diff --git a/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index dc1e0ef60cac..216a64e02380 100644
--- a/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1,6205 +1,6208 @@
 //===--- 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 "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/Initialization.h"
 #include "clang/Sema/Lookup.h"
 #include "clang/Sema/SemaInternal.h"
 #include "clang/Sema/Template.h"
 #include "clang/Sema/TemplateInstCallback.h"
 #include "llvm/Support/TimeProfiler.h"
 
 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 {
     TypeSourceInfo *Result = S.SubstType(Aligned->getAlignmentType(),
                                          TemplateArgs, Aligned->getLocation(),
                                          DeclarationName());
     if (Result)
       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;
   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);
   SmallVector<Expr *, 4> Args;
   Args.reserve(Attr->args_size());
   for (auto *E : Attr->args()) {
     ExprResult Result = S.SubstExpr(E, TemplateArgs);
     if (!Result.isUsable())
       return;
     Args.push_back(Result.get());
   }
   S.AddAnnotationAttr(New, *Attr, Attr->getAnnotation(), 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>();
   }
 
   S.AddLaunchBoundsAttr(New, Attr, MaxThreads, MinBlocks);
 }
 
 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.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).
   Optional<std::pair<FunctionDecl *, Expr *>> DeclVarData =
       S.checkOpenMPDeclareVariantFunction(S.ConvertDeclToDeclGroup(New),
                                           VariantFuncRef.get(), TI,
                                           Attr.getRange());
 
   if (!DeclVarData)
     return;
 
   E = DeclVarData.getValue().second;
   FD = DeclVarData.getValue().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_RValue);
       }
     }
   }
 
   S.ActOnOpenMPDeclareVariantDirective(FD, E, TI, 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.addAMDGPUFlatWorkGroupSizeAttr(New, Attr, MinExpr, MaxExpr);
 }
 
 static ExplicitSpecifier
 instantiateExplicitSpecifier(Sema &S,
                              const MultiLevelTemplateArgumentList &TemplateArgs,
                              ExplicitSpecifier ES, FunctionDecl *New) {
   if (!ES.getExpr())
     return ES;
   Expr *OldCond = ES.getExpr();
   Expr *Cond = nullptr;
   {
     EnterExpressionEvaluationContext Unevaluated(
         S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
     ExprResult SubstResult = S.SubstExpr(OldCond, TemplateArgs);
     if (SubstResult.isInvalid()) {
       return ExplicitSpecifier::Invalid();
     }
     Cond = SubstResult.get();
   }
   ExplicitSpecifier Result(Cond, ES.getKind());
   if (!Cond->isTypeDependent())
     S.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.addAMDGPUWavesPerEUAttr(New, Attr, MinExpr, MaxExpr);
 }
 
 /// Determine whether the attribute A might be relevent 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;
   }
 
   return true;
 }
 
 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);
     }
 
     // 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)) {
       AddParameterABIAttr(New, *ABIAttr, ABIAttr->getABI());
       continue;
     }
 
     if (isa<NSConsumedAttr>(TmplAttr) || isa<OSConsumedAttr>(TmplAttr) ||
         isa<CFConsumedAttr>(TmplAttr)) {
       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;
     }
 
     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);
     }
   }
 }
 
 /// 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 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));
     DiscardCleanupsInEvaluationContext();
   }
 }
 
 /// 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::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::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: 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.
   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());
 
   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::VisitTypeAliasTemplateDecl(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();
 
   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);
 
   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.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()) {
     QualType ReturnType = cast<FunctionDecl>(DC)->getReturnType();
     if (SemaRef.isCopyElisionCandidate(ReturnType, Var, Sema::CES_Strict))
       Var->setNRVOVariable(true);
   }
 
   Var->setImplicit(D->isImplicit());
 
   if (Var->isStaticLocal())
     SemaRef.CheckStaticLocalForDllExport(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 = SemaRef.CheckFriendTypeDecl(D->getBeginLoc(),
                                                  D->getFriendLoc(), InstTy);
     if (!FD)
       return nullptr;
 
     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;
 
   return SemaRef.BuildStaticAssertDeclaration(D->getLocation(),
                                               InstantiatedAssertExpr.get(),
                                               D->getMessage(),
                                               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)
         << D->getTemplatedDecl()->getTagKind() << Pattern->getDeclName() << DC
         << QualifierLoc.getSourceRange();
       return nullptr;
     }
 
     bool AdoptedPreviousTemplateParams = false;
     if (PrevClassTemplate) {
       bool Complain = true;
 
       // HACK: libstdc++ 4.2.1 contains an ill-formed friend class
       // template for struct std::tr1::__detail::_Map_base, where the
       // template parameters of the friend declaration don't match the
       // template parameters of the original declaration. In this one
       // case, we don't complain about the ill-formed friend
       // declaration.
       if (isFriend && Pattern->getIdentifier() &&
           Pattern->getIdentifier()->isStr("_Map_base") &&
           DC->isNamespace() &&
           cast<NamespaceDecl>(DC)->getIdentifier() &&
           cast<NamespaceDecl>(DC)->getIdentifier()->isStr("__detail")) {
         DeclContext *DCParent = DC->getParent();
         if (DCParent->isNamespace() &&
             cast<NamespaceDecl>(DCParent)->getIdentifier() &&
             cast<NamespaceDecl>(DCParent)->getIdentifier()->isStr("tr1")) {
           if (cast<Decl>(DCParent)->isInStdNamespace())
             Complain = false;
         }
       }
 
