[PATCH] D90529: Allow nonnull attribute to accept poison

[Nuno Lopes via Phabricator via llvm-commits]

nlopes added a comment.

I like where this is going. Most of LLVM's alias analysis produce information that only holds if the value is not poison. Since these attributes are derived from said analysis, then it makes sense then they have the same "X is poison or foo(X) holds" semantics.
I agree that certain attributes are different, like dereferenceable. It is useless if the value might be poison as well. Though we may go with the same semantics and then require the `noundef` attribute to make it useful. Seems like a good way to go as well.

For the partial undef memory access example that Juneyoung gave.. Well, maybe we need to make it UB to dereference a non-deterministic value. Doesn't seem like it's a very useful thing to do, and this non-determinism comes from some previous undefined behavior, so it seems fine to just make dereference of partial undef UB. Simplifies things.


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  https://reviews.llvm.org/D90529/new/

https://reviews.llvm.org/D90529