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| author | Cameron McInally <cameron.mcinally@nyu.edu> | 2019-05-09 19:28:52 +0000 |
|---|---|---|
| committer | Cameron McInally <cameron.mcinally@nyu.edu> | 2019-05-09 19:28:52 +0000 |
| commit | 156eb2828994376108c5d3920533d03e4be71f97 (patch) | |
| tree | cba3640edfc3678f4bd27431549126cc5b8b7dac | |
| parent | 412254af75084f8845de8b1959c8e5c29dd12909 (diff) | |
| download | bcm5719-llvm-156eb2828994376108c5d3920533d03e4be71f97.tar.gz bcm5719-llvm-156eb2828994376108c5d3920533d03e4be71f97.zip | |
[CodeGen] Add comment about FSUB <-> FNEG xforms
Differential Revision: https://reviews.llvm.org/D61741
llvm-svn: 360366
| -rw-r--r-- | llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 4c9e34b533e..59f7af01e8b 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -11629,6 +11629,10 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) { } // (fsub -0.0, N1) -> -N1 + // NOTE: It is safe to transform an FSUB(-0.0,X) into an FNEG(X), since the + // FSUB does not specify the sign bit of a NaN. Also note that for + // the same reason, the inverse transform is not safe, unless fast math + // flags are in play. if (N0CFP && N0CFP->isZero()) { if (N0CFP->isNegative() || (Options.NoSignedZerosFPMath || Flags.hasNoSignedZeros())) { |
