[PATCH] D25276: [LoopVectorizer] Interleaved-mem-accesses analysis and getPtrStride

[Dorit Nuzman via llvm-commits]

dorit added a comment.

> I think deferring these pointer wrapping checks until after we've formed the interleaved groups should work.

Makes sense. So, to summarize:

1. during collectConstStrideAccesses we want to call getPtrStride with Assume=false (*), ShouldCheckWrap=false (optimistic).
2. towards the end of analyzeInterleaving we will revisit groups (of loads) with gaps and for those call getPtrStride with Assume=false (**), shouldCheckWrap=true.

(*) As far as I can see when ShouldCheckWrap=false then Assume is pretty much a don't-care in terms of runtime checks; no new runtime checks will be added by getPtrStride. See below.

(**) I would set Assume=false initially, but I think in the long run we may want to allow runtime checks here if the budget allows (as you noted earlier, so that we don't end up failing vectorization altogether due to these extra checks). That can be done in a followup patch.

Agreed?

> It can happen for example with the following loop

Thanks for the example!

> Without Assume = true (and further run-time checks) we wouldn't be able to recognize a[index] as a strided pointer (because it isn't when y < x).

Yes; but my point was that when ShouldCheckWrap=false we never get to consider adding new runtime checks in getPtrStride, even if Assume=true. Unless I'm missing something?

thanks,
Dorit


https://reviews.llvm.org/D25276