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Re: [PATCH 1/N] x86_64 vectorization support: vectorized math functions addition to Glibc


On 09/12/2014 11:01 AM, H.J. Lu wrote:
> On Thu, Sep 11, 2014 at 5:10 PM, Carlos O'Donell <carlos@redhat.com> wrote:
>> On 09/11/2014 04:57 PM, H.J. Lu wrote:
>>>> That doesn't answer my question.  Maybe glibc 2.21 provides such versions
>>>> for all x86 ISAs there are at present, up to AVX512 - and then a new
>>>> extension AVX1024 appears.  When GCC 7 is used with glibc 2.21 headers and
>>>> -mavx1024, it must not try to generate calls to the AVX1024 functions,
>>>> because glibc 2.21 doesn't have such functions.  But maybe glibc 2.26 adds
>>>> the AVX1024 functions.  So something needs to be different in the headers
>>>> of 2.26 to inform GCC 7 that AVX1024 versions of the functions are
>>>> available.  And I think that means the directive that communicates
>>>> function availability to the compiler needs to identify the set of ISAs
>>>> for which versions of the function in question are available.
>>>>
>>>
>>> Wouldn't it be better to put libmvec in GCC instead?
>>
>> That's certainly a discussion we can have.
>>
>> What do you see as the pros and cons?
>>
> 
> It depends on who are the main target users of this library.
> If it is mainly for programmers to use them directly in their
> applications, mostly independent of compilers, it should be
> in glibc.  But if it is mainly used by GCC, it should be in
> GCC, just like other run-time libraries.

The former. I want users to be able to call these functions
directly regardless of the compiler. The same goes for the
ppc-related API that has been in use for a long time by
developers there.

The compiler can certainly make use of these functions, and
any more standard cross-machine GNU API we design, but it
should always be possible to call them directly.

Does this mean libmvec should be in glibc?

Cheers,
Carlos.
 
 


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