Re: RAFTS-like optimiser; progress report

From	"Rod Pemberton" <dont_use_email@nohavenotit.com>
Newsgroups	comp.lang.forth
Subject	Re: RAFTS-like optimiser; progress report
Date	2013-09-10 04:30 -0400
Organization	Aioe.org NNTP Server
Message-ID	<op.w26slxdy0e5s1z@-> (permalink)
References	(1 earlier) <LPqdnRhGztBg07fPnZ2dnUVZ_oadnZ2d@supernews.com> <2013Sep7.170614@mips.complang.tuwien.ac.at> <laqdnaQ8I6t7CLbPnZ2dnUVZ_q2XnZ2d@supernews.com> <2013Sep9.144131@mips.complang.tuwien.ac.at> <DKydncrylYLrTrDPnZ2dnUVZ_gWdnZ2d@supernews.com>

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On Mon, 09 Sep 2013 09:56:06 -0400, Andrew Haley  
<andrew29@littlepinkcloud.invalid> wrote:

> [...]
>
> C's volatile is useless.
>

I've never had any real problems with it.

The "volatile" keyword just tells the compiler to *not* optimize
away read or write access to the memory where the data is stored.

I.e., it's for memory mapped devices and their data, e.g., text
screen.  This can be used to ensure updated input from something
outside C application's scope is available to the application
without being optimized away, or to ensure data is written to a
memory location without being optimized away, etc.

I.e., you can think of volatile as "no register", "no optimization",
or forced read/write to memory.  It'll only be used with something
which is memory mapped and outside C's application space.  This
device will be undeclared within C's scope, i.e., typically
accessed via indirection on a pointer directly accessing memory.

E.g., if you output an incrementing integer to a memory mapped
text screen, the loop will appear to "do nothing" from the C
compiler's perspective.  It's not "aware" that the data _must_
be written to that address to be displayed.  There is no
declared C object representing the text screen since it's memory
mapped.  So, the compiler "sees" a useless loop that just increments
a variable or value which could be stored in a register.  The
compiler will optimized away the output to the memory using
registers instead.  After which, there won't be any text output
since the loop is no longer writing to memory mapped area for
the screen.

AIR, you mentioned this issue once previously and I responded
to it then too.  Should I stop?  It seems you still think
"volatile" is worthless when it has a valid use, unlike almost
all other the qualifiers in C, except "unsigned".

Rod Pemberton

Thread

RAFTS-like optimiser; progress report Alex McDonald <blog@rivadpm.com> - 2013-09-06 14:12 -0700
  Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-06 16:54 -0500
    Re: RAFTS-like optimiser; progress report Alex McDonald <blog@rivadpm.com> - 2013-09-06 16:02 -0700
      Re: RAFTS-like optimiser; progress report Bernd Paysan <bernd.paysan@gmx.de> - 2013-09-07 03:01 +0200
        Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-07 03:21 -0500
          Re: RAFTS-like optimiser; progress report albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-09-07 19:56 +0000
    Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-07 15:06 +0000
      Re: RAFTS-like optimiser; progress report "Alex McDonald" <blog@rivadpm.com> - 2013-09-07 19:01 +0100
        Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-09 12:23 +0000
          Re: RAFTS-like optimiser; progress report "Alex McDonald" <blog@rivadpm.com> - 2013-09-10 12:01 +0100
            Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-10 12:45 +0000
              Re: RAFTS-like optimiser; progress report "Alex McDonald" <blog@rivadpm.com> - 2013-09-10 16:33 +0100
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-11 15:02 +0000
                Re: RAFTS-like optimiser; progress report "Alex McDonald" <blog@rivadpm.com> - 2013-09-11 17:44 +0100
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-13 11:58 +0000
                Re: RAFTS-like optimiser; progress report "Rod Pemberton" <dont_use_email@nohavenotit.com> - 2013-09-14 22:47 -0400
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-15 16:05 +0000
      Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-07 16:08 -0500
        Re: RAFTS-like optimiser; progress report mhx@iae.nl - 2013-09-08 03:21 -0700
          Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-08 06:42 -0500
            Re: RAFTS-like optimiser; progress report mhx@iae.nl - 2013-09-08 04:51 -0700
              Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-08 07:02 -0500
                Re: RAFTS-like optimiser; progress report Paul Rubin <no.email@nospam.invalid> - 2013-09-08 10:08 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-08 12:47 -0500
                Re: RAFTS-like optimiser; progress report Paul Rubin <no.email@nospam.invalid> - 2013-09-08 11:10 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-08 15:16 -0500
                Re: RAFTS-like optimiser; progress report Paul Rubin <no.email@nospam.invalid> - 2013-09-08 16:08 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-09 04:57 -0500
        Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-09 12:41 +0000
          Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-09 08:56 -0500
            Re: RAFTS-like optimiser; progress report albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-09-09 14:20 +0000
              Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-09 09:27 -0500
                Re: RAFTS-like optimiser; progress report "Rod Pemberton" <dont_use_email@nohavenotit.com> - 2013-09-10 04:31 -0400
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-10 05:11 -0500
            Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-09 15:08 +0000
              Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-09 10:45 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-11 15:21 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-11 12:04 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-11 17:46 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-11 14:45 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-13 13:00 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-13 10:46 -0500
                Re: RAFTS-like optimiser; progress report stephenXXX@mpeforth.com (Stephen Pelc) - 2013-09-13 17:44 +0000
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-14 15:31 +0000
                Re: RAFTS-like optimiser; progress report Paul Rubin <no.email@nospam.invalid> - 2013-09-14 10:33 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-14 12:39 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-15 15:05 +0000
                Re: RAFTS-like optimiser; progress report Alex McDonald <blog@rivadpm.com> - 2013-09-15 08:32 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-15 13:20 -0500
                Re: RAFTS-like optimiser; progress report stephenXXX@mpeforth.com (Stephen Pelc) - 2013-09-15 16:54 +0000
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-15 17:02 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-15 12:54 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-16 09:21 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-16 08:39 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-16 15:48 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-16 15:03 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-17 10:15 +0000
                Re: RAFTS-like optimiser; progress report "Rod Pemberton" <dont_use_email@nohavenotit.com> - 2013-09-17 17:24 -0400
                Re: RAFTS-like optimiser; progress report stephenXXX@mpeforth.com (Stephen Pelc) - 2013-09-17 13:10 +0000
            Re: RAFTS-like optimiser; progress report "Rod Pemberton" <dont_use_email@nohavenotit.com> - 2013-09-10 04:30 -0400
              Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-10 05:14 -0500
  Re: RAFTS-like optimiser; progress report mhx@iae.nl - 2013-09-07 03:22 -0700
  Re: RAFTS-like optimiser; progress report mhx@iae.nl - 2013-09-07 03:32 -0700

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