[llvm] 8591640 - [InstCombine] add DeMorgan folds for logical ops in select form

[Sanjay Patel via llvm-commits]

Thanks! Constant expressions strike again...working on a reduction now.

On Sun, Jun 20, 2021 at 5:49 AM Florian Hahn <florian_hahn at apple.com> wrote:

>
>
> On Jun 14, 2021, at 17:55, Sanjay Patel via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>
> Author: Sanjay Patel
> Date: 2021-06-14T12:54:35-04:00
> New Revision: 8591640379ac9175a8a8493126ecf0b44e3bb4af
>
> URL:
> https://github.com/llvm/llvm-project/commit/8591640379ac9175a8a8493126ecf0b44e3bb4af
> DIFF:
> https://github.com/llvm/llvm-project/commit/8591640379ac9175a8a8493126ecf0b44e3bb4af.diff
>
> LOG: [InstCombine] add DeMorgan folds for logical ops in select form
>
> We canonicalized to these select patterns (poison-safe logic)
> with D101191, so we need to reduce 'not' ops when possible
> as we would with 'and'/'or' instructions.
>
> This is shown in a secondary example in:
> https://llvm.org/PR50389
>
> https://alive2.llvm.org/ce/z/BvsESh
>
>
> It looks like this is causing an infinite loop in InstCombine:
> https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=35399
>
> Cheers,
> Florian
>
>
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