[PATCH] D86396: [Attributor] Change AANoUndef not to deduce noundef for dead returned positions

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a comment.

In D86396#2236597 <https://reviews.llvm.org/D86396#2236597>, @okura wrote:

> When I fix the identification of AANoUndef in `identifyDefaultAbstractAttributes`, I noticed that noundef should not be deduced for dead argument and dead call site argument position too. (I found wrong transformation in e.g. `callbacks.ll`)
> Not to deduce for dead positions, we should not indicate optimistic fixpoint in `initialize` because once fixpoint is indicated we cannot change the state. However, it weakens the deduction significantly.
> So I want to suggest that we check not only noundef but also liveness in AAUndefinedBehavior.

I don't understand the comment.

Should we check in the manifest of AANoUndef if the position is dead and not manifest it? I'm not sure we necessarily call updateImpl before with a known dead state, so this approach might not always work.


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https://reviews.llvm.org/D86396