[PATCH 4/5] x86/APX: extend SSE2AVX coverage

[Jan Beulich]

On 29.03.2024 10:10, Cui, Lili wrote:
>> Legacy encoded SIMD insns are converted to AVX ones in that mode. When
>> eGPR-s are in use, i.e. with APX, convert to AVX10 insns (where
>> available; there are quite a few which can't be converted).
>>
>> For GFNI alter the gfni template such that VexW would be emitted even
>> for the SSE templates: There the attribute is simply meaningless, but
>> it simplifies the template quite a bit.
> 
> For this part, although adding VexW to the SSE template is more concise, it also breaks the rules and creates hidden dangers, it feels a bit unworthy.

Coming back to this: What rules is this breaking?

I can see your point of "hidden dangers", yet I'm unsure about drawing
the conclusion that it's "unworthy": The <gfni> template would need
dropping altogether in the alternative approach, doubling the number of
insn template lines. That's not _that_ much, but still worthwhile to
weigh against those latent risks.

>  GFNI SSE does not support eGPR-s, I'm not sure if we should give it an error instead of converting it.

Well, this would mean not converting various others either. One of the
goals, however, was to allow conversion of as many of the insns as
possible, even if their legacy forms has no REX2 representation.

Jan