       TemplateParameterList *PrevParams
         = PrevClassTemplate->getMostRecentDecl()->getTemplateParameters();
 
       // Make sure the parameter lists match.
       if (!SemaRef.TemplateParameterListsAreEqual(InstParams, PrevParams,
                                                   Complain,
                                                   Sema::TPL_TemplateMatch)) {
         if (Complain)
           return nullptr;
 
         AdoptedPreviousTemplateParams = true;
         InstParams = PrevParams;
       }
 
       // Do some additional validation, then merge default arguments
       // from the existing declarations.
       if (!AdoptedPreviousTemplateParams &&
           SemaRef.CheckTemplateParameterList(InstParams, PrevParams,
                                              Sema::TPC_ClassTemplate))
         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);
   assert(!(isFriend && Owner->isDependentContext()));
   Inst->setPreviousDecl(PrevClassTemplate);
 
   RecordInst->setDescribedClassTemplate(Inst);
 
   if (isFriend) {
     if (PrevClassTemplate)
       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);
   }
 
   // Trigger creation of the type for the instantiation.
   SemaRef.Context.getInjectedClassNameType(RecordInst,
                                     Inst->getInjectedClassNameSpecialization());
 
   // Finish handling of friends.
   if (isFriend) {
     DC->makeDeclVisibleInContext(Inst);
     Inst->setLexicalDeclContext(Owner);
     RecordInst->setLexicalDeclContext(Owner);
     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);
 
   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 (D->isInjectedClassName())
     PrevDecl = cast<CXXRecordDecl>(Owner);
   else if (CXXRecordDecl *PatternPrev = getPreviousDeclForInstantiation(D)) {
     NamedDecl *Prev = SemaRef.FindInstantiatedDecl(D->getLocation(),
                                                    PatternPrev,
                                                    TemplateArgs);
     if (!Prev) return nullptr;
     PrevDecl = cast<CXXRecordDecl>(Prev);
   }
 
   CXXRecordDecl *Record = CXXRecordDecl::Create(
       SemaRef.Context, D->getTagKind(), Owner, D->getBeginLoc(),
       D->getLocation(), D->getIdentifier(), PrevDecl);
 
   // 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 (!D->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);
 
   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 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 = instantiateExplicitSpecifier(
         SemaRef, TemplateArgs, DGuide->getExplicitSpecifier(), DGuide);
     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;
   }
 
   // FIXME: Concepts: Do not substitute into constraint expressions
   Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
   if (TrailingRequiresClause) {
     EnterExpressionEvaluationContext ConstantEvaluated(
         SemaRef, Sema::ExpressionEvaluationContext::Unevaluated);
     ExprResult SubstRC = SemaRef.SubstExpr(TrailingRequiresClause,
                                            TemplateArgs);
     if (SubstRC.isInvalid())
       return nullptr;
     TrailingRequiresClause = SubstRC.get();
     if (!SemaRef.CheckConstraintExpression(TrailingRequiresClause))
       return nullptr;
   }
 
   // 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());
     if (DGuide->isCopyDeductionCandidate())
       cast<CXXDeductionGuideDecl>(Function)->setIsCopyDeductionCandidate();
     Function->setAccess(D->getAccess());
   } else {
     Function = FunctionDecl::Create(
         SemaRef.Context, DC, D->getInnerLocStart(), NameInfo, T, TInfo,
         D->getCanonicalDecl()->getStorageClass(), D->isInlineSpecified(),
         D->hasWrittenPrototype(), D->getConstexprKind(),
         TrailingRequiresClause);
     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();
   }
 
   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) {
     // Record this function template specialization.
     ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
     Function->setFunctionTemplateSpecialization(FunctionTemplate,
                             TemplateArgumentList::CreateCopy(SemaRef.Context,
                                                              Innermost),
                                                 /*InsertPos=*/nullptr);
   } else 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);
   }
 
   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() ? Sema::ForExternalRedeclaration
                              : SemaRef.forRedeclarationInCurContext());
 
   if (DependentFunctionTemplateSpecializationInfo *Info
         = D->getDependentSpecializationInfo()) {
     assert(isFriend && "non-friend has dependent specialization info?");
 
     // Instantiate the explicit template arguments.
     TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
                                           Info->getRAngleLoc());
     if (SemaRef.Subst(Info->getTemplateArgs(), Info->getNumTemplateArgs(),
                       ExplicitArgs, TemplateArgs))
       return nullptr;
 
     // Map the candidate templates to their instantiations.
     for (unsigned I = 0, E = Info->getNumTemplates(); I != E; ++I) {
       Decl *Temp = SemaRef.FindInstantiatedDecl(D->getLocation(),
                                                 Info->getTemplate(I),
                                                 TemplateArgs);
       if (!Temp) return nullptr;
 
       Previous.addDecl(cast<FunctionTemplateDecl>(Temp));
     }
 
     if (SemaRef.CheckFunctionTemplateSpecialization(Function,
                                                     &ExplicitArgs,
                                                     Previous))
       Function->setInvalidDecl();
 
     IsExplicitSpecialization = true;
   } else if (const ASTTemplateArgumentListInfo *Info =
                  D->getTemplateSpecializationArgsAsWritten()) {
     // The name of this function was written as a template-id.
     SemaRef.LookupQualifiedName(Previous, DC);
 
