[PATCH] D88921: [MemCpyOpt] Fix thread-safety of call slot opimization

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a comment.

Commit message:

>> If the destination is captured, we need to check that the copy instruction is executed, to exclude concurrent access from another thread.



In D88921#2315685 <https://reviews.llvm.org/D88921#2315685>, @efriedma wrote:

>> If the caller is nosync there is no need for all this thread safety checking.
>
> I'm not sure nosync helps here?  The issue this patch is trying to solve is the case where the memcpy is dynamically dead due to an infinite loop; there isn't any synchronization involved.

If it is nosync there is no concurrent access without it being a race and therefore UB.


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