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[InstCombine] Pull vector reverse through fneg #146349

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Merged
merged 1 commit into from
Jun 30, 2025
+10 −20
Merged

[InstCombine] Pull vector reverse through fneg #146349

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6 changes: 6 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3049,6 +3049,12 @@ Instruction *InstCombinerImpl::visitFNeg(UnaryOperator &I) {
if (match(OneUse, m_Shuffle(m_Value(X), m_Poison(), m_Mask(Mask))))
return new ShuffleVectorInst(Builder.CreateFNegFMF(X, &I), Mask);

// fneg (reverse x) --> reverse (fneg x)
if (match(OneUse, m_VecReverse(m_Value(X)))) {
Value *Reverse = Builder.CreateVectorReverse(Builder.CreateFNegFMF(X, &I));
return replaceInstUsesWith(I, Reverse);
}

return nullptr;
}

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18 changes: 1 addition & 17 deletions llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Expand Up @@ -3549,30 +3549,14 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
}
break;
}
case Intrinsic::vector_reverse: {
Value *Vec = II->getArgOperand(0);
// Note: We canonicalize reverse after binops, so we don't need a
// corresponding binop case here. TODO: Consider canonicalizing
// reverse after fneg?

// rev(unop rev(X)) --> unop X
Value *X;
if (match(Vec, m_OneUse(m_UnOp(m_VecReverse(m_Value(X)))))) {
auto *OldUnOp = cast<UnaryOperator>(Vec);
auto *NewUnOp = UnaryOperator::CreateWithCopiedFlags(
OldUnOp->getOpcode(), X, OldUnOp, OldUnOp->getName(),
II->getIterator());
return replaceInstUsesWith(CI, NewUnOp);
}
break;
}
case Intrinsic::experimental_vp_reverse: {
Value *X;
Value *Vec = II->getArgOperand(0);
Value *Mask = II->getArgOperand(1);
if (!match(Mask, m_AllOnes()))
break;
Value *EVL = II->getArgOperand(2);
// TODO: Canonicalize experimental.vp.reverse after unop/binops?
// rev(unop rev(X)) --> unop X
if (match(Vec,
m_OneUse(m_UnOp(m_Intrinsic<Intrinsic::experimental_vp_reverse>(
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6 changes: 3 additions & 3 deletions llvm/test/Transforms/InstCombine/vector-reverse.ll
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Expand Up @@ -161,9 +161,9 @@ define <vscale x 4 x i32> @binop_reverse_splat_LHS_1(<vscale x 4 x i32> %a, i32

define <vscale x 4 x float> @unop_reverse(<vscale x 4 x float> %a) {
; CHECK-LABEL: @unop_reverse(
; CHECK-NEXT: [[A_REV:%.*]] = tail call <vscale x 4 x float> @llvm.vector.reverse.nxv4f32(<vscale x 4 x float> [[A:%.*]])
; CHECK-NEXT: [[NEG:%.*]] = fneg fast <vscale x 4 x float> [[A_REV]]
; CHECK-NEXT: ret <vscale x 4 x float> [[NEG]]
; CHECK-NEXT: [[NEG:%.*]] = fneg fast <vscale x 4 x float> [[A_REV:%.*]]
; CHECK-NEXT: [[NEG1:%.*]] = call <vscale x 4 x float> @llvm.vector.reverse.nxv4f32(<vscale x 4 x float> [[NEG]])
; CHECK-NEXT: ret <vscale x 4 x float> [[NEG1]]
;
%a.rev = tail call <vscale x 4 x float> @llvm.vector.reverse.nxv4f32(<vscale x 4 x float> %a)
%neg = fneg fast <vscale x 4 x float> %a.rev
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