Decl *TemplateDeclInstantiator::VisitOMPRequiresDecl(OMPRequiresDecl *D) {
   llvm_unreachable(
       "Requires directive cannot be instantiated within a dependent context");
 }
 
 Decl *TemplateDeclInstantiator::VisitOMPDeclareReductionDecl(
     OMPDeclareReductionDecl *D) {
   // Instantiate type and check if it is allowed.
   const bool RequiresInstantiation =
       D->getType()->isDependentType() ||
       D->getType()->isInstantiationDependentType() ||
       D->getType()->containsUnexpandedParameterPack();
   QualType SubstReductionType;
   if (RequiresInstantiation) {
     SubstReductionType = SemaRef.OpenMP().ActOnOpenMPDeclareReductionType(
         D->getLocation(),
         ParsedType::make(SemaRef.SubstType(
             D->getType(), TemplateArgs, D->getLocation(), DeclarationName())));
   } else {
     SubstReductionType = D->getType();
   }
   if (SubstReductionType.isNull())
     return nullptr;
   Expr *Combiner = D->getCombiner();
   Expr *Init = D->getInitializer();
   bool IsCorrect = true;
   // Create instantiated copy.
   std::pair<QualType, SourceLocation> ReductionTypes[] = {
       std::make_pair(SubstReductionType, D->getLocation())};
   auto *PrevDeclInScope = D->getPrevDeclInScope();
   if (PrevDeclInScope && !PrevDeclInScope->isInvalidDecl()) {
     PrevDeclInScope = cast<OMPDeclareReductionDecl>(
         SemaRef.CurrentInstantiationScope->findInstantiationOf(PrevDeclInScope)
             ->get<Decl *>());
   }
   auto DRD = SemaRef.OpenMP().ActOnOpenMPDeclareReductionDirectiveStart(
       /*S=*/nullptr, Owner, D->getDeclName(), ReductionTypes, D->getAccess(),
       PrevDeclInScope);
   auto *NewDRD = cast<OMPDeclareReductionDecl>(DRD.get().getSingleDecl());
   SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewDRD);
   Expr *SubstCombiner = nullptr;
   Expr *SubstInitializer = nullptr;
   // Combiners instantiation sequence.
   if (Combiner) {
     SemaRef.OpenMP().ActOnOpenMPDeclareReductionCombinerStart(
         /*S=*/nullptr, NewDRD);
     SemaRef.CurrentInstantiationScope->InstantiatedLocal(
         cast<DeclRefExpr>(D->getCombinerIn())->getDecl(),
         cast<DeclRefExpr>(NewDRD->getCombinerIn())->getDecl());
     SemaRef.CurrentInstantiationScope->InstantiatedLocal(
         cast<DeclRefExpr>(D->getCombinerOut())->getDecl(),
         cast<DeclRefExpr>(NewDRD->getCombinerOut())->getDecl());
     auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(Owner);
     Sema::CXXThisScopeRAII ThisScope(SemaRef, ThisContext, Qualifiers(),
                                      ThisContext);
     SubstCombiner = SemaRef.SubstExpr(Combiner, TemplateArgs).get();
     SemaRef.OpenMP().ActOnOpenMPDeclareReductionCombinerEnd(NewDRD,
                                                             SubstCombiner);
   }
   // Initializers instantiation sequence.
   if (Init) {
     VarDecl *OmpPrivParm =
         SemaRef.OpenMP().ActOnOpenMPDeclareReductionInitializerStart(
             /*S=*/nullptr, NewDRD);
     SemaRef.CurrentInstantiationScope->InstantiatedLocal(
         cast<DeclRefExpr>(D->getInitOrig())->getDecl(),
         cast<DeclRefExpr>(NewDRD->getInitOrig())->getDecl());
     SemaRef.CurrentInstantiationScope->InstantiatedLocal(
         cast<DeclRefExpr>(D->getInitPriv())->getDecl(),
         cast<DeclRefExpr>(NewDRD->getInitPriv())->getDecl());
     if (D->getInitializerKind() == OMPDeclareReductionInitKind::Call) {
       SubstInitializer = SemaRef.SubstExpr(Init, TemplateArgs).get();
     } else {
       auto *OldPrivParm =
           cast<VarDecl>(cast<DeclRefExpr>(D->getInitPriv())->getDecl());
       IsCorrect = IsCorrect && OldPrivParm->hasInit();
       if (IsCorrect)
         SemaRef.InstantiateVariableInitializer(OmpPrivParm, OldPrivParm,
                                                TemplateArgs);
     }
     SemaRef.OpenMP().ActOnOpenMPDeclareReductionInitializerEnd(
         NewDRD, SubstInitializer, OmpPrivParm);
   }
   IsCorrect = IsCorrect && SubstCombiner &&
               (!Init ||
                (D->getInitializerKind() == OMPDeclareReductionInitKind::Call &&
                 SubstInitializer) ||
                (D->getInitializerKind() != OMPDeclareReductionInitKind::Call &&
                 !SubstInitializer));
 
   (void)SemaRef.OpenMP().ActOnOpenMPDeclareReductionDirectiveEnd(
       /*S=*/nullptr, DRD, IsCorrect && !D->isInvalidDecl());
 
   return NewDRD;
 }
 
 Decl *
 TemplateDeclInstantiator::VisitOMPDeclareMapperDecl(OMPDeclareMapperDecl *D) {
   // Instantiate type and check if it is allowed.
   const bool RequiresInstantiation =
       D->getType()->isDependentType() ||
       D->getType()->isInstantiationDependentType() ||
       D->getType()->containsUnexpandedParameterPack();
   QualType SubstMapperTy;
   DeclarationName VN = D->getVarName();
   if (RequiresInstantiation) {
     SubstMapperTy = SemaRef.OpenMP().ActOnOpenMPDeclareMapperType(
         D->getLocation(),
         ParsedType::make(SemaRef.SubstType(D->getType(), TemplateArgs,
                                            D->getLocation(), VN)));
   } else {
     SubstMapperTy = D->getType();
   }
   if (SubstMapperTy.isNull())
     return nullptr;
   // Create an instantiated copy of mapper.
   auto *PrevDeclInScope = D->getPrevDeclInScope();
   if (PrevDeclInScope && !PrevDeclInScope->isInvalidDecl()) {
     PrevDeclInScope = cast<OMPDeclareMapperDecl>(
         SemaRef.CurrentInstantiationScope->findInstantiationOf(PrevDeclInScope)
             ->get<Decl *>());
   }
   bool IsCorrect = true;
   SmallVector<OMPClause *, 6> Clauses;
   // Instantiate the mapper variable.
   DeclarationNameInfo DirName;
   SemaRef.OpenMP().StartOpenMPDSABlock(llvm::omp::OMPD_declare_mapper, DirName,
                                        /*S=*/nullptr,
                                        (*D->clauselist_begin())->getBeginLoc());
   ExprResult MapperVarRef =
       SemaRef.OpenMP().ActOnOpenMPDeclareMapperDirectiveVarDecl(
           /*S=*/nullptr, SubstMapperTy, D->getLocation(), VN);
   SemaRef.CurrentInstantiationScope->InstantiatedLocal(
       cast<DeclRefExpr>(D->getMapperVarRef())->getDecl(),
       cast<DeclRefExpr>(MapperVarRef.get())->getDecl());
   auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(Owner);
   Sema::CXXThisScopeRAII ThisScope(SemaRef, ThisContext, Qualifiers(),
                                    ThisContext);
   // Instantiate map clauses.
   for (OMPClause *C : D->clauselists()) {
     auto *OldC = cast<OMPMapClause>(C);
     SmallVector<Expr *, 4> NewVars;
     for (Expr *OE : OldC->varlists()) {
       Expr *NE = SemaRef.SubstExpr(OE, TemplateArgs).get();
       if (!NE) {
         IsCorrect = false;
         break;
       }
       NewVars.push_back(NE);
     }
     if (!IsCorrect)
       break;
     NestedNameSpecifierLoc NewQualifierLoc =
         SemaRef.SubstNestedNameSpecifierLoc(OldC->getMapperQualifierLoc(),
                                             TemplateArgs);
     CXXScopeSpec SS;
     SS.Adopt(NewQualifierLoc);
     DeclarationNameInfo NewNameInfo =
         SemaRef.SubstDeclarationNameInfo(OldC->getMapperIdInfo(), TemplateArgs);
     OMPVarListLocTy Locs(OldC->getBeginLoc(), OldC->getLParenLoc(),
                          OldC->getEndLoc());
     OMPClause *NewC = SemaRef.OpenMP().ActOnOpenMPMapClause(
         OldC->getIteratorModifier(), OldC->getMapTypeModifiers(),
         OldC->getMapTypeModifiersLoc(), SS, NewNameInfo, OldC->getMapType(),
         OldC->isImplicitMapType(), OldC->getMapLoc(), OldC->getColonLoc(),
         NewVars, Locs);
     Clauses.push_back(NewC);
   }
   SemaRef.OpenMP().EndOpenMPDSABlock(nullptr);
   if (!IsCorrect)
     return nullptr;
   Sema::DeclGroupPtrTy DG = SemaRef.OpenMP().ActOnOpenMPDeclareMapperDirective(
       /*S=*/nullptr, Owner, D->getDeclName(), SubstMapperTy, D->getLocation(),
       VN, D->getAccess(), MapperVarRef.get(), Clauses, PrevDeclInScope);
   Decl *NewDMD = DG.get().getSingleDecl();
   SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewDMD);
   return NewDMD;
 }
 
 Decl *TemplateDeclInstantiator::VisitOMPCapturedExprDecl(
     OMPCapturedExprDecl * /*D*/) {
   llvm_unreachable("Should not be met in templates");
 }
 
 Decl *TemplateDeclInstantiator::VisitFunctionDecl(FunctionDecl *D) {
   return VisitFunctionDecl(D, nullptr);
 }
 
 Decl *
 TemplateDeclInstantiator::VisitCXXDeductionGuideDecl(CXXDeductionGuideDecl *D) {
   Decl *Inst = VisitFunctionDecl(D, nullptr);
   if (Inst && !D->getDescribedFunctionTemplate())
     Owner->addDecl(Inst);
   return Inst;
 }
 
 Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(CXXMethodDecl *D) {
   return VisitCXXMethodDecl(D, nullptr);
 }
 
 Decl *TemplateDeclInstantiator::VisitRecordDecl(RecordDecl *D) {
   llvm_unreachable("There are only CXXRecordDecls in C++");
 }
 
 Decl *
 TemplateDeclInstantiator::VisitClassTemplateSpecializationDecl(
     ClassTemplateSpecializationDecl *D) {
   // As a MS extension, we permit class-scope explicit specialization
   // of member class templates.
   ClassTemplateDecl *ClassTemplate = D->getSpecializedTemplate();
   assert(ClassTemplate->getDeclContext()->isRecord() &&
          D->getTemplateSpecializationKind() == TSK_ExplicitSpecialization &&
          "can only instantiate an explicit specialization "
          "for a member class template");
 
   // Lookup the already-instantiated declaration in the instantiation
   // of the class template.
   ClassTemplateDecl *InstClassTemplate =
       cast_or_null<ClassTemplateDecl>(SemaRef.FindInstantiatedDecl(
           D->getLocation(), ClassTemplate, TemplateArgs));
   if (!InstClassTemplate)
     return nullptr;
 
   // Substitute into the template arguments of the class template explicit
   // specialization.
   TemplateArgumentListInfo InstTemplateArgs;
   if (const ASTTemplateArgumentListInfo *TemplateArgsInfo =
           D->getTemplateArgsAsWritten()) {
     InstTemplateArgs.setLAngleLoc(TemplateArgsInfo->getLAngleLoc());
     InstTemplateArgs.setRAngleLoc(TemplateArgsInfo->getRAngleLoc());
 
     if (SemaRef.SubstTemplateArguments(TemplateArgsInfo->arguments(),
                                        TemplateArgs, InstTemplateArgs))
       return nullptr;
   }
 
   // Check that the template argument list is well-formed for this
   // class template.
   SmallVector<TemplateArgument, 4> SugaredConverted, CanonicalConverted;
   if (SemaRef.CheckTemplateArgumentList(InstClassTemplate, D->getLocation(),
                                         InstTemplateArgs, false,
                                         SugaredConverted, CanonicalConverted,
                                         /*UpdateArgsWithConversions=*/true))
     return nullptr;
 
   // Figure out where to insert this class template explicit specialization
   // in the member template's set of class template explicit specializations.
   void *InsertPos = nullptr;
   ClassTemplateSpecializationDecl *PrevDecl =
       InstClassTemplate->findSpecialization(CanonicalConverted, InsertPos);
 
   // Check whether we've already seen a conflicting instantiation of this
   // declaration (for instance, if there was a prior implicit instantiation).
   bool Ignored;
   if (PrevDecl &&
       SemaRef.CheckSpecializationInstantiationRedecl(D->getLocation(),
                                                      D->getSpecializationKind(),
                                                      PrevDecl,
                                                      PrevDecl->getSpecializationKind(),
                                                      PrevDecl->getPointOfInstantiation(),
                                                      Ignored))
     return nullptr;
 
   // If PrevDecl was a definition and D is also a definition, diagnose.
   // This happens in cases like:
   //
   //   template<typename T, typename U>
   //   struct Outer {
   //     template<typename X> struct Inner;
   //     template<> struct Inner<T> {};
   //     template<> struct Inner<U> {};
   //   };
   //
   //   Outer<int, int> outer; // error: the explicit specializations of Inner
   //                          // have the same signature.
   if (PrevDecl && PrevDecl->getDefinition() &&
       D->isThisDeclarationADefinition()) {
     SemaRef.Diag(D->getLocation(), diag::err_redefinition) << PrevDecl;
     SemaRef.Diag(PrevDecl->getDefinition()->getLocation(),
                  diag::note_previous_definition);
     return nullptr;
   }
 
   // Create the class template partial specialization declaration.
   ClassTemplateSpecializationDecl *InstD =
       ClassTemplateSpecializationDecl::Create(
           SemaRef.Context, D->getTagKind(), Owner, D->getBeginLoc(),
           D->getLocation(), InstClassTemplate, CanonicalConverted, PrevDecl);
   InstD->setTemplateArgsAsWritten(InstTemplateArgs);
 
   // Add this partial specialization to the set of class template partial
   // specializations.
   if (!PrevDecl)
     InstClassTemplate->AddSpecialization(InstD, InsertPos);
 
   // Substitute the nested name specifier, if any.
   if (SubstQualifier(D, InstD))
     return nullptr;
 
   InstD->setAccess(D->getAccess());
   InstD->setInstantiationOfMemberClass(D, TSK_ImplicitInstantiation);
   InstD->setSpecializationKind(D->getSpecializationKind());
   InstD->setExternKeywordLoc(D->getExternKeywordLoc());
   InstD->setTemplateKeywordLoc(D->getTemplateKeywordLoc());
 
   Owner->addDecl(InstD);
 
   // Instantiate the members of the class-scope explicit specialization eagerly.
   // We don't have support for lazy instantiation of an explicit specialization
   // yet, and MSVC eagerly instantiates in this case.
   // FIXME: This is wrong in standard C++.
   if (D->isThisDeclarationADefinition() &&
       SemaRef.InstantiateClass(D->getLocation(), InstD, D, TemplateArgs,
                                TSK_ImplicitInstantiation,
                                /*Complain=*/true))
     return nullptr;
 
   return InstD;
 }
 
 Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
     VarTemplateSpecializationDecl *D) {
 