     // Instantiate the explicit template arguments.
     TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
                                           Info->getRAngleLoc());
     if (SemaRef.Subst(Info->getTemplateArgs(), Info->getNumTemplateArgs(),
                       ExplicitArgs, TemplateArgs))
       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 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.
     SemaRef.FilterLookupForScope(Previous, DC, /*Scope*/ nullptr,
                                  /*ConsiderLinkage*/ true,
                                  QualifierLoc.hasQualifier());
   }
 
   SemaRef.CheckFunctionDeclaration(/*Scope*/ nullptr, Function, Previous,
                                    IsExplicitSpecialization);
 
   // 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());
 
   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,
     Optional<const ASTTemplateArgumentListInfo *> ClassScopeSpecializationArgs,
     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);
 
   // 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;
     }
   }
 
   ExplicitSpecifier InstantiatedExplicitSpecifier =
       instantiateExplicitSpecifier(SemaRef, TemplateArgs,
                                    ExplicitSpecifier::getFromDecl(D), D);
   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;
   }
 
   // FIXME: Concepts: Do not substitute into constraint expressions
   Expr *TrailingRequiresClause = D->getTrailingRequiresClause();
   if (TrailingRequiresClause) {
     EnterExpressionEvaluationContext ConstantEvaluated(
         SemaRef, Sema::ExpressionEvaluationContext::Unevaluated);
     auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(Owner);
     Sema::CXXThisScopeRAII ThisScope(SemaRef, ThisContext,
                                      D->getMethodQualifiers(), ThisContext);
     ExprResult SubstRC = SemaRef.SubstExpr(TrailingRequiresClause,
                                            TemplateArgs);
     if (SubstRC.isInvalid())
       return nullptr;
     TrailingRequiresClause = SubstRC.get();
     if (!SemaRef.CheckConstraintExpression(TrailingRequiresClause))
       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;
   }
 
   DeclarationNameInfo NameInfo
     = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
 
   if (FunctionRewriteKind != RewriteKind::None)
     adjustForRewrite(FunctionRewriteKind, D, T, TInfo, NameInfo);
 
   // Build the instantiated method declaration.
   CXXRecordDecl *Record = cast<CXXRecordDecl>(DC);
   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->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->isInlineSpecified(), false, Destructor->getConstexprKind(),
         TrailingRequiresClause);
     Method->setRangeEnd(Destructor->getEndLoc());
   } else if (CXXConversionDecl *Conversion = dyn_cast<CXXConversionDecl>(D)) {
     Method = CXXConversionDecl::Create(
         SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
         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->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) {
     // 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::makeArrayRef(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,
                         Sema::ForExternalRedeclaration);
 
   bool IsExplicitSpecialization = false;
 
   // If the name of this function was written as a template-id, instantiate
   // the explicit template arguments.
   if (DependentFunctionTemplateSpecializationInfo *Info
         = D->getDependentSpecializationInfo()) {
     assert(isFriend && "non-friend has dependent specialization info?");
 
     // Instantiate the explicit template arguments.
     TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
                                           Info->getRAngleLoc());
     if (SemaRef.Subst(Info->getTemplateArgs(), Info->getNumTemplateArgs(),
                       ExplicitArgs, TemplateArgs))
       return nullptr;
 
     // Map the candidate templates to their instantiations.
     for (unsigned I = 0, E = Info->getNumTemplates(); I != E; ++I) {
       Decl *Temp = SemaRef.FindInstantiatedDecl(D->getLocation(),
                                                 Info->getTemplate(I),
                                                 TemplateArgs);
       if (!Temp) return nullptr;
 
       Previous.addDecl(cast<FunctionTemplateDecl>(Temp));
     }
 
     if (SemaRef.CheckFunctionTemplateSpecialization(Method,
                                                     &ExplicitArgs,
                                                     Previous))
       Method->setInvalidDecl();
 
     IsExplicitSpecialization = true;
   } else if (const ASTTemplateArgumentListInfo *Info =
                  ClassScopeSpecializationArgs.getValueOr(
                      D->getTemplateSpecializationArgsAsWritten())) {
     SemaRef.LookupQualifiedName(Previous, DC);
 
     TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
                                           Info->getRAngleLoc());
     if (SemaRef.Subst(Info->getTemplateArgs(), Info->getNumTemplateArgs(),
                       ExplicitArgs, TemplateArgs))
       return nullptr;
 
     if (SemaRef.CheckFunctionTemplateSpecialization(Method,
                                                     &ExplicitArgs,
                                                     Previous))
       Method->setInvalidDecl();
 
     IsExplicitSpecialization = true;
   } else if (ClassScopeSpecializationArgs) {
     // Class-scope explicit specialization written without explicit template
     // arguments.
     SemaRef.LookupQualifiedName(Previous, DC);
     if (SemaRef.CheckFunctionTemplateSpecialization(Method, nullptr, 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 does not apply if we're declaring a
     // typedef (C++ [dcl.typedef]p4).
     if (Previous.isSingleTagDecl())
       Previous.clear();
   }
 
   SemaRef.CheckFunctionDeclaration(nullptr, Method, Previous,
                                    IsExplicitSpecialization);
 
   if (D->isPure())
     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());
 
   // 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 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, None,
                                   /*ExpectParameterPack=*/ false);
 }
 
 Decl *TemplateDeclInstantiator::VisitTemplateTypeParmDecl(
                                                     TemplateTypeParmDecl *D) {
   // TODO: don't always clone when decls are refcounted.
   assert(D->getTypeForDecl()->isTemplateTypeParmType());
 
   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.
 
