[PATCH] D67356: [InstCombine] Simplify @llvm.usub.with.overflow+non-zero check (PR43251)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In D67356#1674601 <https://reviews.llvm.org/D67356#1674601>, @xbolva00 wrote:

> Btw, I am in favour of this patch.
>
> >> It both blocks the UBSan patch itself,
>
> Well, I dont think so. ubsan patch works now, right? these folds just makes overhead a bit smaller, right? I would not connect ubsan patch with these folds. We could have ubsan patch in tree and these folds would land a bit later - no problem I think. Or miss I something?


No, you are correct, these aren't *required* for the ubsan patch, but they are
very much welcomed - i suspect they will reduce the extra overhead significantly.
(Random guess - down from extra 26% to extra 10%, but i won't know until these folds are in place.)
(for optimized builds, not much can help `-O0` :S)


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