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From: Paul Winalski <paul.winalski@gmail.com>
To: The Unix Heritage Society mailing list <tuhs@tuhs.org>
Subject: Re: [TUHS] v7 K&R C
Date: Tue, 12 May 2020 14:36:38 -0400	[thread overview]
Message-ID: <CABH=_VSxKyKp0CbBY8zy3sSi_bDymaNQjGmQa5KNHY1dS=gUbg@mail.gmail.com> (raw)
In-Reply-To: <b08fb44804d3ac8d1d5a84990f3e4826.squirrel@squirrelmail.tuffmail.net>

On 5/12/20, ron@ronnatalie.com <ron@ronnatalie.com> wrote:
>> On 5/11/20, Larry McVoy <lm@mcvoy.com> wrote:
>
>> o all std:: and STL functions
>>
>> The last two of these are mainly for performance reasons.  throw and
>> catch play merry hell with compiler optimizations, especially of
>> global variables.
>
> You'll have to explain to me how templates or the standard library (which
> by the way includes all of the C stuff) affects performance.   In fact, we
> use templates to INCREASE rather than decrease performance.    Templating
> is almost entirely compile time rewrites.

The C++ standard libraries make heavy use of throw/catch exception
handling.  If routine A calls routine B, and B is known by the
compiler to have the capability to throw exceptions, a bunch of
important optimizations can't be done.  For example:

o You can't keep global values in registers around the call to B
because the handler that catches an exception that B throws might use
that global variable.  So you have to spill the value around the call.

o You can't do value propagation of global variables around the call
to B because a handler might change their values.

And it gets a lot worse when you start doing parallel loop execution.
I implemented a new design for exception handling in a C/C++ compiler
back end, and I found lots of corner cases where the C++ standard was
silent as to what should happen when exceptions are thrown or caught
from parallel threads.  Things such as the order of execution of
constructors and destructors for parallel routines when a thrown
exception is unwound, and which side of the parallelization executes
constructors and destructors under those conditions.  The committee
just plain never considered those issues.

-Paul W.

  parent reply	other threads:[~2020-05-12 18:37 UTC|newest]

