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From: Jamie Lokier <egcs@tantalophile.demon.co.uk>
To: mark@codesourcery.com
Cc: ak@muc.de, toon@moene.indiv.nluug.nl, law@cygnus.com,
	jbuck@Synopsys.COM, torvalds@transmeta.com, craig@jcb-sc.com,
	davem@redhat.com, chip@perlsupport.com, egcs@egcs.cygnus.com
Subject: Re: Linux and aliasing?
Date: Sat, 05 Jun 1999 12:41:00 -0000	[thread overview]
Message-ID: <19990605214133.A15508@pcep-jamie.cern.ch> (raw)
In-Reply-To: <19990605104107T.mitchell@codesourcery.com>

mark@codesourcery.com suggests:

>   Put expressions of the form `*((foo*) (&x))' in alias set zero if
>   x does not have type foo, or one of the types that is allowed
>   to alias it.
> 
> This proposal only affects nonconforming code, and thus changing the
> behavior of the compiler will not pessimize any conforming code.

I don't like this because it's not what we do in C++.
In C++ when we want to do these naughty things, we used to do:

  *(foo*)(void*)(&x)

I bet there's still a fair bit of that around.
In the modern world we've got *reinterpret_cast<foo*>(&x), which
is presumably treated specially w.r.t. aliases.

[Could someone tell me if reinterpret_cast does the right thing with
aliases please?]

thanks,
-- Jamie

WARNING: multiple messages have this Message-ID
From: Jamie Lokier <egcs@tantalophile.demon.co.uk>
To: mark@codesourcery.com
Cc: ak@muc.de, toon@moene.indiv.nluug.nl, law@cygnus.com,
	jbuck@Synopsys.COM, torvalds@transmeta.com, craig@jcb-sc.com,
	davem@redhat.com, chip@perlsupport.com, egcs@egcs.cygnus.com
Subject: Re: Linux and aliasing?
Date: Wed, 30 Jun 1999 15:43:00 -0000	[thread overview]
Message-ID: <19990605214133.A15508@pcep-jamie.cern.ch> (raw)
Message-ID: <19990630154300.zrnnPwMrAeIkf2VM7G3rGeG_-zhJ2U1JwJTWE--yV28@z> (raw)
In-Reply-To: <19990605104107T.mitchell@codesourcery.com>

mark@codesourcery.com suggests:

>   Put expressions of the form `*((foo*) (&x))' in alias set zero if
>   x does not have type foo, or one of the types that is allowed
>   to alias it.
> 
> This proposal only affects nonconforming code, and thus changing the
> behavior of the compiler will not pessimize any conforming code.

I don't like this because it's not what we do in C++.
In C++ when we want to do these naughty things, we used to do:

  *(foo*)(void*)(&x)

I bet there's still a fair bit of that around.
In the modern world we've got *reinterpret_cast<foo*>(&x), which
is presumably treated specially w.r.t. aliases.

[Could someone tell me if reinterpret_cast does the right thing with
aliases please?]

thanks,
-- Jamie

  parent reply	other threads:[~1999-06-05 12:41 UTC|newest]

