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[InstCombine] fold fsub+fneg with fdiv/fmul between 

The backend already does this via isNegatibleForFree(),
but we may want to alter the fneg IR canonicalizations
that currently exist, so we need to try harder to fold
fneg in IR to avoid regressions.

llvm-svn: 367194
This commit is contained in:
Sanjay Patel 2019-07-28 17:10:06 +00:00
parent 2c8098374b
commit 99c57c6daf
2 changed files with 23 additions and 8 deletions
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15
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1964,6 +1964,21 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
if (match(Op1, m_OneUse(m_FPExt(m_FNeg(m_Value(Y))))))
return BinaryOperator::CreateFAddFMF(Op0, Builder.CreateFPExt(Y, Ty), &I);
// Similar to above, but look through fmul/fdiv of the negated value:
// Op0 - (-X * Y) --> Op0 + (X * Y)
// Op0 - (Y * -X) --> Op0 + (X * Y)
if (match(Op1, m_OneUse(m_c_FMul(m_FNeg(m_Value(X)), m_Value(Y))))) {
Value *FMul = Builder.CreateFMulFMF(X, Y, &I);
return BinaryOperator::CreateFAddFMF(Op0, FMul, &I);
}
// Op0 - (-X / Y) --> Op0 + (X / Y)
// Op0 - (X / -Y) --> Op0 + (X / Y)
if (match(Op1, m_OneUse(m_FDiv(m_FNeg(m_Value(X)), m_Value(Y)))) ||
match(Op1, m_OneUse(m_FDiv(m_Value(X), m_FNeg(m_Value(Y)))))) {
Value *FDiv = Builder.CreateFDivFMF(X, Y, &I);
return BinaryOperator::CreateFAddFMF(Op0, FDiv, &I);
}
// Handle special cases for FSub with selects feeding the operation
if (Value *V = SimplifySelectsFeedingBinaryOp(I, Op0, Op1))
return replaceInstUsesWith(I, V);

16
llvm/test/Transforms/InstCombine/fsub.ll
View File

@ -518,8 +518,8 @@ define float @fsub_fdiv_fneg1_extra_use2(float %x, float %y, float %z) {
; CHECK-LABEL: @fsub_fdiv_fneg1_extra_use2(
; CHECK-NEXT: [[NEG:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
; CHECK-NEXT: call void @use(float [[NEG]])
; CHECK-NEXT: [[DIV:%.*]] = fdiv float [[NEG]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fsub float [[Z:%.*]], [[DIV]]
; CHECK-NEXT: [[TMP1:%.*]] = fdiv float [[X]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fadd float [[TMP1]], [[Z:%.*]]
; CHECK-NEXT: ret float [[R]]
;
%neg = fsub float -0.000000e+00, %x
@ -533,8 +533,8 @@ define float @fsub_fdiv_fneg2_extra_use2(float %x, float %y, float %z) {
; CHECK-LABEL: @fsub_fdiv_fneg2_extra_use2(
; CHECK-NEXT: [[NEG:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
; CHECK-NEXT: call void @use(float [[NEG]])
; CHECK-NEXT: [[DIV:%.*]] = fdiv float [[Y:%.*]], [[NEG]]
; CHECK-NEXT: [[R:%.*]] = fsub float [[Z:%.*]], [[DIV]]
; CHECK-NEXT: [[TMP1:%.*]] = fdiv float [[Y:%.*]], [[X]]
; CHECK-NEXT: [[R:%.*]] = fadd float [[TMP1]], [[Z:%.*]]
; CHECK-NEXT: ret float [[R]]
;
%neg = fsub float -0.000000e+00, %x
@ -548,8 +548,8 @@ define <2 x float> @fsub_fmul_fneg1_extra_use2(<2 x float> %x, <2 x float> %y, <
; CHECK-LABEL: @fsub_fmul_fneg1_extra_use2(
; CHECK-NEXT: [[NEG:%.*]] = fsub <2 x float> <float -0.000000e+00, float -0.000000e+00>, [[X:%.*]]
; CHECK-NEXT: call void @use_vec(<2 x float> [[NEG]])
; CHECK-NEXT: [[MUL:%.*]] = fmul <2 x float> [[NEG]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fsub <2 x float> [[Z:%.*]], [[MUL]]
; CHECK-NEXT: [[TMP1:%.*]] = fmul <2 x float> [[X]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fadd <2 x float> [[TMP1]], [[Z:%.*]]
; CHECK-NEXT: ret <2 x float> [[R]]
;
%neg = fsub <2 x float> <float -0.0, float -0.0>, %x
@ -563,8 +563,8 @@ define float @fsub_fmul_fneg2_extra_use2(float %x, float %y, float %z) {
; CHECK-LABEL: @fsub_fmul_fneg2_extra_use2(
; CHECK-NEXT: [[NEG:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
; CHECK-NEXT: call void @use(float [[NEG]])
; CHECK-NEXT: [[MUL:%.*]] = fmul float [[NEG]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fsub float [[Z:%.*]], [[MUL]]
; CHECK-NEXT: [[TMP1:%.*]] = fmul float [[X]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fadd float [[TMP1]], [[Z:%.*]]
; CHECK-NEXT: ret float [[R]]
;
%neg = fsub float -0.000000e+00, %x