[PATCH] D146199: [LoopVectorize] Don't tail-fold for scalable VFs when there is no scalar tail

[Dave Green via Phabricator via llvm-commits]

dmgreen added a comment.

I had written a very similar patch recently, but it would only use the fixed length if the scalable was unknown. The performance of it was pretty bad though, so I ended up dropping it. I had noticed that there is an xfail in llvm/test/Transforms/LoopVectorize/AArch64/eliminate-tail-predication.ll at the moment. Can it now be replaced with a check for `store <vscale x 4 x i32>`?

TargetTransformInfo::isVScaleKnownToBeAPowerOfTwo isn't going to be useable from all the places that need it like instcombine. It might be best to add it to somewhere like vscale_range in the long run?


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