Groups > comp.lang.c > #62052

Re: Sequence points and commit to memory

From	James Kuyper <jameskuyper@verizon.net>
Newsgroups	comp.lang.c
Subject	Re: Sequence points and commit to memory
Date	2015-05-15 13:27 -0400
Organization	Self
Message-ID	<55562C90.1020309@verizon.net> (permalink)
References	(2 earlier) <928a9f76-7417-4e84-81b1-a92f71517ab0@googlegroups.com> <chine.bleu-754459.10443214052015@news.eternal-september.org> <2921f8f5-64e5-461f-9dd0-092ba73bcb1e@googlegroups.com> <mj3478$jvp$1@speranza.aioe.org> <fc257249-9ce5-4994-90d9-c3cce55696cb@googlegroups.com>

Show all headers | View raw

On 05/15/2015 12:52 PM, David Kleinecke wrote:
...
> Now I have seen some recent code using "register". But wouldn't the code
> give the same result without the "register"s ?
> 
> I assume there must be some efficiency gain or you wouldn't have coded
> it that way. But isn't that gain an artifact of your compiler and your
> hardware ?

"A declaration of an identifier for an object with storage-class
specifier register suggests that access to the object be as fast as
possible. The extent to which such suggestions are effective is
implementation-defined." (6..1p6)

You'll get the same result with and without the register keyword only if
an implementation chooses to completely ignore it - which is permitted,
and a fairly popular approach.

However, if an implementation does decide to pay attention to the
"register" keyword, it should affect the efficiency of the resulting
code. It will increase the efficiency if you use it in the right places,
and it will actually reduce the efficiency if you use it in the wrong
places, and which places are "right" and which are "wrong" is
implementation-dependent. From what I've heard, most modern compilers do
a far better job than most programmers, of deciding which variables to
put in registers, so interfering in that decision making can be
counter-productive.
Our client requires that our delivered code NOT have any
compiler-dependent parts, so I have no use for "register" - other
people, who are allowed and even encouraged to write code targeted at a
particular platform, may find it more useful.