   TemplateArgumentListInfo VarTemplateArgsInfo;
   VarTemplateDecl *VarTemplate = D->getSpecializedTemplate();
   assert(VarTemplate &&
          "A template specialization without specialized template?");
 
   VarTemplateDecl *InstVarTemplate =
       cast_or_null<VarTemplateDecl>(SemaRef.FindInstantiatedDecl(
           D->getLocation(), VarTemplate, TemplateArgs));
   if (!InstVarTemplate)
     return nullptr;
 
   // Substitute the current template arguments.
   if (const ASTTemplateArgumentListInfo *TemplateArgsInfo =
           D->getTemplateArgsAsWritten()) {
     VarTemplateArgsInfo.setLAngleLoc(TemplateArgsInfo->getLAngleLoc());
     VarTemplateArgsInfo.setRAngleLoc(TemplateArgsInfo->getRAngleLoc());
 
     if (SemaRef.SubstTemplateArguments(TemplateArgsInfo->arguments(),
                                        TemplateArgs, VarTemplateArgsInfo))
       return nullptr;
   }
 
   // Check that the template argument list is well-formed for this template.
   SmallVector<TemplateArgument, 4> SugaredConverted, CanonicalConverted;
   if (SemaRef.CheckTemplateArgumentList(InstVarTemplate, D->getLocation(),
                                         VarTemplateArgsInfo, false,
                                         SugaredConverted, CanonicalConverted,
                                         /*UpdateArgsWithConversions=*/true))
     return nullptr;
 
   // Check whether we've already seen a declaration of this specialization.
   void *InsertPos = nullptr;
   VarTemplateSpecializationDecl *PrevDecl =
       InstVarTemplate->findSpecialization(CanonicalConverted, InsertPos);
 
   // Check whether we've already seen a conflicting instantiation of this
   // declaration (for instance, if there was a prior implicit instantiation).
   bool Ignored;
   if (PrevDecl && SemaRef.CheckSpecializationInstantiationRedecl(
                       D->getLocation(), D->getSpecializationKind(), PrevDecl,
                       PrevDecl->getSpecializationKind(),
                       PrevDecl->getPointOfInstantiation(), Ignored))
     return nullptr;
 
   return VisitVarTemplateSpecializationDecl(
       InstVarTemplate, D, VarTemplateArgsInfo, CanonicalConverted, PrevDecl);
 }
 
 Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
     VarTemplateDecl *VarTemplate, VarDecl *D,
     const TemplateArgumentListInfo &TemplateArgsInfo,
     ArrayRef<TemplateArgument> Converted,
     VarTemplateSpecializationDecl *PrevDecl) {
 
   // Do substitution on the type of the declaration
   TypeSourceInfo *DI =
       SemaRef.SubstType(D->getTypeSourceInfo(), TemplateArgs,
                         D->getTypeSpecStartLoc(), D->getDeclName());
   if (!DI)
     return nullptr;
 
   if (DI->getType()->isFunctionType()) {
     SemaRef.Diag(D->getLocation(), diag::err_variable_instantiates_to_function)
         << D->isStaticDataMember() << DI->getType();
     return nullptr;
   }
 
   // Build the instantiated declaration
   VarTemplateSpecializationDecl *Var = VarTemplateSpecializationDecl::Create(
       SemaRef.Context, Owner, D->getInnerLocStart(), D->getLocation(),
       VarTemplate, DI->getType(), DI, D->getStorageClass(), Converted);
   Var->setTemplateArgsAsWritten(TemplateArgsInfo);
   if (!PrevDecl) {
     void *InsertPos = nullptr;
     VarTemplate->findSpecialization(Converted, InsertPos);
     VarTemplate->AddSpecialization(Var, InsertPos);
   }
 
   if (SemaRef.getLangOpts().OpenCL)
     SemaRef.deduceOpenCLAddressSpace(Var);
 
   // Substitute the nested name specifier, if any.
   if (SubstQualifier(D, Var))
     return nullptr;
 
   SemaRef.BuildVariableInstantiation(Var, D, TemplateArgs, LateAttrs, Owner,
                                      StartingScope, false, PrevDecl);
 
   return Var;
 }
 
 Decl *TemplateDeclInstantiator::VisitObjCAtDefsFieldDecl(ObjCAtDefsFieldDecl *D) {
   llvm_unreachable("@defs is not supported in Objective-C++");
 }
 
 Decl *TemplateDeclInstantiator::VisitFriendTemplateDecl(FriendTemplateDecl *D) {
   // FIXME: We need to be able to instantiate FriendTemplateDecls.
   unsigned DiagID = SemaRef.getDiagnostics().getCustomDiagID(
                                                DiagnosticsEngine::Error,
                                                "cannot instantiate %0 yet");
   SemaRef.Diag(D->getLocation(), DiagID)
     << D->getDeclKindName();
 
   return nullptr;
 }
 
 Decl *TemplateDeclInstantiator::VisitConceptDecl(ConceptDecl *D) {
   llvm_unreachable("Concept definitions cannot reside inside a template");
 }
 
 Decl *TemplateDeclInstantiator::VisitImplicitConceptSpecializationDecl(
     ImplicitConceptSpecializationDecl *D) {
   llvm_unreachable("Concept specializations cannot reside inside a template");
 }
 
 Decl *
 TemplateDeclInstantiator::VisitRequiresExprBodyDecl(RequiresExprBodyDecl *D) {
   return RequiresExprBodyDecl::Create(SemaRef.Context, D->getDeclContext(),
                                       D->getBeginLoc());
 }
 
 Decl *TemplateDeclInstantiator::VisitDecl(Decl *D) {
   llvm_unreachable("Unexpected decl");
 }
 
 Decl *Sema::SubstDecl(Decl *D, DeclContext *Owner,
                       const MultiLevelTemplateArgumentList &TemplateArgs) {
   TemplateDeclInstantiator Instantiator(*this, Owner, TemplateArgs);
   if (D->isInvalidDecl())
     return nullptr;
 
   Decl *SubstD;
   runWithSufficientStackSpace(D->getLocation(), [&] {
     SubstD = Instantiator.Visit(D);
   });
   return SubstD;
 }
 
 void TemplateDeclInstantiator::adjustForRewrite(RewriteKind RK,
                                                 FunctionDecl *Orig, QualType &T,
                                                 TypeSourceInfo *&TInfo,
                                                 DeclarationNameInfo &NameInfo) {
   assert(RK == RewriteKind::RewriteSpaceshipAsEqualEqual);
 
   // C++2a [class.compare.default]p3:
   //   the return type is replaced with bool
   auto *FPT = T->castAs<FunctionProtoType>();
   T = SemaRef.Context.getFunctionType(
       SemaRef.Context.BoolTy, FPT->getParamTypes(), FPT->getExtProtoInfo());
 
   // Update the return type in the source info too. The most straightforward
   // way is to create new TypeSourceInfo for the new type. Use the location of
   // the '= default' as the location of the new type.
   //
   // FIXME: Set the correct return type when we initially transform the type,
   // rather than delaying it to now.
   TypeSourceInfo *NewTInfo =
       SemaRef.Context.getTrivialTypeSourceInfo(T, Orig->getEndLoc());
   auto OldLoc = TInfo->getTypeLoc().getAsAdjusted<FunctionProtoTypeLoc>();
   assert(OldLoc && "type of function is not a function type?");
   auto NewLoc = NewTInfo->getTypeLoc().castAs<FunctionProtoTypeLoc>();
   for (unsigned I = 0, N = OldLoc.getNumParams(); I != N; ++I)
     NewLoc.setParam(I, OldLoc.getParam(I));
   TInfo = NewTInfo;
 
   //   and the declarator-id is replaced with operator==
   NameInfo.setName(
       SemaRef.Context.DeclarationNames.getCXXOperatorName(OO_EqualEqual));
 }
 
 FunctionDecl *Sema::SubstSpaceshipAsEqualEqual(CXXRecordDecl *RD,
                                                FunctionDecl *Spaceship) {
   if (Spaceship->isInvalidDecl())
     return nullptr;
 
   // C++2a [class.compare.default]p3:
   //   an == operator function is declared implicitly [...] with the same
   //   access and function-definition and in the same class scope as the
   //   three-way comparison operator function
   MultiLevelTemplateArgumentList NoTemplateArgs;
   NoTemplateArgs.setKind(TemplateSubstitutionKind::Rewrite);
   NoTemplateArgs.addOuterRetainedLevels(RD->getTemplateDepth());
   TemplateDeclInstantiator Instantiator(*this, RD, NoTemplateArgs);
   Decl *R;
   if (auto *MD = dyn_cast<CXXMethodDecl>(Spaceship)) {
     R = Instantiator.VisitCXXMethodDecl(
         MD, /*TemplateParams=*/nullptr,
         TemplateDeclInstantiator::RewriteKind::RewriteSpaceshipAsEqualEqual);
   } else {
     assert(Spaceship->getFriendObjectKind() &&
            "defaulted spaceship is neither a member nor a friend");
 
     R = Instantiator.VisitFunctionDecl(
         Spaceship, /*TemplateParams=*/nullptr,
         TemplateDeclInstantiator::RewriteKind::RewriteSpaceshipAsEqualEqual);
     if (!R)
       return nullptr;
 
     FriendDecl *FD =
         FriendDecl::Create(Context, RD, Spaceship->getLocation(),
                            cast<NamedDecl>(R), Spaceship->getBeginLoc());
     FD->setAccess(AS_public);
     RD->addDecl(FD);
   }
   return cast_or_null<FunctionDecl>(R);
 }
 
 /// Instantiates a nested template parameter list in the current
 /// instantiation context.
 ///
 /// \param L The parameter list to instantiate
 ///
 /// \returns NULL if there was an error
 TemplateParameterList *
 TemplateDeclInstantiator::SubstTemplateParams(TemplateParameterList *L) {
   // Get errors for all the parameters before bailing out.
   bool Invalid = false;
 
   unsigned N = L->size();
   typedef SmallVector<NamedDecl *, 8> ParamVector;
   ParamVector Params;
   Params.reserve(N);
   for (auto &P : *L) {
     NamedDecl *D = cast_or_null<NamedDecl>(Visit(P));
     Params.push_back(D);
     Invalid = Invalid || !D || D->isInvalidDecl();
   }
 
   // Clean up if we had an error.
   if (Invalid)
     return nullptr;
 
   Expr *InstRequiresClause = L->getRequiresClause();
 
   TemplateParameterList *InstL
     = TemplateParameterList::Create(SemaRef.Context, L->getTemplateLoc(),
                                     L->getLAngleLoc(), Params,
                                     L->getRAngleLoc(), InstRequiresClause);
   return InstL;
 }
 
 TemplateParameterList *
 Sema::SubstTemplateParams(TemplateParameterList *Params, DeclContext *Owner,
                           const MultiLevelTemplateArgumentList &TemplateArgs,
                           bool EvaluateConstraints) {
   TemplateDeclInstantiator Instantiator(*this, Owner, TemplateArgs);
   Instantiator.setEvaluateConstraints(EvaluateConstraints);
   return Instantiator.SubstTemplateParams(Params);
 }
 
 /// Instantiate the declaration of a class template partial
 /// specialization.
 ///
 /// \param ClassTemplate the (instantiated) class template that is partially
 // specialized by the instantiation of \p PartialSpec.
 ///
 /// \param PartialSpec the (uninstantiated) class template partial
 /// specialization that we are instantiating.
 ///
 /// \returns The instantiated partial specialization, if successful; otherwise,
 /// NULL to indicate an error.
 ClassTemplatePartialSpecializationDecl *
 TemplateDeclInstantiator::InstantiateClassTemplatePartialSpecialization(
                                             ClassTemplateDecl *ClassTemplate,
                           ClassTemplatePartialSpecializationDecl *PartialSpec) {
   // Create a local instantiation scope for this class template partial
   // specialization, which will contain the instantiations of the template
   // parameters.
   LocalInstantiationScope Scope(SemaRef);
 
   // Substitute into the template parameters of the class template partial
   // specialization.
   TemplateParameterList *TempParams = PartialSpec->getTemplateParameters();
   TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
   if (!InstParams)
     return nullptr;
 
   // Substitute into the template arguments of the class template partial
   // specialization.
   const ASTTemplateArgumentListInfo *TemplArgInfo
     = PartialSpec->getTemplateArgsAsWritten();
   TemplateArgumentListInfo InstTemplateArgs(TemplArgInfo->LAngleLoc,
                                             TemplArgInfo->RAngleLoc);
   if (SemaRef.SubstTemplateArguments(TemplArgInfo->arguments(), TemplateArgs,
                                      InstTemplateArgs))
     return nullptr;
 
   // Check that the template argument list is well-formed for this
   // class template.
   SmallVector<TemplateArgument, 4> SugaredConverted, CanonicalConverted;
   if (SemaRef.CheckTemplateArgumentList(
           ClassTemplate, PartialSpec->getLocation(), InstTemplateArgs,
           /*PartialTemplateArgs=*/false, SugaredConverted, CanonicalConverted))
     return nullptr;
 
   // Check these arguments are valid for a template partial specialization.
   if (SemaRef.CheckTemplatePartialSpecializationArgs(
           PartialSpec->getLocation(), ClassTemplate, InstTemplateArgs.size(),
           CanonicalConverted))
     return nullptr;
 
   // Figure out where to insert this class template partial specialization
   // in the member template's set of class template partial specializations.
   void *InsertPos = nullptr;
   ClassTemplateSpecializationDecl *PrevDecl =
       ClassTemplate->findPartialSpecialization(CanonicalConverted, InstParams,
                                                InsertPos);
 
   // Build the canonical type that describes the converted template
   // arguments of the class template partial specialization.
   QualType CanonType = SemaRef.Context.getTemplateSpecializationType(
       TemplateName(ClassTemplate), CanonicalConverted);
 
   // Create the class template partial specialization declaration.
   ClassTemplatePartialSpecializationDecl *InstPartialSpec =
       ClassTemplatePartialSpecializationDecl::Create(
           SemaRef.Context, PartialSpec->getTagKind(), Owner,
           PartialSpec->getBeginLoc(), PartialSpec->getLocation(), InstParams,
           ClassTemplate, CanonicalConverted, CanonType,
           /*PrevDecl=*/nullptr);
 
   InstPartialSpec->setTemplateArgsAsWritten(InstTemplateArgs);
 
   // Substitute the nested name specifier, if any.
   if (SubstQualifier(PartialSpec, InstPartialSpec))
     return nullptr;
 
   InstPartialSpec->setInstantiatedFromMember(PartialSpec);
 
   if (PrevDecl) {
     // We've already seen a partial specialization with the same template
     // parameters and template arguments. This can happen, for example, when
     // substituting the outer template arguments ends up causing two
     // class template partial specializations of a member class template
     // to have identical forms, e.g.,
     //
     //   template<typename T, typename U>
     //   struct Outer {
     //     template<typename X, typename Y> struct Inner;
     //     template<typename Y> struct Inner<T, Y>;
     //     template<typename Y> struct Inner<U, Y>;
     //   };
     //
     //   Outer<int, int> outer; // error: the partial specializations of Inner
     //                          // have the same signature.
     SemaRef.Diag(InstPartialSpec->getLocation(),
                  diag::err_partial_spec_redeclared)
         << InstPartialSpec;
     SemaRef.Diag(PrevDecl->getLocation(), diag::note_prev_partial_spec_here)
       << SemaRef.Context.getTypeDeclType(PrevDecl);
     return nullptr;
   }
 
