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[InstCombine] Drop noundef in foldSelectCttzCtlz #121692

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Merged
merged 2 commits into from
Jan 5, 2025
Merged

[InstCombine] Drop noundef in foldSelectCttzCtlz #121692

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0e75af8
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Jan 5, 2025
2e5c5eb
[InstCombine] Drop noundef in `foldSelectCttzCtlz`
dtcxzyw Jan 5, 2025
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6 changes: 5 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1225,8 +1225,12 @@ static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
// zext/trunc) have one use (ending at the select), the cttz/ctlz result will
// not be used if the input is zero. Relax to 'zero is poison' for that case.
if (II->hasOneUse() && SelectArg->hasOneUse() &&
!match(II->getArgOperand(1), m_One()))
!match(II->getArgOperand(1), m_One())) {
II->setArgOperand(1, ConstantInt::getTrue(II->getContext()));
// noundef attribute on the intrinsic may no longer be valid.
II->dropUBImplyingAttrsAndMetadata();
IC.addToWorklist(II);
}

return nullptr;
}
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13 changes: 13 additions & 0 deletions llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
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Expand Up @@ -495,6 +495,19 @@ define i32 @test_cttz_not_bw(i32 %x) {
ret i32 %res
}

define i32 @test_cttz_not_bw_noundef(i32 %x) {
; CHECK-LABEL: @test_cttz_not_bw_noundef(
; CHECK-NEXT: [[CT:%.*]] = tail call range(i32 0, 33) i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 true)
; CHECK-NEXT: [[CMP_NOT:%.*]] = icmp eq i32 [[X]], 0
; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP_NOT]], i32 123, i32 [[CT]]
; CHECK-NEXT: ret i32 [[RES]]
;
%ct = tail call noundef i32 @llvm.cttz.i32(i32 %x, i1 false)
%cmp = icmp ne i32 %x, 0
%res = select i1 %cmp, i32 %ct, i32 123
ret i32 %res
}

define i32 @test_cttz_not_bw_multiuse(i32 %x) {
; CHECK-LABEL: @test_cttz_not_bw_multiuse(
; CHECK-NEXT: [[CT:%.*]] = tail call range(i32 0, 33) i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 false)
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