From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexandre Oliva <aoliva@redhat.com>
To: Peter Osterlund <peter.osterlund@mailbox.swipnet.se>
Cc: 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 19:55:00 -0000
Message-id: <ork88ldwtr.fsf@guarana.lsd.ic.unicamp.br>
References: <718D38CAB6E0D011B2C90060970C28A5642545@EXCHANGESERVER> <m2snn9qvov.fsf@ppro.localdomain>
X-SW-Source: 2000-12/msg00785.html

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.

-- 
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