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[InstCombine] fneg(X + C) --> -C - X 

This is 1 of the potential folds uncovered by extending D72521.

We don't seem to do this in the backend either (unless I'm not
seeing some target-specific transform).

icc and gcc (appears to be target-specific) do this transform.

Differential Revision: https://reviews.llvm.org/D73057
This commit is contained in:
Sanjay Patel 2020-01-22 09:29:19 -05:00
parent dc69265eea
commit 0ade2abdb0
2 changed files with 44 additions and 12 deletions
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6
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -2132,6 +2132,12 @@ static Instruction *foldFNegIntoConstant(Instruction &I) {
if (match(&I, m_FNeg(m_OneUse(m_FDiv(m_Constant(C), m_Value(X))))))
return BinaryOperator::CreateFDivFMF(ConstantExpr::getFNeg(C), X, &I);
// With NSZ [ counter-example with -0.0: -(-0.0 + 0.0) != 0.0 + -0.0 ]:
// -(X + C) --> -X + -C --> -C - X
if (I.hasNoSignedZeros() &&
match(&I, m_FNeg(m_OneUse(m_FAdd(m_Value(X), m_Constant(C))))))
return BinaryOperator::CreateFSubFMF(ConstantExpr::getFNeg(C), X, &I);
return nullptr;
}

50
llvm/test/Transforms/InstCombine/fneg.ll
View File

@ -378,6 +378,8 @@ define float @fneg_fneg_sel_extra_use3(float %x, float %y, i1 %cond) {
ret float %sel
}
; Negative test
define float @fneg_fadd_constant(float %x) {
; CHECK-LABEL: @fneg_fadd_constant(
; CHECK-NEXT: [[A:%.*]] = fadd float [[X:%.*]], 4.200000e+01
@ -389,6 +391,8 @@ define float @fneg_fadd_constant(float %x) {
ret float %r
}
; Negative test
define float @fake_nsz_fadd_constant(float %x) {
; CHECK-LABEL: @fake_nsz_fadd_constant(
; CHECK-NEXT: [[A:%.*]] = fadd float [[X:%.*]], 4.200000e+01
@ -400,12 +404,11 @@ define float @fake_nsz_fadd_constant(float %x) {
ret float %r
}
; TODO: -(X + C) --> -C - X
; -(X + C) --> -C - X
define float @fneg_nsz_fadd_constant(float %x) {
; CHECK-LABEL: @fneg_nsz_fadd_constant(
; CHECK-NEXT: [[A:%.*]] = fadd float [[X:%.*]], 4.200000e+01
; CHECK-NEXT: [[R:%.*]] = fneg nsz float [[A]]
; CHECK-NEXT: [[R:%.*]] = fsub nsz float -4.200000e+01, [[X:%.*]]
; CHECK-NEXT: ret float [[R]]
;
%a = fadd float %x, 42.0
@ -413,12 +416,11 @@ define float @fneg_nsz_fadd_constant(float %x) {
ret float %r
}
; TODO: -(X + C) --> -C - X
; -(X + C) --> -C - X
define float @fake_fneg_nsz_fadd_constant(float %x) {
; CHECK-LABEL: @fake_fneg_nsz_fadd_constant(
; CHECK-NEXT: [[A:%.*]] = fadd float [[X:%.*]], 4.200000e+01
; CHECK-NEXT: [[R:%.*]] = fsub fast float -0.000000e+00, [[A]]
; CHECK-NEXT: [[R:%.*]] = fsub fast float -4.200000e+01, [[X:%.*]]
; CHECK-NEXT: ret float [[R]]
;
%a = fadd float %x, 42.0
@ -426,6 +428,8 @@ define float @fake_fneg_nsz_fadd_constant(float %x) {
ret float %r
}
; Negative test
define float @fneg_nsz_fadd_constant_extra_use(float %x) {
; CHECK-LABEL: @fneg_nsz_fadd_constant_extra_use(
; CHECK-NEXT: [[A:%.*]] = fadd float [[X:%.*]], 4.200000e+01
@ -439,6 +443,8 @@ define float @fneg_nsz_fadd_constant_extra_use(float %x) {
ret float %r
}
; Negative test
define float @fake_fneg_nsz_fadd_constant_extra_use(float %x) {
; CHECK-LABEL: @fake_fneg_nsz_fadd_constant_extra_use(
; CHECK-NEXT: [[A:%.*]] = fadd float [[X:%.*]], 4.200000e+01
@ -452,12 +458,11 @@ define float @fake_fneg_nsz_fadd_constant_extra_use(float %x) {
ret float %r
}
; TODO: -(X + C) --> -C - X
; -(X + C) --> -C - X
define <2 x float> @fneg_nsz_fadd_constant_vec(<2 x float> %x) {
; CHECK-LABEL: @fneg_nsz_fadd_constant_vec(
; CHECK-NEXT: [[A:%.*]] = fadd <2 x float> [[X:%.*]], <float 4.200000e+01, float 4.300000e+01>
; CHECK-NEXT: [[R:%.*]] = fneg reassoc nnan nsz <2 x float> [[A]]
; CHECK-NEXT: [[R:%.*]] = fsub reassoc nnan nsz <2 x float> <float -4.200000e+01, float -4.300000e+01>, [[X:%.*]]
; CHECK-NEXT: ret <2 x float> [[R]]
;
%a = fadd <2 x float> %x, <float 42.0, float 43.0>
@ -465,15 +470,36 @@ define <2 x float> @fneg_nsz_fadd_constant_vec(<2 x float> %x) {
ret <2 x float> %r
}
; TODO: -(X + C) --> -C - X
; -(X + C) --> -C - X
define <2 x float> @fake_fneg_nsz_fadd_constant_vec(<2 x float> %x) {
; CHECK-LABEL: @fake_fneg_nsz_fadd_constant_vec(
; CHECK-NEXT: [[A:%.*]] = fadd <2 x float> [[X:%.*]], <float 4.200000e+01, float undef>
; CHECK-NEXT: [[R:%.*]] = fsub nsz <2 x float> <float undef, float -0.000000e+00>, [[A]]
; CHECK-NEXT: [[R:%.*]] = fsub nsz <2 x float> <float -4.200000e+01, float undef>, [[X:%.*]]
; CHECK-NEXT: ret <2 x float> [[R]]
;
%a = fadd <2 x float> %x, <float 42.0, float undef>
%r = fsub nsz <2 x float> <float undef, float -0.0>, %a
ret <2 x float> %r
}
@g = external global i16, align 1
define float @fneg_nsz_fadd_constant_expr(float %x) {
; CHECK-LABEL: @fneg_nsz_fadd_constant_expr(
; CHECK-NEXT: [[R:%.*]] = fsub nsz float fneg (float bitcast (i32 ptrtoint (i16* @g to i32) to float)), [[X:%.*]]
; CHECK-NEXT: ret float [[R]]
;
%a = fadd float %x, bitcast (i32 ptrtoint (i16* @g to i32) to float)
%r = fneg nsz float %a
ret float %r
}
define float @fake_fneg_nsz_fadd_constant_expr(float %x) {
; CHECK-LABEL: @fake_fneg_nsz_fadd_constant_expr(
; CHECK-NEXT: [[R:%.*]] = fsub nsz float fneg (float bitcast (i32 ptrtoint (i16* @g to i32) to float)), [[X:%.*]]
; CHECK-NEXT: ret float [[R]]
;
%a = fadd float %x, bitcast (i32 ptrtoint (i16* @g to i32) to float)
%r = fsub nsz float -0.0, %a
ret float %r
}