[Bug middle-end/39895] gcc-4.4 -Wstrict-aliasing and -Wstrict-aliasing=3 behaves like -Wstrict-aliasing=2 in gcc-4.3

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #6 from rguenther at suse dot de  2009-04-25 14:17 -------
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 #4 from edwintorok at gmail dot com  2009-04-25 14:12 -------
> (In reply to comment #3)
> > 
> > The above is properly optimized.  Why do you think that an inline
> > function taking void * would fix anything?
> 
> I can't know if memcpy will be inlined, it may just be a function call on
> certain systems, with certain compilers.
> The inline function should be a more portable way of expressing what I need,
> and it shouldn't cause any bugs with -fstrict-aliasing, since gcc already knows
> I gave my pointer to a function taking void*, so anything could happen with it,
> right?

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).

Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39895