This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Bug in loop optimize (invalid postinc to preinc transformation)
On Dec 28, 2000, Torbjorn Granlund <tege@swox.com> wrote:
> Alexandre Oliva <aoliva@redhat.com> writes:
> On Dec 27, 2000, Peter Osterlund <peter.osterlund@mailbox.swipnet.se> wrote:
>> Compiling without optimization indicates that the compiler is
>> transforming (p++ < x) into (++p < (x+1)), even when not optimizing.
>> This transformation is incorrect because x+1 wraps around.
> Overflow invokes undefined behavior. Since incrementing p in this
> case involves overflow, I think the transformation is ok, as far as
> undefined behavior goes.
> Overflow of *unsigned* types is well-defined.
Indeed. But I don't think pointers are unsigned by default, are they?
--
Alexandre Oliva Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist *Please* write to mailing lists, not to me