       // TODO: Concepts: do not instantiate the constraint (delayed constraint
       // substitution)
       const ASTTemplateArgumentListInfo *TemplArgInfo
         = TC->getTemplateArgsAsWritten();
       TemplateArgumentListInfo InstArgs;
 
       if (TemplArgInfo) {
         InstArgs.setLAngleLoc(TemplArgInfo->LAngleLoc);
         InstArgs.setRAngleLoc(TemplArgInfo->RAngleLoc);
         if (SemaRef.Subst(TemplArgInfo->getTemplateArgs(),
                           TemplArgInfo->NumTemplateArgs,
                           InstArgs, TemplateArgs))
           return nullptr;
       }
       if (SemaRef.AttachTypeConstraint(
               TC->getNestedNameSpecifierLoc(), TC->getConceptNameInfo(),
               TC->getNamedConcept(), &InstArgs, Inst,
               D->isParameterPack()
                   ? cast<CXXFoldExpr>(TC->getImmediatelyDeclaredConstraint())
                       ->getEllipsisLoc()
                   : SourceLocation()))
         return nullptr;
     }
   }
   if (D->hasDefaultArgument() && !D->defaultArgumentWasInherited()) {
     TypeSourceInfo *InstantiatedDefaultArg =
         SemaRef.SubstType(D->getDefaultArgumentInfo(), TemplateArgs,
                           D->getDefaultArgumentLoc(), D->getDeclName());
     if (InstantiatedDefaultArg)
       Inst->setDefaultArgument(InstantiatedDefaultArg);
   }
 
   // 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;
     Optional<unsigned> OrigNumExpansions
       = Expansion.getTypePtr()->getNumExpansions();
     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())
       if (SemaRef.AttachTypeConstraint(
               AutoLoc, Param,
               IsExpandedParameterPack
                 ? DI->getTypeLoc().getAs<PackExpansionTypeLoc>()
                     .getEllipsisLoc()
                 : SourceLocation()))
         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);
     ExprResult Value = SemaRef.SubstExpr(D->getDefaultArgument(), TemplateArgs);
     if (!Value.isInvalid())
       Param->setDefaultArgument(Value.get());
   }
 
   // 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;
     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(), InstParams, ExpandedParams);
   else
     Param = TemplateTemplateParmDecl::Create(
         SemaRef.Context, Owner, D->getLocation(),
         D->getDepth() - TemplateArgs.getNumSubstitutedLevels(),
         D->getPosition(), D->isParameterPack(), D->getIdentifier(), 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::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,
                     Sema::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()))
     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 (NameInfo.getName().getNameKind() == DeclarationName::CXXConstructorName)
     SemaRef.CheckInheritingConstructorUsingDecl(NewUD);
 
   bool isFunctionScope = Owner->isFunctionOrMethod();
 
   // Process the shadow decls.
   for (auto *Shadow : D->shadows()) {
     // FIXME: UsingShadowDecl doesn't preserve its immediate target, so
     // reconstruct it in the case where it matters.
     NamedDecl *OldTarget = Shadow->getTargetDecl();
     if (auto *CUSD = dyn_cast<ConstructorUsingShadowDecl>(Shadow))
       if (auto *BaseShadow = CUSD->getNominatedBaseClassShadowDecl())
         OldTarget = BaseShadow;
 
     NamedDecl *InstTarget =
         cast_or_null<NamedDecl>(SemaRef.FindInstantiatedDecl(
             Shadow->getLocation(), OldTarget, TemplateArgs));
     if (!InstTarget)
       return nullptr;
 
     UsingShadowDecl *PrevDecl = nullptr;
     if (CheckRedeclaration) {
       if (SemaRef.CheckUsingShadowDecl(NewUD, InstTarget, Prev, PrevDecl))
         continue;
     } else if (UsingShadowDecl *OldPrev =
                    getPreviousDeclForInstantiation(Shadow)) {
       PrevDecl = cast_or_null<UsingShadowDecl>(SemaRef.FindInstantiatedDecl(
           Shadow->getLocation(), OldPrev, TemplateArgs));
     }
 
     UsingShadowDecl *InstShadow =
         SemaRef.BuildUsingShadowDecl(/*Scope*/nullptr, NewUD, InstTarget,
                                      PrevDecl);
     SemaRef.Context.setInstantiatedFromUsingShadowDecl(InstShadow, Shadow);
 
     if (isFunctionScope)
       SemaRef.CurrentInstantiationScope->InstantiatedLocal(Shadow, InstShadow);
   }
 
   return NewUD;
 }
 
 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;
     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();
 
   NamedDecl *UD = SemaRef.BuildUsingDeclaration(
       /*Scope*/ nullptr, D->getAccess(), D->getUsingLoc(),
       /*HasTypename*/ TD, TypenameLoc, SS, NameInfo, EllipsisLoc,
       ParsedAttributesView(),
       /*IsInstantiation*/ true);
   if (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::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::VisitClassScopeFunctionSpecializationDecl(
     ClassScopeFunctionSpecializationDecl *Decl) {
   CXXMethodDecl *OldFD = Decl->getSpecialization();
   return cast_or_null<CXXMethodDecl>(
       VisitCXXMethodDecl(OldFD, nullptr, Decl->getTemplateArgsAsWritten()));
 }
 
