From: Bernd Schmidt <bernds AT cygnus.co.uk>
To: Marcel Cox <Marcel.Cox AT cie.etat.lu>
Cc: gcc AT gcc.gnu.org, jbuck AT synopsys.COM, rms AT gnu.org
Subject: Re: type based aliasing again
Date: Tue, 14 Sep 1999 06:50:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.10.9909141448330.20868-100000@biriani.cygnus.co.uk> (raw)
In-Reply-To: <37DE51A9.F939A1D3@cie.etat.lu>
> I used the following test program with the following version of GCC:
> gcc version 2.96 19990912 (experimental) i486-pc-linux-gnu
>
> It showed that all union constructs were alias safe when compared to the
> plain typecast version
You can't show that something is safe this way. If your programs work, then
the compiler did not choose to take advantage of its aliasing information
for this input. That doesn't mean it won't do so for any other program. It
takes only one counterexample to show that the "cast to union" method is not
safe either, and such an example exists.
Bernd
WARNING: multiple messages have this Message-ID
From: Bernd Schmidt <bernds@cygnus.co.uk>
To: Marcel Cox <Marcel.Cox@cie.etat.lu>
Cc: gcc@gcc.gnu.org, jbuck@synopsys.COM, rms@gnu.org
Subject: Re: type based aliasing again
Date: Thu, 30 Sep 1999 18:02:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.10.9909141448330.20868-100000@biriani.cygnus.co.uk> (raw)
Message-ID: <19990930180200.dnQLM-Jsbpt7RDZ94z4Pv23ATYDYfSWk9ohyzy8rYHc@z> (raw)
In-Reply-To: <37DE51A9.F939A1D3@cie.etat.lu>
> I used the following test program with the following version of GCC:
> gcc version 2.96 19990912 (experimental) i486-pc-linux-gnu
>
> It showed that all union constructs were alias safe when compared to the
> plain typecast version
You can't show that something is safe this way. If your programs work, then
the compiler did not choose to take advantage of its aliasing information
for this input. That doesn't mean it won't do so for any other program. It
takes only one counterexample to show that the "cast to union" method is not
safe either, and such an example exists.
Bernd
next prev parent reply other threads:[~1999-09-14 6:50 UTC|newest]
Thread overview: 404+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-09-14 6:46 Marcel Cox
1999-09-14 6:50 ` Bernd Schmidt [this message]
1999-09-14 7:14 ` Marcel Cox
1999-09-14 8:45 ` Jamie Lokier
1999-09-30 18:02 ` Jamie Lokier
1999-09-30 18:02 ` Marcel Cox
1999-09-30 18:02 ` Bernd Schmidt
1999-09-30 18:02 ` Marcel Cox
[not found] <19990921182843.25292.qmail@deer>
1999-09-21 15:47 ` John W. Stevens
1999-09-21 16:15 ` craig
1999-09-21 20:37 ` David Edelsohn
1999-09-30 18:02 ` David Edelsohn
1999-09-23 9:06 ` John W. Stevens
1999-09-23 11:06 ` craig
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` John W. Stevens
1999-09-30 18:02 ` craig
1999-09-27 6:56 ` Rask Ingemann Lambertsen
1999-09-27 8:32 ` Joe Buck
1999-09-30 18:02 ` Joe Buck
1999-09-30 18:02 ` Rask Ingemann Lambertsen
1999-09-30 18:02 ` John W. Stevens
-- strict thread matches above, loose matches on Subject: below --
1999-09-21 8:48 Harvey J. Stein
1999-09-22 12:15 ` Richard Stallman
1999-09-22 13:08 ` Harvey J. Stein
1999-09-24 23:37 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Harvey J. Stein
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Harvey J. Stein
1999-09-18 8:33 N8TM
1999-09-30 18:02 ` N8TM
1999-09-18 7:30 Stephen L Moshier
1999-09-30 18:02 ` Stephen L Moshier
1999-09-18 3:25 Artem Hodyush
1999-09-18 11:29 ` Russ Allbery
1999-09-20 5:54 ` Joern Rennecke
1999-09-30 18:02 ` Joern Rennecke
1999-09-30 18:02 ` Russ Allbery
1999-09-19 13:54 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-21 8:50 ` Harvey J. Stein
1999-09-30 18:02 ` Harvey J. Stein
1999-09-30 18:02 ` Artem Hodyush
