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[InstCombine] intersect nsz and ninf fast-math-flags (FMF) for fneg(fdiv) fold 

https://alive2.llvm.org/ce/z/3KPvih

https://llvm.org/PR49654
This commit is contained in:
Sanjay Patel 2021-06-07 13:05:04 -04:00
parent 519e98cd9a
commit 4675beaa21
2 changed files with 15 additions and 5 deletions
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14
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -2143,9 +2143,19 @@ static Instruction *foldFNegIntoConstant(Instruction &I) {
if (match(FNegOp, m_FDiv(m_Value(X), m_Constant(C)))) if (match(FNegOp, m_FDiv(m_Value(X), m_Constant(C))))
return BinaryOperator::CreateFDivFMF(X, ConstantExpr::getFNeg(C), &I); return BinaryOperator::CreateFDivFMF(X, ConstantExpr::getFNeg(C), &I);
// -(C / X) --> (-C) / X // -(C / X) --> (-C) / X
if (match(FNegOp, m_FDiv(m_Constant(C), m_Value(X)))) if (match(FNegOp, m_FDiv(m_Constant(C), m_Value(X)))) {
return BinaryOperator::CreateFDivFMF(ConstantExpr::getFNeg(C), X, &I); Instruction *FDiv =
BinaryOperator::CreateFDivFMF(ConstantExpr::getFNeg(C), X, &I);
// Intersect 'nsz' and 'ninf' because those special value exceptions may not
// apply to the fdiv. Everything else propagates from the fneg.
// TODO: We could propagate nsz/ninf from fdiv alone?
FastMathFlags FMF = I.getFastMathFlags();
FastMathFlags OpFMF = FNegOp->getFastMathFlags();
FDiv->setHasNoSignedZeros(FMF.noSignedZeros() & OpFMF.noSignedZeros());
FDiv->setHasNoInfs(FMF.noInfs() & OpFMF.noInfs());
return FDiv;
}
// With NSZ [ counter-example with -0.0: -(-0.0 + 0.0) != 0.0 + -0.0 ]: // With NSZ [ counter-example with -0.0: -(-0.0 + 0.0) != 0.0 + -0.0 ]:
// -(X + C) --> -X + -C --> -C - X // -(X + C) --> -X + -C --> -C - X
if (I.hasNoSignedZeros() && match(FNegOp, m_FAdd(m_Value(X), m_Constant(C)))) if (I.hasNoSignedZeros() && match(FNegOp, m_FAdd(m_Value(X), m_Constant(C))))

6
llvm/test/Transforms/InstCombine/fneg.ll
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@ -237,7 +237,7 @@ define float @fdiv_op0_constant_fneg_fast_fast(float %x) {
define float @fdiv_op0_constant_fneg_fast(float %x) { define float @fdiv_op0_constant_fneg_fast(float %x) {
; CHECK-LABEL: @fdiv_op0_constant_fneg_fast( ; CHECK-LABEL: @fdiv_op0_constant_fneg_fast(
; CHECK-NEXT: [[R:%.*]] = fdiv fast float -4.200000e+01, [[X:%.*]] ; CHECK-NEXT: [[R:%.*]] = fdiv reassoc nnan arcp contract afn float -4.200000e+01, [[X:%.*]]
; CHECK-NEXT: ret float [[R]] ; CHECK-NEXT: ret float [[R]]
; ;
%d = fdiv float 42.0, %x %d = fdiv float 42.0, %x
@ -257,7 +257,7 @@ define float @fdiv_op0_constant_fneg_nsz_nsz(float %x) {
define float @fdiv_op0_constant_fneg_nsz(float %x) { define float @fdiv_op0_constant_fneg_nsz(float %x) {
; CHECK-LABEL: @fdiv_op0_constant_fneg_nsz( ; CHECK-LABEL: @fdiv_op0_constant_fneg_nsz(
; CHECK-NEXT: [[R:%.*]] = fdiv nsz float -4.200000e+01, [[X:%.*]] ; CHECK-NEXT: [[R:%.*]] = fdiv float -4.200000e+01, [[X:%.*]]
; CHECK-NEXT: ret float [[R]] ; CHECK-NEXT: ret float [[R]]
; ;
%d = fdiv float 42.0, %x %d = fdiv float 42.0, %x
@ -277,7 +277,7 @@ define float @fdiv_op0_constant_fneg_ninf_ninf(float %x) {
define float @fdiv_op0_constant_fneg_ninf(float %x) { define float @fdiv_op0_constant_fneg_ninf(float %x) {
; CHECK-LABEL: @fdiv_op0_constant_fneg_ninf( ; CHECK-LABEL: @fdiv_op0_constant_fneg_ninf(
; CHECK-NEXT: [[R:%.*]] = fdiv ninf float -4.200000e+01, [[X:%.*]] ; CHECK-NEXT: [[R:%.*]] = fdiv float -4.200000e+01, [[X:%.*]]
; CHECK-NEXT: ret float [[R]] ; CHECK-NEXT: ret float [[R]]
; ;
%d = fdiv float 42.0, %x %d = fdiv float 42.0, %x