[vector] ARM SVE

[Roland Westrelin]

Hi Paul,

> For SVE It makes less sense to refer to explicit shapes we currently
> have now, the implementations are far less useful for any cross
> x86/ARM CPU platform code, and in general the guidance is where
> possible to code algorithms in a shape agnostic manner.
>
> Might it be useful to expose such a shape explicitly as a type, such
> as Shapes.SPreferred? does this imply in the long run that shape is
> not required as the sweet spot is shape agnostic code?

I'm somewhat confused by this. Are you suggesting to expose
Shapes.SPreferred as a way to help better take advantage of ARM SVE?

I thought the guideline/goal was, whether on x86 or other hardware, to
write shape agnostic code anyway?

My understanding, also, was that shape agnostic code in the vector API
is built on top of fixed size shapes. Those shapes are then what the
JIT works with and where interfacing with the hardware is happening so
exposing Shapes.SPreferred higher up wouldn't affect code generation.

What am I misunderstanding?

Roland.