[PATCH] D138180: InstCombine: Fold negations of is_fpclass intrinsics

[Serge Pavlov via Phabricator via llvm-commits]

sepavloff accepted this revision.
sepavloff added a comment.
This revision is now accepted and ready to land.

LGTM.



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Comment at: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp:3715-3717
+      II->setArgOperand(
+          1, ConstantInt::get(ClassMask->getType(),
+                              ~ClassMask->getZExtValue() & fcAllFlags));
----------------
arsenm wrote:
> sepavloff wrote:
> > It must work for IEEE numbers. But for non-IEEE it is possible that a value does not belong to any of the classes known to `is_fpclass`. For example, type `x86_fp80` has so-called unsupported values. Do you think this transformation can be safely applied to such numbers also or it is better to limit it to IEEE numbers only?
> I don't know anything about x87. How is the intrinsic lowered for it?
> 
> Is it just these "pseudo-X" cases? I'd assume those are covered by the non-pseudo tests?
Yes, these are pseudo numbers. They are mapped to IEEE classes in more complex way, for example glibc recognizes pseudo-infinity as a NaN, and pseudo-denormals as normals.

Nevertheless any such number is mapped to one of IEEE classes and this optimization must work no matter how the mapping is realized.


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  https://reviews.llvm.org/D138180/new/

https://reviews.llvm.org/D138180