[llvm] r224583 - use -0.0 when creating an fneg instruction
Sanjay Patel
spatel at rotateright.com
Fri Dec 19 08:44:08 PST 2014
Author: spatel
Date: Fri Dec 19 10:44:08 2014
New Revision: 224583
URL: http://llvm.org/viewvc/llvm-project?rev=224583&view=rev
Log:
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
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
llvm/trunk/test/Transforms/InstCombine/fast-math.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp?rev=224583&r1=224582&r2=224583&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp Fri Dec 19 10:44:08 2014
@@ -759,7 +759,7 @@ Value *FAddCombine::createFSub(Value *Op
}
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.
Modified: llvm/trunk/test/Transforms/InstCombine/fast-math.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fast-math.ll?rev=224583&r1=224582&r2=224583&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/fast-math.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/fast-math.ll Fri Dec 19 10:44:08 2014
@@ -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
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