[PATCH] D115143: [AArch64][Analysis] Add on overhead costs for SVE gathers and scatters

Tue Dec 7 01:30:42 PST 2021

david-arm added a comment.

In D115143#3175743 <https://reviews.llvm.org/D115143#3175743>, @dmgreen wrote:

> 10 sounds high, but from looking at some of the software optimization guides it does not seem like a bad worse case value.
>
> Is it worth making it a option (that can default to 10), to allow experimentation with other values?

I guess that might be useful?

>From the benchmarks I ran for tight loops with a single gather or scatter with a variety of different strides the vector loops with SVE gathers and scatters overall didn't perform better than a scalar loop! Even worse, in loops with a high density of gathers and scatters the runtime can even be 2x-3x worse than a scalar loop. The optimisation guides do suggest there is a very low throughput.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D115143/new/

https://reviews.llvm.org/D115143