[AMDGPU] NFC. Refactor GISel for cmp intrinsics

[Joe_Nash]

Summary

Combine the logic for fcmp and icmp intrinsics and use operand presence
instead.

[foad]

Looks fine to me.

[kosarev]

Thanks.

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

if (!CmpInst::isIntPredicate(Pred) && !CmpInst::isFPPredicate(Pred)) {
     I.eraseFromParent();
     return RBI.constrainGenericRegister(Dst, *TRI.getBoolRC(), *MRI);
   }
 
   const int Opcode = getV_CMPOpcode(Pred, Size, *Subtarget);
   if (Opcode == -1)
     return false;
 
-  MachineInstr *SelectedMI;
-  if (CmpInst::isFPPredicate(Pred)) {
-    MachineOperand &LHS = I.getOperand(2);
-    MachineOperand &RHS = I.getOperand(3);
-    auto [Src0, Src0Mods] = selectVOP3ModsImpl(LHS);
-    auto [Src1, Src1Mods] = selectVOP3ModsImpl(RHS);
-    Register Src0Reg =
-        copyToVGPRIfSrcFolded(Src0, Src0Mods, LHS, &I, /*ForceVGPR*/ true);
-    Register Src1Reg =
-        copyToVGPRIfSrcFolded(Src1, Src1Mods, RHS, &I, /*ForceVGPR*/ true);
-    SelectedMI = BuildMI(*BB, &I, DL, TII.get(Opcode), Dst)
-                     .addImm(Src0Mods)
-                     .addReg(Src0Reg)
-                     .addImm(Src1Mods)
-                     .addReg(Src1Reg)
-                     .addImm(0); // clamp
-  } else {
-    SelectedMI = BuildMI(*BB, &I, DL, TII.get(Opcode), Dst)
-                     .add(I.getOperand(2))
-                     .add(I.getOperand(3));
-  }
+  MachineInstrBuilder SelectedMI;
+  SelectedMI = BuildMI(*BB, &I, DL, TII.get(Opcode), Dst);
+  if (AMDGPU::hasNamedOperand(Opcode, AMDGPU::OpName::src0_modifiers))
+    SelectedMI.addImm(Src0Mods);
+  SelectedMI.addReg(Src0Reg);
+  if (AMDGPU::hasNamedOperand(Opcode, AMDGPU::OpName::src1_modifiers))
+    SelectedMI.addImm(Src1Mods);
+  SelectedMI.addReg(Src1Reg);
+  if (AMDGPU::hasNamedOperand(Opcode, AMDGPU::OpName::clamp))
+    SelectedMI.addImm(0); // clamp
+  if (AMDGPU::hasNamedOperand(Opcode, AMDGPU::OpName::op_sel))
+    SelectedMI.addImm(0); // op_sel
 
   RBI.constrainGenericRegister(Dst, *TRI.getBoolRC(), *MRI);
   if (!constrainSelectedInstRegOperands(*SelectedMI, TII, TRI, RBI))
     return false;
 
   I.eraseFromParent();
   return true;
 }