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

Wed Aug 26 06:10:09 PDT 2020

okura added a comment.

In D86396#2236684 <https://reviews.llvm.org/D86396#2236684>, @jdoerfert wrote:

> 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 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 <https://reviews.llvm.org/D86565> for the problem.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D86396/new/

https://reviews.llvm.org/D86396