x86: Support Intel AVX VNNI

[Jan Beulich]

On 20.10.2020 19:17, H.J. Lu wrote:
> On Tue, Oct 20, 2020 at 1:00 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 19.10.2020 21:52, H.J. Lu wrote:
>>> I probably lost the track.   Let me rephrase it again.  The {vex}
>>> prefix for AVX VNNI is mandatory.
>>
>> And let me re-ask: Why? You've made your point for the gas side
>> (which I don't agree with, but that's a different aspect). I'm
>> still not understanding your reasoning on the disassembler side.
>> This is why I did point out that for e.g. vaddps the different
>> possible encodings can't be told apart either.
> 
> We should enable to tell VEX from EVEX in the output of
> 
> $ objdump -dw --no-show-raw-insn

But not by default (and --show-raw-insn is off by default), only
if some option (possibly --no-show-raw-insn, but I'm not convinced
of such a "reuse") was specified explicitly. Just like other cases
of multiple possible encodings don't get disambiguated by default
(simply because by default it doesn't matter which encoding was
chosen) - swap_operand(), for example, gets enabled by -Msuffix,
and I think extending the meaning of this option would be more
sensible.

But the main point in the context here is: The printing of {vex}
for AVX-VNNI insns should _also_ be similarly conditional.

Jan