[PATCH] D70246: [InstCombine] remove identity shuffle simplification for mask with undefs

[Nuno Lopes via Phabricator via llvm-commits]

nlopes added a comment.

Let me give my 2c: eliminating this transformation is a good thing, since it's incorrect (end-to-end miscompilation testcase in the cited bug report).
It can be re-instated if/when we switch from initializing vectors with undef with poison, but I don't know when that will happen. We'll try to push for the poison patches soonish, but it will take time.
Anyway, thanks Sanjay for handling this :)


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  https://reviews.llvm.org/D70246/new/

https://reviews.llvm.org/D70246