[PATCH] D138814: [InstCombine] Combine lshr of add -> (a + b < a)

Tue Jan 10 02:10:45 PST 2023

nikic added a comment.

In D138814#4039101 <https://reviews.llvm.org/D138814#4039101>, @foad wrote:

> In D138814#3973599 <https://reviews.llvm.org/D138814#3973599>, @nikic wrote:
>
>> FWIW our historical stance has always been that uadd.with.overflow is non-canonical, and the canonical pattern is `a + b < a` (for non-constant `b`). uadd.with.overflow generally has worse optimization support, which is why we only form it during CGP for backend purposes.
>
> What's the historical stance on sadd.with.overflow?

sadd.with.overflow (and generally, all signed overflow intrinsics) are considered canonical, and we do produce them in InstCombine.

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