Re: [PATCH v2] Support Intel AVX10.1

[Jan Beulich <jbeulich@suse.com>]

On 16.08.2023 10:21, Jiang, Haochen wrote:
>>> After I think twice on that, I suppose maybe it is not that appropriate to put it
>>> into i386_opcode_modifier since in AVX10, the vector width is depends on CPU.
>>> I suppose i386_opcode_modifier is a feature for instructions but not CPU.
>>
>> I disagree. See the uses of EVex, for example. As said above, I think
>> maximum vector width and ISA extensions want dealing with separately,
>> and only the latter would generally qualify for Cpu* flags. Furthermore
>> recall that the attribute wants widening sooner or later, and Cpu*
>> flags are uniformly boolean. Only attributes may have numeric values.
> 
> After I checked code, I still miss the point here.
> 
> My concern is how to actually disable the zmm registers for AVX10/256
> and ymm registers for theoretical AVX10/128.

That's the easy part: That'll want doing in check_register(). The issue
is with insns which do 512-bit operation despite not using zmm registers
(think of vfpclassp* with memory operand).

> I suppose i386_opcode_modifier
> is more related to building up the whole encoding. But each AVX10.X/256 is an
> actual arch.

I wouldn't agree with the last sentence, but ...

> Adding a feature in i386_opcode_modifier can indicate what is the maximum
> vector length the instruction is allowed on all archs but has nothing to do with
> disabling zmm registers on an 256-bit only arch.

... you still have a point here. Maybe it only wants to be a boolean,
indicating that an insn is vector-length sensitive. Yet re-using the
EVex attribute continues to be an option: With vector length
constrained to 256 (or 128) bits, EVEX512 (or EVEX256) simply become
unavailable for encoding, and EVEXDYN would be equally constrained.
And if re-using that attribute continues to be an option, adding a
new non-boolean attribute clearly is also possible.

So I guess there may have been a slight misunderstanding: I was
suggesting an attribute expressing permissible vector lengths (hence
the consideration of re-using EVex), which would then be checked
against the established (through whatever directive / command line
option) maximum vector length. I did not suggest a new "max vector
length" attribute.

Jan