maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[InstCombine] fold fneg into constant operand of fmul/fdiv 

This accounts for the missing IR fold noted in D50195. We don't need any fast-math to enable the negation transform. 
FP negation can always be folded into an fmul/fdiv constant to eliminate the fneg.

I've limited this to one-use to ensure that we are eliminating an instruction rather than replacing fneg by a 
potentially expensive fdiv or fmul.

Differential Revision: https://reviews.llvm.org/D50417

llvm-svn: 339248
This commit is contained in:
Sanjay Patel 2018-08-08 14:29:08 +00:00
parent 9f5b8f093e
commit a194b2d2ff
3 changed files with 29 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1847,13 +1847,27 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
if (I.hasNoSignedZeros() && match(Op0, m_PosZeroFP()))
return BinaryOperator::CreateFNegFMF(Op1, &I);
Value *X, *Y;
Constant *C;
// Fold negation into constant operand. This is limited with one-use because
// fneg is assumed better for analysis and cheaper in codegen than fmul/fdiv.
// -(X * C) --> X * (-C)
if (match(&I, m_FNeg(m_OneUse(m_FMul(m_Value(X), m_Constant(C))))))
return BinaryOperator::CreateFMulFMF(X, ConstantExpr::getFNeg(C), &I);
// -(X / C) --> X / (-C)
if (match(&I, m_FNeg(m_OneUse(m_FDiv(m_Value(X), m_Constant(C))))))
return BinaryOperator::CreateFDivFMF(X, ConstantExpr::getFNeg(C), &I);
// -(C / X) --> (-C) / X
if (match(&I, m_FNeg(m_OneUse(m_FDiv(m_Constant(C), m_Value(X))))))
return BinaryOperator::CreateFDivFMF(ConstantExpr::getFNeg(C), X, &I);
// If Op0 is not -0.0 or we can ignore -0.0: Z - (X - Y) --> Z + (Y - X)
// Canonicalize to fadd to make analysis easier.
// This can also help codegen because fadd is commutative.
// Note that if this fsub was really an fneg, the fadd with -0.0 will get
// killed later. We still limit that particular transform with 'hasOneUse'
// because an fneg is assumed better/cheaper than a generic fsub.
Value *X, *Y;
if (I.hasNoSignedZeros() || CannotBeNegativeZero(Op0, SQ.TLI)) {
if (match(Op1, m_OneUse(m_FSub(m_Value(X), m_Value(Y))))) {
Value *NewSub = Builder.CreateFSubFMF(Y, X, &I);
@ -1869,7 +1883,6 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
// X - C --> X + (-C)
// But don't transform constant expressions because there's an inverse fold
// for X + (-Y) --> X - Y.
Constant *C;
if (match(Op1, m_Constant(C)) && !isa<ConstantExpr>(Op1))
return BinaryOperator::CreateFAddFMF(Op0, ConstantExpr::getFNeg(C), &I);

