Re: what is the right value about a = a++;

From	Kaz Kylheku <kaz@kylheku.com>
Newsgroups	comp.lang.c
Subject	Re: what is the right value about a = a++;
Date	2012-02-09 00:18 +0000
Organization	A noiseless patient Spider
Message-ID	<20120208161646.35@kylheku.com> (permalink)
References	(5 earlier) <qdadndbp0NhHGKzSnZ2dnUVZ_uCdnZ2d@bestweb.net> <4f319955.234650417@text.giganews.com> <jgs9t7$5se$1@dont-email.me> <rjv3j7p3ntaitmqapv0hf6o6ov7l87bdnh@4ax.com> <jguko9$q87$1@dont-email.me>

Show all headers | View raw

On 2012-02-08, Stephen Sprunk <stephen@sprunk.org> wrote:
> On 07-Feb-12 22:49, Robert Wessel wrote:
>> On Tue, 07 Feb 2012 16:51:17 -0600, Stephen Sprunk
>> <stephen@sprunk.org> wrote:
>>> On 07-Feb-12 15:50, Richard Harter wrote:
>>>> Well, no, he isn't saying any such thing.  You just made it up.  The
>>>> fact that evaluation order in C is left to the compilers has very
>>>> little to do with optimization; it is a historical artifact that came
>>>> from endorsing existing practice when the ANSI standard was put
>>>> together.  Existing practice then was that compiler writers could do
>>>> evaluations in whatever they pleased and they did.
>>>
>>> No, they did evaluations in the order that made the most sense (i.e. had
>>> the best performance) for their particular implementation--and
>>> implementations vary.
>>>
>>> For instance, varargs is more straightforward to implement with
>>> right-to-left evaluation of arguments, at least with a stack-based
>>> calling convention.  Order of evaluation may not matter for
>>> register-based calling conventions, but if an implementation uses both,
>>> it makes sense to use the same order.
>> 
>> Depends on which way your stack grows - with downward growth it's
>> usually easiest to evaluate varargs right-to-left, but for an upwards
>> growing stack left-to-right is usually easier.
>
> How would stack growth direction matter?  What matters for varargs is
> that the first argument is on the top of the stack, regardless of which
> way it grows.  If you push the arguments from right to left, the first
> argument ends up on top.  You _could_ evaluate the arguments from left
> to right, store them in registers or elsewhere in memory, and then push
> from right to left, but why go through that extra effort?

Or you could wake up and realize that the stack can be indexed like an array,
unless you're working with a target language that really has only push and
pop, with no other access to the stack. (Good luck implementing local
variables efficiently, etc).

You can allocate the space for N arguments, and then store valuews into
that stack space in whatever order is convenient, while obeying
the abstract evaluation order (in those situations where it potentially
makes a difference).

Thread

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

csiph-web