Thread overview: 218+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
1999-06-03 10:23 Chip Salzenberg
1999-06-03 10:37 ` mark
1999-06-03 11:26   ` David S. Miller
1999-06-03 12:03     ` mark
1999-06-03 12:25       ` David S. Miller
1999-06-03 20:06         ` craig
1999-06-03 23:03           ` Linus Torvalds
1999-06-03 23:45             ` mark
1999-06-04  0:04               ` Linus Torvalds
1999-06-04  1:08                 ` Branko Cibej
1999-06-30 15:43                   ` Branko Cibej
1999-06-04  1:24                 ` Joe Buck
1999-06-04  1:50                   ` Linus Torvalds
1999-06-04  5:46                     ` craig
1999-06-04  7:22                       ` burley (was Re: Linux and aliasing?) Mark Hahn
1999-06-04  8:16                         ` craig
1999-06-30 15:43                           ` craig
1999-06-30 15:43                         ` Mark Hahn
1999-06-04  8:35                       ` Linux and aliasing? Linus Torvalds
1999-06-04 10:04                         ` Joe Buck
1999-06-04 10:22                           ` Jeffrey A Law
1999-06-04 10:31                             ` Joe Buck
1999-06-04 10:53                               ` Jeffrey A Law
1999-06-30 15:43                                 ` Jeffrey A Law
1999-06-30 15:43                               ` Joe Buck
1999-07-11 10:55                               ` Jeffrey A Law
1999-07-31 23:33                                 ` Jeffrey A Law
1999-06-04 11:11                             ` Toon Moene
1999-06-04 12:20                               ` Jeffrey A Law
1999-06-05  5:45                                 ` Toon Moene
1999-06-05  6:23                                   ` Andi Kleen
1999-06-05 10:32                                     ` Toon Moene
1999-06-05 13:26                                       ` Jamie Lokier
1999-06-05 19:35                                         ` Linus Torvalds
1999-06-06  1:18                                           ` Martin v. Loewis
1999-06-06 10:46                                             ` Linus Torvalds
1999-06-30 15:43                                               ` Linus Torvalds
1999-06-06 17:56                                             ` Jason Merrill
1999-06-06 19:24                                               ` Tim Hollebeek
1999-06-30 15:43                                                 ` Tim Hollebeek
1999-06-06 22:23                                               ` Jeffrey A Law
1999-06-30 15:43                                                 ` Jeffrey A Law
     [not found]                                               ` <199906070645.IAA00615@mira.isdn.cs.tu-berlin.de>
1999-06-07  2:14                                                 ` Jason Merrill
1999-06-07  8:02                                                   ` mark
1999-06-07  8:41                                                     ` David S. Miller
1999-06-07  9:24                                                       ` Jeffrey A Law
1999-06-07  9:29                                                         ` David S. Miller
1999-06-30 15:43                                                           ` David S. Miller
1999-06-30 15:43                                                         ` Jeffrey A Law
1999-06-07  9:32                                                       ` Joe Buck
1999-06-30 15:43                                                         ` Joe Buck
1999-06-30 15:43                                                       ` David S. Miller
1999-06-30 15:43                                                     ` mark
1999-06-07 13:11                                                   ` Jeffrey A Law
1999-06-30 15:43                                                     ` Jeffrey A Law
1999-06-30 15:43                                                   ` Jason Merrill
1999-06-30 15:43                                               ` Jason Merrill
1999-06-30 15:43                                             ` Martin v. Loewis
1999-06-30 15:43                                           ` Linus Torvalds
1999-06-30 15:43                                         ` Jamie Lokier
1999-06-05 18:48                                       ` Linus Torvalds
1999-06-30 15:43                                         ` Linus Torvalds
1999-06-30 15:43                                       ` Toon Moene
