From mboxrd@z Thu Jan  1 00:00:00 1970
From: Torbjorn Granlund <tege@swox.com>
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 21:09:00 -0000
Message-id: <86hf3pm8s6.fsf@king.swox.se>
References: <718D38CAB6E0D011B2C90060970C28A5642545@EXCHANGESERVER> <m2snn9qvov.fsf@ppro.localdomain> <ork88ldwtr.fsf@guarana.lsd.ic.unicamp.br>
X-SW-Source: 2000-12/msg00787.html

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.  

-- 
Torbjörn