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Re: [PATCH, i386] Handle extended family cpuid info for AMD


On Fri, Aug 1, 2014 at 5:00 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>> --- a/gcc/config/i386/driver-i386.c
>> +++ b/gcc/config/i386/driver-i386.c
>> @@ -432,7 +432,8 @@ const char *host_detect_local_cpu (int argc, const char **argv)
>>
>>    model = (eax >> 4) & 0x0f;
>>    family = (eax >> 8) & 0x0f;
>> -  if (vendor == signature_INTEL_ebx)
>> +  if ((vendor == signature_INTEL_ebx) ||
>> +      (vendor == signature_AMD_ebx))
>
> Wrong formatting.  No ()s around the comparisons needed, and
> || should go on the second line, not first.
>
>> @@ -576,7 +577,7 @@ const char *host_detect_local_cpu (int argc, const char **argv)
>>
>>        if (name == signature_NSC_ebx)
>>       processor = PROCESSOR_GEODE;
>> -      else if (has_movbe)
>> +      else if (family == 22)
>>       processor = PROCESSOR_BTVER2;
>
> Wouldn't it be safer to use has_movbe && family == 22?
> I mean, especially with emulators which choose to provide some architecture,
> but disable some CPUID flags it is IMHO safer to also check the flags.

OK, after rethinking this, let's go with the safer original patch
(sorry for a bit of confusion, but we cleared a lot of open questions
during the discussion).

The original patch is OK for mainline and branches.

OTOH, it looks we will have to redesign -march=native someday to only
pass options, derived from cpuid and eventually pass -mtune based on
detected family.

Thanks,
Uros.


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