[clang] [llvm] [AMDGPU] Fix opsel for scaled MFMA operations (PR #140183)

[Matt Arsenault via cfe-commits]

================
@@ -8811,6 +8820,68 @@ void AMDGPUAsmParser::cvtVINTERP(MCInst &Inst, const OperandVector &Operands)
     Inst.getOperand(ModIdx).setImm(ModVal);
   }
 }
+void AMDGPUAsmParser::cvtScaledMFMA(MCInst &Inst,
+                                    const OperandVector &Operands) {
+  OptionalImmIndexMap OptionalIdx;
+  unsigned Opc = Inst.getOpcode();
+  unsigned I = 1;
+
+  const MCInstrDesc &Desc = MII.get(Opc);
+
+  for (unsigned J = 0; J < Desc.getNumDefs(); ++J)
+    static_cast<AMDGPUOperand &>(*Operands[I++]).addRegOperands(Inst, 1);
+
+  for (unsigned E = Operands.size(); I != E; ++I) {
+    AMDGPUOperand &Op = static_cast<AMDGPUOperand &>(*Operands[I]);
+
+    if (isRegOrImmWithInputMods(Desc, Inst.getNumOperands())) {
+      Op.addRegOrImmWithFPInputModsOperands(Inst, 2);
+    } else if (Op.isImmModifier()) {
+      OptionalIdx[Op.getImmTy()] = I;
+    } else {
+      Op.addRegOrImmOperands(Inst, 1);
+    }
+  }
+
+  // Insert CBSZ and BLGP operands for F8F6F4 variants
+  int InsertPos = AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::cbsz);
+  addOptionalImmOperand(Inst, Operands, OptionalIdx, AMDGPUOperand::ImmTyCBSZ,
+                        0, InsertPos);
+  InsertPos = AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::blgp);
+  addOptionalImmOperand(Inst, Operands, OptionalIdx, AMDGPUOperand::ImmTyBLGP,
+                        0, InsertPos);
+
+  // Add dummy src_modifiers
+  Inst.addOperand(MCOperand::createImm(0));
+  Inst.addOperand(MCOperand::createImm(0));
+
+  // Handle op_sel fields
+
+  unsigned OpSel = 0;
+  auto OpselIdx = OptionalIdx.find(AMDGPUOperand::ImmTyOpSel);
+  if (OpselIdx != OptionalIdx.end())
+    OpSel = static_cast<const AMDGPUOperand &>(*Operands[OpselIdx->second])
+                .getImm();
+
+  unsigned OpSelHi = 0;
+  auto OpselHiIdx = OptionalIdx.find(AMDGPUOperand::ImmTyOpSelHi);
+  if (OpselHiIdx != OptionalIdx.end())
+    OpSelHi = static_cast<const AMDGPUOperand &>(*Operands[OpselHiIdx->second])
+                  .getImm();
----------------
arsenm wrote:

```suggestion
  if (OpselHiIdx != OptionalIdx.end()) {
    OpSelHi = static_cast<const AMDGPUOperand &>(*Operands[OpselHiIdx->second])
                  .getImm();
  }                  
```

https://github.com/llvm/llvm-project/pull/140183