[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

2 files changed, 14 insertions, 23 deletions

diff --git a/llvm/test/Transforms/InstCombine/fneg.ll b/llvm/test/Transforms/InstCombine/fneg.ll
index 69ad3541641..df1d5f570db 100644
--- a/llvm/test/Transforms/InstCombine/fneg.ll
+++ b/llvm/test/Transforms/InstCombine/fneg.ll
@@ -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
diff --git a/llvm/test/Transforms/InstCombine/fsub.ll b/llvm/test/Transforms/InstCombine/fsub.ll
index b4567500df0..4868ece222d 100644
--- a/llvm/test/Transforms/InstCombine/fsub.ll
+++ b/llvm/test/Transforms/InstCombine/fsub.ll
@@ -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
 }