 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.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()) {
     auto *AC = cast<OMPAllocatorClause>(C);
     ExprResult NewE = SemaRef.SubstExpr(AC->getAllocator(), TemplateArgs);
     if (!NewE.isUsable())
       continue;
     OMPClause *IC = SemaRef.ActOnOpenMPAllocatorClause(
         NewE.get(), AC->getBeginLoc(), AC->getLParenLoc(), AC->getEndLoc());
     Clauses.push_back(IC);
   }
 
   Sema::DeclGroupPtrTy Res = SemaRef.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.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.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.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.ActOnOpenMPDeclareReductionCombinerEnd(NewDRD, SubstCombiner);
   }
   // Initializers instantiation sequence.
   if (Init) {
     VarDecl *OmpPrivParm = SemaRef.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() == OMPDeclareReductionDecl::CallInit) {
       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.ActOnOpenMPDeclareReductionInitializerEnd(NewDRD, SubstInitializer,
                                                       OmpPrivParm);
   }
   IsCorrect = IsCorrect && SubstCombiner &&
               (!Init ||
                (D->getInitializerKind() == OMPDeclareReductionDecl::CallInit &&
                 SubstInitializer) ||
                (D->getInitializerKind() != OMPDeclareReductionDecl::CallInit &&
                 !SubstInitializer));
 
   (void)SemaRef.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.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.StartOpenMPDSABlock(llvm::omp::OMPD_declare_mapper, DirName,
                               /*S=*/nullptr,
                               (*D->clauselist_begin())->getBeginLoc());
   ExprResult MapperVarRef = SemaRef.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.ActOnOpenMPMapClause(
         OldC->getMapTypeModifiers(), OldC->getMapTypeModifiersLoc(), SS,
         NewNameInfo, OldC->getMapType(), OldC->isImplicitMapType(),
         OldC->getMapLoc(), OldC->getColonLoc(), NewVars, Locs);
     Clauses.push_back(NewC);
   }
   SemaRef.EndOpenMPDSABlock(nullptr);
   if (!IsCorrect)
     return nullptr;
   Sema::DeclGroupPtrTy DG = SemaRef.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.
   TemplateSpecializationTypeLoc Loc = D->getTypeAsWritten()->getTypeLoc().
                                         castAs<TemplateSpecializationTypeLoc>();
   TemplateArgumentListInfo InstTemplateArgs(Loc.getLAngleLoc(),
                                             Loc.getRAngleLoc());
   SmallVector<TemplateArgumentLoc, 4> ArgLocs;
   for (unsigned I = 0; I != Loc.getNumArgs(); ++I)
     ArgLocs.push_back(Loc.getArgLoc(I));
   if (SemaRef.Subst(ArgLocs.data(), ArgLocs.size(),
                     InstTemplateArgs, TemplateArgs))
     return nullptr;
 
   // Check that the template argument list is well-formed for this
   // class template.
   SmallVector<TemplateArgument, 4> Converted;
   if (SemaRef.CheckTemplateArgumentList(InstClassTemplate,
                                         D->getLocation(),
                                         InstTemplateArgs,
                                         false,
                                         Converted,
                                         /*UpdateArgsWithConversion=*/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(Converted, 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, Converted, PrevDecl);
 
   // 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;
 
   // Build the canonical type that describes the converted template
   // arguments of the class template explicit specialization.
   QualType CanonType = SemaRef.Context.getTemplateSpecializationType(
       TemplateName(InstClassTemplate), Converted,
       SemaRef.Context.getRecordType(InstD));
 
   // Build the fully-sugared type for this class template
   // specialization as the user wrote in the specialization
   // itself. This means that we'll pretty-print the type retrieved
   // from the specialization's declaration the way that the user
   // actually wrote the specialization, rather than formatting the
   // name based on the "canonical" representation used to store the
   // template arguments in the specialization.
   TypeSourceInfo *WrittenTy = SemaRef.Context.getTemplateSpecializationTypeInfo(
       TemplateName(InstClassTemplate), D->getLocation(), InstTemplateArgs,
       CanonType);
 
   InstD->setAccess(D->getAccess());
   InstD->setInstantiationOfMemberClass(D, TSK_ImplicitInstantiation);
   InstD->setSpecializationKind(D->getSpecializationKind());
   InstD->setTypeAsWritten(WrittenTy);
   InstD->setExternLoc(D->getExternLoc());
   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.
   const TemplateArgumentListInfo &TemplateArgsInfo = D->getTemplateArgsInfo();
   VarTemplateArgsInfo.setLAngleLoc(TemplateArgsInfo.getLAngleLoc());
   VarTemplateArgsInfo.setRAngleLoc(TemplateArgsInfo.getRAngleLoc());
 
   if (SemaRef.Subst(TemplateArgsInfo.getArgumentArray(),
                     TemplateArgsInfo.size(), VarTemplateArgsInfo, TemplateArgs))
     return nullptr;
 
