[RISCV][MC] Create an AsmOperand for carry-in vmask (#124317)

Previously we used a fixed assembly string as well as encoding for the
carry-in vector mask, since it will always be there. However, this makes
both AsmParser and disassembler to either create a garbage MCOperand for
the mask or fail to add one as a whole. This wouldn't be a problem for
majority of the cases but tools like llvm-mca who relies on MCInst will
fail to account for the register dependency on these mask operands.

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
index a0b87f7..1c4f322 100644
--- a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
+++ b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
@@ -297,6 +297,16 @@ static DecodeStatus DecodeVRM8RegisterClass(MCInst &Inst, uint32_t RegNo,
   return MCDisassembler::Success;
 }
 
+static DecodeStatus DecodeVMV0RegisterClass(MCInst &Inst, uint32_t RegNo,
+                                            uint64_t Address,
+                                            const MCDisassembler *Decoder) {
+  if (RegNo)
+    return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::createReg(RISCV::V0));
+  return MCDisassembler::Success;
+}
+
 static DecodeStatus decodeVMaskReg(MCInst &Inst, uint32_t RegNo,
                                    uint64_t Address,
                                    const MCDisassembler *Decoder) {