[Bug libstdc++/81706] std::sin vectorization bug

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81706

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 41923
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41923&action=edit
gcc8-pr81706.patch

The reason for why cmath does this is that C++ wants to have sin overloads. 
And the problem is that we have the simd attributes only on ::sinf, ::sin etc.,
but not on __builtin_sinf, __builtin_sin etc.
So, either we change libstdc++ like with this untested patch, or change the
compiler, so that when seeing a matching decl for a builtin which has simd
attribute on it, we duplicate the attribute to the __builtin_* decl too.

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #2)
> Created attachment 41923 [details]
> gcc8-pr81706.patch
> 
> The reason for why cmath does this is that C++ wants to have sin overloads. 
> And the problem is that we have the simd attributes only on ::sinf, ::sin
> etc., but not on __builtin_sinf, __builtin_sin etc.
> So, either we change libstdc++ like with this untested patch, or change the
> compiler, so that when seeing a matching decl for a builtin which has simd
> attribute on it, we duplicate the attribute to the __builtin_* decl too.

I'd prefer the attached patch to libstdc++ (which is incomplete of course).