Re: weird optimization in sin+cos, x86 backend

[Jakub Jelinek <jakub at redhat dot com>]

On Mon, Feb 13, 2012 at 02:48:05PM +0100, Richard Guenther wrote:
> > I think there is some consensus that crlibm is a great place to start
> > for correctly-rounded elementary functions. ?I think we'd need, or at
> > least greatly appreciate, some help from your team.
> 
> I agree.  If crlibm can provide a solid basis for a correctly implemented
> set of C99 math functions then use it.  It would be nice to have a
> GCC linking exception on it though, otherwise static linking or
> re-optimizing with LTO will be difficult.

Last time I've looked, crlibm even for double provides only a subset of
functions you are looking for for the math library, so you need to take
the various *signbit*/*scal*/fpclassify*/nexttoward*/nextafter*/rint*/round*
etc. from some other source (glibc, something else).
Furthermore, crlibm_init changes the i?86/x86_64 rounding mode globally,
that is not appropriate for a general purpose math library, there you either
need to cope with extended precision, or rely on SSE/SSE2 for float/double,
or change the rounding mode dynamically on entry and reset back to previous
state in all functions that rely on it.

	Jakub