   // Check the completed partial specialization.
   SemaRef.CheckTemplatePartialSpecialization(InstPartialSpec);
 
   // Add this partial specialization to the set of class template partial
   // specializations.
   ClassTemplate->AddPartialSpecialization(InstPartialSpec,
                                           /*InsertPos=*/nullptr);
   return InstPartialSpec;
 }
 
 /// Instantiate the declaration of a variable template partial
 /// specialization.
 ///
 /// \param VarTemplate the (instantiated) variable template that is partially
 /// specialized by the instantiation of \p PartialSpec.
 ///
 /// \param PartialSpec the (uninstantiated) variable template partial
 /// specialization that we are instantiating.
 ///
 /// \returns The instantiated partial specialization, if successful; otherwise,
 /// NULL to indicate an error.
 VarTemplatePartialSpecializationDecl *
 TemplateDeclInstantiator::InstantiateVarTemplatePartialSpecialization(
     VarTemplateDecl *VarTemplate,
     VarTemplatePartialSpecializationDecl *PartialSpec) {
   // Create a local instantiation scope for this variable template partial
   // specialization, which will contain the instantiations of the template
   // parameters.
   LocalInstantiationScope Scope(SemaRef);
 
   // Substitute into the template parameters of the variable template partial
   // specialization.
   TemplateParameterList *TempParams = PartialSpec->getTemplateParameters();
   TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
   if (!InstParams)
     return nullptr;
 
   // Substitute into the template arguments of the variable template partial
   // specialization.
   const ASTTemplateArgumentListInfo *TemplArgInfo
     = PartialSpec->getTemplateArgsAsWritten();
   TemplateArgumentListInfo InstTemplateArgs(TemplArgInfo->LAngleLoc,
                                             TemplArgInfo->RAngleLoc);
   if (SemaRef.SubstTemplateArguments(TemplArgInfo->arguments(), TemplateArgs,
                                      InstTemplateArgs))
     return nullptr;
 
   // Check that the template argument list is well-formed for this
   // class template.
   SmallVector<TemplateArgument, 4> SugaredConverted, CanonicalConverted;
   if (SemaRef.CheckTemplateArgumentList(
           VarTemplate, PartialSpec->getLocation(), InstTemplateArgs,
           /*PartialTemplateArgs=*/false, SugaredConverted, CanonicalConverted))
     return nullptr;
 
   // Check these arguments are valid for a template partial specialization.
   if (SemaRef.CheckTemplatePartialSpecializationArgs(
           PartialSpec->getLocation(), VarTemplate, InstTemplateArgs.size(),
           CanonicalConverted))
     return nullptr;
 
   // Figure out where to insert this variable template partial specialization
   // in the member template's set of variable template partial specializations.
   void *InsertPos = nullptr;
   VarTemplateSpecializationDecl *PrevDecl =
       VarTemplate->findPartialSpecialization(CanonicalConverted, InstParams,
                                              InsertPos);
 
   // Do substitution on the type of the declaration
   TypeSourceInfo *DI = SemaRef.SubstType(
       PartialSpec->getTypeSourceInfo(), TemplateArgs,
       PartialSpec->getTypeSpecStartLoc(), PartialSpec->getDeclName());
   if (!DI)
     return nullptr;
 
   if (DI->getType()->isFunctionType()) {
     SemaRef.Diag(PartialSpec->getLocation(),
                  diag::err_variable_instantiates_to_function)
         << PartialSpec->isStaticDataMember() << DI->getType();
     return nullptr;
   }
 
   // Create the variable template partial specialization declaration.
   VarTemplatePartialSpecializationDecl *InstPartialSpec =
       VarTemplatePartialSpecializationDecl::Create(
           SemaRef.Context, Owner, PartialSpec->getInnerLocStart(),
           PartialSpec->getLocation(), InstParams, VarTemplate, DI->getType(),
           DI, PartialSpec->getStorageClass(), CanonicalConverted);
 
   InstPartialSpec->setTemplateArgsAsWritten(InstTemplateArgs);
 
   // Substitute the nested name specifier, if any.
   if (SubstQualifier(PartialSpec, InstPartialSpec))
     return nullptr;
 
   InstPartialSpec->setInstantiatedFromMember(PartialSpec);
 
   if (PrevDecl) {
     // We've already seen a partial specialization with the same template
     // parameters and template arguments. This can happen, for example, when
     // substituting the outer template arguments ends up causing two
     // variable template partial specializations of a member variable template
     // to have identical forms, e.g.,
     //
     //   template<typename T, typename U>
     //   struct Outer {
     //     template<typename X, typename Y> pair<X,Y> p;
     //     template<typename Y> pair<T, Y> p;
     //     template<typename Y> pair<U, Y> p;
     //   };
     //
     //   Outer<int, int> outer; // error: the partial specializations of Inner
     //                          // have the same signature.
     SemaRef.Diag(PartialSpec->getLocation(),
                  diag::err_var_partial_spec_redeclared)
         << InstPartialSpec;
     SemaRef.Diag(PrevDecl->getLocation(),
                  diag::note_var_prev_partial_spec_here);
     return nullptr;
   }
   // Check the completed partial specialization.
   SemaRef.CheckTemplatePartialSpecialization(InstPartialSpec);
 
   // Add this partial specialization to the set of variable template partial
   // specializations. The instantiation of the initializer is not necessary.
   VarTemplate->AddPartialSpecialization(InstPartialSpec, /*InsertPos=*/nullptr);
 
   SemaRef.BuildVariableInstantiation(InstPartialSpec, PartialSpec, TemplateArgs,
                                      LateAttrs, Owner, StartingScope);
 
   return InstPartialSpec;
 }
 
 TypeSourceInfo*
 TemplateDeclInstantiator::SubstFunctionType(FunctionDecl *D,
                               SmallVectorImpl<ParmVarDecl *> &Params) {
   TypeSourceInfo *OldTInfo = D->getTypeSourceInfo();
   assert(OldTInfo && "substituting function without type source info");
   assert(Params.empty() && "parameter vector is non-empty at start");
 
   CXXRecordDecl *ThisContext = nullptr;
   Qualifiers ThisTypeQuals;
   if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(D)) {
     ThisContext = cast<CXXRecordDecl>(Owner);
     ThisTypeQuals = Method->getFunctionObjectParameterType().getQualifiers();
   }
 
   TypeSourceInfo *NewTInfo = SemaRef.SubstFunctionDeclType(
       OldTInfo, TemplateArgs, D->getTypeSpecStartLoc(), D->getDeclName(),
       ThisContext, ThisTypeQuals, EvaluateConstraints);
   if (!NewTInfo)
     return nullptr;
 
   TypeLoc OldTL = OldTInfo->getTypeLoc().IgnoreParens();
   if (FunctionProtoTypeLoc OldProtoLoc = OldTL.getAs<FunctionProtoTypeLoc>()) {
     if (NewTInfo != OldTInfo) {
       // Get parameters from the new type info.
       TypeLoc NewTL = NewTInfo->getTypeLoc().IgnoreParens();
       FunctionProtoTypeLoc NewProtoLoc = NewTL.castAs<FunctionProtoTypeLoc>();
       unsigned NewIdx = 0;
       for (unsigned OldIdx = 0, NumOldParams = OldProtoLoc.getNumParams();
            OldIdx != NumOldParams; ++OldIdx) {
         ParmVarDecl *OldParam = OldProtoLoc.getParam(OldIdx);
         if (!OldParam)
           return nullptr;
 
         LocalInstantiationScope *Scope = SemaRef.CurrentInstantiationScope;
 
         std::optional<unsigned> NumArgumentsInExpansion;
         if (OldParam->isParameterPack())
           NumArgumentsInExpansion =
               SemaRef.getNumArgumentsInExpansion(OldParam->getType(),
                                                  TemplateArgs);
         if (!NumArgumentsInExpansion) {
           // Simple case: normal parameter, or a parameter pack that's
           // instantiated to a (still-dependent) parameter pack.
           ParmVarDecl *NewParam = NewProtoLoc.getParam(NewIdx++);
           Params.push_back(NewParam);
           Scope->InstantiatedLocal(OldParam, NewParam);
         } else {
           // Parameter pack expansion: make the instantiation an argument pack.
           Scope->MakeInstantiatedLocalArgPack(OldParam);
           for (unsigned I = 0; I != *NumArgumentsInExpansion; ++I) {
             ParmVarDecl *NewParam = NewProtoLoc.getParam(NewIdx++);
             Params.push_back(NewParam);
             Scope->InstantiatedLocalPackArg(OldParam, NewParam);
           }
         }
       }
     } else {
       // The function type itself was not dependent and therefore no
       // substitution occurred. However, we still need to instantiate
       // the function parameters themselves.
       const FunctionProtoType *OldProto =
           cast<FunctionProtoType>(OldProtoLoc.getType());
       for (unsigned i = 0, i_end = OldProtoLoc.getNumParams(); i != i_end;
            ++i) {
         ParmVarDecl *OldParam = OldProtoLoc.getParam(i);
         if (!OldParam) {
           Params.push_back(SemaRef.BuildParmVarDeclForTypedef(
               D, D->getLocation(), OldProto->getParamType(i)));
           continue;
         }
 
         ParmVarDecl *Parm =
             cast_or_null<ParmVarDecl>(VisitParmVarDecl(OldParam));
         if (!Parm)
           return nullptr;
         Params.push_back(Parm);
       }
     }
   } else {
     // If the type of this function, after ignoring parentheses, is not
     // *directly* a function type, then we're instantiating a function that
     // was declared via a typedef or with attributes, e.g.,
     //
     //   typedef int functype(int, int);
     //   functype func;
     //   int __cdecl meth(int, int);
     //
     // In this case, we'll just go instantiate the ParmVarDecls that we
     // synthesized in the method declaration.
     SmallVector<QualType, 4> ParamTypes;
     Sema::ExtParameterInfoBuilder ExtParamInfos;
     if (SemaRef.SubstParmTypes(D->getLocation(), D->parameters(), nullptr,
                                TemplateArgs, ParamTypes, &Params,
                                ExtParamInfos))
       return nullptr;
   }
 
   return NewTInfo;
 }
 
 void Sema::addInstantiatedLocalVarsToScope(FunctionDecl *Function,
                                            const FunctionDecl *PatternDecl,
                                            LocalInstantiationScope &Scope) {
   LambdaScopeInfo *LSI = cast<LambdaScopeInfo>(getFunctionScopes().back());
 
   for (auto *decl : PatternDecl->decls()) {
     if (!isa<VarDecl>(decl) || isa<ParmVarDecl>(decl))
       continue;
 
     VarDecl *VD = cast<VarDecl>(decl);
     IdentifierInfo *II = VD->getIdentifier();
 
     auto it = llvm::find_if(Function->decls(), [&](Decl *inst) {
       VarDecl *InstVD = dyn_cast<VarDecl>(inst);
       return InstVD && InstVD->isLocalVarDecl() &&
              InstVD->getIdentifier() == II;
     });
 
     if (it == Function->decls().end())
       continue;
 
     Scope.InstantiatedLocal(VD, *it);
     LSI->addCapture(cast<VarDecl>(*it), /*isBlock=*/false, /*isByref=*/false,
                     /*isNested=*/false, VD->getLocation(), SourceLocation(),
                     VD->getType(), /*Invalid=*/false);
   }
 }
 
 bool Sema::addInstantiatedParametersToScope(
     FunctionDecl *Function, const FunctionDecl *PatternDecl,
     LocalInstantiationScope &Scope,
     const MultiLevelTemplateArgumentList &TemplateArgs) {
   unsigned FParamIdx = 0;
   for (unsigned I = 0, N = PatternDecl->getNumParams(); I != N; ++I) {
     const ParmVarDecl *PatternParam = PatternDecl->getParamDecl(I);
     if (!PatternParam->isParameterPack()) {
       // Simple case: not a parameter pack.
       assert(FParamIdx < Function->getNumParams());
       ParmVarDecl *FunctionParam = Function->getParamDecl(FParamIdx);
       FunctionParam->setDeclName(PatternParam->getDeclName());
       // If the parameter's type is not dependent, update it to match the type
       // in the pattern. They can differ in top-level cv-qualifiers, and we want
       // the pattern's type here. If the type is dependent, they can't differ,
       // per core issue 1668. Substitute into the type from the pattern, in case
       // it's instantiation-dependent.
       // FIXME: Updating the type to work around this is at best fragile.
       if (!PatternDecl->getType()->isDependentType()) {
         QualType T = SubstType(PatternParam->getType(), TemplateArgs,
                                FunctionParam->getLocation(),
                                FunctionParam->getDeclName());
         if (T.isNull())
           return true;
         FunctionParam->setType(T);
       }
 
       Scope.InstantiatedLocal(PatternParam, FunctionParam);
       ++FParamIdx;
       continue;
     }
 
     // Expand the parameter pack.
     Scope.MakeInstantiatedLocalArgPack(PatternParam);
     std::optional<unsigned> NumArgumentsInExpansion =
         getNumArgumentsInExpansion(PatternParam->getType(), TemplateArgs);
     if (NumArgumentsInExpansion) {
       QualType PatternType =
           PatternParam->getType()->castAs<PackExpansionType>()->getPattern();
       for (unsigned Arg = 0; Arg < *NumArgumentsInExpansion; ++Arg) {
         ParmVarDecl *FunctionParam = Function->getParamDecl(FParamIdx);
         FunctionParam->setDeclName(PatternParam->getDeclName());
         if (!PatternDecl->getType()->isDependentType()) {
           Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this, Arg);
           QualType T =
               SubstType(PatternType, TemplateArgs, FunctionParam->getLocation(),
                         FunctionParam->getDeclName());
           if (T.isNull())
             return true;
           FunctionParam->setType(T);
         }
 
         Scope.InstantiatedLocalPackArg(PatternParam, FunctionParam);
         ++FParamIdx;
       }
     }
   }
 
   return false;
 }
 
 bool Sema::InstantiateDefaultArgument(SourceLocation CallLoc, FunctionDecl *FD,
                                       ParmVarDecl *Param) {
   assert(Param->hasUninstantiatedDefaultArg());
 
   // Instantiate the expression.
   //
   // FIXME: Pass in a correct Pattern argument, otherwise
   // getTemplateInstantiationArgs uses the lexical context of FD, e.g.
   //
   // template<typename T>
   // struct A {
   //   static int FooImpl();
   //
   //   template<typename Tp>
   //   // bug: default argument A<T>::FooImpl() is evaluated with 2-level
   //   // template argument list [[T], [Tp]], should be [[Tp]].
   //   friend A<Tp> Foo(int a);
   // };
   //
   // template<typename T>
   // A<T> Foo(int a = A<T>::FooImpl());
-  MultiLevelTemplateArgumentList TemplateArgs =
-      getTemplateInstantiationArgs(FD, FD->getLexicalDeclContext(),
-                                   /*Final=*/false, /*Innermost=*/std::nullopt,
-                                   /*RelativeToPrimary=*/true);
+  MultiLevelTemplateArgumentList TemplateArgs = getTemplateInstantiationArgs(
+      FD, FD->getLexicalDeclContext(),
+      /*Final=*/false, /*Innermost=*/std::nullopt,
+      /*RelativeToPrimary=*/true, /*Pattern=*/nullptr,
+      /*ForConstraintInstantiation=*/false, /*SkipForSpecialization=*/false,
+      /*ForDefaultArgumentSubstitution=*/true);
 
   if (SubstDefaultArgument(CallLoc, Param, TemplateArgs, /*ForCallExpr*/ true))
     return true;
 
   if (ASTMutationListener *L = getASTMutationListener())
     L->DefaultArgumentInstantiated(Param);
 
   return false;
 }
 
 void Sema::InstantiateExceptionSpec(SourceLocation PointOfInstantiation,
                                     FunctionDecl *Decl) {
   const FunctionProtoType *Proto = Decl->getType()->castAs<FunctionProtoType>();
   if (Proto->getExceptionSpecType() != EST_Uninstantiated)
     return;
 
