use -0.0 when creating an fneg instruction

Backends recognize (-0.0 - X) as the canonical form for fneg
and produce better code. Eg, ppc64 with 0.0:

   lis r2, ha16(LCPI0_0)
   lfs f0, lo16(LCPI0_0)(r2)
   fsubs f1, f0, f1
   blr

vs. -0.0:

   fneg f1, f1
   blr

Differential Revision: http://reviews.llvm.org/D6723

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224583 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 39b71f37f8b2795a0b4be863532b967f634d63dc..c2d2eec3fc3f78a88196212e23eee789de6c4632 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -759,7 +759,7 @@ Value *FAddCombine::createFSub(Value *Opnd0, Value *Opnd1) {
 }
 
 Value *FAddCombine::createFNeg(Value *V) {
-  Value *Zero = cast<Value>(ConstantFP::get(V->getType(), 0.0));
+  Value *Zero = cast<Value>(ConstantFP::getZeroValueForNegation(V->getType()));
   Value *NewV = createFSub(Zero, V);
   if (Instruction *I = dyn_cast<Instruction>(NewV))
     createInstPostProc(I, true); // fneg's don't receive instruction numbers.

diff --git a/test/Transforms/InstCombine/fast-math.ll b/test/Transforms/InstCombine/fast-math.ll
index b0ec8952bb33052a7bceea932e551bcd9c7632d8..f39adba656015a45b4ad05731fb554d5f806ee56 100644 (file)
--- a/test/Transforms/InstCombine/fast-math.ll
+++ b/test/Transforms/InstCombine/fast-math.ll
@@ -93,7 +93,7 @@ define float @fold9(float %f1, float %f2) {
   ret float %t3
 
 ; CHECK-LABEL: @fold9(
-; CHECK: fsub fast float 0.000000e+00, %f2
+; CHECK: fsub fast float -0.000000e+00, %f2
 }
 
 ; Let C3 = C1 + C2. (f1 + C1) + (f2 + C2) => (f1 + f2) + C3 instead of