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[InstCombine] Fix poison safety of folding shufflevector into select #115483

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Merged
merged 2 commits into from
Nov 10, 2024
Merged

[InstCombine] Fix poison safety of folding shufflevector into select #115483

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3f2be7a
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Nov 8, 2024
24ee5fc
[InstCombine] Fix poison safety of folding shufflevector into select
dtcxzyw Nov 8, 2024
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4 changes: 3 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2904,7 +2904,9 @@ Instruction *InstCombinerImpl::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
if (auto *SI = dyn_cast<SelectInst>(LHS)) {
// We cannot do this fold for elementwise select since ShuffleVector is
// not elementwise.
if (SI->getCondition()->getType()->isIntegerTy()) {
if (SI->getCondition()->getType()->isIntegerTy() &&
(isa<PoisonValue>(RHS) ||
isGuaranteedNotToBePoison(SI->getCondition()))) {
if (Instruction *I = FoldOpIntoSelect(SVI, SI))
return I;
}
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12 changes: 12 additions & 0 deletions llvm/test/Transforms/InstCombine/vec_shuffle.ll
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Expand Up @@ -2411,6 +2411,18 @@ define <4 x i32> @shuf_same_length_vec_select(<4 x i1> %cond) {
ret <4 x i32> %shuf
}

; Make sure we do not fold in this case.
define <4 x i8> @shuf_cmp_may_be_poison(<4 x i8> %x, <4 x i8> %y, i1 %cmp) {
; CHECK-LABEL: @shuf_cmp_may_be_poison(
; CHECK-NEXT: [[Y:%.*]] = select i1 [[CMP:%.*]], <4 x i8> [[Y1:%.*]], <4 x i8> <i8 0, i8 poison, i8 0, i8 poison>
; CHECK-NEXT: [[TMP1:%.*]] = shufflevector <4 x i8> [[Y]], <4 x i8> <i8 poison, i8 1, i8 poison, i8 3>, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
; CHECK-NEXT: ret <4 x i8> [[TMP1]]
;
%sel = select i1 %cmp, <4 x i8> %y, <4 x i8> <i8 0, i8 poison, i8 0, i8 poison>
%shuf = shufflevector <4 x i8> %sel, <4 x i8> <i8 poison, i8 1, i8 poison, i8 3>, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
ret <4 x i8> %shuf
}

declare i1 @cond()
declare <4 x i32> @value()

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