[Bug c/51628] __attribute__((packed)) is unsafe in some cases

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51628

--- Comment #8 from rguenther at suse dot de <rguenther at suse dot de> 2011-12-20 11:23:48 UTC ---
On Tue, 20 Dec 2011, ebotcazou at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51628
> 
> --- Comment #7 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-12-20 11:18:24 UTC ---
> > Huh, it's not.  It's the same as a packed struct or enum type.
> 
> No, it isn't, the mode is integral instead of BLKmode.  In Ada we do support
> misaligned integers, but we simply wrap them in a BLKmode record.
> 
> > Why can't you strict-align people simply fix this case?
> 
> Because integral modes are naturally aligned.  The only reasonable way to
> support the aforementioned abomination is to use the Ada approach.

You mean that handling the TYPE_ALIGN != MODE_ALIGN case when
expanding a MEM_REF (thus, INDIRECT_REF on old branches) won't work?
Why not?  You'd simply have to emit the same RTL as when expanding
that wrapped struct case.

Richard.