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| From | Kaz Kylheku <kaz@kylheku.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: what is the right value about a = a++; |
| Date | 2012-02-09 23:57 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <20120209155340.204@kylheku.com> (permalink) |
| References | (5 earlier) <qdadndbp0NhHGKzSnZ2dnUVZ_uCdnZ2d@bestweb.net> <4f319955.234650417@text.giganews.com> <27WdnWl1SYYBQK_SnZ2dnUVZ_q2dnZ2d@bestweb.net> <93794fd7-14e9-4bef-b9bc-f027dd734ce7@o13g2000vbf.googlegroups.com> <vradnUC0CLnukKnSnZ2dnUVZ_r6dnZ2d@bestweb.net> |
On 2012-02-09, Kenneth Brody <kenbrody@spamcop.net> wrote: > On 2/8/2012 8:41 PM, John Bode wrote: >> On Feb 8, 2:39 pm, Kenneth Brody<kenbr...@spamcop.net> wrote: > [...] >>> The truth of the matter is, is that when, precisely, a side effect most >>> efficiently takes effect, is very platform-dependent, and can even vary from >>> expression to expression on a given platform. >>> >> >> Is this anything more than received wisdom? Does anyone have a >> concrete example (read: generated machine code) showing *how* >> rearranging evaluation order can make an operation more efficient? >> >> I mean, I've parroted that line more than once, but I certainly can't >> point to an example of where it makes a difference. > > foo(a++,a++); > > On my system, this code is generated: > > mov eax, DWORD PTR _a > push eax > push eax > add eax, 2 > mov DWORD PTR _a, eax > call _foo > add esp, 8 > > By delaying the post-increment, the code is more efficient than requiring > two separate increments. Note that this is still allowed under strict left-right, bottom-up evaluation. Because a is not volatile, the code does not require two actual increments. That is merely the abstract semantics. So this is really tangential to the debate. (Yes, rearranging computations is important and crucial necessary for optimization.)
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what is the right value about a = a++; lujnan <lujnan@gmail.com> - 2012-02-06 00:10 -0800
Re: what is the right value about a = a++; Ruben Mikkonen <camu.umac@gmail.com> - 2012-02-06 00:28 -0800
Re: what is the right value about a = a++; Keith Thompson <kst-u@mib.org> - 2012-02-06 21:27 -0800
Re: what is the right value about a = a++; Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-02-06 22:39 -0700
Re: what is the right value about a = a++; bert <bert.hutchings@btinternet.com> - 2012-02-06 01:45 -0800
Re: what is the right value about a = a++; lujnan <lujnan@gmail.com> - 2012-02-06 02:33 -0800
Re: what is the right value about a = a++; "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-02-06 14:57 -0800
Re: what is the right value about a = a++; Barry Schwarz <schwarzb@dqel.com> - 2012-02-06 22:50 -0800
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-07 08:15 +0000
Re: what is the right value about a = a++; lujnan <lujnan@gmail.com> - 2012-02-07 00:31 -0800
Re: what is the right value about a = a++; Keith Thompson <kst-u@mib.org> - 2012-02-07 09:07 -0800
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-07 17:31 +0000
Re: what is the right value about a = a++; Joshua Maurice <joshuamaurice@gmail.com> - 2012-02-09 17:50 -0800
Re: what is the right value about a = a++; Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-21 23:42 +0200
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-22 04:28 +0000
Re: what is the right value about a = a++; Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-25 00:01 +0200
Re: what is the right value about a = a++; Shao Miller <sha0.miller@gmail.com> - 2012-02-25 02:25 -0500
Re: what is the right value about a = a++; Ike Naar <ike@iceland.freeshell.org> - 2012-02-25 09:00 +0000
Re: what is the right value about a = a++; Philip Lantz <prl@canterey.us> - 2012-02-25 11:13 -0800
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-25 19:34 +0000
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-25 16:51 -0500
Re: what is the right value about a = a++; lawrence.jones@siemens.com - 2012-02-27 16:12 -0500
Re: what is the right value about a = a++; Ike Naar <ike@iceland.freeshell.org> - 2012-02-27 22:42 +0000
Re: what is the right value about a = a++; Shao Miller <sha0.miller@gmail.com> - 2012-02-27 18:54 -0500
Re: what is the right value about a = a++; Barry Schwarz <schwarzb@dqel.com> - 2012-02-07 09:26 -0800
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-07 15:12 -0500
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-07 21:50 +0000
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-07 16:51 -0600
Re: what is the right value about a = a++; Robert Wessel <robertwessel2@yahoo.com> - 2012-02-07 22:49 -0600
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-08 14:08 -0600
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 00:18 +0000
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-09 13:06 -0500
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-09 13:58 -0600
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 23:52 +0000
Re: what is the right value about a = a++; jgk@panix.com (Joe keane) - 2012-02-10 21:45 +0000
Re: what is the right value about a = a++; Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-22 00:09 +0200
Re: what is the right value about a = a++; Robert Wessel <robertwessel2@yahoo.com> - 2012-02-08 22:35 -0600
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-08 15:42 -0500
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-08 14:47 +0000
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-08 14:29 -0600
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-10 02:27 +0000
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-09 23:10 -0500
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-10 09:11 +0000
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-10 07:26 -0500
