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[InstCombine] Revert FSub optimization from #157757 #158315

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Merged
merged 1 commit into from
Sep 12, 2025
Merged

[InstCombine] Revert FSub optimization from #157757 #158315

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10 changes: 0 additions & 10 deletions llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3155,16 +3155,6 @@ Instruction *InstCombinerImpl::visitFSub(BinaryOperator &I) {
Value *X, *Y;
Constant *C;

// B = fsub A, 0.0
// Z = Op B
// can be transformed into
// Z = Op A
// Where Op is such that we can ignore sign of 0 in fsub
Value *A;
if (match(&I, m_OneUse(m_FSub(m_Value(A), m_AnyZeroFP()))) &&
canIgnoreSignBitOfZero(*I.use_begin()))
return replaceInstUsesWith(I, A);

Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
// If Op0 is not -0.0 or we can ignore -0.0: Z - (X - Y) --> Z + (Y - X)
// Canonicalize to fadd to make analysis easier.
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11 changes: 0 additions & 11 deletions llvm/test/Transforms/InstCombine/fold-fadd-with-zero-gh154238.ll
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Expand Up @@ -24,14 +24,3 @@ define float @src2(float %arg1) {
%v4 = fsub float %v2, %v3
ret float %v4
}

define float @src_sub(float %arg1) {
; CHECK-LABEL: define float @src_sub(
; CHECK-SAME: float [[ARG1:%.*]]) {
; CHECK-NEXT: [[V3:%.*]] = call float @llvm.fabs.f32(float [[ARG1]])
; CHECK-NEXT: ret float [[V3]]
;
%v2 = fsub float %arg1, 0.000000e+00
%v3 = call float @llvm.fabs.f32(float %v2)
ret float %v3
}
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