Re: weird optimization in sin+cos, x86 backend

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Thu, 16 Feb 2012, Andrew Haley wrote:

> On 02/16/2012 02:42 PM, Vincent Lefevre wrote:
> > On 2012-02-15 15:18:45 +0000, Andrew Haley wrote:
> > > >  On 02/15/2012 09:30 AM, Vincent Lefevre wrote:
> > > > > >  >>  But to be absolutely clear, glibc's libm doesn't have a problem
> > > > > > > >>  meeting C99, AFAIK.
> > > > >  >  That's not quite correct. It is completely broken in directed
> > > > >  >  rounding modes (up to crashes).
> > > >
> > > >  Eh?  C99 doesn't require directed rounding modes.  I'll grant you,
> > > >  if they are provided they shouldn't crash.  :-)
> > C99 doesn't require directed rounding modes, but as long as they
> > are claimed to be supported by<fenv.h>, they should work:
> 
> Ah, I see.  So, we could bring gcc+glibc into compliance by not
> defining the rounding mode macros.

I don't think that's a good approach; I think we should fix the GCC bugs 
with -frounding-math etc. (and implement the standard pragmas).  It's just 
that completing the support for exceptions and rounding modes will involve 
a fair amount of work and user demand seems limited, so it hasn't been 
done yet.

-- 
Joseph S. Myers
joseph@codesourcery.com