[PATCH] D102275: [x86] try to use PCMPGT instead of not-of-PCMPEQ

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D102275#2753807 <https://reviews.llvm.org/D102275#2753807>, @spatel wrote:

> In D102275#2753333 <https://reviews.llvm.org/D102275#2753333>, @RKSimon wrote:
>
>> Is the inverse (known negative) case worth it do you think?
>
> Yes - I didn't draft that one yet to see if existing tests will show it, but we probably want that for symmetry. I'll look at that next.

I don't see a known-bits way to capture it. We need a `isKnownNotPositive` (if any non-sign-bit is set, then sign-bit is also set).
The Alive2 example you showed is correct because the result is always true. We want this instead:
https://alive2.llvm.org/ce/z/v7jxhL


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https://reviews.llvm.org/D102275