1999-06-05 10:37                                     ` mark
1999-06-05 11:09                                       ` David S. Miller
1999-06-05 12:11                                         ` Toon Moene
1999-06-05 12:21                                           ` David S. Miller
1999-06-05 16:51                                             ` mark
1999-06-30 15:43                                               ` mark
1999-06-30 15:43                                             ` David S. Miller
1999-06-30 15:43                                           ` Toon Moene
1999-06-07  6:01                                         ` Joern Rennecke
1999-06-30 15:43                                           ` Joern Rennecke
1999-06-30 15:43                                         ` David S. Miller
1999-06-05 11:35                                       ` Andi Kleen
1999-06-30 15:43                                         ` Andi Kleen
1999-06-05 12:41                                       ` Jamie Lokier [this message]
1999-06-05 14:43                                         ` Martin v. Loewis
1999-06-30 15:43                                           ` Martin v. Loewis
1999-06-05 16:53                                         ` mark
1999-06-07  2:36                                           ` Jamie Lokier
1999-06-07  8:04                                             ` mark
1999-06-30 15:43                                               ` mark
1999-06-30 15:43                                             ` Jamie Lokier
1999-06-30 15:43                                           ` mark
1999-06-30 15:43                                         ` Jamie Lokier
1999-06-30 15:43                                       ` mark
1999-06-30 15:43                                     ` Andi Kleen
1999-06-06 23:12                                   ` f77 vs type based alias analysis Jeffrey A Law
1999-06-30 15:43                                     ` Jeffrey A Law
1999-06-06 23:20                                   ` Linux and aliasing? Jeffrey A Law
1999-06-30 15:43                                     ` Jeffrey A Law
1999-06-30 15:43                                   ` Toon Moene
1999-06-30 15:43                                 ` Jeffrey A Law
1999-06-05  4:05                               ` Andi Kleen
1999-06-30 15:43                                 ` Andi Kleen
1999-06-30 15:43                               ` Toon Moene
1999-06-30 15:43                             ` Jeffrey A Law
1999-06-04 11:49                           ` Linus Torvalds
1999-06-04 13:03                             ` Gabriel Dos_Reis
1999-06-04 13:13                               ` Joe Buck
1999-06-30 15:43                                 ` Joe Buck
1999-06-30 15:43                               ` Gabriel Dos_Reis
1999-06-30 15:43                             ` Linus Torvalds
1999-06-04 12:59                           ` Alexandre Oliva
1999-06-04 13:29                             ` Joe Buck
1999-06-04 13:39                               ` Alexandre Oliva
1999-06-30 15:43                                 ` Alexandre Oliva
1999-06-30 15:43                               ` Joe Buck
1999-06-30 15:43                             ` Alexandre Oliva
1999-06-30 15:43                           ` Joe Buck
1999-06-30 15:43                         ` Linus Torvalds
1999-06-30 15:43                       ` craig
1999-06-30 15:43                     ` Linus Torvalds
1999-06-30 15:43                   ` Joe Buck
1999-06-04  5:47                 ` craig
1999-06-30 15:43                   ` craig
1999-06-04  7:11                 ` mark
1999-06-04  8:38                   ` Linus Torvalds
1999-06-30 15:43                     ` Linus Torvalds
1999-06-30 15:43                   ` mark
1999-06-04  8:41                 ` Tim Hollebeek
1999-06-04  8:53                   ` Jeffrey A Law
1999-06-30 15:43                     ` Jeffrey A Law
1999-06-30 15:43                   ` Tim Hollebeek
1999-06-30 15:43                 ` Linus Torvalds
1999-06-30 15:43               ` mark
1999-06-04  5:47             ` craig
1999-06-04  8:17               ` Linus Torvalds
1999-06-04  8:49                 ` craig
1999-06-04  8:57                   ` Linus Torvalds
1999-06-04  9:02                     ` Jean-Pierre Radley
1999-06-30 15:43                       ` Jean-Pierre Radley
