Re: [Xen-devel] [PATCH v8 30/50] x86emul: support AVX512{F, _VBMI2} compress/expand insns

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.06.19 at 16:51, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 15/03/2019 10:56, Jan Beulich wrote:
>> +#if __GNUC__ > 7 /* can't check for __AVX512VBMI2__ here */
> 
> Why not?

Because that would require passing -mavx512vbmi2 (or enabling the
feature via #pragma) which in turn would need gating on compiler
version, or else the harness couldn't be built with gcc7 at all anymore.

>> --- a/xen/tools/gen-cpuid.py
>> +++ b/xen/tools/gen-cpuid.py
>> @@ -266,10 +266,10 @@ def crunch_numbers(state):
>>                    AVX512BW, AVX512VL, AVX512_4VNNIW, AVX512_4FMAPS,
>>                    AVX512_VPOPCNTDQ],
>>  
>> -        # AVX512 extensions acting solely on vectors of bytes/words are made
>> +        # AVX512 extensions acting (solely) on vectors of bytes/words are 
>> made

Because VBMI2 doesn't act _solely_ on vectors of bytes/words.
There are also shift insns acting on vectors of dwords/qwords.

Jan



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