   InstantiatingTemplate Inst(*this, PointOfInstantiation, Decl,
                              InstantiatingTemplate::ExceptionSpecification());
   if (Inst.isInvalid()) {
     // We hit the instantiation depth limit. Clear the exception specification
     // so that our callers don't have to cope with EST_Uninstantiated.
     UpdateExceptionSpec(Decl, EST_None);
     return;
   }
   if (Inst.isAlreadyInstantiating()) {
     // This exception specification indirectly depends on itself. Reject.
     // FIXME: Corresponding rule in the standard?
     Diag(PointOfInstantiation, diag::err_exception_spec_cycle) << Decl;
     UpdateExceptionSpec(Decl, EST_None);
     return;
   }
 
   // Enter the scope of this instantiation. We don't use
   // PushDeclContext because we don't have a scope.
   Sema::ContextRAII savedContext(*this, Decl);
   LocalInstantiationScope Scope(*this);
 
   MultiLevelTemplateArgumentList TemplateArgs =
       getTemplateInstantiationArgs(Decl, Decl->getLexicalDeclContext(),
                                    /*Final=*/false, /*Innermost=*/std::nullopt,
                                    /*RelativeToPrimary*/ true);
 
   // FIXME: We can't use getTemplateInstantiationPattern(false) in general
   // here, because for a non-defining friend declaration in a class template,
   // we don't store enough information to map back to the friend declaration in
   // the template.
   FunctionDecl *Template = Proto->getExceptionSpecTemplate();
   if (addInstantiatedParametersToScope(Decl, Template, Scope, TemplateArgs)) {
     UpdateExceptionSpec(Decl, EST_None);
     return;
   }
 
   // The noexcept specification could reference any lambda captures. Ensure
   // those are added to the LocalInstantiationScope.
   LambdaScopeForCallOperatorInstantiationRAII PushLambdaCaptures(
       *this, Decl, TemplateArgs, Scope,
       /*ShouldAddDeclsFromParentScope=*/false);
 
   SubstExceptionSpec(Decl, Template->getType()->castAs<FunctionProtoType>(),
                      TemplateArgs);
 }
 
 /// Initializes the common fields of an instantiation function
 /// declaration (New) from the corresponding fields of its template (Tmpl).
 ///
 /// \returns true if there was an error
 bool
 TemplateDeclInstantiator::InitFunctionInstantiation(FunctionDecl *New,
                                                     FunctionDecl *Tmpl) {
   New->setImplicit(Tmpl->isImplicit());
 
   // Forward the mangling number from the template to the instantiated decl.
   SemaRef.Context.setManglingNumber(New,
                                     SemaRef.Context.getManglingNumber(Tmpl));
 
   // If we are performing substituting explicitly-specified template arguments
   // or deduced template arguments into a function template and we reach this
   // point, we are now past the point where SFINAE applies and have committed
   // to keeping the new function template specialization. We therefore
   // convert the active template instantiation for the function template
   // into a template instantiation for this specific function template
   // specialization, which is not a SFINAE context, so that we diagnose any
   // further errors in the declaration itself.
   //
   // FIXME: This is a hack.
   typedef Sema::CodeSynthesisContext ActiveInstType;
   ActiveInstType &ActiveInst = SemaRef.CodeSynthesisContexts.back();
   if (ActiveInst.Kind == ActiveInstType::ExplicitTemplateArgumentSubstitution ||
       ActiveInst.Kind == ActiveInstType::DeducedTemplateArgumentSubstitution) {
     if (isa<FunctionTemplateDecl>(ActiveInst.Entity)) {
       SemaRef.InstantiatingSpecializations.erase(
           {ActiveInst.Entity->getCanonicalDecl(), ActiveInst.Kind});
       atTemplateEnd(SemaRef.TemplateInstCallbacks, SemaRef, ActiveInst);
       ActiveInst.Kind = ActiveInstType::TemplateInstantiation;
       ActiveInst.Entity = New;
       atTemplateBegin(SemaRef.TemplateInstCallbacks, SemaRef, ActiveInst);
     }
   }
 
   const FunctionProtoType *Proto = Tmpl->getType()->getAs<FunctionProtoType>();
   assert(Proto && "Function template without prototype?");
 
   if (Proto->hasExceptionSpec() || Proto->getNoReturnAttr()) {
     FunctionProtoType::ExtProtoInfo EPI = Proto->getExtProtoInfo();
 
     // DR1330: In C++11, defer instantiation of a non-trivial
     // exception specification.
     // DR1484: Local classes and their members are instantiated along with the
     // containing function.
     if (SemaRef.getLangOpts().CPlusPlus11 &&
         EPI.ExceptionSpec.Type != EST_None &&
         EPI.ExceptionSpec.Type != EST_DynamicNone &&
         EPI.ExceptionSpec.Type != EST_BasicNoexcept &&
         !Tmpl->isInLocalScopeForInstantiation()) {
       FunctionDecl *ExceptionSpecTemplate = Tmpl;
       if (EPI.ExceptionSpec.Type == EST_Uninstantiated)
         ExceptionSpecTemplate = EPI.ExceptionSpec.SourceTemplate;
       ExceptionSpecificationType NewEST = EST_Uninstantiated;
       if (EPI.ExceptionSpec.Type == EST_Unevaluated)
         NewEST = EST_Unevaluated;
 
       // Mark the function has having an uninstantiated exception specification.
       const FunctionProtoType *NewProto
         = New->getType()->getAs<FunctionProtoType>();
       assert(NewProto && "Template instantiation without function prototype?");
       EPI = NewProto->getExtProtoInfo();
       EPI.ExceptionSpec.Type = NewEST;
       EPI.ExceptionSpec.SourceDecl = New;
       EPI.ExceptionSpec.SourceTemplate = ExceptionSpecTemplate;
       New->setType(SemaRef.Context.getFunctionType(
           NewProto->getReturnType(), NewProto->getParamTypes(), EPI));
     } else {
       Sema::ContextRAII SwitchContext(SemaRef, New);
       SemaRef.SubstExceptionSpec(New, Proto, TemplateArgs);
     }
   }
 
   // Get the definition. Leaves the variable unchanged if undefined.
   const FunctionDecl *Definition = Tmpl;
   Tmpl->isDefined(Definition);
 
   SemaRef.InstantiateAttrs(TemplateArgs, Definition, New,
                            LateAttrs, StartingScope);
 
   return false;
 }
 
 /// Initializes common fields of an instantiated method
 /// declaration (New) from the corresponding fields of its template
 /// (Tmpl).
 ///
 /// \returns true if there was an error
 bool
 TemplateDeclInstantiator::InitMethodInstantiation(CXXMethodDecl *New,
                                                   CXXMethodDecl *Tmpl) {
   if (InitFunctionInstantiation(New, Tmpl))
     return true;
 
   if (isa<CXXDestructorDecl>(New) && SemaRef.getLangOpts().CPlusPlus11)
     SemaRef.AdjustDestructorExceptionSpec(cast<CXXDestructorDecl>(New));
 
   New->setAccess(Tmpl->getAccess());
   if (Tmpl->isVirtualAsWritten())
     New->setVirtualAsWritten(true);
 
   // FIXME: New needs a pointer to Tmpl
   return false;
 }
 
 bool TemplateDeclInstantiator::SubstDefaultedFunction(FunctionDecl *New,
                                                       FunctionDecl *Tmpl) {
   // Transfer across any unqualified lookups.
   if (auto *DFI = Tmpl->getDefalutedOrDeletedInfo()) {
     SmallVector<DeclAccessPair, 32> Lookups;
     Lookups.reserve(DFI->getUnqualifiedLookups().size());
     bool AnyChanged = false;
     for (DeclAccessPair DA : DFI->getUnqualifiedLookups()) {
       NamedDecl *D = SemaRef.FindInstantiatedDecl(New->getLocation(),
                                                   DA.getDecl(), TemplateArgs);
       if (!D)
         return true;
       AnyChanged |= (D != DA.getDecl());
       Lookups.push_back(DeclAccessPair::make(D, DA.getAccess()));
     }
 
     // It's unlikely that substitution will change any declarations. Don't
     // store an unnecessary copy in that case.
     New->setDefaultedOrDeletedInfo(
         AnyChanged ? FunctionDecl::DefaultedOrDeletedFunctionInfo::Create(
                          SemaRef.Context, Lookups)
                    : DFI);
   }
 
   SemaRef.SetDeclDefaulted(New, Tmpl->getLocation());
   return false;
 }
 
 FunctionDecl *Sema::InstantiateFunctionDeclaration(
     FunctionTemplateDecl *FTD, const TemplateArgumentList *Args,
     SourceLocation Loc, CodeSynthesisContext::SynthesisKind CSC) {
   FunctionDecl *FD = FTD->getTemplatedDecl();
 
   sema::TemplateDeductionInfo Info(Loc);
   InstantiatingTemplate Inst(*this, Loc, FTD, Args->asArray(), CSC, Info);
   if (Inst.isInvalid())
     return nullptr;
 
   ContextRAII SavedContext(*this, FD);
   MultiLevelTemplateArgumentList MArgs(FTD, Args->asArray(),
                                        /*Final=*/false);
 
   return cast_or_null<FunctionDecl>(SubstDecl(FD, FD->getParent(), MArgs));
 }
 
 void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
                                          FunctionDecl *Function,
                                          bool Recursive,
                                          bool DefinitionRequired,
                                          bool AtEndOfTU) {
   if (Function->isInvalidDecl() || isa<CXXDeductionGuideDecl>(Function))
     return;
 
   // Never instantiate an explicit specialization except if it is a class scope
   // explicit specialization.
   TemplateSpecializationKind TSK =
       Function->getTemplateSpecializationKindForInstantiation();
   if (TSK == TSK_ExplicitSpecialization)
     return;
 
   // Never implicitly instantiate a builtin; we don't actually need a function
   // body.
   if (Function->getBuiltinID() && TSK == TSK_ImplicitInstantiation &&
       !DefinitionRequired)
     return;
 
   // Don't instantiate a definition if we already have one.
   const FunctionDecl *ExistingDefn = nullptr;
   if (Function->isDefined(ExistingDefn,
                           /*CheckForPendingFriendDefinition=*/true)) {
     if (ExistingDefn->isThisDeclarationADefinition())
       return;
 
     // If we're asked to instantiate a function whose body comes from an
     // instantiated friend declaration, attach the instantiated body to the
     // corresponding declaration of the function.
     assert(ExistingDefn->isThisDeclarationInstantiatedFromAFriendDefinition());
     Function = const_cast<FunctionDecl*>(ExistingDefn);
   }
 
   // Find the function body that we'll be substituting.
   const FunctionDecl *PatternDecl = Function->getTemplateInstantiationPattern();
   assert(PatternDecl && "instantiating a non-template");
 
   const FunctionDecl *PatternDef = PatternDecl->getDefinition();
   Stmt *Pattern = nullptr;
   if (PatternDef) {
     Pattern = PatternDef->getBody(PatternDef);
     PatternDecl = PatternDef;
     if (PatternDef->willHaveBody())
       PatternDef = nullptr;
   }
 
   // FIXME: We need to track the instantiation stack in order to know which
   // definitions should be visible within this instantiation.
   if (DiagnoseUninstantiableTemplate(PointOfInstantiation, Function,
                                 Function->getInstantiatedFromMemberFunction(),
                                      PatternDecl, PatternDef, TSK,
                                      /*Complain*/DefinitionRequired)) {
     if (DefinitionRequired)
       Function->setInvalidDecl();
     else if (TSK == TSK_ExplicitInstantiationDefinition ||
              (Function->isConstexpr() && !Recursive)) {
       // Try again at the end of the translation unit (at which point a
       // definition will be required).
       assert(!Recursive);
       Function->setInstantiationIsPending(true);
       PendingInstantiations.push_back(
         std::make_pair(Function, PointOfInstantiation));
     } else if (TSK == TSK_ImplicitInstantiation) {
       if (AtEndOfTU && !getDiagnostics().hasErrorOccurred() &&
           !getSourceManager().isInSystemHeader(PatternDecl->getBeginLoc())) {
         Diag(PointOfInstantiation, diag::warn_func_template_missing)
           << Function;
         Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
         if (getLangOpts().CPlusPlus11)
           Diag(PointOfInstantiation, diag::note_inst_declaration_hint)
               << Function;
       }
     }
 
     return;
   }
 
   // Postpone late parsed template instantiations.
   if (PatternDecl->isLateTemplateParsed() &&
       !LateTemplateParser) {
     Function->setInstantiationIsPending(true);
     LateParsedInstantiations.push_back(
         std::make_pair(Function, PointOfInstantiation));
     return;
   }
 
   llvm::TimeTraceScope TimeScope("InstantiateFunction", [&]() {
     llvm::TimeTraceMetadata M;
     llvm::raw_string_ostream OS(M.Detail);
     Function->getNameForDiagnostic(OS, getPrintingPolicy(),
                                    /*Qualified=*/true);
     if (llvm::isTimeTraceVerbose()) {
       auto Loc = SourceMgr.getExpansionLoc(Function->getLocation());
       M.File = SourceMgr.getFilename(Loc);
       M.Line = SourceMgr.getExpansionLineNumber(Loc);
     }
     return M;
   });
 
   // If we're performing recursive template instantiation, create our own
   // queue of pending implicit instantiations that we will instantiate later,
   // while we're still within our own instantiation context.
   // This has to happen before LateTemplateParser below is called, so that
   // it marks vtables used in late parsed templates as used.
   GlobalEagerInstantiationScope GlobalInstantiations(*this,
                                                      /*Enabled=*/Recursive);
   LocalEagerInstantiationScope LocalInstantiations(*this);
 
   // Call the LateTemplateParser callback if there is a need to late parse
   // a templated function definition.
   if (!Pattern && PatternDecl->isLateTemplateParsed() &&
       LateTemplateParser) {
     // FIXME: Optimize to allow individual templates to be deserialized.
     if (PatternDecl->isFromASTFile())
       ExternalSource->ReadLateParsedTemplates(LateParsedTemplateMap);
 
     auto LPTIter = LateParsedTemplateMap.find(PatternDecl);
     assert(LPTIter != LateParsedTemplateMap.end() &&
            "missing LateParsedTemplate");
     LateTemplateParser(OpaqueParser, *LPTIter->second);
     Pattern = PatternDecl->getBody(PatternDecl);
     updateAttrsForLateParsedTemplate(PatternDecl, Function);
   }
 
   // Note, we should never try to instantiate a deleted function template.
   assert((Pattern || PatternDecl->isDefaulted() ||
           PatternDecl->hasSkippedBody()) &&
          "unexpected kind of function template definition");
 
