[PATCH] D71799: [Attributor] AAUndefinedBehavior: Check for branches on undef value.

[Hideto Ueno via Phabricator via llvm-commits]

uenoku added a comment.

> I agree but I assumed wrongly apparently. You see, with "we can assume it is undef" I thought that I should also add it to the UBInsts set. Up to that point, if I were to do that, it would be wrong since
>  if something is added to UBInsts, it would never be checked again. But apparently Johannes did not mean this.

I got the point! I missed that UB is intended to be used for liveness. Sorry about that. I'll rethink the problem. But it seems for me that current implementation regards *assumed* `UBInsts` as *known* `UBInsts`. Because once `I` is assumed to have UB, we never visit `I`. I guess this will cause invalid deduction.

> I agree yes. My point was: At some point, we _will_ get a concrete value (or, candidate), aren't we? If so, why add it and then remove it from the set instead of just waiting until we get a value? Hence my initial code.

I think we won't get a concrete value for `None` in the iterations.


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https://reviews.llvm.org/D71799