[RFC] How to add vector math functions to Glibc

[Joseph S. Myers]

On Mon, 27 Oct 2014, Andrew Senkevich wrote:

> >> +#  define __DECL_SIMD_cos  __DECL_SIMD_AVX2
> >> +#  define __DECL_SIMD_cosf __DECL_SIMD_SSE4
> >> +# elif defined _CILKPLUS && _CILKPLUS >= 0
> >> +/* CilkPlus case. TODO _CILKPLUS currently nowhere defined */
> >> +#  define __DECL_SIMD_AVX2 __attribute__((__vector__(nomask)))
> >> +#  define __DECL_SIMD_SSE4 __attribute__((__vector__(processor(core_i7_sse4_2),\
> >> +                                                  nomask)))
> >
> > And as previously noted, this needs to be fixed to be namespace-clean -
> > using __nomask__, __processor__, __core_i7_sse4_2__.
> 
> It seems there are no such reserved-namespace word versions now...

Then fix the compiler to have such reserved-namespace versions and put 
appropriate conditionals on a fixed compiler version in the header.  It's 
not OK to put random identifiers into an installed header like that.

> >> +#if defined TEST_MATHVEC
> >
> > No, you can't have such conditionals on a macro in the user's namespace in
> > an installed header.
> 
> Then we have to build vector tests with -D__FAST_MATH__
> -DTEST_FAST_MATH -D_OPENMP=201307 to be sure we have needed
> definitions from math.h?

Yes, -D__FAST_MATH__ is used for some other libm tests.

> >> diff --git a/sysdeps/x86_64/configure.ac b/sysdeps/x86_64/configure.ac
> >> index c9f9a51..91c4cdf 100644
> >> --- a/sysdeps/x86_64/configure.ac
> >> +++ b/sysdeps/x86_64/configure.ac
> >> @@ -5,6 +5,24 @@ AC_CHECK_HEADER([cpuid.h], ,
> >>    [AC_MSG_ERROR([gcc must provide the <cpuid.h> header])],
> >>    [/* No default includes.  */])
> >>
> >> +dnl Check if compiler target is x86_64.
> >
> > Not needed.  preconfigure fragments in sysdeps directories need to check
> > the architecture, but configure ones don't (they'll only be run for the
> > relevant architecture, unless one fragment explicitly sources another).
> 
> Clear, then it can be done in root configure like so:
> +if test x"$build_mathvec" = xnotset; then
> +  if test x"$machine" = xx86_64/64; then

No.  Such conditionals on particular systems do not go in the toplevel 
configure script.

If you want something for x86_64 (both -m64 and -mx32), it can go in 
sysdeps/x86_64/configure.ac, without any machine conditionals.  And if 
there's a good reason (please state the reason if so) something won't work 
for x32, put it in sysdeps/x86_64/64/configure.ac, again with no machine 
conditionals (and in that case, the implementation files would also go in 
sysdeps/x86_64/64/ directories).

-- 
Joseph S. Myers
joseph@codesourcery.com