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[InstCombine] Handle -(X-Y) --> (Y-X) for unary fneg when NSZ

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Differential Revision: https://reviews.llvm.org/D62612

llvm-svn: 363082
This commit is contained in:
Cameron McInally 2019-06-11 16:21:21 +00:00
parent f743742a51
commit e131342efa
2 changed files with 11 additions and 4 deletions
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11
lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1857,13 +1857,22 @@ static Instruction *foldFNegIntoConstant(Instruction &I) {
}
Instruction *InstCombiner::visitFNeg(UnaryOperator &I) {
if (Value *V = SimplifyFNegInst(I.getOperand(0), I.getFastMathFlags(),
Value *Op = I.getOperand(0);
if (Value *V = SimplifyFNegInst(Op, I.getFastMathFlags(),
SQ.getWithInstruction(&I)))
return replaceInstUsesWith(I, V);
if (Instruction *X = foldFNegIntoConstant(I))
return X;
Value *X, *Y;
// If we can ignore the sign of zeros: -(X - Y) --> (Y - X)
if (I.hasNoSignedZeros() &&
match(Op, m_OneUse(m_FSub(m_Value(X), m_Value(Y)))))
return BinaryOperator::CreateFSubFMF(Y, X, &I);
return nullptr;
}

4
test/Transforms/InstCombine/fsub.ll
View File

@ -38,11 +38,9 @@ define float @neg_sub_nsz(float %x, float %y) {
ret float %t2
}
; FIXME: This combine isn't working.
define float @unary_neg_sub_nsz(float %x, float %y) {
; CHECK-LABEL: @unary_neg_sub_nsz(
; CHECK-NEXT: [[T1:%.*]] = fsub float [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[T2:%.*]] = fneg nsz float [[T1]]
; CHECK-NEXT: [[T2:%.*]] = fsub nsz float [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret float [[T2]]
;
%t1 = fsub float %x, %y