From: Jamie Lokier <egcs@tantalophile.demon.co.uk>
To: Robert Dewar <dewar@gnat.com>
Cc: aoliva@redhat.com, denisc@overta.ru, dkorn@pixelpower.com,
gcc@gcc.gnu.org, peter.osterlund@mailbox.swipnet.se
Subject: Re: Bug in loop optimize (invalid postinc to preinc transformation)
Date: Fri, 29 Dec 2000 18:36:00 -0000 [thread overview]
Message-ID: <20001230033626.A9314@thefinal.cern.ch> (raw)
In-Reply-To: <20001228063958.B325234D80@nile.gnat.com>
Robert Dewar wrote:
> <<Overflow of unsigned integers has defined behaviour -- they wrap. The
> question is, what rule applies to pointer comparisons?
> >>
>
> This is a malformed question. Any pointer increment is constrained
> to require that the resulting pointer be valid. Wrapping is simply
> not an issue.
>
> If p points to a valid address in an allocated array, then P+1 is also
> valid, and there is no question of wrap. But P+2 may be beyond the
> array and therefore ill-defined, and this has nothing to do with wrapping.
Quite. There's a pointer constant in the offending code. It's not in
any array. Do we offer implementation defined behaviour for numerical
pointer constants or not? They do come in useful occasionally.
-- Jamie
next prev parent reply other threads:[~2000-12-29 18:36 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-12-27 22:40 Robert Dewar
2000-12-29 18:36 ` Jamie Lokier [this message]
-- strict thread matches above, loose matches on Subject: below --
2000-12-31 8:30 dewar
2001-01-03 0:52 ` Jamie Lokier
2000-12-29 18:43 dewar
2000-12-30 15:18 ` Toon Moene
2000-12-28 20:33 dewar
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 1:14 Richard Kenner
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
2000-12-31 8:25 ` Andreas Schwab
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