   // C++1y [temp.explicit]p10:
   //   Except for inline functions, declarations with types deduced from their
   //   initializer or return value, and class template specializations, other
   //   explicit instantiation declarations have the effect of suppressing the
   //   implicit instantiation of the entity to which they refer.
   if (TSK == TSK_ExplicitInstantiationDeclaration &&
       !PatternDecl->isInlined() &&
       !PatternDecl->getReturnType()->getContainedAutoType())
     return;
 
   if (PatternDecl->isInlined()) {
     // Function, and all later redeclarations of it (from imported modules,
     // for instance), are now implicitly inline.
     for (auto *D = Function->getMostRecentDecl(); /**/;
          D = D->getPreviousDecl()) {
       D->setImplicitlyInline();
       if (D == Function)
         break;
     }
   }
 
   InstantiatingTemplate Inst(*this, PointOfInstantiation, Function);
   if (Inst.isInvalid() || Inst.isAlreadyInstantiating())
     return;
   PrettyDeclStackTraceEntry CrashInfo(Context, Function, SourceLocation(),
                                       "instantiating function definition");
 
   // The instantiation is visible here, even if it was first declared in an
   // unimported module.
   Function->setVisibleDespiteOwningModule();
 
   // Copy the source locations from the pattern.
   Function->setLocation(PatternDecl->getLocation());
   Function->setInnerLocStart(PatternDecl->getInnerLocStart());
   Function->setRangeEnd(PatternDecl->getEndLoc());
   Function->setDeclarationNameLoc(PatternDecl->getNameInfo().getInfo());
 
   EnterExpressionEvaluationContext EvalContext(
       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
 
   Qualifiers ThisTypeQuals;
   CXXRecordDecl *ThisContext = nullptr;
   if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Function)) {
     ThisContext = Method->getParent();
     ThisTypeQuals = Method->getMethodQualifiers();
   }
   CXXThisScopeRAII ThisScope(*this, ThisContext, ThisTypeQuals);
 
   // Introduce a new scope where local variable instantiations will be
   // recorded, unless we're actually a member function within a local
   // class, in which case we need to merge our results with the parent
   // scope (of the enclosing function). The exception is instantiating
   // a function template specialization, since the template to be
   // instantiated already has references to locals properly substituted.
   bool MergeWithParentScope = false;
   if (CXXRecordDecl *Rec = dyn_cast<CXXRecordDecl>(Function->getDeclContext()))
     MergeWithParentScope =
         Rec->isLocalClass() && !Function->isFunctionTemplateSpecialization();
 
   LocalInstantiationScope Scope(*this, MergeWithParentScope);
   auto RebuildTypeSourceInfoForDefaultSpecialMembers = [&]() {
     // Special members might get their TypeSourceInfo set up w.r.t the
     // PatternDecl context, in which case parameters could still be pointing
     // back to the original class, make sure arguments are bound to the
     // instantiated record instead.
     assert(PatternDecl->isDefaulted() &&
            "Special member needs to be defaulted");
     auto PatternSM = getDefaultedFunctionKind(PatternDecl).asSpecialMember();
     if (!(PatternSM == CXXSpecialMemberKind::CopyConstructor ||
           PatternSM == CXXSpecialMemberKind::CopyAssignment ||
           PatternSM == CXXSpecialMemberKind::MoveConstructor ||
           PatternSM == CXXSpecialMemberKind::MoveAssignment))
       return;
 
     auto *NewRec = dyn_cast<CXXRecordDecl>(Function->getDeclContext());
     const auto *PatternRec =
         dyn_cast<CXXRecordDecl>(PatternDecl->getDeclContext());
     if (!NewRec || !PatternRec)
       return;
     if (!PatternRec->isLambda())
       return;
 
     struct SpecialMemberTypeInfoRebuilder
         : TreeTransform<SpecialMemberTypeInfoRebuilder> {
       using Base = TreeTransform<SpecialMemberTypeInfoRebuilder>;
       const CXXRecordDecl *OldDecl;
       CXXRecordDecl *NewDecl;
 
       SpecialMemberTypeInfoRebuilder(Sema &SemaRef, const CXXRecordDecl *O,
                                      CXXRecordDecl *N)
           : TreeTransform(SemaRef), OldDecl(O), NewDecl(N) {}
 
       bool TransformExceptionSpec(SourceLocation Loc,
                                   FunctionProtoType::ExceptionSpecInfo &ESI,
                                   SmallVectorImpl<QualType> &Exceptions,
                                   bool &Changed) {
         return false;
       }
 
       QualType TransformRecordType(TypeLocBuilder &TLB, RecordTypeLoc TL) {
         const RecordType *T = TL.getTypePtr();
         RecordDecl *Record = cast_or_null<RecordDecl>(
             getDerived().TransformDecl(TL.getNameLoc(), T->getDecl()));
         if (Record != OldDecl)
           return Base::TransformRecordType(TLB, TL);
 
         QualType Result = getDerived().RebuildRecordType(NewDecl);
         if (Result.isNull())
           return QualType();
 
         RecordTypeLoc NewTL = TLB.push<RecordTypeLoc>(Result);
         NewTL.setNameLoc(TL.getNameLoc());
         return Result;
       }
     } IR{*this, PatternRec, NewRec};
 
     TypeSourceInfo *NewSI = IR.TransformType(Function->getTypeSourceInfo());
     assert(NewSI && "Type Transform failed?");
     Function->setType(NewSI->getType());
     Function->setTypeSourceInfo(NewSI);
 
     ParmVarDecl *Parm = Function->getParamDecl(0);
     TypeSourceInfo *NewParmSI = IR.TransformType(Parm->getTypeSourceInfo());
     assert(NewParmSI && "Type transformation failed.");
     Parm->setType(NewParmSI->getType());
     Parm->setTypeSourceInfo(NewParmSI);
   };
 
   if (PatternDecl->isDefaulted()) {
     RebuildTypeSourceInfoForDefaultSpecialMembers();
     SetDeclDefaulted(Function, PatternDecl->getLocation());
   } else {
     MultiLevelTemplateArgumentList TemplateArgs = getTemplateInstantiationArgs(
         Function, Function->getLexicalDeclContext(), /*Final=*/false,
         /*Innermost=*/std::nullopt, false, PatternDecl);
 
     // Substitute into the qualifier; we can get a substitution failure here
     // through evil use of alias templates.
     // FIXME: Is CurContext correct for this? Should we go to the (instantiation
     // of the) lexical context of the pattern?
     SubstQualifier(*this, PatternDecl, Function, TemplateArgs);
 
     ActOnStartOfFunctionDef(nullptr, Function);
 
     // Enter the scope of this instantiation. We don't use
     // PushDeclContext because we don't have a scope.
     Sema::ContextRAII savedContext(*this, Function);
 
     FPFeaturesStateRAII SavedFPFeatures(*this);
     CurFPFeatures = FPOptions(getLangOpts());
     FpPragmaStack.CurrentValue = FPOptionsOverride();
 
     if (addInstantiatedParametersToScope(Function, PatternDecl, Scope,
                                          TemplateArgs))
       return;
 
     StmtResult Body;
     if (PatternDecl->hasSkippedBody()) {
       ActOnSkippedFunctionBody(Function);
       Body = nullptr;
     } else {
       if (CXXConstructorDecl *Ctor = dyn_cast<CXXConstructorDecl>(Function)) {
         // If this is a constructor, instantiate the member initializers.
         InstantiateMemInitializers(Ctor, cast<CXXConstructorDecl>(PatternDecl),
                                    TemplateArgs);
 
         // If this is an MS ABI dllexport default constructor, instantiate any
         // default arguments.
         if (Context.getTargetInfo().getCXXABI().isMicrosoft() &&
             Ctor->isDefaultConstructor()) {
           InstantiateDefaultCtorDefaultArgs(Ctor);
         }
       }
 
       // Instantiate the function body.
       Body = SubstStmt(Pattern, TemplateArgs);
 
       if (Body.isInvalid())
         Function->setInvalidDecl();
     }
     // FIXME: finishing the function body while in an expression evaluation
     // context seems wrong. Investigate more.
     ActOnFinishFunctionBody(Function, Body.get(), /*IsInstantiation=*/true);
 
     PerformDependentDiagnostics(PatternDecl, TemplateArgs);
 
     if (auto *Listener = getASTMutationListener())
       Listener->FunctionDefinitionInstantiated(Function);
 
     savedContext.pop();
   }
 
   DeclGroupRef DG(Function);
   Consumer.HandleTopLevelDecl(DG);
 
   // This class may have local implicit instantiations that need to be
   // instantiation within this scope.
   LocalInstantiations.perform();
   Scope.Exit();
   GlobalInstantiations.perform();
 }
 
 VarTemplateSpecializationDecl *Sema::BuildVarTemplateInstantiation(
     VarTemplateDecl *VarTemplate, VarDecl *FromVar,
     const TemplateArgumentList *PartialSpecArgs,
     const TemplateArgumentListInfo &TemplateArgsInfo,
     SmallVectorImpl<TemplateArgument> &Converted,
     SourceLocation PointOfInstantiation, LateInstantiatedAttrVec *LateAttrs,
     LocalInstantiationScope *StartingScope) {
   if (FromVar->isInvalidDecl())
     return nullptr;
 
   InstantiatingTemplate Inst(*this, PointOfInstantiation, FromVar);
   if (Inst.isInvalid())
     return nullptr;
 
   // Instantiate the first declaration of the variable template: for a partial
   // specialization of a static data member template, the first declaration may
   // or may not be the declaration in the class; if it's in the class, we want
   // to instantiate a member in the class (a declaration), and if it's outside,
   // we want to instantiate a definition.
   //
   // If we're instantiating an explicitly-specialized member template or member
   // partial specialization, don't do this. The member specialization completely
   // replaces the original declaration in this case.
   bool IsMemberSpec = false;
   MultiLevelTemplateArgumentList MultiLevelList;
   if (auto *PartialSpec =
           dyn_cast<VarTemplatePartialSpecializationDecl>(FromVar)) {
     assert(PartialSpecArgs);
     IsMemberSpec = PartialSpec->isMemberSpecialization();
     MultiLevelList.addOuterTemplateArguments(
         PartialSpec, PartialSpecArgs->asArray(), /*Final=*/false);
   } else {
     assert(VarTemplate == FromVar->getDescribedVarTemplate());
     IsMemberSpec = VarTemplate->isMemberSpecialization();
     MultiLevelList.addOuterTemplateArguments(VarTemplate, Converted,
                                              /*Final=*/false);
   }
   if (!IsMemberSpec)
     FromVar = FromVar->getFirstDecl();
 
   TemplateDeclInstantiator Instantiator(*this, FromVar->getDeclContext(),
                                         MultiLevelList);
 
   // TODO: Set LateAttrs and StartingScope ...
 
   return cast_or_null<VarTemplateSpecializationDecl>(
       Instantiator.VisitVarTemplateSpecializationDecl(
           VarTemplate, FromVar, TemplateArgsInfo, Converted));
 }
 
 VarTemplateSpecializationDecl *Sema::CompleteVarTemplateSpecializationDecl(
     VarTemplateSpecializationDecl *VarSpec, VarDecl *PatternDecl,
     const MultiLevelTemplateArgumentList &TemplateArgs) {
   assert(PatternDecl->isThisDeclarationADefinition() &&
          "don't have a definition to instantiate from");
 
   // Do substitution on the type of the declaration
   TypeSourceInfo *DI =
       SubstType(PatternDecl->getTypeSourceInfo(), TemplateArgs,
                 PatternDecl->getTypeSpecStartLoc(), PatternDecl->getDeclName());
   if (!DI)
     return nullptr;
 
   // Update the type of this variable template specialization.
   VarSpec->setType(DI->getType());
 
   // Convert the declaration into a definition now.
   VarSpec->setCompleteDefinition();
 
   // Instantiate the initializer.
   InstantiateVariableInitializer(VarSpec, PatternDecl, TemplateArgs);
 
   if (getLangOpts().OpenCL)
     deduceOpenCLAddressSpace(VarSpec);
 
   return VarSpec;
 }
 
 void Sema::BuildVariableInstantiation(
     VarDecl *NewVar, VarDecl *OldVar,
     const MultiLevelTemplateArgumentList &TemplateArgs,
     LateInstantiatedAttrVec *LateAttrs, DeclContext *Owner,
     LocalInstantiationScope *StartingScope,
     bool InstantiatingVarTemplate,
     VarTemplateSpecializationDecl *PrevDeclForVarTemplateSpecialization) {
   // Instantiating a partial specialization to produce a partial
   // specialization.
   bool InstantiatingVarTemplatePartialSpec =
       isa<VarTemplatePartialSpecializationDecl>(OldVar) &&
       isa<VarTemplatePartialSpecializationDecl>(NewVar);
   // Instantiating from a variable template (or partial specialization) to
   // produce a variable template specialization.
   bool InstantiatingSpecFromTemplate =
       isa<VarTemplateSpecializationDecl>(NewVar) &&
       (OldVar->getDescribedVarTemplate() ||
        isa<VarTemplatePartialSpecializationDecl>(OldVar));
 
   // If we are instantiating a local extern declaration, the
   // instantiation belongs lexically to the containing function.
   // If we are instantiating a static data member defined
   // out-of-line, the instantiation will have the same lexical
   // context (which will be a namespace scope) as the template.
   if (OldVar->isLocalExternDecl()) {
     NewVar->setLocalExternDecl();
     NewVar->setLexicalDeclContext(Owner);
   } else if (OldVar->isOutOfLine())
     NewVar->setLexicalDeclContext(OldVar->getLexicalDeclContext());
   NewVar->setTSCSpec(OldVar->getTSCSpec());
   NewVar->setInitStyle(OldVar->getInitStyle());
   NewVar->setCXXForRangeDecl(OldVar->isCXXForRangeDecl());
   NewVar->setObjCForDecl(OldVar->isObjCForDecl());
   NewVar->setConstexpr(OldVar->isConstexpr());
   NewVar->setInitCapture(OldVar->isInitCapture());
   NewVar->setPreviousDeclInSameBlockScope(
       OldVar->isPreviousDeclInSameBlockScope());
   NewVar->setAccess(OldVar->getAccess());
 
   if (!OldVar->isStaticDataMember()) {
     if (OldVar->isUsed(false))
       NewVar->setIsUsed();
     NewVar->setReferenced(OldVar->isReferenced());
   }
 
   InstantiateAttrs(TemplateArgs, OldVar, NewVar, LateAttrs, StartingScope);
 
