[llvm] [AMDGPU] Enable CSE in the GlobalISel post-legalizer combiner (PR #217258)

[Matt Arsenault via llvm-commits]

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@@ -189,6 +189,13 @@ bool CombinerHelper::isConstantLegalOrBeforeLegalizer(const LLT Ty) const {
 
 void CombinerHelper::replaceRegWith(MachineRegisterInfo &MRI, Register FromReg,
                                     Register ToReg) const {
+  // constrainRegAttrs may change attributes that are part of the CSE profile
+  // for every instruction that references ToReg.
+  SmallVector<MachineInstr *, 4> ToRegInstrs;
+  for (MachineInstr &MI : MRI.reg_instructions(ToReg)) {
+    Observer.changingInstr(MI);
+    ToRegInstrs.push_back(&MI);
+  }
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arsenm wrote:

Should not need to do this

https://github.com/llvm/llvm-project/pull/217258