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

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

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e325b41
[InstCombine] Precommit test
c-rhodes Jun 23, 2025
110cb6e
[InstCombine] Treat identical operands as one in pushFreezeToPreventP…
c-rhodes Jun 23, 2025
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4 changes: 3 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4774,7 +4774,9 @@ InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
Use *MaybePoisonOperand = nullptr;
for (Use &U : OrigOpInst->operands()) {
if (isa<MetadataAsValue>(U.get()) ||
isGuaranteedNotToBeUndefOrPoison(U.get()))
isGuaranteedNotToBeUndefOrPoison(U.get()) ||
// Treat identical operands as a single operand.
(MaybePoisonOperand && MaybePoisonOperand->get() == U.get()))
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The code below is still only replacing one of the uses. We should be replacing all of them.

You kind of get away with it because we'll later try to freeze other uses in a separate transform, but this needs to be individually correct.

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You should probably switch this code from working on Use* to working on Value*.

continue;
if (!MaybePoisonOperand)
MaybePoisonOperand = &U;
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11 changes: 11 additions & 0 deletions llvm/test/Transforms/InstCombine/freeze.ll
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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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