------- Comment #11 from rguenther at suse dot de 2009-04-25 14:28 -------
Subject: Re: gcc-4.4 -Wstrict-aliasing and
-Wstrict-aliasing=3 behaves like -Wstrict-aliasing=2 in gcc-4.3
On Sat, 25 Apr 2009, edwintorok at gmail dot com wrote:
> ------- Comment #9 from edwintorok at gmail dot com 2009-04-25 14:22 -------
> (In reply to comment #6)
> > No, not if it is inlined (and if not you can as well use memcpy).
> >
> > You can also do (GCC extension)
> >
> > union union_t {
> > unsigned un;
> > char c[4];
> > };
> >
> > unsigned bar(char *x)
> > {
> > union union_t u;
> > u.c[0] = x[0];
> > u.c[1] = x[1];
> > u.c[2] = x[2];
> > u.c[3] = x[3];
> > return u.un;
> > }
> >
> > but that will even generate worse code with GCC than the
> > memcpy (it's even horrible code).
>
> Hmm, looks like the only way out is for me to put #if defined(__GNUC__) &&
> (__GNUC__ > 4) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 4) and use memcpy.
> Either that or add a configure rule to add -fno-strict-aliasing.
Another GCC extension is the following (this is what GCC 4.4 makes
out of the memcpy very early during optimization)
typedef unsigned __attribute__((may_alias,aligned(1))) my_unsigned;
unsigned bar(char *x)
{
return *(my_unsigned *)x;
}
That should work with even ancient GCC (I checked 3.3)
Richard.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39895
