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[InstCombine] fold fadd+fneg with fdiv/fmul betweena 

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: 367227
This commit is contained in:
Sanjay Patel 2019-07-29 13:50:25 +00:00
parent 98d281a99f
commit e9ee7b47d4
2 changed files with 26 additions and 8 deletions
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18
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1387,6 +1387,24 @@ Instruction *InstCombiner::visitFAdd(BinaryOperator &I) {
if (match(&I, m_c_FAdd(m_FNeg(m_Value(X)), m_Value(Y))))
return BinaryOperator::CreateFSubFMF(Y, X, &I);
// Similar to above, but look through fmul/fdiv for the negated term.
// (-X * Y) + Z --> Z - (X * Y) [4 commuted variants]
Value *Z;
if (match(&I, m_c_FAdd(m_OneUse(m_c_FMul(m_FNeg(m_Value(X)), m_Value(Y))),
m_Value(Z)))) {
Value *XY = Builder.CreateFMulFMF(X, Y, &I);
return BinaryOperator::CreateFSubFMF(Z, XY, &I);
}
// (-X / Y) + Z --> Z - (X / Y) [2 commuted variants]
// (X / -Y) + Z --> Z - (X / Y) [2 commuted variants]
if (match(&I, m_c_FAdd(m_OneUse(m_FDiv(m_FNeg(m_Value(X)), m_Value(Y))),
m_Value(Z))) ||
match(&I, m_c_FAdd(m_OneUse(m_FDiv(m_Value(X), m_FNeg(m_Value(Y)))),
m_Value(Z)))) {
Value *XY = Builder.CreateFDivFMF(X, Y, &I);
return BinaryOperator::CreateFSubFMF(Z, XY, &I);
}
// Check for (fadd double (sitofp x), y), see if we can merge this into an
// integer add followed by a promotion.
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);

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

@ -246,8 +246,8 @@ define float @fdiv_fneg1_extra_use2(float %x, float %y, float %z) {
; CHECK-LABEL: @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:%.*]] = fadd float [[DIV]], [[Z:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = fdiv float [[X]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fsub float [[Z:%.*]], [[TMP1]]
; CHECK-NEXT: ret float [[R]]
;
%neg = fsub float -0.000000e+00, %x
@ -263,8 +263,8 @@ define float @fdiv_fneg2_extra_use2(float %x, float %y, float %z) {
; CHECK-LABEL: @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:%.*]] = fadd float [[DIV]], [[Z:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = fdiv float [[Y:%.*]], [[X]]
; CHECK-NEXT: [[R:%.*]] = fsub float [[Z:%.*]], [[TMP1]]
; CHECK-NEXT: ret float [[R]]
;
%neg = fsub float -0.000000e+00, %x
@ -280,8 +280,8 @@ define <2 x float> @fmul_fneg1_extra_use2(<2 x float> %x, <2 x float> %y, <2 x f
; CHECK-LABEL: @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:%.*]] = fadd <2 x float> [[MUL]], [[Z:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = fmul <2 x float> [[X]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = fsub <2 x float> [[Z:%.*]], [[TMP1]]
; CHECK-NEXT: ret <2 x float> [[R]]
;
%neg = fsub <2 x float> <float -0.0, float -0.0>, %x
@ -298,8 +298,8 @@ define float @fmul_fneg2_extra_use2(float %x, float %py, float %z) {
; CHECK-NEXT: [[Y:%.*]] = frem float -4.200000e+01, [[PY:%.*]]
; CHECK-NEXT: [[NEG:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
; CHECK-NEXT: call void @use(float [[NEG]])
; CHECK-NEXT: [[MUL:%.*]] = fmul float [[Y]], [[NEG]]
; CHECK-NEXT: [[R:%.*]] = fadd float [[MUL]], [[Z:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = fmul float [[Y]], [[X]]
; CHECK-NEXT: [[R:%.*]] = fsub float [[Z:%.*]], [[TMP1]]
; CHECK-NEXT: ret float [[R]]
;
%y = frem float -42.0, %py ; thwart complexity-based canonicalization