   LookupResult Previous(
       *this, NewVar->getDeclName(), NewVar->getLocation(),
       NewVar->isLocalExternDecl() ? Sema::LookupRedeclarationWithLinkage
                                   : Sema::LookupOrdinaryName,
       NewVar->isLocalExternDecl() ? RedeclarationKind::ForExternalRedeclaration
                                   : forRedeclarationInCurContext());
 
   if (NewVar->isLocalExternDecl() && OldVar->getPreviousDecl() &&
       (!OldVar->getPreviousDecl()->getDeclContext()->isDependentContext() ||
        OldVar->getPreviousDecl()->getDeclContext()==OldVar->getDeclContext())) {
     // We have a previous declaration. Use that one, so we merge with the
     // right type.
     if (NamedDecl *NewPrev = FindInstantiatedDecl(
             NewVar->getLocation(), OldVar->getPreviousDecl(), TemplateArgs))
       Previous.addDecl(NewPrev);
   } else if (!isa<VarTemplateSpecializationDecl>(NewVar) &&
              OldVar->hasLinkage()) {
     LookupQualifiedName(Previous, NewVar->getDeclContext(), false);
   } else if (PrevDeclForVarTemplateSpecialization) {
     Previous.addDecl(PrevDeclForVarTemplateSpecialization);
   }
   CheckVariableDeclaration(NewVar, Previous);
 
   if (!InstantiatingVarTemplate) {
     NewVar->getLexicalDeclContext()->addHiddenDecl(NewVar);
     if (!NewVar->isLocalExternDecl() || !NewVar->getPreviousDecl())
       NewVar->getDeclContext()->makeDeclVisibleInContext(NewVar);
   }
 
   if (!OldVar->isOutOfLine()) {
     if (NewVar->getDeclContext()->isFunctionOrMethod())
       CurrentInstantiationScope->InstantiatedLocal(OldVar, NewVar);
   }
 
   // Link instantiations of static data members back to the template from
   // which they were instantiated.
   //
   // Don't do this when instantiating a template (we link the template itself
   // back in that case) nor when instantiating a static data member template
   // (that's not a member specialization).
   if (NewVar->isStaticDataMember() && !InstantiatingVarTemplate &&
       !InstantiatingSpecFromTemplate)
     NewVar->setInstantiationOfStaticDataMember(OldVar,
                                                TSK_ImplicitInstantiation);
 
   // If the pattern is an (in-class) explicit specialization, then the result
   // is also an explicit specialization.
   if (VarTemplateSpecializationDecl *OldVTSD =
           dyn_cast<VarTemplateSpecializationDecl>(OldVar)) {
     if (OldVTSD->getSpecializationKind() == TSK_ExplicitSpecialization &&
         !isa<VarTemplatePartialSpecializationDecl>(OldVTSD))
       cast<VarTemplateSpecializationDecl>(NewVar)->setSpecializationKind(
           TSK_ExplicitSpecialization);
   }
 
   // Forward the mangling number from the template to the instantiated decl.
   Context.setManglingNumber(NewVar, Context.getManglingNumber(OldVar));
   Context.setStaticLocalNumber(NewVar, Context.getStaticLocalNumber(OldVar));
 
   // Figure out whether to eagerly instantiate the initializer.
   if (InstantiatingVarTemplate || InstantiatingVarTemplatePartialSpec) {
     // We're producing a template. Don't instantiate the initializer yet.
   } else if (NewVar->getType()->isUndeducedType()) {
     // We need the type to complete the declaration of the variable.
     InstantiateVariableInitializer(NewVar, OldVar, TemplateArgs);
   } else if (InstantiatingSpecFromTemplate ||
              (OldVar->isInline() && OldVar->isThisDeclarationADefinition() &&
               !NewVar->isThisDeclarationADefinition())) {
     // Delay instantiation of the initializer for variable template
     // specializations or inline static data members until a definition of the
     // variable is needed.
   } else {
     InstantiateVariableInitializer(NewVar, OldVar, TemplateArgs);
   }
 
   // Diagnose unused local variables with dependent types, where the diagnostic
   // will have been deferred.
   if (!NewVar->isInvalidDecl() &&
       NewVar->getDeclContext()->isFunctionOrMethod() &&
       OldVar->getType()->isDependentType())
     DiagnoseUnusedDecl(NewVar);
 }
 
 void Sema::InstantiateVariableInitializer(
     VarDecl *Var, VarDecl *OldVar,
     const MultiLevelTemplateArgumentList &TemplateArgs) {
   if (ASTMutationListener *L = getASTContext().getASTMutationListener())
     L->VariableDefinitionInstantiated(Var);
 
   // We propagate the 'inline' flag with the initializer, because it
   // would otherwise imply that the variable is a definition for a
   // non-static data member.
   if (OldVar->isInlineSpecified())
     Var->setInlineSpecified();
   else if (OldVar->isInline())
     Var->setImplicitlyInline();
 
   if (OldVar->getInit()) {
     EnterExpressionEvaluationContext Evaluated(
         *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated, Var);
 
     keepInLifetimeExtendingContext();
     // Instantiate the initializer.
     ExprResult Init;
 
     {
       ContextRAII SwitchContext(*this, Var->getDeclContext());
       Init = SubstInitializer(OldVar->getInit(), TemplateArgs,
                               OldVar->getInitStyle() == VarDecl::CallInit);
     }
 
     if (!Init.isInvalid()) {
       Expr *InitExpr = Init.get();
 
       if (Var->hasAttr<DLLImportAttr>() &&
           (!InitExpr ||
            !InitExpr->isConstantInitializer(getASTContext(), false))) {
         // Do not dynamically initialize dllimport variables.
       } else if (InitExpr) {
         bool DirectInit = OldVar->isDirectInit();
         AddInitializerToDecl(Var, InitExpr, DirectInit);
       } else
         ActOnUninitializedDecl(Var);
     } else {
       // FIXME: Not too happy about invalidating the declaration
       // because of a bogus initializer.
       Var->setInvalidDecl();
     }
   } else {
     // `inline` variables are a definition and declaration all in one; we won't
     // pick up an initializer from anywhere else.
     if (Var->isStaticDataMember() && !Var->isInline()) {
       if (!Var->isOutOfLine())
         return;
 
       // If the declaration inside the class had an initializer, don't add
       // another one to the out-of-line definition.
       if (OldVar->getFirstDecl()->hasInit())
         return;
     }
 
     // We'll add an initializer to a for-range declaration later.
     if (Var->isCXXForRangeDecl() || Var->isObjCForDecl())
       return;
 
     ActOnUninitializedDecl(Var);
   }
 
   if (getLangOpts().CUDA)
     CUDA().checkAllowedInitializer(Var);
 }
 
 void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
                                          VarDecl *Var, bool Recursive,
                                       bool DefinitionRequired, bool AtEndOfTU) {
   if (Var->isInvalidDecl())
     return;
 
   // Never instantiate an explicitly-specialized entity.
   TemplateSpecializationKind TSK =
       Var->getTemplateSpecializationKindForInstantiation();
   if (TSK == TSK_ExplicitSpecialization)
     return;
 
   // Find the pattern and the arguments to substitute into it.
   VarDecl *PatternDecl = Var->getTemplateInstantiationPattern();
   assert(PatternDecl && "no pattern for templated variable");
   MultiLevelTemplateArgumentList TemplateArgs =
       getTemplateInstantiationArgs(Var);
 
   VarTemplateSpecializationDecl *VarSpec =
       dyn_cast<VarTemplateSpecializationDecl>(Var);
   if (VarSpec) {
     // If this is a static data member template, there might be an
     // uninstantiated initializer on the declaration. If so, instantiate
     // it now.
     //
     // FIXME: This largely duplicates what we would do below. The difference
     // is that along this path we may instantiate an initializer from an
     // in-class declaration of the template and instantiate the definition
     // from a separate out-of-class definition.
     if (PatternDecl->isStaticDataMember() &&
         (PatternDecl = PatternDecl->getFirstDecl())->hasInit() &&
         !Var->hasInit()) {
       // FIXME: Factor out the duplicated instantiation context setup/tear down
       // code here.
       InstantiatingTemplate Inst(*this, PointOfInstantiation, Var);
       if (Inst.isInvalid() || Inst.isAlreadyInstantiating())
         return;
       PrettyDeclStackTraceEntry CrashInfo(Context, Var, SourceLocation(),
                                           "instantiating variable initializer");
 
       // The instantiation is visible here, even if it was first declared in an
       // unimported module.
       Var->setVisibleDespiteOwningModule();
 
       // If we're performing recursive template instantiation, create our own
       // queue of pending implicit instantiations that we will instantiate
       // later, while we're still within our own instantiation context.
       GlobalEagerInstantiationScope GlobalInstantiations(*this,
                                                          /*Enabled=*/Recursive);
       LocalInstantiationScope Local(*this);
       LocalEagerInstantiationScope LocalInstantiations(*this);
 
       // Enter the scope of this instantiation. We don't use
       // PushDeclContext because we don't have a scope.
       ContextRAII PreviousContext(*this, Var->getDeclContext());
       InstantiateVariableInitializer(Var, PatternDecl, TemplateArgs);
       PreviousContext.pop();
 
       // This variable may have local implicit instantiations that need to be
       // instantiated within this scope.
       LocalInstantiations.perform();
       Local.Exit();
       GlobalInstantiations.perform();
     }
   } else {
     assert(Var->isStaticDataMember() && PatternDecl->isStaticDataMember() &&
            "not a static data member?");
   }
 
   VarDecl *Def = PatternDecl->getDefinition(getASTContext());
 
   // If we don't have a definition of the variable template, we won't perform
   // any instantiation. Rather, we rely on the user to instantiate this
   // definition (or provide a specialization for it) in another translation
   // unit.
   if (!Def && !DefinitionRequired) {
     if (TSK == TSK_ExplicitInstantiationDefinition) {
       PendingInstantiations.push_back(
         std::make_pair(Var, PointOfInstantiation));
     } else if (TSK == TSK_ImplicitInstantiation) {
       // Warn about missing definition at the end of translation unit.
       if (AtEndOfTU && !getDiagnostics().hasErrorOccurred() &&
           !getSourceManager().isInSystemHeader(PatternDecl->getBeginLoc())) {
         Diag(PointOfInstantiation, diag::warn_var_template_missing)
           << Var;
         Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
         if (getLangOpts().CPlusPlus11)
           Diag(PointOfInstantiation, diag::note_inst_declaration_hint) << Var;
       }
       return;
     }
   }
 
   // FIXME: We need to track the instantiation stack in order to know which
   // definitions should be visible within this instantiation.
   // FIXME: Produce diagnostics when Var->getInstantiatedFromStaticDataMember().
   if (DiagnoseUninstantiableTemplate(PointOfInstantiation, Var,
                                      /*InstantiatedFromMember*/false,
                                      PatternDecl, Def, TSK,
                                      /*Complain*/DefinitionRequired))
     return;
 
   // C++11 [temp.explicit]p10:
   //   Except for inline functions, const variables of literal types, variables
   //   of reference types, [...] explicit instantiation declarations
   //   have the effect of suppressing the implicit instantiation of the entity
   //   to which they refer.
   //
   // FIXME: That's not exactly the same as "might be usable in constant
   // expressions", which only allows constexpr variables and const integral
   // types, not arbitrary const literal types.
   if (TSK == TSK_ExplicitInstantiationDeclaration &&
       !Var->mightBeUsableInConstantExpressions(getASTContext()))
     return;
 
   // Make sure to pass the instantiated variable to the consumer at the end.
   struct PassToConsumerRAII {
     ASTConsumer &Consumer;
     VarDecl *Var;
 
     PassToConsumerRAII(ASTConsumer &Consumer, VarDecl *Var)
       : Consumer(Consumer), Var(Var) { }
 
     ~PassToConsumerRAII() {
       Consumer.HandleCXXStaticMemberVarInstantiation(Var);
     }
   } PassToConsumerRAII(Consumer, Var);
 
   // If we already have a definition, we're done.
   if (VarDecl *Def = Var->getDefinition()) {
     // We may be explicitly instantiating something we've already implicitly
     // instantiated.
     Def->setTemplateSpecializationKind(Var->getTemplateSpecializationKind(),
                                        PointOfInstantiation);
     return;
   }
 
   InstantiatingTemplate Inst(*this, PointOfInstantiation, Var);
   if (Inst.isInvalid() || Inst.isAlreadyInstantiating())
     return;
   PrettyDeclStackTraceEntry CrashInfo(Context, Var, SourceLocation(),
                                       "instantiating variable definition");
 
   // If we're performing recursive template instantiation, create our own
   // queue of pending implicit instantiations that we will instantiate later,
   // while we're still within our own instantiation context.
   GlobalEagerInstantiationScope GlobalInstantiations(*this,
                                                      /*Enabled=*/Recursive);
 
   // Enter the scope of this instantiation. We don't use
   // PushDeclContext because we don't have a scope.
   ContextRAII PreviousContext(*this, Var->getDeclContext());
   LocalInstantiationScope Local(*this);
 
   LocalEagerInstantiationScope LocalInstantiations(*this);
 
   VarDecl *OldVar = Var;
   if (Def->isStaticDataMember() && !Def->isOutOfLine()) {
     // We're instantiating an inline static data member whose definition was
     // provided inside the class.
     InstantiateVariableInitializer(Var, Def, TemplateArgs);
   } else if (!VarSpec) {
     Var = cast_or_null<VarDecl>(SubstDecl(Def, Var->getDeclContext(),
                                           TemplateArgs));
   } else if (Var->isStaticDataMember() &&
              Var->getLexicalDeclContext()->isRecord()) {
     // We need to instantiate the definition of a static data member template,
     // and all we have is the in-class declaration of it. Instantiate a separate
     // declaration of the definition.
     TemplateDeclInstantiator Instantiator(*this, Var->getDeclContext(),
                                           TemplateArgs);
 
     TemplateArgumentListInfo TemplateArgInfo;
     if (const ASTTemplateArgumentListInfo *ArgInfo =
             VarSpec->getTemplateArgsAsWritten()) {
       TemplateArgInfo.setLAngleLoc(ArgInfo->getLAngleLoc());
       TemplateArgInfo.setRAngleLoc(ArgInfo->getRAngleLoc());
       for (const TemplateArgumentLoc &Arg : ArgInfo->arguments())
         TemplateArgInfo.addArgument(Arg);
     }
 
     Var = cast_or_null<VarDecl>(Instantiator.VisitVarTemplateSpecializationDecl(
         VarSpec->getSpecializedTemplate(), Def, TemplateArgInfo,
         VarSpec->getTemplateArgs().asArray(), VarSpec));
     if (Var) {
       llvm::PointerUnion<VarTemplateDecl *,
                          VarTemplatePartialSpecializationDecl *> PatternPtr =
           VarSpec->getSpecializedTemplateOrPartial();
       if (VarTemplatePartialSpecializationDecl *Partial =
           PatternPtr.dyn_cast<VarTemplatePartialSpecializationDecl *>())
         cast<VarTemplateSpecializationDecl>(Var)->setInstantiationOf(
             Partial, &VarSpec->getTemplateInstantiationArgs());
 
       // Attach the initializer.
       InstantiateVariableInitializer(Var, Def, TemplateArgs);
     }
   } else
     // Complete the existing variable's definition with an appropriately
     // substituted type and initializer.
     Var = CompleteVarTemplateSpecializationDecl(VarSpec, Def, TemplateArgs);
 
   PreviousContext.pop();
 
   if (Var) {
     PassToConsumerRAII.Var = Var;
     Var->setTemplateSpecializationKind(OldVar->getTemplateSpecializationKind(),
                                        OldVar->getPointOfInstantiation());
   }
 
   // This variable may have local implicit instantiations that need to be
   // instantiated within this scope.
   LocalInstantiations.perform();
   Local.Exit();
   GlobalInstantiations.perform();
 }
 
 void
 Sema::InstantiateMemInitializers(CXXConstructorDecl *New,
                                  const CXXConstructorDecl *Tmpl,
                            const MultiLevelTemplateArgumentList &TemplateArgs) {
 
   SmallVector<CXXCtorInitializer*, 4> NewInits;
   bool AnyErrors = Tmpl->isInvalidDecl();
 
