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 [thread overview]
Message-ID: <20001228071627.C4578@thefinal.cern.ch> (raw)
In-Reply-To: <ork88ldwtr.fsf@guarana.lsd.ic.unicamp.br>
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
next prev parent reply other threads:[~2000-12-27 22:24 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-12-27 3:04 Bug in loop optimize (TREE stage) David Korn
2000-12-27 15:42 ` Bug in loop optimize (invalid postinc to preinc transformation) Peter Osterlund
2000-12-27 19:55 ` Alexandre Oliva
2000-12-27 21:09 ` Torbjorn Granlund
2000-12-27 21:20 ` Alexandre Oliva
2000-12-27 22:24 ` Jamie Lokier [this message]
2000-12-31 8:25 ` Andreas Schwab
2000-12-27 22:40 Robert Dewar
2000-12-29 18:36 ` Jamie Lokier
2000-12-28 1:14 Richard Kenner
2000-12-28 5:40 Robert Dewar
2000-12-28 12:21 ` Alexandre Oliva
2000-12-28 14:32 ` Geoff Keating
2000-12-28 15:22 ` Tim Hollebeek
2000-12-28 22:20 ` Dave Korn
2000-12-29 0:52 ` Richard Henderson
2000-12-29 1:51 ` Tim Hollebeek
2000-12-28 20:33 dewar
2000-12-29 18:43 dewar
2000-12-30 15:18 ` Toon Moene
2000-12-31 8:30 dewar
2001-01-03 0:52 ` Jamie Lokier
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