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

Tue Dec 24 03:56:11 PST 2019

uenoku added a comment.

In D71799#1795477 <https://reviews.llvm.org/D71799#1795477>, @baziotis wrote:

> It seems to me that for constants or `undef`, this should be known. Looking at `initialize()` of `AAValueSimplifyFloating`, for constants and `undef`, it indicates a //pessimistic// fixpoint and I don't understand why.

At first concept of `AAValueSimplify`, I set the semantics of optimistic state as that the value is **simplified actually**. So if the state is pessimistic, `getAssumedSimplifiedValue` returns the original associated value. 
 (https://reviews.llvm.org/D66967#1659664)

Base on that, if the associated value is constant or undef, I fixed the state as pessimistic because we can't simplify the value more.
But now it seems it's more useful to reach an optimistic fixpoint when the value is constant or undef, so I can agree to change it.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71799/new/

https://reviews.llvm.org/D71799