[RISCV] Simplify some code in RISCVInstrInfo::verifyInstruction. NFCI

[craig.topper]

Summary

This code was written as if it lived in the MC layer instead of
the CodeGen layer. We get the MCInstrDesc directly from MachineInstr.
And we can use RISCVSubtarget::is64Bit instead of going to the
Triple.

[reames]

LGTM

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

if (MI.getOperand(1).isReg() && MI.getOperand(2).isReg() &&
       return DestSourcePair{MI.getOperand(0), MI.getOperand(1)};
     break;
   }
   return None;
 }
 
 bool RISCVInstrInfo::verifyInstruction(const MachineInstr &MI,
                                        StringRef &ErrInfo) const {
-  const MCInstrInfo *MCII = STI.getInstrInfo();
-  MCInstrDesc const &Desc = MCII->get(MI.getOpcode());
+  MCInstrDesc const &Desc = MI.getDesc();
 
   for (auto &OI : enumerate(Desc.operands())) {
     unsigned OpType = OI.value().OperandType;
     if (OpType >= RISCVOp::OPERAND_FIRST_RISCV_IMM &&
         OpType <= RISCVOp::OPERAND_LAST_RISCV_IMM) {
       const MachineOperand &MO = MI.getOperand(OI.index());
       if (MO.isImm()) {
         int64_t Imm = MO.getImm();
break;
           break;
         case RISCVOp::OPERAND_SIMM12:
           Ok = isInt<12>(Imm);
           break;
         case RISCVOp::OPERAND_SIMM12_LSB00000:
           Ok = isShiftedInt<7, 5>(Imm);
           break;
         case RISCVOp::OPERAND_UIMMLOG2XLEN:
-          Ok = STI.getTargetTriple().isArch64Bit() ? isUInt<6>(Imm)
-                                                   : isUInt<5>(Imm);
+          Ok = STI.is64Bit() ? isUInt<6>(Imm) : isUInt<5>(Imm);
           break;
         case RISCVOp::OPERAND_UIMMLOG2XLEN_NONZERO:
-          Ok = STI.getTargetTriple().isArch64Bit() ? isUInt<6>(Imm)
-                                                   : isUInt<5>(Imm);
+          Ok = STI.is64Bit() ? isUInt<6>(Imm) : isUInt<5>(Imm);
           Ok = Ok && Imm != 0;
           break;
         case RISCVOp::OPERAND_UIMM_SHFL:
-          Ok = STI.getTargetTriple().isArch64Bit() ? isUInt<5>(Imm)
-                                                   : isUInt<4>(Imm);
+          Ok = STI.is64Bit() ? isUInt<5>(Imm) : isUInt<4>(Imm);
           break;
         case RISCVOp::OPERAND_RVKRNUM:
           Ok = Imm >= 0 && Imm <= 10;
           break;
         }
         if (!Ok) {
           ErrInfo = "Invalid immediate";
           return false;