[RFC, VECTOR ABI] Allow __attribute__((vector)) in GCC by default.

[Joseph Myers]

On Mon, 5 Oct 2015, Kirill Yukhin wrote:

> To enable vectorization of loops w/ calls to math functions it is reasonable
> to enable parsing of attribute vector for functions unconditionally and
> change GlibC's header file not to use `omp declare simd', but use 
> __attribute__((vector)) instead.

I assume you mean __vector__, for namespace reasons.  Obviously you need 
appropriate GCC version conditionals in the headers to use the attribute 
only when supported.  In addition, (a) this attribute doesn't seem to be 
documented in extend.texi, and you'll need to include documentation in 
your GCC patch that makes this a generic extension rather than just part 
of Cilkplus, and (b) you'll need to agree with the x86_64 ABI mailing list 
an extension of the ABI document (as attached to 
<https://sourceware.org/glibc/wiki/libmvec>) to cover this attribute, and 
update the document there.

-- 
Joseph S. Myers
joseph@codesourcery.com