   // Check that the template argument list is well-formed for this template.
   SmallVector<TemplateArgument, 4> Converted;
   if (SemaRef.CheckTemplateArgumentList(InstVarTemplate, D->getLocation(),
                                         VarTemplateArgsInfo, false, Converted,
                                         /*UpdateArgsWithConversion=*/true))
     return nullptr;
 
   // Check whether we've already seen a declaration of this specialization.
   void *InsertPos = nullptr;
   VarTemplateSpecializationDecl *PrevDecl =
       InstVarTemplate->findSpecialization(Converted, 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, Converted, 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->setTemplateArgsInfo(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::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, nullptr, None,
         TemplateDeclInstantiator::RewriteKind::RewriteSpaceshipAsEqualEqual);
   } else {
     assert(Spaceship->getFriendObjectKind() &&
            "defaulted spaceship is neither a member nor a friend");
 
     R = Instantiator.VisitFunctionDecl(
         Spaceship, 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;
 
   // FIXME: Concepts: Substitution into requires clause should only happen when
   // checking satisfaction.
   Expr *InstRequiresClause = nullptr;
   if (Expr *E = L->getRequiresClause()) {
     EnterExpressionEvaluationContext ConstantEvaluated(
         SemaRef, Sema::ExpressionEvaluationContext::Unevaluated);
     ExprResult Res = SemaRef.SubstExpr(E, TemplateArgs);
     if (Res.isInvalid() || !Res.isUsable()) {
       return nullptr;
     }
     InstRequiresClause = Res.get();
   }
 
   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) {
   TemplateDeclInstantiator Instantiator(*this, Owner, TemplateArgs);
   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.Subst(TemplArgInfo->getTemplateArgs(),
                     TemplArgInfo->NumTemplateArgs,
                     InstTemplateArgs, TemplateArgs))
     return nullptr;
 
   // Check that the template argument list is well-formed for this
   // class template.
   SmallVector<TemplateArgument, 4> Converted;
   if (SemaRef.CheckTemplateArgumentList(ClassTemplate,
                                         PartialSpec->getLocation(),
                                         InstTemplateArgs,
                                         false,
                                         Converted))
     return nullptr;
 
   // Check these arguments are valid for a template partial specialization.
   if (SemaRef.CheckTemplatePartialSpecializationArgs(
           PartialSpec->getLocation(), ClassTemplate, InstTemplateArgs.size(),
           Converted))
     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(Converted, 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),
                                                     Converted);
 
   // Build the fully-sugared type for this class template
   // specialization as the user wrote in the specialization
   // itself. This means that we'll pretty-print the type retrieved
   // from the specialization's declaration the way that the user
   // actually wrote the specialization, rather than formatting the
   // name based on the "canonical" representation used to store the
   // template arguments in the specialization.
   TypeSourceInfo *WrittenTy
     = SemaRef.Context.getTemplateSpecializationTypeInfo(
                                                     TemplateName(ClassTemplate),
                                                     PartialSpec->getLocation(),
                                                     InstTemplateArgs,
                                                     CanonType);
 
   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(PartialSpec->getLocation(), diag::err_partial_spec_redeclared)
       << WrittenTy->getType();
     SemaRef.Diag(PrevDecl->getLocation(), diag::note_prev_partial_spec_here)
       << SemaRef.Context.getTypeDeclType(PrevDecl);
     return nullptr;
   }
 
 
   // Create the class template partial specialization declaration.
   ClassTemplatePartialSpecializationDecl *InstPartialSpec =
       ClassTemplatePartialSpecializationDecl::Create(
           SemaRef.Context, PartialSpec->getTagKind(), Owner,
           PartialSpec->getBeginLoc(), PartialSpec->getLocation(), InstParams,
           ClassTemplate, Converted, InstTemplateArgs, CanonType, nullptr);
   // Substitute the nested name specifier, if any.
   if (SubstQualifier(PartialSpec, InstPartialSpec))
     return nullptr;
 
   InstPartialSpec->setInstantiatedFromMember(PartialSpec);
   InstPartialSpec->setTypeAsWritten(WrittenTy);
 
   // 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.Subst(TemplArgInfo->getTemplateArgs(),
                     TemplArgInfo->NumTemplateArgs,
                     InstTemplateArgs, TemplateArgs))
     return nullptr;
 
   // Check that the template argument list is well-formed for this
   // class template.
   SmallVector<TemplateArgument, 4> Converted;
   if (SemaRef.CheckTemplateArgumentList(VarTemplate, PartialSpec->getLocation(),
                                         InstTemplateArgs, false, Converted))
     return nullptr;
 
   // Check these arguments are valid for a template partial specialization.
   if (SemaRef.CheckTemplatePartialSpecializationArgs(
           PartialSpec->getLocation(), VarTemplate, InstTemplateArgs.size(),
           Converted))
     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(Converted, InstParams, InsertPos);
 
   // Build the canonical type that describes the converted template
   // arguments of the variable template partial specialization.
   QualType CanonType = SemaRef.Context.getTemplateSpecializationType(
       TemplateName(VarTemplate), Converted);
 
   // Build the fully-sugared type for this variable template
   // specialization as the user wrote in the specialization
   // itself. This means that we'll pretty-print the type retrieved
   // from the specialization's declaration the way that the user
   // actually wrote the specialization, rather than formatting the
   // name based on the "canonical" representation used to store the
   // template arguments in the specialization.
   TypeSourceInfo *WrittenTy = SemaRef.Context.getTemplateSpecializationTypeInfo(
       TemplateName(VarTemplate), PartialSpec->getLocation(), InstTemplateArgs,
       CanonType);
 