1999-06-30 15:43                     ` Linus Torvalds
1999-06-30 15:43                   ` craig
1999-06-30 15:43                 ` Linus Torvalds
1999-06-30 15:43               ` craig
1999-06-04  8:39             ` Tim Hollebeek
1999-06-04  8:55               ` Linus Torvalds
1999-06-04 15:20                 ` Richard Henderson
1999-06-05  9:50                   ` Linus Torvalds
1999-06-05 11:00                     ` mark
1999-06-06 10:30                       ` Linus Torvalds
1999-06-06 10:44                         ` mark
1999-06-06 14:17                           ` Linus Torvalds
1999-06-06 17:41                             ` mark
1999-06-07  8:58                               ` Linus Torvalds
1999-06-07  9:18                                 ` mark
1999-06-07  9:29                                   ` Linus Torvalds
1999-06-07  9:38                                     ` Tim Hollebeek
1999-06-07 10:05                                       ` Jamie Lokier
1999-06-30 15:43                                         ` Jamie Lokier
1999-06-07 10:44                                       ` Linus Torvalds
1999-06-07 11:22                                         ` Jeffrey A Law
1999-06-08  1:34                                           ` Nick Ing-Simmons
1999-06-08  1:48                                             ` Jeffrey A Law
1999-06-30 15:43                                               ` Jeffrey A Law
1999-06-30 15:43                                             ` Nick Ing-Simmons
1999-06-30 15:43                                           ` Jeffrey A Law
1999-06-30 15:43                                         ` Linus Torvalds
1999-06-30 15:43                                       ` Tim Hollebeek
1999-06-30 15:43                                     ` Linus Torvalds
1999-06-30 15:43                                   ` mark
1999-06-07 13:34                                 ` Jamie Lokier
1999-06-30 15:43                                   ` Jamie Lokier
1999-06-30 15:43                                 ` Linus Torvalds
1999-06-30 15:43                               ` mark
1999-06-30 15:43                             ` Linus Torvalds
1999-06-30 15:43                           ` mark
1999-06-30 15:43                         ` Linus Torvalds
1999-06-30 15:43                       ` mark
1999-06-30 15:43                     ` Linus Torvalds
1999-06-30 15:43                   ` Richard Henderson
1999-06-30 15:43                 ` Linus Torvalds
1999-06-30 15:43               ` Tim Hollebeek
1999-06-04 15:02             ` Richard Henderson
1999-06-04 16:50               ` Bernd Schmidt
1999-06-30 15:43                 ` Bernd Schmidt
1999-06-05  9:35               ` Linus Torvalds
1999-06-05 13:34                 ` Richard Henderson
1999-06-05 18:40                   ` Linus Torvalds
1999-06-30 15:43                     ` Linus Torvalds
1999-06-05 21:38                   ` Jakub Jelinek
1999-06-30 15:43                     ` Jakub Jelinek
1999-06-30 15:43                   ` Richard Henderson
1999-06-30 15:43                 ` Linus Torvalds
1999-06-30 15:43               ` Richard Henderson
1999-06-30 15:43             ` Linus Torvalds
1999-06-03 23:53           ` Martin v. Loewis
1999-06-30 15:43             ` Martin v. Loewis
     [not found]           ` <v04205101b37d700fbf8d@[192.168.1.254]>
1999-06-04  7:01             ` craig
1999-06-30 15:43               ` craig
1999-06-30 15:43           ` craig
1999-06-30 15:43         ` David S. Miller
1999-06-03 13:31       ` Andi Kleen
1999-06-30 15:43         ` Andi Kleen
1999-06-30 15:43       ` mark
1999-06-30 15:43     ` David S. Miller
1999-06-03 12:02   ` Andi Kleen
1999-06-03 15:38     ` Martin v. Loewis
1999-06-30 15:43       ` Martin v. Loewis
1999-06-30 15:43     ` Andi Kleen
1999-06-30 15:43   ` mark
1999-06-30 15:43 ` Chip Salzenberg
1999-06-04 11:54 Mike Stump
1999-06-04 12:13 ` Jeffrey A Law
1999-06-04 13:25   ` Sylvain Pion
1999-06-04 13:32     ` Jeffrey A Law
1999-06-30 15:43       ` Jeffrey A Law
1999-06-30 15:43     ` Sylvain Pion
1999-06-30 15:43   ` Jeffrey A Law
1999-06-30 15:43 ` Mike Stump
1999-06-06 15:08 Ross Harvey
1999-06-06 15:46 ` Linus Torvalds
1999-06-30 15:43   ` Linus Torvalds
1999-06-06 17:29 ` David S. Miller
1999-06-30 15:43   ` David S. Miller
1999-06-30 15:43 ` Ross Harvey

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