   // Instantiate all the initializers.
   for (const auto *Init : Tmpl->inits()) {
     // Only instantiate written initializers, let Sema re-construct implicit
     // ones.
     if (!Init->isWritten())
       continue;
 
     SourceLocation EllipsisLoc;
 
     if (Init->isPackExpansion()) {
       // This is a pack expansion. We should expand it now.
       TypeLoc BaseTL = Init->getTypeSourceInfo()->getTypeLoc();
       SmallVector<UnexpandedParameterPack, 4> Unexpanded;
       collectUnexpandedParameterPacks(BaseTL, Unexpanded);
       collectUnexpandedParameterPacks(Init->getInit(), Unexpanded);
       bool ShouldExpand = false;
       bool RetainExpansion = false;
       std::optional<unsigned> NumExpansions;
       if (CheckParameterPacksForExpansion(Init->getEllipsisLoc(),
                                           BaseTL.getSourceRange(),
                                           Unexpanded,
                                           TemplateArgs, ShouldExpand,
                                           RetainExpansion,
                                           NumExpansions)) {
         AnyErrors = true;
         New->setInvalidDecl();
         continue;
       }
       assert(ShouldExpand && "Partial instantiation of base initializer?");
 
       // Loop over all of the arguments in the argument pack(s),
       for (unsigned I = 0; I != *NumExpansions; ++I) {
         Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this, I);
 
         // Instantiate the initializer.
         ExprResult TempInit = SubstInitializer(Init->getInit(), TemplateArgs,
                                                /*CXXDirectInit=*/true);
         if (TempInit.isInvalid()) {
           AnyErrors = true;
           break;
         }
 
         // Instantiate the base type.
         TypeSourceInfo *BaseTInfo = SubstType(Init->getTypeSourceInfo(),
                                               TemplateArgs,
                                               Init->getSourceLocation(),
                                               New->getDeclName());
         if (!BaseTInfo) {
           AnyErrors = true;
           break;
         }
 
         // Build the initializer.
         MemInitResult NewInit = BuildBaseInitializer(BaseTInfo->getType(),
                                                      BaseTInfo, TempInit.get(),
                                                      New->getParent(),
                                                      SourceLocation());
         if (NewInit.isInvalid()) {
           AnyErrors = true;
           break;
         }
 
         NewInits.push_back(NewInit.get());
       }
 
       continue;
     }
 
     // Instantiate the initializer.
     ExprResult TempInit = SubstInitializer(Init->getInit(), TemplateArgs,
                                            /*CXXDirectInit=*/true);
     if (TempInit.isInvalid()) {
       AnyErrors = true;
       continue;
     }
 
     MemInitResult NewInit;
     if (Init->isDelegatingInitializer() || Init->isBaseInitializer()) {
       TypeSourceInfo *TInfo = SubstType(Init->getTypeSourceInfo(),
                                         TemplateArgs,
                                         Init->getSourceLocation(),
                                         New->getDeclName());
       if (!TInfo) {
         AnyErrors = true;
         New->setInvalidDecl();
         continue;
       }
 
       if (Init->isBaseInitializer())
         NewInit = BuildBaseInitializer(TInfo->getType(), TInfo, TempInit.get(),
                                        New->getParent(), EllipsisLoc);
       else
         NewInit = BuildDelegatingInitializer(TInfo, TempInit.get(),
                                   cast<CXXRecordDecl>(CurContext->getParent()));
     } else if (Init->isMemberInitializer()) {
       FieldDecl *Member = cast_or_null<FieldDecl>(FindInstantiatedDecl(
                                                      Init->getMemberLocation(),
                                                      Init->getMember(),
                                                      TemplateArgs));
       if (!Member) {
         AnyErrors = true;
         New->setInvalidDecl();
         continue;
       }
 
       NewInit = BuildMemberInitializer(Member, TempInit.get(),
                                        Init->getSourceLocation());
     } else if (Init->isIndirectMemberInitializer()) {
       IndirectFieldDecl *IndirectMember =
          cast_or_null<IndirectFieldDecl>(FindInstantiatedDecl(
                                  Init->getMemberLocation(),
                                  Init->getIndirectMember(), TemplateArgs));
 
       if (!IndirectMember) {
         AnyErrors = true;
         New->setInvalidDecl();
         continue;
       }
 
       NewInit = BuildMemberInitializer(IndirectMember, TempInit.get(),
                                        Init->getSourceLocation());
     }
 
     if (NewInit.isInvalid()) {
       AnyErrors = true;
       New->setInvalidDecl();
     } else {
       NewInits.push_back(NewInit.get());
     }
   }
 
   // Assign all the initializers to the new constructor.
   ActOnMemInitializers(New,
                        /*FIXME: ColonLoc */
                        SourceLocation(),
                        NewInits,
                        AnyErrors);
 }
 
 // TODO: this could be templated if the various decl types used the
 // same method name.
 static bool isInstantiationOf(ClassTemplateDecl *Pattern,
                               ClassTemplateDecl *Instance) {
   Pattern = Pattern->getCanonicalDecl();
 
   do {
     Instance = Instance->getCanonicalDecl();
     if (Pattern == Instance) return true;
     Instance = Instance->getInstantiatedFromMemberTemplate();
   } while (Instance);
 
   return false;
 }
 
 static bool isInstantiationOf(FunctionTemplateDecl *Pattern,
                               FunctionTemplateDecl *Instance) {
   Pattern = Pattern->getCanonicalDecl();
 
   do {
     Instance = Instance->getCanonicalDecl();
     if (Pattern == Instance) return true;
     Instance = Instance->getInstantiatedFromMemberTemplate();
   } while (Instance);
 
   return false;
 }
 
 static bool
 isInstantiationOf(ClassTemplatePartialSpecializationDecl *Pattern,
                   ClassTemplatePartialSpecializationDecl *Instance) {
   Pattern
     = cast<ClassTemplatePartialSpecializationDecl>(Pattern->getCanonicalDecl());
   do {
     Instance = cast<ClassTemplatePartialSpecializationDecl>(
                                                 Instance->getCanonicalDecl());
     if (Pattern == Instance)
       return true;
     Instance = Instance->getInstantiatedFromMember();
   } while (Instance);
 
   return false;
 }
 
 static bool isInstantiationOf(CXXRecordDecl *Pattern,
                               CXXRecordDecl *Instance) {
   Pattern = Pattern->getCanonicalDecl();
 
   do {
     Instance = Instance->getCanonicalDecl();
     if (Pattern == Instance) return true;
     Instance = Instance->getInstantiatedFromMemberClass();
   } while (Instance);
 
   return false;
 }
 
 static bool isInstantiationOf(FunctionDecl *Pattern,
                               FunctionDecl *Instance) {
   Pattern = Pattern->getCanonicalDecl();
 
   do {
     Instance = Instance->getCanonicalDecl();
     if (Pattern == Instance) return true;
     Instance = Instance->getInstantiatedFromMemberFunction();
   } while (Instance);
 
   return false;
 }
 
 static bool isInstantiationOf(EnumDecl *Pattern,
                               EnumDecl *Instance) {
   Pattern = Pattern->getCanonicalDecl();
 
   do {
     Instance = Instance->getCanonicalDecl();
     if (Pattern == Instance) return true;
     Instance = Instance->getInstantiatedFromMemberEnum();
   } while (Instance);
 
   return false;
 }
 
 static bool isInstantiationOf(UsingShadowDecl *Pattern,
                               UsingShadowDecl *Instance,
                               ASTContext &C) {
   return declaresSameEntity(C.getInstantiatedFromUsingShadowDecl(Instance),
                             Pattern);
 }
 
 static bool isInstantiationOf(UsingDecl *Pattern, UsingDecl *Instance,
                               ASTContext &C) {
   return declaresSameEntity(C.getInstantiatedFromUsingDecl(Instance), Pattern);
 }
 
 template<typename T>
 static bool isInstantiationOfUnresolvedUsingDecl(T *Pattern, Decl *Other,
                                                  ASTContext &Ctx) {
   // An unresolved using declaration can instantiate to an unresolved using
   // declaration, or to a using declaration or a using declaration pack.
   //
   // Multiple declarations can claim to be instantiated from an unresolved
   // using declaration if it's a pack expansion. We want the UsingPackDecl
   // in that case, not the individual UsingDecls within the pack.
   bool OtherIsPackExpansion;
   NamedDecl *OtherFrom;
   if (auto *OtherUUD = dyn_cast<T>(Other)) {
     OtherIsPackExpansion = OtherUUD->isPackExpansion();
     OtherFrom = Ctx.getInstantiatedFromUsingDecl(OtherUUD);
   } else if (auto *OtherUPD = dyn_cast<UsingPackDecl>(Other)) {
     OtherIsPackExpansion = true;
     OtherFrom = OtherUPD->getInstantiatedFromUsingDecl();
   } else if (auto *OtherUD = dyn_cast<UsingDecl>(Other)) {
     OtherIsPackExpansion = false;
     OtherFrom = Ctx.getInstantiatedFromUsingDecl(OtherUD);
   } else {
     return false;
   }
   return Pattern->isPackExpansion() == OtherIsPackExpansion &&
          declaresSameEntity(OtherFrom, Pattern);
 }
 
 static bool isInstantiationOfStaticDataMember(VarDecl *Pattern,
                                               VarDecl *Instance) {
   assert(Instance->isStaticDataMember());
 
   Pattern = Pattern->getCanonicalDecl();
 
   do {
     Instance = Instance->getCanonicalDecl();
     if (Pattern == Instance) return true;
     Instance = Instance->getInstantiatedFromStaticDataMember();
   } while (Instance);
 
   return false;
 }
 
 // Other is the prospective instantiation
 // D is the prospective pattern
 static bool isInstantiationOf(ASTContext &Ctx, NamedDecl *D, Decl *Other) {
   if (auto *UUD = dyn_cast<UnresolvedUsingTypenameDecl>(D))
     return isInstantiationOfUnresolvedUsingDecl(UUD, Other, Ctx);
 
   if (auto *UUD = dyn_cast<UnresolvedUsingValueDecl>(D))
     return isInstantiationOfUnresolvedUsingDecl(UUD, Other, Ctx);
 
   if (D->getKind() != Other->getKind())
     return false;
 
   if (auto *Record = dyn_cast<CXXRecordDecl>(Other))
     return isInstantiationOf(cast<CXXRecordDecl>(D), Record);
 
   if (auto *Function = dyn_cast<FunctionDecl>(Other))
     return isInstantiationOf(cast<FunctionDecl>(D), Function);
 
   if (auto *Enum = dyn_cast<EnumDecl>(Other))
     return isInstantiationOf(cast<EnumDecl>(D), Enum);
 
   if (auto *Var = dyn_cast<VarDecl>(Other))
     if (Var->isStaticDataMember())
       return isInstantiationOfStaticDataMember(cast<VarDecl>(D), Var);
 
   if (auto *Temp = dyn_cast<ClassTemplateDecl>(Other))
     return isInstantiationOf(cast<ClassTemplateDecl>(D), Temp);
 
   if (auto *Temp = dyn_cast<FunctionTemplateDecl>(Other))
     return isInstantiationOf(cast<FunctionTemplateDecl>(D), Temp);
 
   if (auto *PartialSpec =
           dyn_cast<ClassTemplatePartialSpecializationDecl>(Other))
     return isInstantiationOf(cast<ClassTemplatePartialSpecializationDecl>(D),
                              PartialSpec);
 
   if (auto *Field = dyn_cast<FieldDecl>(Other)) {
     if (!Field->getDeclName()) {
       // This is an unnamed field.
       return declaresSameEntity(Ctx.getInstantiatedFromUnnamedFieldDecl(Field),
                                 cast<FieldDecl>(D));
     }
   }
 
   if (auto *Using = dyn_cast<UsingDecl>(Other))
     return isInstantiationOf(cast<UsingDecl>(D), Using, Ctx);
 
   if (auto *Shadow = dyn_cast<UsingShadowDecl>(Other))
     return isInstantiationOf(cast<UsingShadowDecl>(D), Shadow, Ctx);
 
   return D->getDeclName() &&
          D->getDeclName() == cast<NamedDecl>(Other)->getDeclName();
 }
 
 template<typename ForwardIterator>
 static NamedDecl *findInstantiationOf(ASTContext &Ctx,
                                       NamedDecl *D,
                                       ForwardIterator first,
                                       ForwardIterator last) {
   for (; first != last; ++first)
     if (isInstantiationOf(Ctx, D, *first))
       return cast<NamedDecl>(*first);
 
   return nullptr;
 }
 
 DeclContext *Sema::FindInstantiatedContext(SourceLocation Loc, DeclContext* DC,
                           const MultiLevelTemplateArgumentList &TemplateArgs) {
   if (NamedDecl *D = dyn_cast<NamedDecl>(DC)) {
     Decl* ID = FindInstantiatedDecl(Loc, D, TemplateArgs, true);
     return cast_or_null<DeclContext>(ID);
   } else return DC;
 }
 
 /// Determine whether the given context is dependent on template parameters at
 /// level \p Level or below.
 ///
 /// Sometimes we only substitute an inner set of template arguments and leave
 /// the outer templates alone. In such cases, contexts dependent only on the
 /// outer levels are not effectively dependent.
 static bool isDependentContextAtLevel(DeclContext *DC, unsigned Level) {
   if (!DC->isDependentContext())
     return false;
   if (!Level)
     return true;
   return cast<Decl>(DC)->getTemplateDepth() > Level;
 }
 
 NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
                           const MultiLevelTemplateArgumentList &TemplateArgs,
                           bool FindingInstantiatedContext) {
   DeclContext *ParentDC = D->getDeclContext();
   // Determine whether our parent context depends on any of the template
   // arguments we're currently substituting.
   bool ParentDependsOnArgs = isDependentContextAtLevel(
       ParentDC, TemplateArgs.getNumRetainedOuterLevels());
   // FIXME: Parameters of pointer to functions (y below) that are themselves
   // parameters (p below) can have their ParentDC set to the translation-unit
   // - thus we can not consistently check if the ParentDC of such a parameter
   // is Dependent or/and a FunctionOrMethod.
   // For e.g. this code, during Template argument deduction tries to
   // find an instantiated decl for (T y) when the ParentDC for y is
   // the translation unit.
   //   e.g. template <class T> void Foo(auto (*p)(T y) -> decltype(y())) {}
   //   float baz(float(*)()) { return 0.0; }
   //   Foo(baz);
   // The better fix here is perhaps to ensure that a ParmVarDecl, by the time
   // it gets here, always has a FunctionOrMethod as its ParentDC??
   // For now:
   //  - as long as we have a ParmVarDecl whose parent is non-dependent and
   //    whose type is not instantiation dependent, do nothing to the decl
   //  - otherwise find its instantiated decl.
   if (isa<ParmVarDecl>(D) && !ParentDependsOnArgs &&
       !cast<ParmVarDecl>(D)->getType()->isInstantiationDependentType())
     return D;
   if (isa<ParmVarDecl>(D) || isa<NonTypeTemplateParmDecl>(D) ||
       isa<TemplateTypeParmDecl>(D) || isa<TemplateTemplateParmDecl>(D) ||
       (ParentDependsOnArgs && (ParentDC->isFunctionOrMethod() ||
                                isa<OMPDeclareReductionDecl>(ParentDC) ||
                                isa<OMPDeclareMapperDecl>(ParentDC))) ||
       (isa<CXXRecordDecl>(D) && cast<CXXRecordDecl>(D)->isLambda() &&
        cast<CXXRecordDecl>(D)->getTemplateDepth() >
            TemplateArgs.getNumRetainedOuterLevels())) {
     // D is a local of some kind. Look into the map of local
     // declarations to their instantiations.
     if (CurrentInstantiationScope) {
       if (auto Found = CurrentInstantiationScope->findInstantiationOf(D)) {
         if (Decl *FD = Found->dyn_cast<Decl *>())
           return cast<NamedDecl>(FD);
 
         int PackIdx = ArgumentPackSubstitutionIndex;
         assert(PackIdx != -1 &&
                "found declaration pack but not pack expanding");
         typedef LocalInstantiationScope::DeclArgumentPack DeclArgumentPack;
         return cast<NamedDecl>((*Found->get<DeclArgumentPack *>())[PackIdx]);
       }
     }
 