   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)
         << WrittenTy->getType();
     SemaRef.Diag(PrevDecl->getLocation(),
                  diag::note_var_prev_partial_spec_here);
     return nullptr;
   }
 
   // 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(), Converted, InstTemplateArgs);
 
   // Substitute the nested name specifier, if any.
   if (SubstQualifier(PartialSpec, InstPartialSpec))
     return nullptr;
 
   InstPartialSpec->setInstantiatedFromMember(PartialSpec);
   InstPartialSpec->setTypeAsWritten(WrittenTy);
 
   // 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->getMethodQualifiers();
   }
 
   TypeSourceInfo *NewTInfo
     = SemaRef.SubstFunctionDeclType(OldTInfo, TemplateArgs,
                                     D->getTypeSpecStartLoc(),
                                     D->getDeclName(),
                                     ThisContext, ThisTypeQuals);
   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;
 
         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;
 }
 
 /// Introduce the instantiated function parameters into the local
 /// instantiation scope, and set the parameter names to those used
 /// in the template.
 static bool addInstantiatedParametersToScope(Sema &S, 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 = S.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);
     Optional<unsigned> NumArgumentsInExpansion
       = S.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(S, Arg);
           QualType T = S.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());
   Expr *UninstExpr = Param->getUninstantiatedDefaultArg();
 
   EnterExpressionEvaluationContext EvalContext(
       *this, ExpressionEvaluationContext::PotentiallyEvaluated, Param);
 
   // 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, nullptr, /*RelativeToPrimary=*/true);
 
   InstantiatingTemplate Inst(*this, CallLoc, 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);
     LocalInstantiationScope Local(*this);
 
     FunctionDecl *Pattern = FD->getTemplateInstantiationPattern(
         /*ForDefinition*/ false);
     if (addInstantiatedParametersToScope(*this, FD, Pattern, Local,
                                          TemplateArgs))
       return true;
 
     runWithSufficientStackSpace(CallLoc, [&] {
       Result = SubstInitializer(UninstExpr, TemplateArgs,
                                 /*DirectInit*/false);
     });
   }
   if (Result.isInvalid())
     return true;
 
   // Check the expression as an initializer for the parameter.
   InitializedEntity Entity
     = InitializedEntity::InitializeParameter(Context, Param);
   InitializationKind Kind = InitializationKind::CreateCopy(
       Param->getLocation(),
       /*FIXME:EqualLoc*/ UninstExpr->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);
   if (Result.isInvalid())
     return true;
 
   // Remember the instantiated default argument.
   Param->setDefaultArg(Result.getAs<Expr>());
   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, nullptr, /*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(*this, Decl, Template, Scope,
                                        TemplateArgs)) {
     UpdateExceptionSpec(Decl, EST_None);
     return;
   }
 
   SubstExceptionSpec(Decl, Template->getType()->castAs<FunctionProtoType>(),
                      TemplateArgs);
 }
 
 bool Sema::CheckInstantiatedFunctionTemplateConstraints(
     SourceLocation PointOfInstantiation, FunctionDecl *Decl,
     ArrayRef<TemplateArgument> TemplateArgs,
     ConstraintSatisfaction &Satisfaction) {
   // In most cases we're not going to have constraints, so check for that first.
   FunctionTemplateDecl *Template = Decl->getPrimaryTemplate();
   // Note - code synthesis context for the constraints check is created
   // inside CheckConstraintsSatisfaction.
   SmallVector<const Expr *, 3> TemplateAC;
   Template->getAssociatedConstraints(TemplateAC);
   if (TemplateAC.empty()) {
     Satisfaction.IsSatisfied = true;
     return false;
   }
 
   // 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);
 
   // If this is not an explicit specialization - we need to get the instantiated
   // version of the template arguments and add them to scope for the
   // substitution.
   if (Decl->isTemplateInstantiation()) {
     InstantiatingTemplate Inst(*this, Decl->getPointOfInstantiation(),
         InstantiatingTemplate::ConstraintsCheck{}, Decl->getPrimaryTemplate(),
         TemplateArgs, SourceRange());
     if (Inst.isInvalid())
       return true;
     MultiLevelTemplateArgumentList MLTAL(
         *Decl->getTemplateSpecializationArgs());
     if (addInstantiatedParametersToScope(
             *this, Decl, Decl->getPrimaryTemplate()->getTemplatedDecl(),
             Scope, MLTAL))
       return true;
   }
   Qualifiers ThisQuals;
   CXXRecordDecl *Record = nullptr;
   if (auto *Method = dyn_cast<CXXMethodDecl>(Decl)) {
     ThisQuals = Method->getMethodQualifiers();
     Record = Method->getParent();
   }
   CXXThisScopeRAII ThisScope(*this, Record, ThisQuals, Record != nullptr);
   return CheckConstraintSatisfaction(Template, TemplateAC, TemplateArgs,
                                      PointOfInstantiation, Satisfaction);
 }
 
 /// 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 (FunctionTemplateDecl *FunTmpl
           = dyn_cast<FunctionTemplateDecl>(ActiveInst.Entity)) {
       assert(FunTmpl->getTemplatedDecl() == Tmpl &&
              "Deduction from the wrong function template?");
       (void) FunTmpl;
       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->getDefaultedFunctionInfo()) {
     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->setDefaultedFunctionInfo(
         AnyChanged ? FunctionDecl::DefaultedFunctionInfo::Create(
                          SemaRef.Context, Lookups)
                    : DFI);
   }
 
