[PATCH] D109432: [LoopVectorize] Permit fixed-width epilogue loops for scalable vector bodies

Mon Oct 4 01:00:39 PDT 2021

david-arm added a comment.

> In D109432#3033037 <https://reviews.llvm.org/D109432#3033037>, @david-arm wrote:
>
>> I found no overall change in performance with SPEC2006 when building with scalable vectorisation on a A64FX machine.
>
> Are you sure that you actually enabled/used tail vectorization? I would have expected differences in performance if this was used.

Yeah I'm sure. I'm happy to run some more tests though on a different machine! This simply points to a couple of things I think:

1. It may suggest that not much hot C/C++ code in SPEC2006 is currently vectorisable. We might see more difference if we could test Fortran benchmarks.
2. If there are any vectorised loops then the main body trip count is possibly far larger than the tail trip count. I imagine tail vectorisation has the largest impact on smaller loops?

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