[aarch64-port-dev ] Adv. SIMD/Neon support in intrinsics/stubs for AArch64

[Andrew Haley]

On 8/8/19 7:15 AM, Patrick Zhang OS wrote:

> Does anyone know the whole picture of the Neon support in intrinsics/stubs?

I'm as likely to know as anyone else.

> I am not sure whether what I observed is correct: 1. Pre-Armv8
> distinguishes between VFP and Neon floating-point support but the
> definitions are not explicitly separated (via any special prefix) in
> assembly_aarch64.hpp.

With AArch64 there's no need: AdvSIMD is part of the spec.

> 2. There are some intrinsics/stubs implemented using VFP for
> vectorizing, where we still have opportunities to improve by aid of
> Neon 2x64-bit integer/floating-point operations, such as
> string_compare [1].

How would that help anything? string_compare already uses vector ops.

> 3. More intrinsics need vectorizing, with reference to other archs.

Maybe. In theory it would help, but in practice meaningful speedups
are quite difficult to achieve without compromising performance with
small strings. But please feel free to try.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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