RE: [PATCH 5/5] x86: support AVX10.1 vector size restrictions

["Jiang, Haochen" <haochen.jiang@intel.com>]

> > >> I agree it isn't necessary, but as expressed before I view it as desirable.
> > >> Apart from the sentence you quoted the spec later also says "There are
> > >> currently no plans to support an Intel AVX10/128 implementation." For my
> > >> choice of also supporting the 128-bit restriction I'd like to put emphasis
> > >> on "currently". I think I said before that emulation environments (qemu,
> > >> sde to name just two well-known examples) are free to implement such
> > >> further restricted ISAs without then becoming out-of-spec.
> > >>
> > >> Plus supporting this mode right away has made me make certain adjustments
> > >> in what I'd call more clean a way, which I view as desirable as well.
> > >
> > > Since AVX10 spec doesn't specify if mask registers should be limited to
> > > 16 bits for AVX10/128, doing it in assembler is premature.
> >
> > It's hard to see why they would remain wider. The more that they were 16
> > bits only in AVX512F.
> >
> > Plus of course nobody needs to use the options to enforce the 128-bit
> > limit. The way I've coded it, it matches what the specification says.
> >
> 
> AVX10 spec only has
> 
> Quadword opmask instructions will only be supported on processors
> supporting vector lengths of 512 bits.
> 
> It doesn't say anything about 32-bit mask.   32-bit mask can be useful
> even with 16 byte vector.
> 
> --
> H.J.

The concern form my side is if there is an extreme case that overloads
registers, we might need to spill 32-bit register to 32-bit mask register
in the compiler.

Another minor concern is if there is finally a AVX10/128, although I do
not see that could happen, if we get a wrong choice here, it will take
some more time to correct the final assembler on the user side, which
I mean on the real OS.

However, I suppose both ok for me whether to allow 32-bit mask since
AVX10/128 is nowhere near in the future and it is a toy code to play with.
We could be some kind of conservative at first by just allowing 16-bit
mask register. Also, the code change is quite easy and no much worry on
changing that.

Thx,
Haochen