[llvm] 84812b9 - [InstCombine] drop FMF in select->copysign transform

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2022-03-01T08:51:41-05:00
New Revision: 84812b9b072a513acfa76149c5a481d4eb8a511d

URL: https://github.com/llvm/llvm-project/commit/84812b9b072a513acfa76149c5a481d4eb8a511d
DIFF: https://github.com/llvm/llvm-project/commit/84812b9b072a513acfa76149c5a481d4eb8a511d.diff

LOG: [InstCombine] drop FMF in select->copysign transform

It is not correct to propagate flags from the select
to the new instructions:
https://alive2.llvm.org/ce/z/tNATrd
https://alive2.llvm.org/ce/z/VwcVzn

Fixes #54077

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
    llvm/test/Transforms/InstCombine/select.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index a9745cf38a77e..a46600a261fe3 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2353,17 +2353,16 @@ static Instruction *foldSelectToCopysign(SelectInst &Sel,
   // (bitcast X) <  0 ?  TC : -TC --> copysign(TC, -X)
   // (bitcast X) >= 0 ? -TC :  TC --> copysign(TC, -X)
   // (bitcast X) >= 0 ?  TC : -TC --> copysign(TC,  X)
+  // Note: FMF from the select can not be propagated to the new instructions.
   if (IsTrueIfSignSet ^ TC->isNegative())
-    X = Builder.CreateFNegFMF(X, &Sel);
+    X = Builder.CreateFNeg(X);
 
   // Canonicalize the magnitude argument as the positive constant since we do
   // not care about its sign.
   Value *MagArg = TC->isNegative() ? FVal : TVal;
   Function *F = Intrinsic::getDeclaration(Sel.getModule(), Intrinsic::copysign,
                                           Sel.getType());
-  Instruction *CopySign = CallInst::Create(F, { MagArg, X });
-  CopySign->setFastMathFlags(Sel.getFastMathFlags());
-  return CopySign;
+  return CallInst::Create(F, { MagArg, X });
 }
 
 Instruction *InstCombinerImpl::foldVectorSelect(SelectInst &Sel) {

diff  --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 124d96f743646..d05336bddcc6d 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -1656,7 +1656,7 @@ define float @copysign1(float %x) {
 
 define float @copysign1_fmf(float %x) {
 ; CHECK-LABEL: @copysign1_fmf(
-; CHECK-NEXT:    [[R:%.*]] = call ninf nsz float @llvm.copysign.f32(float 1.000000e+00, float [[X:%.*]])
+; CHECK-NEXT:    [[R:%.*]] = call float @llvm.copysign.f32(float 1.000000e+00, float [[X:%.*]])
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %i = bitcast float %x to i32
@@ -1667,8 +1667,8 @@ define float @copysign1_fmf(float %x) {
 
 define <2 x float> @copysign2(<2 x float> %x) {
 ; CHECK-LABEL: @copysign2(
-; CHECK-NEXT:    [[TMP1:%.*]] = fneg nsz <2 x float> [[X:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = call nsz <2 x float> @llvm.copysign.v2f32(<2 x float> <float 4.200000e+01, float 4.200000e+01>, <2 x float> [[TMP1]])
+; CHECK-NEXT:    [[TMP1:%.*]] = fneg <2 x float> [[X:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = call <2 x float> @llvm.copysign.v2f32(<2 x float> <float 4.200000e+01, float 4.200000e+01>, <2 x float> [[TMP1]])
 ; CHECK-NEXT:    ret <2 x float> [[R]]
 ;
   %i = bitcast <2 x float> %x to <2 x i32>
@@ -1679,8 +1679,8 @@ define <2 x float> @copysign2(<2 x float> %x) {
 
 define float @copysign3(float %x) {
 ; CHECK-LABEL: @copysign3(
-; CHECK-NEXT:    [[TMP1:%.*]] = fneg fast float [[X:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = call fast float @llvm.copysign.f32(float 4.300000e+01, float [[TMP1]])
+; CHECK-NEXT:    [[TMP1:%.*]] = fneg float [[X:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = call float @llvm.copysign.f32(float 4.300000e+01, float [[TMP1]])
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %i = bitcast float %x to i32