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[InstCombine] Propagate neg nsw when folding abs(-x) to abs(x) #150460

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Merged
merged 1 commit into from
Jul 24, 2025
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[InstCombine] Propagate neg nsw when folding abs(-x) to abs(x) #150460

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6 changes: 4 additions & 2 deletions llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1830,10 +1830,12 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
bool IntMinIsPoison = cast<Constant>(II->getArgOperand(1))->isOneValue();

// abs(-x) -> abs(x)
// TODO: Copy nsw if it was present on the neg?
Value *X;
if (match(IIOperand, m_Neg(m_Value(X))))
if (match(IIOperand, m_Neg(m_Value(X)))) {
if (cast<Instruction>(IIOperand)->hasNoSignedWrap() || IntMinIsPoison)
replaceOperand(*II, 1, Builder.getTrue());
return replaceOperand(*II, 0, X);
}
if (match(IIOperand, m_c_Select(m_Neg(m_Value(X)), m_Deferred(X))))
return replaceOperand(*II, 0, X);

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2 changes: 1 addition & 1 deletion llvm/test/Transforms/InstCombine/abs-intrinsic.ll
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Expand Up @@ -229,7 +229,7 @@ define i32 @abs_of_neg(i32 %x) {

define <4 x i32> @abs_of_neg_vec(<4 x i32> %x) {
; CHECK-LABEL: @abs_of_neg_vec(
; CHECK-NEXT: [[B:%.*]] = call <4 x i32> @llvm.abs.v4i32(<4 x i32> [[X:%.*]], i1 false)
; CHECK-NEXT: [[B:%.*]] = call <4 x i32> @llvm.abs.v4i32(<4 x i32> [[X:%.*]], i1 true)
; CHECK-NEXT: ret <4 x i32> [[B]]
;
%a = sub nsw <4 x i32> zeroinitializer, %x
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