   SemaRef.SetDeclDefaulted(New, Tmpl->getLocation());
   return false;
 }
 
 /// 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 *
 Sema::InstantiateFunctionDeclaration(FunctionTemplateDecl *FTD,
                                      const TemplateArgumentList *Args,
                                      SourceLocation Loc) {
   FunctionDecl *FD = FTD->getTemplatedDecl();
 
   sema::TemplateDeductionInfo Info(Loc);
   InstantiatingTemplate Inst(
       *this, Loc, FTD, Args->asArray(),
       CodeSynthesisContext::ExplicitTemplateArgumentSubstitution, Info);
   if (Inst.isInvalid())
     return nullptr;
 
   ContextRAII SavedContext(*this, FD);
   MultiLevelTemplateArgumentList MArgs(*Args);
 
   return cast_or_null<FunctionDecl>(SubstDecl(FD, FD->getParent(), MArgs));
 }
 
 /// 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 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;
 
   // 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) {
       // 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", [&]() {
     std::string Name;
     llvm::raw_string_ostream OS(Name);
     Function->getNameForDiagnostic(OS, getPrintingPolicy(),
                                    /*Qualified=*/true);
     return Name;
   });
 
   // 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);
   }
 
   // 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 inner loc start from the pattern.
   Function->setInnerLocStart(PatternDecl->getInnerLocStart());
 
   EnterExpressionEvaluationContext EvalContext(
       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
 
   // 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).
+  // 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();
+    MergeWithParentScope =
+        Rec->isLocalClass() && !Function->isFunctionTemplateSpecialization();
 
   LocalInstantiationScope Scope(*this, MergeWithParentScope);
 
   if (PatternDecl->isDefaulted())
     SetDeclDefaulted(Function, PatternDecl->getLocation());
   else {
     MultiLevelTemplateArgumentList TemplateArgs =
       getTemplateInstantiationArgs(Function, nullptr, 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);
 
     if (addInstantiatedParametersToScope(*this, 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 &TemplateArgList,
     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;
 
   MultiLevelTemplateArgumentList TemplateArgLists;
   TemplateArgLists.addOuterTemplateArguments(&TemplateArgList);
 
   // 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;
   if (VarTemplatePartialSpecializationDecl *PartialSpec =
           dyn_cast<VarTemplatePartialSpecializationDecl>(FromVar))
     IsMemberSpec = PartialSpec->isMemberSpecialization();
   else if (VarTemplateDecl *FromTemplate = FromVar->getDescribedVarTemplate())
     IsMemberSpec = FromTemplate->isMemberSpecialization();
   if (!IsMemberSpec)
     FromVar = FromVar->getFirstDecl();
 
   MultiLevelTemplateArgumentList MultiLevelList(TemplateArgList);
   TemplateDeclInstantiator Instantiator(*this, FromVar->getDeclContext(),
                                         MultiLevelList);
 
   // TODO: Set LateAttrs and StartingScope ...
 
   return cast_or_null<VarTemplateSpecializationDecl>(
       Instantiator.VisitVarTemplateSpecializationDecl(
           VarTemplate, FromVar, TemplateArgsInfo, Converted));
 }
 
 /// Instantiates a variable template specialization by completing it
 /// with appropriate type information and initializer.
 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;
 }
 
 /// BuildVariableInstantiation - Used after a new variable has been created.
 /// Sets basic variable data and decides whether to postpone the
 /// variable instantiation.
 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());
   MaybeAddCUDAConstantAttr(NewVar);
   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() ? Sema::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);
 }
 
 /// Instantiate the initializer of a variable.
 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);
 
     // 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)
     checkAllowedCUDAInitializer(Var);
 }
 
 /// 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 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);
     Var = cast_or_null<VarDecl>(Instantiator.VisitVarTemplateSpecializationDecl(
         VarSpec->getSpecializedTemplate(), Def, VarSpec->getTemplateArgsInfo(),
         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;
       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;
 }
 
 /// Finds the instantiation of the given declaration context
 /// within the current instantiation.
 ///
 /// \returns NULL if there was an error
 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;
 }
 
 /// 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 *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 tempalte
   // arguments we're currently substituting.
   bool ParentDependsOnArgs = isDependentContextAtLevel(
       ParentDC, TemplateArgs.getNumRetainedOuterLevels());
   // FIXME: Parmeters 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())) {
     // 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 partial specialization.
     ClassTemplateDecl *ClassTemplate = Record->getDescribedClassTemplate();
     if (ClassTemplate)
       ClassTemplate = ClassTemplate->getCanonicalDecl();
     else if (ClassTemplatePartialSpecializationDecl *PartialSpec
                = dyn_cast<ClassTemplatePartialSpecializationDecl>(Record))
       ClassTemplate = PartialSpec->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->getDeclContext()->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);
           if (T.isNull())
             return nullptr;
           auto *SubstRecord = T->getAsCXXRecordDecl();
           assert(SubstRecord && "class template id not a class type?");
           // 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;
 }
 
 /// Performs template instantiation for all implicit template
 /// instantiations we have seen until this point.
 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;
     }
   }
 }