[PATCH] D89566: [LV] Epilogue Vectorization with Optimal Control Flow

[Dave Green via Phabricator via llvm-commits]

dmgreen added a comment.

> As it stands right now, VPlan can only model control-flow inside a loop. Since epilogue vectorization is concerned with control-flow around (and outside) the loop, there isn't much that can be done today to make the transformation "VPlany". I understand the ultimate goal of vplan is to also model the context around subject loops (eg the entire loop nest or other code surrounding loops). I wondered about whether it's worth to delay this work until that becomes available, but most of the feedback I received was in the direction of let's get it done now and then do it in vplan when it's capable of representing surrounding context.

Yeah. I don't think VPlan should slow this down. The problem is that if no-one pushes on vplan to have those extra features, they will never appear :)

> Absolutely, that can be a nice follow on to this work. I think any target that supports predicated vector instructions could benefit, specially if the predicated vector instructions perform better than scalar instructions but not as good as non-predicated vector instructions. If predicated and non-predicated vector instructions have similar throughput and latency, then perhaps tail-folding the main loop would be a better fit.

I think this can depend upon.. a lot of things. Good to hear it should be possible.


Repository:
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https://reviews.llvm.org/D89566