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

On Thu, Sep 11, 2014 at 1:52 PM, Joseph S. Myers
<> wrote:
> On Thu, 11 Sep 2014, Zamyatin, Igor wrote:
>> > > * How do we handle different glibc versions having vectorized
>> > > functions for different vector ISA extensions?  You're using a single
>> > > __DECL_SIMD, and having such a function only for AVX2.  But one glibc
>> > > version could have a function vectorized for ISA extensions A and B,
>> > > with another version adding it vectorized for C.  The compiler the
>> > > user uses with the installed glibc headers must be able to tell from
>> > > those headers which functions have what vectorized versions.  That is,
>> > > if a glibc version is released where _Pragma ("omp declare simd") is
>> > > used with a function that only has an AVX2 vectorized version, no past
>> > > or future GCC version can interpret that pragma as meaning that any
>> > > version other than AVX2 is available (it must be possible to use any
>> > > installed glibc headers with both past and future compilers).
>> We can require providing versions for all possible ISAs (we are going to
>> do this for x86) so compiler should do all work itself.
> 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?


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