     // If we're performing a partial substitution during template argument
     // deduction, we may not have values for template parameters yet. They
     // just map to themselves.
     if (isa<NonTypeTemplateParmDecl>(D) || isa<TemplateTypeParmDecl>(D) ||
         isa<TemplateTemplateParmDecl>(D))
       return D;
 
     if (D->isInvalidDecl())
       return nullptr;
 
     // Normally this function only searches for already instantiated declaration
     // however we have to make an exclusion for local types used before
     // definition as in the code:
     //
     //   template<typename T> void f1() {
     //     void g1(struct x1);
     //     struct x1 {};
     //   }
     //
     // In this case instantiation of the type of 'g1' requires definition of
     // 'x1', which is defined later. Error recovery may produce an enum used
     // before definition. In these cases we need to instantiate relevant
     // declarations here.
     bool NeedInstantiate = false;
     if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D))
       NeedInstantiate = RD->isLocalClass();
     else if (isa<TypedefNameDecl>(D) &&
              isa<CXXDeductionGuideDecl>(D->getDeclContext()))
       NeedInstantiate = true;
     else
       NeedInstantiate = isa<EnumDecl>(D);
     if (NeedInstantiate) {
       Decl *Inst = SubstDecl(D, CurContext, TemplateArgs);
       CurrentInstantiationScope->InstantiatedLocal(D, Inst);
       return cast<TypeDecl>(Inst);
     }
 
     // If we didn't find the decl, then we must have a label decl that hasn't
     // been found yet.  Lazily instantiate it and return it now.
     assert(isa<LabelDecl>(D));
 
     Decl *Inst = SubstDecl(D, CurContext, TemplateArgs);
     assert(Inst && "Failed to instantiate label??");
 
     CurrentInstantiationScope->InstantiatedLocal(D, Inst);
     return cast<LabelDecl>(Inst);
   }
 
   if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D)) {
     if (!Record->isDependentContext())
       return D;
 
     // Determine whether this record is the "templated" declaration describing
     // a class template or class template specialization.
     ClassTemplateDecl *ClassTemplate = Record->getDescribedClassTemplate();
     if (ClassTemplate)
       ClassTemplate = ClassTemplate->getCanonicalDecl();
     else if (ClassTemplateSpecializationDecl *Spec =
                  dyn_cast<ClassTemplateSpecializationDecl>(Record))
       ClassTemplate = Spec->getSpecializedTemplate()->getCanonicalDecl();
 
     // Walk the current context to find either the record or an instantiation of
     // it.
     DeclContext *DC = CurContext;
     while (!DC->isFileContext()) {
       // If we're performing substitution while we're inside the template
       // definition, we'll find our own context. We're done.
       if (DC->Equals(Record))
         return Record;
 
       if (CXXRecordDecl *InstRecord = dyn_cast<CXXRecordDecl>(DC)) {
         // Check whether we're in the process of instantiating a class template
         // specialization of the template we're mapping.
         if (ClassTemplateSpecializationDecl *InstSpec
                       = dyn_cast<ClassTemplateSpecializationDecl>(InstRecord)){
           ClassTemplateDecl *SpecTemplate = InstSpec->getSpecializedTemplate();
           if (ClassTemplate && isInstantiationOf(ClassTemplate, SpecTemplate))
             return InstRecord;
         }
 
         // Check whether we're in the process of instantiating a member class.
         if (isInstantiationOf(Record, InstRecord))
           return InstRecord;
       }
 
       // Move to the outer template scope.
       if (FunctionDecl *FD = dyn_cast<FunctionDecl>(DC)) {
         if (FD->getFriendObjectKind() &&
             FD->getNonTransparentDeclContext()->isFileContext()) {
           DC = FD->getLexicalDeclContext();
           continue;
         }
         // An implicit deduction guide acts as if it's within the class template
         // specialization described by its name and first N template params.
         auto *Guide = dyn_cast<CXXDeductionGuideDecl>(FD);
         if (Guide && Guide->isImplicit()) {
           TemplateDecl *TD = Guide->getDeducedTemplate();
           // Convert the arguments to an "as-written" list.
           TemplateArgumentListInfo Args(Loc, Loc);
           for (TemplateArgument Arg : TemplateArgs.getInnermost().take_front(
                                         TD->getTemplateParameters()->size())) {
             ArrayRef<TemplateArgument> Unpacked(Arg);
             if (Arg.getKind() == TemplateArgument::Pack)
               Unpacked = Arg.pack_elements();
             for (TemplateArgument UnpackedArg : Unpacked)
               Args.addArgument(
                   getTrivialTemplateArgumentLoc(UnpackedArg, QualType(), Loc));
           }
           QualType T = CheckTemplateIdType(TemplateName(TD), Loc, Args);
           // We may get a non-null type with errors, in which case
           // `getAsCXXRecordDecl` will return `nullptr`. For instance, this
           // happens when one of the template arguments is an invalid
           // expression. We return early to avoid triggering the assertion
           // about the `CodeSynthesisContext`.
           if (T.isNull() || T->containsErrors())
             return nullptr;
           CXXRecordDecl *SubstRecord = T->getAsCXXRecordDecl();
 
           if (!SubstRecord) {
             // T can be a dependent TemplateSpecializationType when performing a
             // substitution for building a deduction guide.
             assert(CodeSynthesisContexts.back().Kind ==
                    CodeSynthesisContext::BuildingDeductionGuides);
             // Return a nullptr as a sentinel value, we handle it properly in
             // the TemplateInstantiator::TransformInjectedClassNameType
             // override, which we transform it to a TemplateSpecializationType.
             return nullptr;
           }
           // Check that this template-id names the primary template and not a
           // partial or explicit specialization. (In the latter cases, it's
           // meaningless to attempt to find an instantiation of D within the
           // specialization.)
           // FIXME: The standard doesn't say what should happen here.
           if (FindingInstantiatedContext &&
               usesPartialOrExplicitSpecialization(
                   Loc, cast<ClassTemplateSpecializationDecl>(SubstRecord))) {
             Diag(Loc, diag::err_specialization_not_primary_template)
               << T << (SubstRecord->getTemplateSpecializationKind() ==
                            TSK_ExplicitSpecialization);
             return nullptr;
           }
           DC = SubstRecord;
           continue;
         }
       }
 
       DC = DC->getParent();
     }
 
     // Fall through to deal with other dependent record types (e.g.,
     // anonymous unions in class templates).
   }
 
   if (!ParentDependsOnArgs)
     return D;
 
   ParentDC = FindInstantiatedContext(Loc, ParentDC, TemplateArgs);
   if (!ParentDC)
     return nullptr;
 
   if (ParentDC != D->getDeclContext()) {
     // We performed some kind of instantiation in the parent context,
     // so now we need to look into the instantiated parent context to
     // find the instantiation of the declaration D.
 
     // If our context used to be dependent, we may need to instantiate
     // it before performing lookup into that context.
     bool IsBeingInstantiated = false;
     if (CXXRecordDecl *Spec = dyn_cast<CXXRecordDecl>(ParentDC)) {
       if (!Spec->isDependentContext()) {
         QualType T = Context.getTypeDeclType(Spec);
         const RecordType *Tag = T->getAs<RecordType>();
         assert(Tag && "type of non-dependent record is not a RecordType");
         if (Tag->isBeingDefined())
           IsBeingInstantiated = true;
         if (!Tag->isBeingDefined() &&
             RequireCompleteType(Loc, T, diag::err_incomplete_type))
           return nullptr;
 
         ParentDC = Tag->getDecl();
       }
     }
 
     NamedDecl *Result = nullptr;
     // FIXME: If the name is a dependent name, this lookup won't necessarily
     // find it. Does that ever matter?
     if (auto Name = D->getDeclName()) {
       DeclarationNameInfo NameInfo(Name, D->getLocation());
       DeclarationNameInfo NewNameInfo =
           SubstDeclarationNameInfo(NameInfo, TemplateArgs);
       Name = NewNameInfo.getName();
       if (!Name)
         return nullptr;
       DeclContext::lookup_result Found = ParentDC->lookup(Name);
 
       Result = findInstantiationOf(Context, D, Found.begin(), Found.end());
     } else {
       // Since we don't have a name for the entity we're looking for,
       // our only option is to walk through all of the declarations to
       // find that name. This will occur in a few cases:
       //
       //   - anonymous struct/union within a template
       //   - unnamed class/struct/union/enum within a template
       //
       // FIXME: Find a better way to find these instantiations!
       Result = findInstantiationOf(Context, D,
                                    ParentDC->decls_begin(),
                                    ParentDC->decls_end());
     }
 
     if (!Result) {
       if (isa<UsingShadowDecl>(D)) {
         // UsingShadowDecls can instantiate to nothing because of using hiding.
       } else if (hasUncompilableErrorOccurred()) {
         // We've already complained about some ill-formed code, so most likely
         // this declaration failed to instantiate. There's no point in
         // complaining further, since this is normal in invalid code.
         // FIXME: Use more fine-grained 'invalid' tracking for this.
       } else if (IsBeingInstantiated) {
         // The class in which this member exists is currently being
         // instantiated, and we haven't gotten around to instantiating this
         // member yet. This can happen when the code uses forward declarations
         // of member classes, and introduces ordering dependencies via
         // template instantiation.
         Diag(Loc, diag::err_member_not_yet_instantiated)
           << D->getDeclName()
           << Context.getTypeDeclType(cast<CXXRecordDecl>(ParentDC));
         Diag(D->getLocation(), diag::note_non_instantiated_member_here);
       } else if (EnumConstantDecl *ED = dyn_cast<EnumConstantDecl>(D)) {
         // This enumeration constant was found when the template was defined,
         // but can't be found in the instantiation. This can happen if an
         // unscoped enumeration member is explicitly specialized.
         EnumDecl *Enum = cast<EnumDecl>(ED->getLexicalDeclContext());
         EnumDecl *Spec = cast<EnumDecl>(FindInstantiatedDecl(Loc, Enum,
                                                              TemplateArgs));
         assert(Spec->getTemplateSpecializationKind() ==
                  TSK_ExplicitSpecialization);
         Diag(Loc, diag::err_enumerator_does_not_exist)
           << D->getDeclName()
           << Context.getTypeDeclType(cast<TypeDecl>(Spec->getDeclContext()));
         Diag(Spec->getLocation(), diag::note_enum_specialized_here)
           << Context.getTypeDeclType(Spec);
       } else {
         // We should have found something, but didn't.
         llvm_unreachable("Unable to find instantiation of declaration!");
       }
     }
 
     D = Result;
   }
 
   return D;
 }
 
 void Sema::PerformPendingInstantiations(bool LocalOnly) {
   std::deque<PendingImplicitInstantiation> delayedPCHInstantiations;
   while (!PendingLocalImplicitInstantiations.empty() ||
          (!LocalOnly && !PendingInstantiations.empty())) {
     PendingImplicitInstantiation Inst;
 
     if (PendingLocalImplicitInstantiations.empty()) {
       Inst = PendingInstantiations.front();
       PendingInstantiations.pop_front();
     } else {
       Inst = PendingLocalImplicitInstantiations.front();
       PendingLocalImplicitInstantiations.pop_front();
     }
 
     // Instantiate function definitions
     if (FunctionDecl *Function = dyn_cast<FunctionDecl>(Inst.first)) {
       bool DefinitionRequired = Function->getTemplateSpecializationKind() ==
                                 TSK_ExplicitInstantiationDefinition;
       if (Function->isMultiVersion()) {
         getASTContext().forEachMultiversionedFunctionVersion(
             Function, [this, Inst, DefinitionRequired](FunctionDecl *CurFD) {
               InstantiateFunctionDefinition(/*FIXME:*/ Inst.second, CurFD, true,
                                             DefinitionRequired, true);
               if (CurFD->isDefined())
                 CurFD->setInstantiationIsPending(false);
             });
       } else {
         InstantiateFunctionDefinition(/*FIXME:*/ Inst.second, Function, true,
                                       DefinitionRequired, true);
         if (Function->isDefined())
           Function->setInstantiationIsPending(false);
       }
       // Definition of a PCH-ed template declaration may be available only in the TU.
       if (!LocalOnly && LangOpts.PCHInstantiateTemplates &&
           TUKind == TU_Prefix && Function->instantiationIsPending())
         delayedPCHInstantiations.push_back(Inst);
       continue;
     }
 
     // Instantiate variable definitions
     VarDecl *Var = cast<VarDecl>(Inst.first);
 
     assert((Var->isStaticDataMember() ||
             isa<VarTemplateSpecializationDecl>(Var)) &&
            "Not a static data member, nor a variable template"
            " specialization?");
 
     // Don't try to instantiate declarations if the most recent redeclaration
     // is invalid.
     if (Var->getMostRecentDecl()->isInvalidDecl())
       continue;
 
     // Check if the most recent declaration has changed the specialization kind
     // and removed the need for implicit instantiation.
     switch (Var->getMostRecentDecl()
                 ->getTemplateSpecializationKindForInstantiation()) {
     case TSK_Undeclared:
       llvm_unreachable("Cannot instantitiate an undeclared specialization.");
     case TSK_ExplicitInstantiationDeclaration:
     case TSK_ExplicitSpecialization:
       continue;  // No longer need to instantiate this type.
     case TSK_ExplicitInstantiationDefinition:
       // We only need an instantiation if the pending instantiation *is* the
       // explicit instantiation.
       if (Var != Var->getMostRecentDecl())
         continue;
       break;
     case TSK_ImplicitInstantiation:
       break;
     }
 
     PrettyDeclStackTraceEntry CrashInfo(Context, Var, SourceLocation(),
                                         "instantiating variable definition");
     bool DefinitionRequired = Var->getTemplateSpecializationKind() ==
                               TSK_ExplicitInstantiationDefinition;
 
     // Instantiate static data member definitions or variable template
     // specializations.
     InstantiateVariableDefinition(/*FIXME:*/ Inst.second, Var, true,
                                   DefinitionRequired, true);
   }
 
   if (!LocalOnly && LangOpts.PCHInstantiateTemplates)
     PendingInstantiations.swap(delayedPCHInstantiations);
 }
 
 void Sema::PerformDependentDiagnostics(const DeclContext *Pattern,
                        const MultiLevelTemplateArgumentList &TemplateArgs) {
   for (auto *DD : Pattern->ddiags()) {
     switch (DD->getKind()) {
     case DependentDiagnostic::Access:
       HandleDependentAccessCheck(*DD, TemplateArgs);
       break;
     }
   }
 }