Re: Support for Runtime CPU type detection via builtins (issue5754058)

[Sriraman Tallam <tmsriram at google dot com>]

On Mon, Apr 23, 2012 at 12:16 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Mon, Apr 23, 2012 at 6:59 PM, Sriraman Tallam <tmsriram@google.com> wrote:
>
>>>> i386 maintainers - ?Is this patch ok?
>>>
>>> Has the community reached the consensus on how this kind of
>>> functionality has to be implemented? I have followed the discussion a
>>> bit, but IIRC, there was no clear decision. Without this decision, I
>>> am not able to review the _implementation_ of agreed functionality for
>>> x86 target.
>>>
>>> (I apologize if I have missed the decision, please point me to the
>>> discussion in this case.)
>>
>> The discussions are here:
>>
>> http://gcc.gnu.org/ml/gcc-patches/2011-08/msg01446.html
>> and follow-ups to this.
>>
>> I am not sure about consensus, but the important points raised were:
>>
>> 1) Constructor ordering: What if some constructors fire before
>> cpu_indicator_init?, which determines the CPU. I addressed this
>> problem by making the priority of cpu_indicator_init to be the highest
>> possible. Still, IFUNC initializers will fire before and they have to
>> explicitly call __builtin_cpu_init() before checking the CPU type.
>> 2) Reducing the number of builtins : It is only two now.
>
>> ? ? ? * config/i386/i386.c (build_processor_features_struct): New function.
>> ? ? ? (build_processor_model_struct): New function.
>> ? ? ? (make_var_decl): New function.
>> ? ? ? (get_field_from_struct): New function.
>> ? ? ? (fold_builtin_target): New function.
>> ? ? ? (ix86_fold_builtin): New function.
>> ? ? ? (ix86_expand_builtin): Expand new builtins by folding them.
>> ? ? ? (make_cpu_type_builtin): New functions.
>> ? ? ? (ix86_init_platform_type_builtins): Make the new builtins.
>> ? ? ? (ix86_init_builtins): Make new builtins to detect CPU type.
>> ? ? ? (TARGET_FOLD_BUILTIN): New macro.
>> ? ? ? (IX86_BUILTIN_CPU_INIT): New enum value.
>> ? ? ? (IX86_BUILTIN_CPU_IS): New enum value.
>> ? ? ? (IX86_BUILTIN_CPU_SUPPORTS): New enum value.
>> ? ? ? * config/i386/i386-builtin-types.def: New function type.
>> ? ? ? * testsuite/gcc.target/builtin_target.c: New testcase.
>> ? ? ? * doc/extend.texi: Document builtins.
>>
>> ? ? ? * libgcc/config/i386/i386-cpuinfo.c: New file.
>> ? ? ? * libgcc/config/i386/t-cpuinfo: New file.
>> ? ? ? * libgcc/config.host: Include t-cpuinfo.
>> ? ? ? * libgcc/config/i386/libgcc-glibc.ver: Version symbols __cpu_model
>> ? ? ? and __cpu_features.
>
> The patch is OK.
>
> I guess that AVX is left as an exercise for a x86 maintainer ;)

I will add AVX, and make all the changes.

Thanks,
-Sri.

>
> (I have also CC'd H.J. for his opinion.)
>
> Thanks,
> Uros.