[RISCV] Use decodeUImmLog2XLenNonZeroOperand in decodeRVCInstrRdRs1UImm. NFC (#133759)

decodeUImmLog2XLenNonZeroOperand already contains the uimm5 check for
RV32 so we can reuse it. This makes C_SLLI_HINT code more similar to the
tblgen code for C_SLLI.

Author: topperc

llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp

@@ -488,9 +488,10 @@ static DecodeStatus decodeRVCInstrRdSImm(MCInst &Inst, uint32_t Insn,
                                          uint64_t Address,
                                          const MCDisassembler *Decoder);
 
-static DecodeStatus decodeRVCInstrRdRs1UImm(MCInst &Inst, uint32_t Insn,
-                                            uint64_t Address,
-                                            const MCDisassembler *Decoder);
+static DecodeStatus
+decodeRVCInstrRdRs1UImmLog2XLenNonZero(MCInst &Inst, uint32_t Insn,
+                                       uint64_t Address,
+                                       const MCDisassembler *Decoder);
 
 static DecodeStatus decodeRVCInstrRdRs2(MCInst &Inst, uint32_t Insn,
                                         uint64_t Address,
@@ -553,21 +554,16 @@ static DecodeStatus decodeRVCInstrRdSImm(MCInst &Inst, uint32_t Insn,
   return MCDisassembler::Success;
 }
 
-static DecodeStatus decodeRVCInstrRdRs1UImm(MCInst &Inst, uint32_t Insn,
-                                            uint64_t Address,
-                                            const MCDisassembler *Decoder) {
+static DecodeStatus
+decodeRVCInstrRdRs1UImmLog2XLenNonZero(MCInst &Inst, uint32_t Insn,
+                                       uint64_t Address,
+                                       const MCDisassembler *Decoder) {
   Inst.addOperand(MCOperand::createReg(RISCV::X0));
   Inst.addOperand(Inst.getOperand(0));
 
-  uint32_t UImm6 = fieldFromInstruction(Insn, 12, 1) << 5;
-  // On RV32C, uimm[5]=1 is reserved for custom extensions.
-  if (UImm6 != 0 && Decoder->getSubtargetInfo().hasFeature(RISCV::Feature32Bit))
-    return MCDisassembler::Fail;
-  UImm6 |= fieldFromInstruction(Insn, 2, 5);
-  [[maybe_unused]] DecodeStatus Result =
-      decodeUImmOperand<6>(Inst, UImm6, Address, Decoder);
-  assert(Result == MCDisassembler::Success && "Invalid immediate");
-  return MCDisassembler::Success;
+  uint32_t UImm6 =
+      fieldFromInstruction(Insn, 12, 1) << 5 | fieldFromInstruction(Insn, 2, 5);
+  return decodeUImmLog2XLenNonZeroOperand(Inst, UImm6, Address, Decoder);
 }
 
 static DecodeStatus decodeRVCInstrRdRs2(MCInst &Inst, uint32_t Insn,

llvm/lib/Target/RISCV/RISCVInstrInfoC.td

@@ -661,7 +661,7 @@ def C_SLLI_HINT : RVInst16CI<0b000, 0b10, (outs GPRX0:$rd_wb),
                   Sched<[WriteShiftImm, ReadShiftImm]> {
   let Constraints = "$rd = $rd_wb";
   let Inst{11-7} = 0;
-  let DecoderMethod = "decodeRVCInstrRdRs1UImm";
+  let DecoderMethod = "decodeRVCInstrRdRs1UImmLog2XLenNonZero";
 }
 
 def C_SLLI64_HINT : RVInst16CI<0b000, 0b10, (outs GPR:$rd_wb), (ins GPR:$rd),