[llvm] [CodeGen][TII] Allow reassociation on custom operand indices (PR #88306)

[Craig Topper via llvm-commits]

================
@@ -1184,25 +1248,16 @@ void TargetInstrInfo::genAlternativeCodeSequence(
   MachineRegisterInfo &MRI = Root.getMF()->getRegInfo();
 
   // Select the previous instruction in the sequence based on the input pattern.
-  MachineInstr *Prev = nullptr;
-  switch (Pattern) {
-  case MachineCombinerPattern::REASSOC_AX_BY:
-  case MachineCombinerPattern::REASSOC_XA_BY:
-    Prev = MRI.getUniqueVRegDef(Root.getOperand(1).getReg());
-    break;
-  case MachineCombinerPattern::REASSOC_AX_YB:
-  case MachineCombinerPattern::REASSOC_XA_YB:
-    Prev = MRI.getUniqueVRegDef(Root.getOperand(2).getReg());
-    break;
-  default:
-    llvm_unreachable("Unknown pattern for machine combiner");
-  }
+  std::array<unsigned, 5> OpIdx;
+  getReassociateOperandIdx(Root, Pattern, OpIdx);
----------------
topperc wrote:

getReassociateOperandIdx -> getReassociateOperandIndices?

https://github.com/llvm/llvm-project/pull/88306