[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

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVInstPrinter.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVInstPrinter.cpp
index fe37b70811d..d7452200e05 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVInstPrinter.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVInstPrinter.cpp
@@ -112,3 +112,15 @@ void RISCVInstPrinter::printFRMArg(const MCInst *MI, unsigned OpNo,
       static_cast<RISCVFPRndMode::RoundingMode>(MI->getOperand(OpNo).getImm());
   O << RISCVFPRndMode::roundingModeToString(FRMArg);
 }
+
+void RISCVInstPrinter::printAtomicMemOp(const MCInst *MI, unsigned OpNo,
+                                        const MCSubtargetInfo &STI,
+                                        raw_ostream &O) {
+  const MCOperand &MO = MI->getOperand(OpNo);
+
+  assert(MO.isReg() && "printAtomicMemOp can only print register operands");
+  O << "(";
+  printRegName(O, MO.getReg());
+  O << ")";
+  return;
+}