From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jamie Lokier <egcs@tantalophile.demon.co.uk>
To: Alexandre Oliva <aoliva@redhat.com>
Cc: Peter Osterlund <peter.osterlund@mailbox.swipnet.se>, David Korn <dkorn@pixelpower.com>, "'Denis Chertykov'" <denisc@overta.ru>, gcc@gcc.gnu.org
Subject: Re: Bug in loop optimize (invalid postinc to preinc transformation)
Date: Wed, 27 Dec 2000 22:24:00 -0000
Message-id: <20001228071627.C4578@thefinal.cern.ch>
References: <718D38CAB6E0D011B2C90060970C28A5642545@EXCHANGESERVER> <m2snn9qvov.fsf@ppro.localdomain> <ork88ldwtr.fsf@guarana.lsd.ic.unicamp.br>
X-SW-Source: 2000-12/msg00790.html

Alexandre Oliva 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 integers has defined behaviour -- they wrap.  The
question is, what rule applies to pointer comparisons?

-- Jamie