Thread overview: 153+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-25  1:59 Adam Thornton
2020-04-25  2:37 ` Charles Anthony
2020-04-25  2:47   ` Adam Thornton
2020-04-25  2:51     ` Rob Pike
2020-04-25  2:54       ` Rob Pike
2020-04-25  3:04         ` Larry McVoy
2020-04-25  3:30           ` Clem Cole
2020-04-25  3:43             ` Larry McVoy
2020-04-25  3:54               ` Jon Steinhart
2020-04-25 11:44                 ` Michael Kjörling
2020-04-25 13:17             ` Dan Cross
2020-05-11  0:28         ` scj
2020-05-11  0:32           ` Rob Pike
2020-05-11  0:57             ` Larry McVoy
2020-05-11 17:32               ` Greg A. Woods
2020-05-11 18:25                 ` Paul Winalski
2020-05-11 18:37                   ` Clem Cole
2020-05-11 19:12                     ` Paul Winalski
2020-05-11 19:57                       ` joe mcguckin
2020-05-11 20:25                         ` Larry McVoy
2020-05-12 17:23                           ` Paul Winalski
2020-05-12 17:35                             ` ron
2020-05-12 17:42                               ` Larry McVoy
2020-05-12 18:36                               ` Paul Winalski [this message]
2020-05-13 23:36                             ` Dave Horsfall
2020-05-14  0:42                               ` John P. Linderman
2020-05-14  2:44                                 ` Rich Morin
2020-05-14  3:09                                   ` Charles Anthony
2020-05-14 12:27                                     ` ron
2020-05-14 12:27                                     ` ron
2020-05-14 12:27                                     ` ron
2020-05-14  7:38                                   ` Dave Horsfall
2020-05-14 12:25                                     ` ron
2020-05-14 17:13                                   ` Paul Winalski
2020-05-14 17:21                                 ` Larry McVoy
2020-05-17 16:34                                   ` Derek Fawcus
2020-05-14  4:21                               ` Greg A. Woods
2020-05-14  4:40                                 ` Warner Losh
2020-05-14 17:32                               ` Larry McVoy
2020-05-14 22:32                                 ` Tony Finch
2020-05-16 23:53                                   ` Steffen Nurpmeso
2020-05-16 23:59                                     ` [TUHS] v7 K&R C [really lexers] Jon Steinhart
2020-05-17  0:04                                       ` Brantley Coile
2020-05-17  1:23                                         ` Warner Losh
2020-05-17  1:36                                           ` Brantley Coile
2020-06-13 21:24                                           ` scj
2020-06-14  8:47                                             ` arnold
2020-06-14 12:52                                             ` Richard Salz
2020-06-14 14:03                                               ` Ralph Corderoy
2020-06-14 14:26                                                 ` arnold
2020-06-14 14:48                                                   ` Ralph Corderoy
2020-06-15  1:12                                                     ` Warren Toomey
2020-06-15  1:29                                                       ` Warren Toomey
2020-06-15  6:06                                                         ` arnold
2020-05-17 16:31                                       ` Paul Winalski
2020-05-17  0:35                                     ` [TUHS] v7 K&R C Larry McVoy
2020-05-11 18:37                   ` Larry McVoy
2020-05-11  2:08           ` Lawrence Stewart
2020-05-11 11:36           ` Michael Kjörling
2020-04-25  3:37       ` Dave Horsfall
2020-04-27 13:19       ` Tony Finch
2020-04-25  2:50   ` Adam Thornton
2020-04-25  5:59     ` Lars Brinkhoff
2020-04-25 13:11 Noel Chiappa
2020-04-25 13:18 ` Rob Pike
2020-04-25 14:57   ` Warner Losh
2020-04-25 18:03   ` Noel Chiappa
2020-04-25 20:11     ` Michael Kjörling
2020-04-25 21:27       ` Brian L. Stuart
2020-04-26  0:07     ` emanuel stiebler
2020-04-26  0:54     ` Rob Pike
2020-04-26 19:37     ` Derek Fawcus
2020-04-26 20:10       ` Derek Fawcus
2020-04-26 21:59         ` Rich Morin
2020-04-26 22:38         ` Noel Hunt
2020-04-26 23:57         ` Nemo Nusquam
2020-04-27  3:38           ` Rob Pike
2020-04-25 13:35 ` Hellwig Geisse
2020-04-25 13:59   ` Richard Salz
2020-04-25 19:01   ` Brian L. Stuart
2020-04-25 20:07     ` Michael Kjörling
2020-04-25 21:34       ` Brian L. Stuart
2020-04-26  6:40     ` arnold
2020-04-25 19:41 Noel Chiappa
2020-04-25 20:27 ` Steffen Nurpmeso
2020-04-27 17:45 Noel Chiappa
2020-04-27 17:56 ` Richard Salz
2020-04-27 18:02 ` Brantley Coile
2020-04-27 18:47 ` Derek Fawcus
     [not found] <mailman.1.1589421601.13778.tuhs@minnie.tuhs.org>
2020-05-14  3:02 ` Paul McJones
2020-05-14 17:08   ` Paul Winalski
2020-05-14 17:58     ` Clem Cole
2020-05-14 18:41 Doug McIlroy
2020-05-14 18:45 ` Richard Salz
2020-05-14 20:54 ` Clem Cole
2020-05-15  2:44 ` Rob Pike
2020-05-15  3:57   ` Rich Morin
2020-05-15  7:55   ` Dr Iain Maoileoin
2020-05-15 15:01     ` Larry McVoy
2020-05-15 15:36       ` John P. Linderman
2020-05-15 20:01         ` ron
2020-05-15 20:03           ` Larry McVoy
2020-05-15 20:05           ` Clem Cole
2020-05-15 20:18             ` ron
2020-05-15 20:24               ` Clem Cole
2020-05-16  0:57               ` Brantley Coile
2020-05-16 16:14                 ` Dan Cross
2020-05-15 20:56           ` Steve Nickolas
2020-05-16  0:31             ` Peter Jeremy
2020-05-16  8:30               ` Steve Nickolas
2020-05-16  0:43           ` John P. Linderman
2020-05-16 16:28             ` Paul Winalski
2020-05-16 17:39               ` Warner Losh
2020-05-19 19:45                 ` Peter Pentchev
2020-05-20  3:52                   ` Rich Morin
2020-05-21 15:06                     ` Dave Horsfall
2020-05-15 20:34 Doug McIlroy
2020-05-15 20:40 ` Warner Losh
2020-05-15 21:31 Richard Tobin
2020-05-15 21:53 ` Steve Nickolas
2020-05-15 22:33   ` ron
2020-05-15 23:34     ` Steffen Nurpmeso
2020-05-16  1:26       ` Larry McVoy
2020-05-16 21:59       ` Ronald Natalie
2020-05-16 23:26         ` Steffen Nurpmeso
2020-05-17 16:24           ` Paul Winalski
2020-05-17 16:29             ` ron
2020-05-17 16:38               ` Paul Winalski
2020-05-17 20:08                 ` Clem Cole
2020-05-18  8:46                   ` Peter Jeremy
2020-05-19  7:41                     ` Dave Horsfall
2020-05-18 12:04             ` Tony Finch
2020-05-18 13:10               ` Clem Cole
2020-05-18 15:13             ` Rich Morin
2020-05-18 15:51               ` Brantley Coile
2020-05-18 16:11             ` Dan Cross
2020-05-18 21:18               ` ron
2020-05-17 16:10 ` Derek Fawcus
2020-05-17 16:14   ` ron
2020-05-16  0:15 Nelson H. F. Beebe
2020-05-16  0:28 ` Steffen Nurpmeso
2020-05-16  1:52 ` Warner Losh
2020-05-16 16:31   ` Paul Winalski
2020-05-16 20:35     ` Brad Spencer
2020-05-16 20:37       ` Warner Losh
2020-05-18 12:25     ` Tony Finch
2020-05-16 18:45 Richard Tobin
2020-05-16 21:55 ` Ronald Natalie
2020-05-18 13:58 Doug McIlroy
2020-05-18 14:33 Doug McIlroy
2020-05-19  2:29 Doug McIlroy
2020-05-19  3:20 ` Steve Nickolas
2020-05-19 12:29 Noel Chiappa

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