[PATCH] D104648: [Mem2Reg] Use poison instead of undef for read of uninitialized memory

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added a comment.

This is a big change because AFAIK clang intentionally encodes the value of uninitialized variables in a benign way.
For example: https://godbolt.org/z/EYjasxM1M is optimized to 0 even if it is undef ^ undef = undef. If poison is used, this won't work.
I think that to switch to poison reasonable performance benefit should be shown. I have a patch that makes poison propagate better, which will help this change.
BTW, do you have any idea about the failures happening at clang unit tests?


Repository:
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  https://reviews.llvm.org/D104648/new/

https://reviews.llvm.org/D104648