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[InstCombine] Treat identical operands as one in pushFreezeToPreventPoisonFromPropagating #145348

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Merged
merged 4 commits into from
Jul 16, 2025
Merged

[InstCombine] Treat identical operands as one in pushFreezeToPreventPoisonFromPropagating #145348

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97d3aec
[InstCombine] Precommit test
c-rhodes Jun 23, 2025
10e8258
[InstCombine] Treat identical operands as one in pushFreezeToPreventP…
c-rhodes Jun 23, 2025
1e48770
Switch code from working on Use* to Value* and replace all uses
c-rhodes Jul 15, 2025
bac3bf1
address comments
c-rhodes Jul 16, 2025
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17 changes: 9 additions & 8 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4899,13 +4899,14 @@ InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
// If operand is guaranteed not to be poison, there is no need to add freeze
// to the operand. So we first find the operand that is not guaranteed to be
// poison.
Use *MaybePoisonOperand = nullptr;
for (Use &U : OrigOpInst->operands()) {
if (isa<MetadataAsValue>(U.get()) ||
isGuaranteedNotToBeUndefOrPoison(U.get()))
Value *MaybePoisonOperand = nullptr;
for (Value *V : OrigOpInst->operands()) {
if (isa<MetadataAsValue>(V) || isGuaranteedNotToBeUndefOrPoison(V) ||
// Treat identical operands as a single operand.
(MaybePoisonOperand && MaybePoisonOperand == V))
continue;
if (!MaybePoisonOperand)
MaybePoisonOperand = &U;
MaybePoisonOperand = V;
else
return nullptr;
}
Expand All @@ -4917,10 +4918,10 @@ InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
return OrigOp;

Builder.SetInsertPoint(OrigOpInst);
auto *FrozenMaybePoisonOperand = Builder.CreateFreeze(
MaybePoisonOperand->get(), MaybePoisonOperand->get()->getName() + ".fr");
Value *FrozenMaybePoisonOperand = Builder.CreateFreeze(
MaybePoisonOperand, MaybePoisonOperand->getName() + ".fr");

replaceUse(*MaybePoisonOperand, FrozenMaybePoisonOperand);
OrigOpInst->replaceUsesOfWith(MaybePoisonOperand, FrozenMaybePoisonOperand);
return OrigOp;
}

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11 changes: 11 additions & 0 deletions llvm/test/Transforms/InstCombine/freeze.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -142,6 +142,17 @@ define i32 @early_freeze_test3(i32 %v1) {
ret i32 %v4.fr
}

define i32 @early_freeze_test4(i32 %v1) {
; CHECK-LABEL: @early_freeze_test4(
; CHECK-NEXT: [[V2_FR:%.*]] = freeze i32 [[V2:%.*]]
; CHECK-NEXT: [[V3:%.*]] = mul i32 [[V2_FR]], [[V2_FR]]
; CHECK-NEXT: ret i32 [[V3]]
;
%v2 = mul i32 %v1, %v1
%v2.fr = freeze i32 %v2
ret i32 %v2.fr
}

; If replace all dominated uses of v to freeze(v).

define void @freeze_dominated_uses_test1(i32 %v) {
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