[llvm] [GISel][CombinerHelper] Push freeze through non-poison-producing operands (PR #90618)

[Matt Arsenault via llvm-commits]

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@@ -223,6 +223,64 @@ void CombinerHelper::applyCombineCopy(MachineInstr &MI) {
   replaceRegWith(MRI, DstReg, SrcReg);
 }
 
+bool CombinerHelper::matchFreezeOfSingleMaybePoisonOperand(
+    MachineInstr &MI, BuildFnTy &MatchInfo) {
+  // Ported from InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating
+  Register DstOp = MI.getOperand(0).getReg();
+  Register OrigOp = MI.getOperand(1).getReg();
+
+  if (OrigOp.isPhysical() || !MRI.hasOneNonDBGUse(OrigOp))
+    return false;
+
+  MachineInstr *OrigDef = MRI.getUniqueVRegDef(OrigOp);
+  // Avoid trying to fold G_PHI, G_UNMERGE_VALUES, G_FREEZE (the latter is
+  // handled by idempotent_prop)
+  if (!OrigDef || OrigDef->isPHI() || isa<GUnmerge>(OrigDef) ||
+      isa<GFreeze>(OrigDef))
+    return false;
+
+  if (canCreateUndefOrPoison(OrigOp, MRI))
+    return false;
+
+  std::optional<MachineOperand> MaybePoisonOperand = std::nullopt;
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arsenm wrote:

Don't need the initializer 

https://github.com/llvm/llvm-project/pull/90618