From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexandre Oliva <aoliva@redhat.com>
To: Torbjorn Granlund <tege@swox.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 21:20:00 -0000
Message-id: <org0j9dt0t.fsf@guarana.lsd.ic.unicamp.br>
References: <718D38CAB6E0D011B2C90060970C28A5642545@EXCHANGESERVER> <m2snn9qvov.fsf@ppro.localdomain> <ork88ldwtr.fsf@guarana.lsd.ic.unicamp.br> <86hf3pm8s6.fsf@king.swox.se>
X-SW-Source: 2000-12/msg00788.html

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