Re: HEADS-UP: gcc-4.2 import appears to miscompile libm.

On Sun, May 27, 2007 at 08:18:40AM -0700, Steve Kargl wrote:
> On Sun, May 27, 2007 at 10:53:09AM +0200, Stefan Ehmann wrote:
> > On Sunday 27 May 2007 01:31:16 Steve Kargl wrote:
> > > On Sat, May 26, 2007 at 07:09:16PM -0400, Wes Morgan wrote:
> > > > Working from -O towards -O2 based on the info pages, I can "reproduce"
> > > > the problem with "-O -fstrict-aliasing -fgcse"... However, -O2 with
> > > > -fno-strict-aliasing by itself seems to work around the issue. At first
> > > > glance it looks like a possible interaction between several
> > > > optimizations.
> > >
> > > Ths patch fixes the problem.
> > >
> > > --- s_frexpf.c.orig     Sat May 26 16:26:50 2007
> > > +++ s_frexpf.c  Sat May 26 16:28:03 2007
> > > _at__at_ -39,6 +39,9 _at__at_
> > >         }
> > >         *eptr += (ix>>23)-126;
> > >         hx = (hx&0x807fffff)|0x3f000000;
> > > +#if 0
> > >         *(int*)&x = hx;
> > > +#endif
> > > +       SET_FLOAT_WORD(x,hx);
> > >         return x;
> > >  }
> > 
> > -fno-strict-aliasing is used by default for me (i386). Also, if you use -Wall 
> > the compiler outputs a warning.
> 
> You apparently don't have CFLAGS set in /etc/make.conf.
> 
> > [root_at_something /usr/src/lib/msun/src]# cc -O2 -Wall -pipe  -c s_frexpf.c
> > s_frexpf.c: In function 'frexpf':
> > s_frexpf.c:42: warning: dereferencing type-punned pointer will break 
> > strict-aliasing rules
> 
> Yes, I know.
> 
> OTOH, the above patch actually fixes the problem, and libm can then
> be compiled without -fno-strict-aliasing.

OK, so just to confirm, it's not a miscompilation as originally
suggested, but a code bug?

Kris