When a returned position is dead, returned values will be replaced with undef values by AAIsDead.
Therefore we should not deduce noundef for the position. Otherwise, AAUndefinedBehavior caught that and replace them with unreachable incorrectly.
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.
I investigated the problem seen in the module slice patch again. And I realize now that checking liveness in manifestation is sufficient to settle the problem.
I misunderstood we need more things to do so. I was overthinking, sorry.
I will abandon this revision because I have made D86565 for the problem.