[PATCH] InstCombine: fsub nsz 0, X ==> fsub nsz -0.0, X
Sanjay Patel
spatel at rotateright.com
Wed Dec 31 14:15:17 PST 2014
REPOSITORY
rL LLVM
http://reviews.llvm.org/D6731
Files:
llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
llvm/trunk/test/Transforms/InstCombine/fast-math.ll
Index: llvm/trunk/test/Transforms/InstCombine/fast-math.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/fast-math.ll
+++ llvm/trunk/test/Transforms/InstCombine/fast-math.ll
@@ -322,6 +322,14 @@
; CHECK: fmul float %f1, %f2
}
+define float @fneg2(float %x) {
+ %sub = fsub nsz float 0.0, %x
+ ret float %sub
+; CHECK-LABEL: @fneg2(
+; CHECK-NEXT: fsub nsz float -0.000000e+00, %x
+; CHECK-NEXT: ret float
+}
+
; =========================================================================
;
; Testing-cases about div
Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1713,6 +1713,14 @@
TLI, DT, AT))
return ReplaceInstUsesWith(I, V);
+ // fsub nsz 0, X ==> fsub nsz -0.0, X
+ if (I.getFastMathFlags().noSignedZeros() && match(Op0, m_Zero())) {
+ // Subtraction from -0.0 is the canonical form of fneg.
+ Instruction *NewI = BinaryOperator::CreateFNeg(Op1);
+ NewI->copyFastMathFlags(&I);
+ return NewI;
+ }
+
if (isa<Constant>(Op0))
if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
if (Instruction *NV = FoldOpIntoSelect(I, SI))
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