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Re: Any thoughts on ARM FORTH register usage

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On Thu, 19 Jul 2012 00:56:50 -0700 (PDT), "Clyde W. Phillips Jr."
<cwpjr02@gmail.com> wrote:

>Thanks Steve.

My name is Stephen.
 
> If STC = Subroutine Threaded Code I assume you are recommending
> it because of the Link Register as Return Stack Pointer is only
> 1 level. Am I understanding this correctly?

No. Regardless of the so-called data on threading performance,
tests on real systems usually show that naive STC without
inlining or optimisation is two times faster than DTC. This
occurs because of the nest/unnest overhead. This overhead
becomes worse with short definitions.

You need to read the ARM Tech Ref Manual for the core you are
using. In hand-waving terms, a branch costs 3 cycles, a read/write
costs 3 or 2, and register operations happen in 1.

In STC for ARM or Cortex, you need two instructions for the
call
  BL foo 
  ...
foo:
  PUSH LR

and one or two for the return, but mostly
  POP PC

Now start counting clocks for DTC and ITC.
Now inline @ as
  mov  tos, [ tos, # 0 ]
and so on and so on. Then add a real code generator such as VFX 
to the mix and the factor of 2 has become a factor of 10.

That's why our MPE Forth Stamp cross compiler is such a bargain.

Stephen

-- 
Stephen Pelc, stephenXXX@mpeforth.com
MicroProcessor Engineering Ltd - More Real, Less Time
133 Hill Lane, Southampton SO15 5AF, England
tel: +44 (0)23 8063 1441, fax: +44 (0)23 8033 9691
web: http://www.mpeforth.com - free VFX Forth downloads

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Thread

Any thoughts on ARM FORTH register usage Clyde Phillips <cwpjr02@gmail.com> - 2012-07-15 22:01 -0700
  Re: Any thoughts on ARM FORTH register usage stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-16 08:50 +0000
  Re: Any thoughts on ARM FORTH register usage "Clyde W. Phillips Jr." <cwpjr02@gmail.com> - 2012-07-19 00:56 -0700
    Re: Any thoughts on ARM FORTH register usage stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-19 08:56 +0000
  Re: Any thoughts on ARM FORTH register usage "Clyde W. Phillips Jr." <cwpjr02@gmail.com> - 2012-07-19 16:13 -0700
    Re: Any thoughts on ARM FORTH register usage stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-20 05:38 +0000
      Re: Any thoughts on ARM FORTH register usage "Clyde W. Phillips Jr." <cwpjr02@gmail.com> - 2012-07-23 23:08 -0700
        Re: Any thoughts on ARM FORTH register usage stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-24 09:05 +0000
          Re: Any thoughts on ARM FORTH register usage "Clyde W. Phillips Jr." <cwpjr02@gmail.com> - 2012-07-24 16:20 -0700
            Re: Any thoughts on ARM FORTH register usage stephenXXX@mpeforth.com (Stephen Pelc) - 2012-07-25 08:01 +0000

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