[AMDGPU] Allow no-modifier operands in cvtDPP

[Joe_Nash]

Summary

NFC, since no instructions have their AsmMatchConverter
changed, but prepares for that to happen.

llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp

 
 AMDGPUOperand::Ptr AMDGPUAsmParser::defaultFI() const {
   return AMDGPUOperand::CreateImm(this, 0, SMLoc(), AMDGPUOperand::ImmTyDppFi);
 }
 
 void AMDGPUAsmParser::cvtDPP(MCInst &Inst, const OperandVector &Operands, bool IsDPP8) {
   OptionalImmIndexMap OptionalIdx;
 
+  unsigned Opc = Inst.getOpcode();
+  bool HasModifiers =
+      AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::src0_modifiers) != -1;
   unsigned I = 1;
   const MCInstrDesc &Desc = MII.get(Inst.getOpcode());
   for (unsigned J = 0; J < Desc.getNumDefs(); ++J) {
     ((AMDGPUOperand &)*Operands[I++]).addRegOperands(Inst, 1);
   }
 
   int Fi = 0;
   for (unsigned E = Operands.size(); I != E; ++I) {
if (Op.isReg() && validateVccOperand(Op.getReg())) {
       // VOP2b (v_add_u32, v_sub_u32 ...) dpp use "vcc" token.
       // Skip it.
       continue;
     }
 
     if (IsDPP8) {
       if (Op.isDPP8()) {
         Op.addImmOperands(Inst, 1);
-      } else if (isRegOrImmWithInputMods(Desc, Inst.getNumOperands())) {
+      } else if (HasModifiers &&
+                 isRegOrImmWithInputMods(Desc, Inst.getNumOperands())) {
         Op.addRegWithFPInputModsOperands(Inst, 2);
       } else if (Op.isFI()) {
         Fi = Op.getImm();
       } else if (Op.isReg()) {
         Op.addRegOperands(Inst, 1);
       } else {
         llvm_unreachable("Invalid operand type");
       }
     } else {
-      if (isRegOrImmWithInputMods(Desc, Inst.getNumOperands())) {
+      if (HasModifiers &&
+          isRegOrImmWithInputMods(Desc, Inst.getNumOperands())) {
         Op.addRegWithFPInputModsOperands(Inst, 2);
+      } else if (Op.isReg()) {
+        Op.addRegOperands(Inst, 1);
       } else if (Op.isDPPCtrl()) {
         Op.addImmOperands(Inst, 1);
       } else if (Op.isImm()) {
         // Handle optional arguments
         OptionalIdx[Op.getImmTy()] = I;
       } else {
         llvm_unreachable("Invalid operand type");
       }