1999-09-18 2:51 Ross Morgan-Linial
[not found] ` <19990918151905.F1650@cerebro.laendle>
1999-09-18 22:18 ` Ross Morgan-Linial
1999-09-30 18:02 ` Ross Morgan-Linial
1999-09-30 18:02 ` Ross Morgan-Linial
1999-09-17 9:02 Harvey J. Stein
1999-09-30 18:02 ` Harvey J. Stein
[not found] <199909161750.LAA12073@basho.fc.hp.com>
1999-09-16 14:29 ` craig
1999-09-20 15:17 ` John W. Stevens
1999-09-30 18:02 ` John W. Stevens
1999-09-30 18:02 ` craig
1999-09-16 6:12 Artem Hodyush
1999-09-16 23:15 ` Richard Stallman
1999-09-16 23:38 ` Gabriel Dos_Reis
1999-09-17 22:16 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Gabriel Dos_Reis
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Artem Hodyush
[not found] <Pine.SO4.4.05.9909160153420.23533-100000@tamarack.cs.mtu.edu>
1999-09-16 2:19 ` craig
1999-09-30 18:02 ` craig
1999-09-15 21:47 Florin Mateoc
1999-09-16 2:18 ` craig
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Florin Mateoc
1999-09-15 11:42 Michael J. Bedy
1999-09-15 14:32 ` craig
1999-09-16 23:14 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Michael J. Bedy
1999-09-15 8:27 Kaveh R. Ghazi
1999-09-15 8:57 ` Nathan Sidwell
1999-09-30 18:02 ` Nathan Sidwell
1999-09-30 18:02 ` Kaveh R. Ghazi
1999-09-15 7:02 David Ronis
1999-09-30 18:02 ` David Ronis
1999-09-13 21:45 N8TM
1999-09-14 4:01 ` Marc Espie
1999-09-14 9:56 ` David Edelsohn
1999-09-14 10:10 ` Richard Earnshaw
1999-09-14 10:31 ` Nick Ing-Simmons
1999-09-14 10:52 ` David Edelsohn
1999-09-14 11:11 ` craig
1999-09-14 14:44 ` David Edelsohn
1999-09-30 18:02 ` David Edelsohn
1999-09-14 15:06 ` David Edelsohn
1999-09-14 17:35 ` Marc Lehmann
1999-09-30 18:02 ` Marc Lehmann
1999-09-14 23:41 ` craig
1999-09-15 8:28 ` Marc Lehmann
1999-09-30 18:02 ` Marc Lehmann
1999-09-15 9:19 ` David Edelsohn
1999-09-15 9:59 ` Nick Ing-Simmons
1999-09-15 15:33 ` David Edelsohn
1999-09-30 18:02 ` David Edelsohn
1999-09-30 18:02 ` Nick Ing-Simmons
1999-09-15 10:01 ` craig
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` David Edelsohn
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` David Edelsohn
1999-09-30 18:02 ` craig
1999-09-14 11:58 ` Gerald Pfeifer
1999-09-30 18:02 ` Gerald Pfeifer
1999-09-30 18:02 ` David Edelsohn
1999-09-14 11:01 ` craig
1999-09-14 11:14 ` craig
1999-09-30 18:02 ` craig
1999-09-14 11:39 ` Mark Mitchell
1999-09-14 14:48 ` Toon Moene
1999-09-14 15:00 ` David Edelsohn
1999-09-14 16:01 ` Toon Moene
1999-09-14 16:15 ` David Edelsohn
1999-09-14 16:43 ` Mark Mitchell
1999-09-30 18:02 ` Mark Mitchell
1999-09-14 17:39 ` Marc Lehmann
1999-09-30 18:02 ` Marc Lehmann
1999-09-30 18:02 ` David Edelsohn
1999-09-14 16:19 ` dvv
1999-09-14 17:38 ` Michael Meissner
1999-09-30 18:02 ` Michael Meissner
1999-09-30 18:02 ` Dima Volodin
1999-09-30 18:02 ` Toon Moene
1999-09-30 18:02 ` David Edelsohn
1999-09-14 15:08 ` Mark Mitchell
1999-09-30 18:02 ` Mark Mitchell
1999-09-30 18:02 ` Toon Moene
1999-09-30 18:02 ` Mark Mitchell
1999-09-30 18:02 ` craig
1999-09-14 23:46 ` Geoff Keating
1999-09-15 7:47 ` Nick Ing-Simmons
1999-09-30 18:02 ` Nick Ing-Simmons
1999-09-30 18:02 ` Geoff Keating
1999-09-30 18:02 ` Nick Ing-Simmons
1999-09-30 18:02 ` Richard Earnshaw
1999-09-14 17:22 ` Marc Lehmann
1999-09-30 18:02 ` Marc Lehmann
1999-09-30 18:02 ` David Edelsohn
1999-09-14 17:23 ` Marc Lehmann
1999-09-15 1:59 ` Marc Espie
1999-09-15 8:28 ` Marc Lehmann
1999-09-30 18:02 ` Marc Lehmann
1999-09-30 18:02 ` Marc Espie
1999-09-30 18:02 ` Marc Lehmann
1999-09-15 2:01 ` Jeffrey A Law
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Marc Espie
1999-09-30 18:02 ` N8TM
1999-09-13 16:34 Mike Stump
1999-09-14 22:20 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Mike Stump
1999-09-13 10:55 R. Kelley Cook
