[PATCH] D129650: [InstCombine] change conditions for transform of sub to xor

[Sanjay Patel via Phabricator via llvm-commits]

spatel abandoned this revision.
spatel added a comment.

Ok - I reverted the earlier patch that created more xor with:
08091a99ae48 <https://reviews.llvm.org/rG08091a99ae4804f319dfe62e0bd76d876febb188>

That should solve the immediate regressions that were mentioned here (and we still have the PhaseOrdering test in place, so it will be harder to trip over this in the future).

Note: we still convert sub from low-mask constant (eg 0x003fff...) into xor (that was the original fold that's been around for many years). I'm not sure if there's something about that pattern that avoids SCEV trouble, or if there's already a work-around for that pattern in SCEV.


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  https://reviews.llvm.org/D129650/new/

https://reviews.llvm.org/D129650