[llvm] [CodeGen] commuteInstruction should update implicit-def (PR #131361)

[Sander de Smalen via llvm-commits]

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@@ -214,6 +215,24 @@ MachineInstr *TargetInstrInfo::commuteInstructionImpl(MachineInstr &MI,
     SubReg0 = SubReg1;
   }
 
+  // For a case like this:
+  //   %0.sub = INST %0.sub(tied), %1.sub, implicit-def %0
+  // we need to update the implicit-def after commuting to result in:
+  //   %1.sub = INST %1.sub(tied), %0.sub, implicit-def %1
+  SmallVector<unsigned> UpdateImplicitDefIdx;
+  if (HasDef && MI.hasImplicitDef() && MI.getOperand(0).getReg() != Reg0) {
+    const TargetRegisterInfo *TRI =
+        MI.getMF()->getSubtarget().getRegisterInfo();
+    Register OrigReg0 = MI.getOperand(0).getReg();
+    for (auto [OpNo, MO] : llvm::enumerate(MI.implicit_operands())) {
+      Register ImplReg = MO.getReg();
+      if ((ImplReg.isVirtual() && ImplReg == OrigReg0) ||
+          (ImplReg.isPhysical() && OrigReg0.isPhysical() &&
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sdesmalen-arm wrote:

There was actually a SystemZ test that showed a minor regression when I did a `return nullptr` for this case.

https://github.com/llvm/llvm-project/pull/131361