[PATCH] D102834: [SLPVectorizer] Implement initial memory versioning.

[Florian Hahn via Phabricator via llvm-commits]

fhahn added a comment.

In D102834#3173674 <https://reviews.llvm.org/D102834#3173674>, @SjoerdMeijer wrote:

> In D102834#3173543 <https://reviews.llvm.org/D102834#3173543>, @fhahn wrote:
>
>> Address latest sets of comments, thanks! I hope I didn't miss anything.
>
> Thanks for that.
>
> Not directly related to code changes, but more general question: could we see negative performance impact of these runtime checks? For example, if they are emitted in loops? Or are they trivially hoisted out of loops? Any thoughts on these kind of things?

Yes, there could be negative performance impact, for at least the following reasons 1) cost-model bugs overestimating the vector savings and 2)if the vector path is never taken because the runtime checks fail. Cases of 1) will be rather easy to fix, while there won't be too much we can do about 2) unfortunately, unless we have profile info. Note that we have the same issue with LV.


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