27
llvm/test/Transforms/InstCombine/fneg.ll
View File

@ -7,8 +7,7 @@ declare void @use(float)
define float @fmul_fneg(float %x) {
; CHECK-LABEL: @fmul_fneg(
; CHECK-NEXT: [[M:%.*]] = fmul float [[X:%.*]], 4.200000e+01
; CHECK-NEXT: [[R:%.*]] = fsub float -0.000000e+00, [[M]]
; CHECK-NEXT: [[R:%.*]] = fmul float [[X:%.*]], -4.200000e+01
; CHECK-NEXT: ret float [[R]]
;
%m = fmul float %x, 42.0
@ -20,8 +19,7 @@ define float @fmul_fneg(float %x) {
define float @fmul_fneg_fmf(float %x) {
; CHECK-LABEL: @fmul_fneg_fmf(
; CHECK-NEXT: [[M:%.*]] = fmul float [[X:%.*]], 4.200000e+01
; CHECK-NEXT: [[R:%.*]] = fsub reassoc nsz float -0.000000e+00, [[M]]
; CHECK-NEXT: [[R:%.*]] = fmul reassoc nsz float [[X:%.*]], -4.200000e+01
; CHECK-NEXT: ret float [[R]]
;
%m = fmul float %x, 42.0
@ -48,8 +46,7 @@ define float @fmul_fneg_extra_use(float %x) {
define <4 x double> @fmul_fneg_vec(<4 x double> %x) {
; CHECK-LABEL: @fmul_fneg_vec(
; CHECK-NEXT: [[M:%.*]] = fmul <4 x double> [[X:%.*]], <double 4.200000e+01, double 0xFF80000000000000, double 0x7FF0000000000000, double undef>
; CHECK-NEXT: [[R:%.*]] = fsub <4 x double> <double -0.000000e+00, double -0.000000e+00, double -0.000000e+00, double -0.000000e+00>, [[M]]
; CHECK-NEXT: [[R:%.*]] = fmul <4 x double> [[X:%.*]], <double -4.200000e+01, double 0x7F80000000000000, double 0xFFF0000000000000, double 0x7FF8000000000000>
; CHECK-NEXT: ret <4 x double> [[R]]
;
%m = fmul <4 x double> %x, <double 42.0, double 0x7FF80000000000000, double 0x7FF0000000000000, double undef>
@ -61,8 +58,7 @@ define <4 x double> @fmul_fneg_vec(<4 x double> %x) {
define float @fdiv_op1_constant_fneg(float %x) {
; CHECK-LABEL: @fdiv_op1_constant_fneg(
; CHECK-NEXT: [[D:%.*]] = fdiv float [[X:%.*]], -4.200000e+01
; CHECK-NEXT: [[R:%.*]] = fsub float -0.000000e+00, [[D]]
; CHECK-NEXT: [[R:%.*]] = fdiv float [[X:%.*]], 4.200000e+01
; CHECK-NEXT: ret float [[R]]
;
%d = fdiv float %x, -42.0
@ -74,8 +70,7 @@ define float @fdiv_op1_constant_fneg(float %x) {
define float @fdiv_op1_constant_fneg_fmf(float %x) {
; CHECK-LABEL: @fdiv_op1_constant_fneg_fmf(
; CHECK-NEXT: [[D:%.*]] = fdiv float [[X:%.*]], -4.200000e+01
; CHECK-NEXT: [[R:%.*]] = fsub nnan float -0.000000e+00, [[D]]
; CHECK-NEXT: [[R:%.*]] = fdiv nnan float [[X:%.*]], 4.200000e+01
; CHECK-NEXT: ret float [[R]]
;
%d = fdiv float %x, -42.0
@ -102,8 +97,7 @@ define float @fdiv_op1_constant_fneg_extra_use(float %x) {
define <4 x double> @fdiv_op1_constant_fneg_vec(<4 x double> %x) {
; CHECK-LABEL: @fdiv_op1_constant_fneg_vec(
; CHECK-NEXT: [[D:%.*]] = fdiv <4 x double> [[X:%.*]], <double -4.200000e+01, double 0xFFF800000ABCD000, double 0xFFF0000000000000, double undef>
; CHECK-NEXT: [[R:%.*]] = fsub <4 x double> <double -0.000000e+00, double -0.000000e+00, double -0.000000e+00, double -0.000000e+00>, [[D]]
; CHECK-NEXT: [[R:%.*]] = fdiv <4 x double> [[X:%.*]], <double 4.200000e+01, double 0x7FF800000ABCD000, double 0x7FF0000000000000, double 0x7FF8000000000000>
; CHECK-NEXT: ret <4 x double> [[R]]
;
%d = fdiv <4 x double> %x, <double -42.0, double 0xFFF800000ABCD000, double 0xFFF0000000000000, double undef>
@ -115,8 +109,7 @@ define <4 x double> @fdiv_op1_constant_fneg_vec(<4 x double> %x) {
define float @fdiv_op0_constant_fneg(float %x) {
; CHECK-LABEL: @fdiv_op0_constant_fneg(
; CHECK-NEXT: [[D:%.*]] = fdiv float 4.200000e+01, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = fsub float -0.000000e+00, [[D]]
; CHECK-NEXT: [[R:%.*]] = fdiv float -4.200000e+01, [[X:%.*]]
; CHECK-NEXT: ret float [[R]]
;
%d = fdiv float 42.0, %x
@ -128,8 +121,7 @@ define float @fdiv_op0_constant_fneg(float %x) {
define float @fdiv_op0_constant_fneg_fmf(float %x) {
; CHECK-LABEL: @fdiv_op0_constant_fneg_fmf(
; CHECK-NEXT: [[D:%.*]] = fdiv float 4.200000e+01, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = fsub fast float -0.000000e+00, [[D]]
; CHECK-NEXT: [[R:%.*]] = fdiv fast float -4.200000e+01, [[X:%.*]]
; CHECK-NEXT: ret float [[R]]
;
%d = fdiv float 42.0, %x
@ -156,8 +148,7 @@ define float @fdiv_op0_constant_fneg_extra_use(float %x) {
define <4 x double> @fdiv_op0_constant_fneg_vec(<4 x double> %x) {
; CHECK-LABEL: @fdiv_op0_constant_fneg_vec(
; CHECK-NEXT: [[D:%.*]] = fdiv <4 x double> <double -4.200000e+01, double 0xFF80000000000000, double 0xFFF0000000000000, double undef>, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = fsub <4 x double> <double -0.000000e+00, double -0.000000e+00, double -0.000000e+00, double -0.000000e+00>, [[D]]
; CHECK-NEXT: [[R:%.*]] = fdiv <4 x double> <double 4.200000e+01, double 0x7F80000000000000, double 0x7FF0000000000000, double 0x7FF8000000000000>, [[X:%.*]]
; CHECK-NEXT: ret <4 x double> [[R]]
;
%d = fdiv <4 x double> <double -42.0, double 0x7FF80000000000000, double 0xFFF0000000000000, double undef>, %x

10
llvm/test/Transforms/InstCombine/fsub.ll
View File

@ -60,15 +60,15 @@ define float @sub_sub_nsz(float %x, float %y, float %z) {
ret float %t2
}
; With nsz and reassoc: Y - (X + Y) --> -X
; With nsz and reassoc: Y - ((X * 5) + Y) --> X * -5
define float @sub_add_neg_x(float %x, float %y) {
; CHECK-LABEL: @sub_add_neg_x(
; CHECK-NEXT: [[TMP1:%.*]] = fmul float [[X:%.*]], 5.000000e+00
; CHECK-NEXT: [[T2:%.*]] = fsub reassoc nsz float -0.000000e+00, [[TMP1]]
; CHECK-NEXT: ret float [[T2]]
; CHECK-NEXT: [[TMP1:%.*]] = fmul reassoc nsz float [[X:%.*]], -5.000000e+00
; CHECK-NEXT: ret float [[TMP1]]
;
%mul = fmul float %x, 5.000000e+00
%add = fadd float %mul, %y
%add = fadd float %mul, %y
%r = fsub nsz reassoc float %y, %add
ret float %r
}