Re: [PATCH] x86: add missing APX logic to cpu_flags_match()

[Jan Beulich <jbeulich@suse.com>]

On 08.01.2024 09:30, Cui, Lili wrote:
>>>> --- a/gas/config/tc-i386.c
>>>> +++ b/gas/config/tc-i386.c
>>>> @@ -1940,6 +1940,30 @@ cpu_flags_match (const insn_template *t)
>>>>  	      any.bitfield.cpuavx512vl = 0;
>>>>  	    }
>>>>  	}
>>>> +
>>>> +      /* Dual non-APX/APX templates need massaging from what APX_F() in
>> the
>>>> +         opcode table has produced.  While the direct transformation of the
>>>> +         incoming cpuid&(cpuid|APX_F) would be to cpuid&(cpuid) /
>>>> cpuid&(APX_F)
>>>> +         respectively, it's cheaper to move to just cpuid / cpuid&APX_F
>>>> +         instead.  */
>>>> +      if (any.bitfield.cpuapx_f
>>>> +	  && (any.bitfield.cpubmi || any.bitfield.cpubmi2
>>>> +	      || any.bitfield.cpuavx512f || any.bitfield.cpuavx512bw
>>>> +	      || any.bitfield.cpuavx512dq || any.bitfield.cpuamx_tile
>>>> +	      || any.bitfield.cpucmpccxadd))
>>>> +	{
>>>> +	  /* These checks (verifying that APX_F() was properly used in the
>>>> +	     opcode table entry) make sure there's no need for an "else" to
>>>> +	     the "if()" below.  */
>>>> +	  gas_assert (!cpu_flags_all_zero (&all));
>>>> +	  cpu = cpu_flags_and (all, any);
>>>> +	  gas_assert (cpu_flags_equal (&cpu, &all));
>>>> +
>>>> +	  if (need_evex_encoding (t))
>>>> +	    all = any;
>>>> +
>>>
>>>> +	  memset (&any, 0, sizeof (any));
>>>
>>> Wouldn't it make sense to put it in the else branch and clean out APX-F
>> specifically? Just like you did before.
>>>
>>>   if (need_evex_encoding (t))
>>>     all = any;
>>> else
>>>    any.bitfield.cpuapx_f = 0;
>>
>> That was an alternative I did consider, yes, but the way I've done it is overall
>> more self-consistent imo, at the expense of being less consistent with the
>> AVX/AVX512 logic (the moving of "any" to "all" isn't consistent with that
>> anyway).
>>
> 
>   memset (&any, 0, sizeof (any)); 
> 
> I'd say this would make "any" not match the actual value, which might be used later, but it's been cleared here.

I'm afraid I don't get what you're trying to tell me.

Jan