HEADS-UP: gcc-4.2 import appears to miscompile libm.
sgk at troutmask.apl.washington.edu
Sun May 27 15:20:30 UTC 2007
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
> > @@ -39,6 +39,9 @@
> > }
> > *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.
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