caio/clang-p2996
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[InstCombine] fold fnegs around select

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This is one of the folds requested in:
https://llvm.org/PR39480

https://alive2.llvm.org/ce/z/NczU3V

Note - this uses the normal FMF propagation logic
(flags transfer from the final value to new/intermediate ops).
It's not clear if this matches what Alive2 implements,
so we may want to adjust one or the other.
This commit is contained in:
Sanjay Patel
2021-05-17 14:27:32 -04:00
parent e9f600f20a
commit 3cdd05e519
2 changed files with 33 additions and 15 deletions
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19
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@@ -2187,6 +2187,25 @@ Instruction *InstCombinerImpl::visitFNeg(UnaryOperator &I) {
if (Instruction *R = hoistFNegAboveFMulFDiv(I, Builder))
return R;
Value *Cond;
if (match(Op, m_OneUse(m_Select(m_Value(Cond), m_Value(X), m_Value(Y))))) {
Value *P;
if (match(X, m_FNeg(m_Value(P)))) {
IRBuilder<>::FastMathFlagGuard FMFG(Builder);
Builder.setFastMathFlags(I.getFastMathFlags());
Value *NegY = Builder.CreateFNegFMF(Y, &I, Y->getName() + ".neg");
Value *NewSel = Builder.CreateSelect(Cond, P, NegY);
return replaceInstUsesWith(I, NewSel);
}
if (match(Y, m_FNeg(m_Value(P)))) {
IRBuilder<>::FastMathFlagGuard FMFG(Builder);
Builder.setFastMathFlags(I.getFastMathFlags());
Value *NegX = Builder.CreateFNegFMF(X, &I, X->getName() + ".neg");
Value *NewSel = Builder.CreateSelect(Cond, NegX, P);
return replaceInstUsesWith(I, NewSel);
}
}
return nullptr;
}

29
llvm/test/Transforms/InstCombine/fneg.ll
View File

@@ -506,10 +506,9 @@ define float @fake_fneg_nsz_fadd_constant_expr(float %x) {
define float @select_fneg_true(float %x, float %y, i1 %b) {
; CHECK-LABEL: @select_fneg_true(
; CHECK-NEXT: [[NX:%.*]] = fneg float [[X:%.*]]
; CHECK-NEXT: [[S:%.*]] = select i1 [[B:%.*]], float [[NX]], float [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fneg float [[S]]
; CHECK-NEXT: ret float [[R]]
; CHECK-NEXT: [[Y_NEG:%.*]] = fneg float [[Y:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[B:%.*]], float [[X:%.*]], float [[Y_NEG]]
; CHECK-NEXT: ret float [[TMP1]]
;
%nx = fneg float %x
%s = select i1 %b, float %nx, float %y
@@ -519,10 +518,9 @@ define float @select_fneg_true(float %x, float %y, i1 %b) {
define <2 x float> @select_fneg_false(<2 x float> %x, <2 x float> %y, <2 x i1> %b) {
; CHECK-LABEL: @select_fneg_false(
; CHECK-NEXT: [[NY:%.*]] = fneg nnan <2 x float> [[Y:%.*]]
; CHECK-NEXT: [[S:%.*]] = select ninf <2 x i1> [[B:%.*]], <2 x float> [[X:%.*]], <2 x float> [[NY]]
; CHECK-NEXT: [[R:%.*]] = fneg nnan nsz <2 x float> [[S]]
; CHECK-NEXT: ret <2 x float> [[R]]
; CHECK-NEXT: [[X_NEG:%.*]] = fneg nnan nsz <2 x float> [[X:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = select nnan nsz <2 x i1> [[B:%.*]], <2 x float> [[X_NEG]], <2 x float> [[Y:%.*]]
; CHECK-NEXT: ret <2 x float> [[TMP1]]
;
%ny = fneg nnan <2 x float> %y
%s = select ninf <2 x i1> %b, <2 x float> %x, <2 x float> %ny
@@ -546,9 +544,9 @@ define float @select_fneg_use1(float %x, float %y, i1 %b) {
; CHECK-LABEL: @select_fneg_use1(
; CHECK-NEXT: [[NX:%.*]] = fneg ninf float [[X:%.*]]
; CHECK-NEXT: call void @use(float [[NX]])
; CHECK-NEXT: [[S:%.*]] = select fast i1 [[B:%.*]], float [[NX]], float [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fneg float [[S]]
; CHECK-NEXT: ret float [[R]]
; CHECK-NEXT: [[Y_NEG:%.*]] = fneg float [[Y:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[B:%.*]], float [[X]], float [[Y_NEG]]
; CHECK-NEXT: ret float [[TMP1]]
;
%nx = fneg ninf float %x
call void @use(float %nx)
@@ -560,10 +558,9 @@ define float @select_fneg_use1(float %x, float %y, i1 %b) {
define float @select_fneg_use2(float %x, float %y, i1 %b) {
; CHECK-LABEL: @select_fneg_use2(
; CHECK-NEXT: call void @use(float [[Y:%.*]])
; CHECK-NEXT: [[NX:%.*]] = fneg nsz float [[X:%.*]]
; CHECK-NEXT: [[S:%.*]] = select ninf i1 [[B:%.*]], float [[NX]], float [[Y]]
; CHECK-NEXT: [[R:%.*]] = fneg fast float [[S]]
; CHECK-NEXT: ret float [[R]]
; CHECK-NEXT: [[Y_NEG:%.*]] = fneg fast float [[Y]]
; CHECK-NEXT: [[TMP1:%.*]] = select fast i1 [[B:%.*]], float [[X:%.*]], float [[Y_NEG]]
; CHECK-NEXT: ret float [[TMP1]]
;
call void @use(float %y)
%nx = fneg nsz float %x
@@ -572,6 +569,8 @@ define float @select_fneg_use2(float %x, float %y, i1 %b) {
ret float %r
}
; Negative test
define float @select_fneg_use3(float %x, float %y, i1 %b) {
; CHECK-LABEL: @select_fneg_use3(
; CHECK-NEXT: [[NX:%.*]] = fneg float [[X:%.*]]