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

On Fri, 12 Sep 2014, Jakub Jelinek wrote:

> Because GCC supports even another flavor, which presumably the patches
> implement.  The two you are mentioning are for compatibility with existing
> math libraries.  The third one is used by #pragma omp declare simd
> functions and Cilk+ elemental functions.  So, to use those you don't
> need any extra gcc support, glibc headers could just add
> #if defined(__OPENMP) && __OPENMP >= 201307
> #pragma omp declare simd
> #endif
> on the prototypes (of course maybe with some clauses if needed).

That's what this patch does - but we need a way for the headers to declare 
to GCC which vector ISAs have such versions of a given function available, 
in a way that works both for (new GCC, old glibc) (GCC knows about newer 
vector ISAs without function versions in that glibc, and mustn't try to 
generate calls to functions that glibc doesn't have) and (old GCC, new 
glibc) (glibc is declaring availability of vector versions the old GCC 
doesn't know how to use, so the references to those vector versions need 
to be quietly ignored or conditional on GCC version).

Joseph S. Myers

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