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| author | Sanjay Patel <spatel@rotateright.com> | 2014-12-31 22:14:05 +0000 |
|---|---|---|
| committer | Sanjay Patel <spatel@rotateright.com> | 2014-12-31 22:14:05 +0000 |
| commit | e68f71574f9c61f72d1aca2811d85da9e4bc0a69 (patch) | |
| tree | 542273ea5e87168e9ec96a46f80efb3c267b688c /llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp | |
| parent | 0dfd2400688266e688c00b62b38491d4a297c20c (diff) | |
| download | bcm5719-llvm-e68f71574f9c61f72d1aca2811d85da9e4bc0a69.tar.gz bcm5719-llvm-e68f71574f9c61f72d1aca2811d85da9e4bc0a69.zip | |
InstCombine: fsub nsz 0, X ==> fsub nsz -0.0, X
Some day the backend may handle instruction-level fast math flags and make
this transform unnecessary, but it's still better practice to use the canonical
representation of fneg when possible (use a -0.0).
This is a partial fix for PR20870 ( http://llvm.org/bugs/show_bug.cgi?id=20870 ).
See also http://reviews.llvm.org/D6723.
Differential Revision: http://reviews.llvm.org/D6731
llvm-svn: 225050
Diffstat (limited to 'llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp')
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp index 9ea4bc57cf2..7e6ead4190c 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp @@ -1713,6 +1713,14 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) { 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)) |
