Intel AMX and feature detection

[Paul Sandoz]

> On Jun 26, 2024, at 3:55 PM, John Rose <john.r.rose at oracle.com> wrote:
> 
> Actually we have VectorShape.S_64_BIT which, if it is 
> the preferred shape, is really telling you the 
> “vector” processing is inside the CPU not the VPU. 
> That’s a good-enough hint to avoid the Vector API, 
> right?

Yes, I think that is a good proxy for lack of any compiler support.

I would like to hear opinions from the Intel’s folks on “down bit’ing” from 512 to 256 on AVX-512 without VBMI2. It seems pragmatic. What about the auto-vectorizer? We also have HotSpot flags to say uses AVX2 on an AVX-512 machine as a workaround. If we do this perhaps we need a flag to override the “down bit’ing”.

I will log issues for both.

Paul.