[PATCH] D76332: Fix MSan false positive due to select folding.

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

> Is there some reason that we didn't make the select semantics for poison explicit in the LangRef?

The exact semantics were evolving for a while, and nobody actually wrote up where we landed with Alive2.

> Should I remove TryToUnfoldSelectInCurrBB completely? I don't see how it can be saved.

See the documentation comment on TryToUnfoldSelectInCurrBB.  The ultimate transform we're actually hoping to perform, which is jump threading to simplify the select, is legal.  So it's probably worth trying to do that, still, even if the intermediate step TryToUnfoldSelectInCurrBB actually implements isn't legal.

We already have some other code that tries to handle selects; I'm not sure how much of an optimization gap would remain if we just delete TryToUnfoldSelectInCurrBB.


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  https://reviews.llvm.org/D76332/new/

https://reviews.llvm.org/D76332