[RISCV] Add Custom Parser for Atomic Memory Operands

Summary:
GCC Accepts both (reg) and 0(reg) for atomic instruction memory
operands. These instructions do not allow for an offset in their
encoding, so in the latter case, the 0 is silently dropped.

Due to how we have structured the RISCVAsmParser, the easiest way to
add support for parsing this offset is to add a custom AsmOperand and
parser. This parser drops all the parens, and just keeps the
register.

This commit also adds a custom printer for these operands, which
matches the GCC canonical printer, printing both `(a0)` and `0(a0)`
as `(a0)`.

Reviewers: asb, lewis-revill

Reviewed By: asb

Subscribers: s.egerton, hiraditya, rbar, johnrusso, simoncook,
apazos, sabuasal, niosHD, kito-cheng, shiva0217, jrtc27, MaskRay,
zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o,
rkruppe, jfb, PkmX, jocewei, psnobl, benna, Jim, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65205

llvm-svn: 367553

[RISCV] Add FreeBSD targets

Reviewers: asb

Reviewed By: asb

Subscribers: simoncook, s.egerton, lenary, psnobl, benna, mhorne,
emaste, kito-cheng, shiva0217, rogfer01, rkruppe, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D57795

Patch by James Clarke (jrtc27)

llvm-svn: 367557

[DebugInfo] Generate fixups as emitting DWARF .debug_frame/.eh_frame.

It is necessary to generate fixups in .debug_frame or .eh_frame as
relaxation is enabled due to the address delta may be changed after
relaxation.

There is an opcode with 6-bits data in debug frame encoding. So, we
also need 6-bits fixup types.

Differential Revision: https://reviews.llvm.org/D58335

llvm-svn: 366524

[DebugInfo] Some fields do not need relocations even relax is enabled.

In debug frame information, some fields, e.g., Length in CIE/FDE and
Offset in FDE are attributes to describe the structure of CIE/FDE.
They are not related to the relaxed code. However, these attributes
are symbol differences. So, in current design, these attributes will
be filled as zero and LLVM generates relocations for them.

We only need to generate relocations for symbols in executable
sections.  So, if the symbols are not located in executable sections,
we still evaluate their values under relaxation.

Differential Revision: https://reviews.llvm.org/D61584

llvm-svn: 366531

[RISCV] Don't force absolute FK_Data_X fixups to relocs

The current behavior of shouldForceRelocation forces relocations for
the majority of fixups when relaxation is enabled. This makes sense
for fixups which incorporate symbols but is unnecessary for simple
data fixups where the fixup target is already resolved to an absolute
value.

Differential Revision: https://reviews.llvm.org/D63404
Patch by Edward Jones.

llvm-svn: 369257

[RISCV] Implement getExprForFDESymbol to ensure RISCV_32_PCREL is
used for the FDE location

Follow binutils in using RISCV_32_PCREL for the FDE initial location.
As explained in the relevant binutils commit
<https://github.com/riscv/riscv-binutils-gdb/commit/a6cbf936e3dce68114d28cdf60d510a3f78a6d40>,
the ADD/SUB pair of relocations is problematic in the presence of
linker relaxation.

This patch has the same end goal as D64715 but includes test changes
and avoids adding a new global VariantKind to MCExpr.h (preferring
RISCVMCExpr VKs like the rest of the RISC-V backend).

Differential Revision: https://reviews.llvm.org/D66419

llvm-svn: 369375