[PATCH] D92270: [ConstantFold] Fold more operations to poison

Thu Jan 7 20:58:33 PST 2021

aqjune added a comment.

In D92270#2483557 <https://reviews.llvm.org/D92270#2483557>, @thakis wrote:

> It turned out to be UB in our code as far as I can tell, see https://bugs.chromium.org/p/angleproject/issues/detail?id=5500#c36 and the follow-on.
>
> (If this is known to trigger an existing bug more often, it might still be a good idea to undo it until that existing bug is fixed? But we're not affected by this existing bug as far as I can tell, so this is just a suggestion.)

I don't know the policy of LLVM in this case, but it sounds legit. LLVM branching date is also near. @nikic May I ask your opinion?
BTW, shift operation is continually causing this problem interestingly - I guess shift operation with large shift amount hasn't been treated as 'that bad' for some reason.

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https://reviews.llvm.org/D92270