[PATCH] D65803: [MVE] Don't try to unroll vectorised MVE loops

[Dave Green via Phabricator via llvm-commits]

dmgreen added a comment.

> (1) we can't depend on metadata

We can depend on metadata for performance though, that's what it's there for! Just not for correctness (at least, that's what I understood/remember from the language ref). The vectoriser adds llvm.loop.unroll.runtime.disable, being fairly confident that it disables the unrolling for the remainder loop, for example.

> (2) doesn't this also prevent the scalar remainder from being unrolled too?

It will already have no-unroll metadata on it. It's known to be a short loop, at most 3 iterations in this case (as we vectorise x 4).


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  https://reviews.llvm.org/D65803/new/

https://reviews.llvm.org/D65803