Ricky Zhou 30ac5f9e64 [InstCombine] Do not combine atomic and non-atomic loads ...

Before this change, InstCombine was willing to fold atomic and
non-atomic loads through a PHI node as long as the first PHI argument
is not an atomic load. The combined load would be non-atomic, which is
incorrect.

Fix this by only combining the loads in a PHI node when all of the
arguments are non-atomic loads.

Thanks to Eli Friedman for pointing out the bug at
https://github.com/llvm/llvm-project/issues/50777#issuecomment-981045342!

Fixes #50777

Differential Revision: https://reviews.llvm.org/D115113

2022-01-30 10:05:11 -05:00

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