Thread

Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-14 11:43 +0100
  Re: Sequence points and commit to memory Richard Heathfield <rjh@cpax.org.uk> - 2015-05-14 12:02 +0100
    Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-14 13:39 +0200
      Re: Sequence points and commit to memory Richard Heathfield <rjh@cpax.org.uk> - 2015-05-14 13:18 +0100
        Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-14 23:11 +0200
  Re: Sequence points and commit to memory Stephen Sprunk <stephen@sprunk.org> - 2015-05-14 09:06 -0500
  Re: Sequence points and commit to memory Siri Cruz <chine.bleu@yahoo.com> - 2015-05-14 08:35 -0700
    Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-14 10:23 -0700
      Re: Sequence points and commit to memory Siri Cruz <chine.bleu@yahoo.com> - 2015-05-14 10:44 -0700
        Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-14 11:09 -0700
          Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-14 12:58 -0700
          Re: Sequence points and commit to memory Morris Dovey <mrdovey@iedu.com> - 2015-05-14 16:31 -0500
            Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-14 17:24 -0700
              Re: Sequence points and commit to memory Morris Dovey <mrdovey@iedu.com> - 2015-05-14 20:18 -0500
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-15 09:34 +0200
                Re: Sequence points and commit to memory Morris Dovey <mrdovey@iedu.com> - 2015-05-15 10:18 -0500
                Re: 'register' attribute (was: Sequence points and commit to memory) Morris Dovey <mrdovey@iedu.com> - 2015-05-16 01:26 -0500
                Re: 'register' attribute David Brown <david.brown@hesbynett.no> - 2015-05-17 00:02 +0200
                Re: 'register' attribute Morris Dovey <mrdovey@iedu.com> - 2015-05-16 19:29 -0500
            Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-15 09:52 -0700
              Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-15 13:27 -0400
                Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-15 10:50 -0700
              Re: Sequence points and commit to memory Morris Dovey <mrdovey@iedu.com> - 2015-05-15 12:32 -0500
      Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-14 23:23 +0200
        Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-15 09:42 -0700
          Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-15 13:13 -0400
            Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-16 08:32 -0700
          Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-15 10:35 -0700
          Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-15 11:08 -0700
            Re: Sequence points and commit to memory Robert Wessel <robertwessel2@yahoo.com> - 2015-05-15 16:40 -0500
            Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-16 08:48 -0700
          Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-15 21:46 +0100
            Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-16 08:56 -0700
              Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-16 19:35 +0100
                Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-18 09:49 -0700
                Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-19 09:04 +0100
                Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-19 08:42 -0700
    Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-14 22:00 +0100
      Re: Sequence points and commit to memory Siri Cruz <chine.bleu@yahoo.com> - 2015-05-14 14:26 -0700
        Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-14 22:33 +0100
      Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-14 23:38 +0200
        Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-14 23:04 +0100
          Re: Sequence points and commit to memory Stephen Sprunk <stephen@sprunk.org> - 2015-05-15 13:09 -0500
            Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-15 21:56 +0100
              Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-15 17:30 -0400
                Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-16 07:51 +0100
                Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-16 22:10 -0400
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 00:25 +0200
                Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-18 18:55 -0400
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 09:10 +0200
                Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-19 12:05 -0400
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 18:42 +0200
              Re: Sequence points and commit to memory Stephen Sprunk <stephen@sprunk.org> - 2015-05-16 16:33 -0500
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 00:27 +0200
                Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-18 19:05 -0400
                Re: Sequence points and commit to memory glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-19 00:09 +0000
                Re: Sequence points and commit to memory Richard Heathfield <rjh@cpax.org.uk> - 2015-05-19 01:11 +0100
                Re: Sequence points and commit to memory Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-23 07:02 -0700
                Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-18 23:21 -0400
                Re: Sequence points and commit to memory glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-19 06:25 +0000
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 08:58 +0200
                Re: Sequence points and commit to memory glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-19 23:20 +0000
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-20 12:31 +0200
                Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-19 12:10 -0400
                Re: Sequence points and commit to memory glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-19 23:24 +0000
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 09:05 +0200
                Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-19 08:37 -0700
                Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-19 12:14 -0400
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 19:02 +0200
            Re: Sequence points and commit to memory Robert Wessel <robertwessel2@yahoo.com> - 2015-05-15 16:46 -0500
          Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-17 00:20 +0200
            Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-17 18:19 +0100
              Re: Sequence points and commit to memory Philip Lantz <prl@canterey.us> - 2015-05-17 16:11 -0700
                Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-18 08:30 +0100
                Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-18 10:31 -0700
                Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-18 11:11 -0700
                Re: Sequence points and commit to memory David Kleinecke <dkleinecke@gmail.com> - 2015-05-19 09:37 -0700
                Re: Sequence points and commit to memory Ian Collins <ian-news@hotmail.com> - 2015-05-19 17:40 +1200
                Re: Sequence points and commit to memory Morris Dovey <mrdovey@iedu.com> - 2015-05-19 01:31 -0500
                Re: Sequence points and commit to memory Ian Collins <ian-news@hotmail.com> - 2015-05-19 20:38 +1200
                Re: Sequence points and commit to memory Morris Dovey <mrdovey@iedu.com> - 2015-05-19 10:50 -0500
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 00:46 +0200
              Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 00:35 +0200
      Re: Sequence points and commit to memory Robert Wessel <robertwessel2@yahoo.com> - 2015-05-15 16:42 -0500
        Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-16 07:58 +0100
          Re: Sequence points and commit to memory Robert Wessel <robertwessel2@yahoo.com> - 2015-05-16 02:18 -0500
            Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-16 08:36 +0100
              Re: Sequence points and commit to memory Robert Wessel <robertwessel2@yahoo.com> - 2015-05-17 04:31 -0500
                Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-17 18:24 +0100
                Re: Sequence points and commit to memory David Brown <david.brown@hesbynett.no> - 2015-05-19 00:55 +0200
  Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-14 11:26 -0700
    Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-14 22:07 +0100
      Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-14 14:22 -0700
        Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-14 22:36 +0100
    Re: Sequence points and commit to memory Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-22 08:16 -0700
      Re: Sequence points and commit to memory Keith Thompson <kst-u@mib.org> - 2015-05-22 11:31 -0700
  Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-15 00:05 -0400
    Re: Sequence points and commit to memory "James Harris" <james.harris.1@gmail.com> - 2015-05-15 22:25 +0100
      Re: Sequence points and commit to memory James Kuyper <jameskuyper@verizon.net> - 2015-05-15 17:56 -0400
  Re: Sequence points and commit to memory Nobody <nobody@nowhere.invalid> - 2015-05-17 10:04 +0100
  Re: Sequence points and commit to memory Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-24 08:11 -0700

csiph-web