Re: what is the right value about a = a++; Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-10 13:12 +0000
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-10 11:07 -0500
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-10 16:27 +0000
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-10 12:17 -0500
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-10 12:09 -0600
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-10 18:17 -0500
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-11 10:15 +0000
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-13 16:04 -0500
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-10 12:30 -0600
Re: what is the right value about a = a++; Shao Miller <sha0.miller@gmail.com> - 2012-02-09 21:30 -0500
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-10 02:48 +0000
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-10 09:49 +0000
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 00:15 +0000
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-09 12:49 -0500
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 23:51 +0000
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-08 15:39 -0500
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 01:05 +0000
Re: what is the right value about a = a++; Shao Miller <sha0.miller@gmail.com> - 2012-02-09 23:24 -0500
Re: what is the right value about a = a++; Jens Gustedt <jens.gustedt@loria.fr> - 2012-02-10 16:58 +0100
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-10 23:32 +0000
Re: what is the right value about a = a++; John Bode <jfbode1029@gmail.com> - 2012-02-08 17:41 -0800
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-08 22:25 -0500
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-09 13:15 -0500
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 23:57 +0000
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-10 11:15 -0500
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-10 11:58 -0600
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-10 18:14 -0500
Re: what is the right value about a = a++; Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-10 22:43 +0000
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-10 11:53 -0600
Re: what is the right value about a = a++; Joshua Maurice <joshuamaurice@gmail.com> - 2012-02-10 15:19 -0800
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-10 02:32 +0000
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-09 23:13 -0500
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-10 09:34 +0000
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-10 07:32 -0500
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-10 22:24 +0000
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-10 11:35 -0500
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-10 12:23 -0500
Re: what is the right value about a = a++; falk@rahul.net (Edward A. Falk) - 2012-02-08 20:40 +0000
Re: what is the right value about a = a++; Keith Thompson <kst-u@mib.org> - 2012-02-08 15:00 -0800
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 01:10 +0000
Re: what is the right value about a = a++; 88888 Dihedral <dihedral88888@googlemail.com> - 2012-02-09 20:43 -0800
Re: what is the right value about a = a++; Robert Wessel <robertwessel2@yahoo.com> - 2012-02-09 23:36 -0600
Re: what is the right value about a = a++; cri@tiac.net (Richard Harter) - 2012-02-10 02:40 +0000
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-09 23:17 -0500
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-08 23:49 +0000
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-08 23:42 +0000
Re: what is the right value about a = a++; blp@cs.stanford.edu (Ben Pfaff) - 2012-02-07 12:09 -0800
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-07 07:42 -0500
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-07 17:21 +0000
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-07 15:24 -0600
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 01:27 +0000
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-10 21:57 -0600
Re: what is the right value about a = a++; "Joel C. Salomon" <joelcsalomon@gmail.com> - 2012-02-08 01:00 -0500
Re: what is the right value about a = a++; falk@rahul.net (Edward A. Falk) - 2012-02-08 20:33 +0000
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 02:05 +0000
Re: what is the right value about a = a++; Markus Wichmann <nullplan@gmx.net> - 2012-02-09 09:28 +0100
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 10:21 +0000
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-09 11:38 +0000
Re: what is the right value about a = a++; Shao Miller <sha0.miller@gmail.com> - 2012-02-10 00:03 -0500
Re: what is the right value about a = a++; Philip Lantz <prl@canterey.us> - 2012-02-10 01:15 -0800
Re: what is the right value about a = a++; Kenneth Brody <kenbrody@spamcop.net> - 2012-02-09 13:22 -0500
Re: what is the right value about a = a++; Slash QB <slashqb@gmail.com> - 2012-02-06 02:35 -0800
Re: what is the right value about a = a++; Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-02-07 03:07 -0800
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-07 15:19 -0600
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-07 17:00 -0500
Re: what is the right value about a = a++; Stephen Sprunk <stephen@sprunk.org> - 2012-02-10 12:05 -0600
Re: what is the right value about a = a++; James Kuyper <jameskuyper@verizon.net> - 2012-02-10 13:46 -0500
Re: what is the right value about a = a++; Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-02-06 22:37 -0700
Re: what is the right value about a = a++; Kaz Kylheku <kaz@kylheku.com> - 2012-02-07 07:22 +0000
Re: what is the right value about a = a++; Shao Miller <sha0.miller@gmail.com> - 2012-02-07 01:18 -0500
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