1999-09-13 13:22 ` craig
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` R. Kelley Cook
1999-09-12 11:20 Josh Stern
1999-09-30 18:02 ` Josh Stern
[not found] <9377.936981585@upchuck.cygnus.com>
1999-09-12 0:52 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-11 21:48 N8TM
1999-09-30 18:02 ` N8TM
1999-09-11 18:21 Phil Edwards
1999-09-30 18:02 ` Phil Edwards
1999-09-10 8:43 craig
1999-09-12 0:49 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` craig
1999-09-09 21:54 Alex Rosenberg
1999-09-30 18:02 ` Alex Rosenberg
1999-09-09 15:40 Claus Fischer
1999-09-09 15:57 ` David Starner
1999-09-09 16:24 ` Claus Fischer
1999-09-09 16:55 ` Joe Buck
1999-09-09 17:31 ` Claus Fischer
1999-09-30 18:02 ` Claus Fischer
1999-09-30 18:02 ` Joe Buck
1999-09-10 8:42 ` craig
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Claus Fischer
1999-09-30 18:02 ` David Starner
1999-09-09 16:37 ` Jeffrey A Law
1999-09-09 17:15 ` Claus Fischer
1999-09-30 18:02 ` Claus Fischer
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Claus Fischer
1999-09-09 14:26 Mike Stump
1999-09-09 14:38 ` Mark Mitchell
1999-09-11 0:16 ` Richard Stallman
1999-09-15 2:07 ` Jeffrey A Law
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Mark Mitchell
1999-09-30 18:02 ` Mike Stump
1999-09-08 19:13 Mike Stump
1999-09-08 19:31 ` Joe Buck
1999-09-30 18:02 ` Joe Buck
1999-09-09 7:12 ` Marc Espie
1999-09-09 20:35 ` Jeffrey A Law
1999-09-10 12:29 ` Sudish Joseph
1999-09-30 18:02 ` Sudish Joseph
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Marc Espie
1999-09-09 23:25 ` Richard Stallman
1999-09-08 18:11 ` Joe Buck
1999-09-08 18:43 ` Mark Mitchell
1999-09-08 19:25 ` Joe Buck
1999-09-08 19:51 ` David Edelsohn
1999-09-30 18:02 ` David Edelsohn
1999-09-30 18:02 ` Joe Buck
1999-09-08 19:44 ` Joe Buck
1999-09-08 20:26 ` Mark Mitchell
1999-09-08 20:43 ` Joe Buck
1999-09-08 21:45 ` Mark Mitchell
1999-09-08 22:04 ` Joe Buck
1999-09-08 22:25 ` Mark Mitchell
1999-09-30 18:02 ` Mark Mitchell
1999-09-09 2:08 ` Jeffrey A Law
1999-09-09 10:51 ` Joe Buck
1999-09-09 16:51 ` John Vickers
1999-09-09 17:04 ` Joe Buck
1999-09-09 17:12 ` John Vickers
1999-09-30 18:02 ` John Vickers
1999-09-30 18:02 ` Joe Buck
1999-09-30 18:02 ` John Vickers
1999-09-15 2:07 ` Jeffrey A Law
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Joe Buck
1999-09-09 23:26 ` Richard Stallman
1999-09-09 23:38 ` Jeffrey A Law
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Richard Stallman
1999-09-09 23:26 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Jeffrey A Law
1999-09-09 23:25 ` Richard Stallman
1999-09-10 0:06 ` Mark Mitchell
1999-09-10 0:13 ` Joe Buck
1999-09-30 18:02 ` Joe Buck
1999-09-11 0:17 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Mark Mitchell
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Joe Buck
1999-09-08 23:20 ` Richard Henderson
1999-09-08 23:41 ` Mark Mitchell
1999-09-08 23:44 ` Richard Henderson
1999-09-08 23:51 ` Mark Mitchell
1999-09-30 18:02 ` Mark Mitchell
1999-09-09 2:45 ` Jeffrey A Law
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Richard Henderson
1999-09-30 18:02 ` Mark Mitchell
1999-09-30 18:02 ` Richard Henderson
1999-09-30 18:02 ` Mark Mitchell
1999-09-30 18:02 ` Joe Buck
1999-09-08 21:33 ` Joe Buck
1999-09-08 21:56 ` Mark Mitchell
1999-09-30 18:02 ` Mark Mitchell
1999-09-09 1:38 ` Martin v. Loewis
1999-09-30 18:02 ` Martin v. Loewis
1999-09-09 23:25 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Joe Buck
1999-09-09 2:20 ` Jeffrey A Law
1999-09-09 7:58 ` craig
1999-09-09 10:36 ` Joe Buck
1999-09-09 10:55 ` Mark Mitchell
1999-09-11 0:15 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Mark Mitchell
1999-09-09 11:51 ` craig
