[PATCH] D150706: [LAA] Update MaxSafeDepDistBytes when non-unit stride

Mon Jul 17 11:05:12 PDT 2023

fhahn added a comment.

In D150706#4507037 <https://reviews.llvm.org/D150706#4507037>, @michaelmaitland wrote:

> `MaxSafeVectorWidthInBits` value depends on `MaxVFInBits`, whose value depends on `MaxVF`, whose value depends on `MaxSafeDepDistBytes`. `MaxSafeDepDistBytes` is calculated incorrectly prior to the changes introduces in this patch as you can see by the test case diff in this patch. In order for us to avoid a miscompile that is elicited by the example in this patch, we should fix the problem of incorrectly calculating `MaxSafeDepDistBytes`.

But does LV miscompile the case? I think MaxVFInBits should be 2, and it refuses to vectorize with anything larger than VF = 2: https://llvm.godbolt.org/z/6KezshEdW

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  https://reviews.llvm.org/D150706/new/

https://reviews.llvm.org/D150706