[PATCH] D84287: [SelectionDAG] Make LegalizeDAG lower FNEG using integer ops.

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

Do you think the globalisel change has to be done in the same patch?  I guess I can try to look into it.



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Comment at: llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp:1574
+  // Expand using integer operations. (We used to expand to FSUB, but that's
+  // not correct in cases involving NaNs.)
+  SDLoc DL(Node);
----------------
arsenm wrote:
> The explanation is too vague and not quite correct. It's specifically signaling nans (and also possibly denormal flushing). fsub is a canonicalizing operation, but fneg is not
There's also a problem for non-signalling nans: the sign of the result is unspecified.  Maybe common implementations flip the sign?  Not sure.


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https://reviews.llvm.org/D84287