1999-09-09 12:45 ` Joe Buck
1999-09-30 18:02 ` Joe Buck
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Joe Buck
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Jeffrey A Law
1999-09-09 23:26 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Mark Mitchell
1999-09-30 18:02 ` Joe Buck
1999-09-09 23:25 ` Richard Stallman
1999-09-10 0:03 ` Mark Mitchell
1999-09-10 0:23 ` Joe Buck
1999-09-11 0:17 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Joe Buck
1999-09-11 0:17 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Mark Mitchell
1999-09-10 14:29 ` Marc Lehmann
1999-09-30 18:02 ` Marc Lehmann
1999-09-15 2:05 ` Jeffrey A Law
1999-09-15 7:55 ` Nick Ing-Simmons
1999-09-30 18:02 ` Nick Ing-Simmons
1999-09-15 23:14 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Mark Mitchell
1999-09-08 20:44 ` Joe Buck
1999-09-30 18:02 ` Joe Buck
1999-09-14 3:04 ` Alexandre Oliva
1999-09-14 5:34 ` Bernd Schmidt
1999-09-14 5:45 ` Alexandre Oliva
1999-09-14 5:52 ` Bernd Schmidt
1999-09-30 18:02 ` Bernd Schmidt
1999-09-21 1:16 ` Rask Ingemann Lambertsen
1999-09-21 2:02 ` Jamie Lokier
1999-09-30 18:02 ` Jamie Lokier
1999-09-30 18:02 ` Rask Ingemann Lambertsen
1999-09-30 18:02 ` Alexandre Oliva
1999-09-14 9:31 ` Andi Kleen
1999-09-30 18:02 ` Andi Kleen
1999-09-30 18:02 ` Bernd Schmidt
1999-09-14 22:22 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Alexandre Oliva
1999-09-30 18:02 ` Joe Buck
1999-09-10 0:11 ` Joe Buck
1999-09-10 8:43 ` craig
1999-09-10 18:25 ` Jonathan Larmour
1999-09-11 3:50 ` craig
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Jonathan Larmour
1999-09-11 0:15 ` Richard Stallman
1999-09-11 3:51 ` craig
1999-09-12 0:51 ` Richard Stallman
1999-09-12 8:54 ` craig
1999-09-13 0:47 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` craig
1999-09-11 0:14 ` Richard Stallman
1999-09-11 15:20 ` Mark Mitchell
1999-09-11 18:04 ` David Edelsohn
1999-09-11 18:20 ` Mark Mitchell
1999-09-11 23:40 ` Sudish Joseph
1999-09-30 18:02 ` Sudish Joseph
1999-09-12 8:16 ` Robert Lipe
1999-09-30 18:02 ` Robert Lipe
1999-09-30 18:02 ` Mark Mitchell
1999-09-13 0:47 ` Richard Stallman
1999-09-15 2:06 ` Jeffrey A Law
1999-09-15 8:02 ` Nick Ing-Simmons
1999-09-15 9:20 ` Jeffrey A Law
1999-09-15 9:31 ` David Edelsohn
1999-09-15 10:02 ` craig
1999-09-16 23:13 ` Richard Stallman
1999-09-17 1:51 ` craig
1999-09-17 22:16 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` David Edelsohn
1999-09-15 9:56 ` Nick Ing-Simmons
1999-09-15 10:08 ` craig
1999-09-15 10:48 ` Nick Ing-Simmons
1999-09-15 14:32 ` craig
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Nick Ing-Simmons
1999-09-16 10:54 ` Andi Kleen
1999-09-16 12:08 ` Joern Rennecke
1999-09-16 12:18 ` Mark Mitchell
1999-09-30 18:02 ` Mark Mitchell
1999-09-30 18:02 ` Joern Rennecke
1999-09-16 14:29 ` craig
1999-09-16 22:19 ` Andi Kleen
1999-09-30 18:02 ` Andi Kleen
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Andi Kleen
1999-09-16 23:13 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` craig
1999-09-30 18:02 ` Nick Ing-Simmons
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Nick Ing-Simmons
1999-09-15 23:14 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` David Edelsohn
1999-09-12 9:45 ` Jonathan Larmour
1999-09-30 18:02 ` Jonathan Larmour
1999-09-13 0:47 ` Richard Stallman
1999-09-30 18:02 ` Richard Stallman
1999-09-13 4:05 ` Richard Earnshaw
1999-09-15 2:05 ` Jeffrey A Law
1999-09-30 18:02 ` Jeffrey A Law
1999-09-30 18:02 ` Richard Earnshaw
1999-09-30 18:02 ` Mark Mitchell
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Joe Buck
1999-09-30 18:02 ` Richard Stallman
1999-09-30 18:02 ` Mike Stump
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