Re: Stack Sizes

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: Stack Sizes
Date	2016-10-09 16:03 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2016Oct9.180314@mips.complang.tuwien.ac.at> (permalink)
References	(6 earlier) <nt7f6v$r4e$1@dont-email.me> <87fuo8wsr0.fsf@nightsong.com> <xY-dnVB12fghPWrKnZ2dnUU7-eXNnZ2d@supernews.com> <2016Oct7.185348@mips.complang.tuwien.ac.at> <veGdnSHzHOHw2mfKnZ2dnUU7-f3NnZ2d@supernews.com>

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Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>> Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>>>Paul Rubin <no.email@nospam.invalid> wrote:
>>>> The SPARC had a 24-register window, where each level of call got 8 local
>>>> registers and could also see the local sets of the two higher calls.
>> 
>> Not quite.  When shifting the window, it is shifted by 16 registers.
>> You typically shift in one direction on call, and in the other on
>> return.  So the callee (B) sees 8 of the registers that the caller (A)
>> saw, and the caller uses these to pass parameters; if the B wants to
>> make a call itself, it puts the parameters in the 8 registers at the
>> other end of the window; the 8 registers in between can only be used
>> for local data.  The remaining 8 (or 7?) registers were not managed in
>> Windows.
>> 
>>>The decision to go with register windows was based on a bunch of
>>>benchmarks which seemed to indicate a performance improvement over
>>>something more conventional.  But the benchmarks weren't
>>>representative enough
>> 
>> Representative of what?
>
>AIUI, of much of the real-world code which is run on SPARC processors.

Do you have any evidence for this claim?

>>>and the fixed size of the windows was problematic because registers
>>>are left unused.  In the end, register windows are a loss:
>>>sophisticated register allocators can generate better code which
>>>uses fewer physical registers.
>> 
>> Except that these sophisticated register allocators never
>> materialized in the real world. 
>
>I guess that depends on whether your glass is half empty or half full.
>There's no getting around register allocation being NP-complete, but
>IME approximate algorithms run in reasonable time on reasonably small
>programs.

Sure, but that does nothing to address the issues that register
windows address.  A function that calls another function and has, say,
6 registers live across the call, needs to save 6 registers and
restore 6 registers somewhere (either save calle-saved registers on
entry and exit, or save caller-saved registers around the call).
Register Windows reduce that overhead.  In theory, one can use
interprocedural register allocation to reduce these overheads.  In
practice, one does not do that (except when compiling SPEC CPU
benchmarks).

>GCC's old register allocator has now
>successfully been replaced.

Since which version?

>> so let's look at other stuff: Applications that are dynamically
>> linked (SPEC CPU benchmarks usually are statically linked for
>> performance) and use polymorphic calls (no interprocedural register
>> allocation for that, but fortunately rare in SPEC CPU); static
>> compiler sophistication will not help for these cases.
>
>Well, sure: an optimizing compiler can't optimize beyond its
>"optimization horizon": the amount of code that it can see.  That's
>obvious, surely.  You can't optimize what you can't see.

But register windows work even for such calls.

>> The IA-64 designers had too much rather than too little faith in
>> sophisticated compilers, yet they included the register stack
>> (something like register windows, but without fixed shifts, avoiding
>> the waste "problem"); so they certainly did not buy the "sophisticated
>> register allocators can generate better code" argument.
>
>The register stack isn't on the face of it such a terrible idea, but
>it's certainly questionable whether it's the best way to use the
>silicon.  But the IA-64 does not, as you note, have fixed-size
>windows, which are the real Achilles' heel of the SPARC.

I doubt that it's the Achilles' heel.  Sure, variable shifts would
have made better use of the physical registers, but as long as the
number of overflows/underflows is small, that makes little difference.
And the number of physical registers was selected such that the number
of overflows was small in practice.

The Achilles' heel of SPARC were slow implementations.

>And the
>reason that architecture hasn't much been imitated.

I think the paper that claimed that interprocedural register
allocation makes register windows unnecessary played a big role.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2016: http://www.euroforth.org/ef16/

Thread

Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-03 08:22 -0400
  Re: Stack Sizes foxaudioresearch@gmail.com - 2016-10-03 07:00 -0700
    Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-03 11:14 -0400
      Re: Stack Sizes Bernd Linsel <bl1@gmx.com> - 2016-10-03 18:20 +0200
        Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-03 11:30 -0500
          Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-03 15:27 -0400
          Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-03 18:12 -0400
            Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-03 17:52 -0500
            Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-03 16:06 -0700
        Re: Stack Sizes Jan Coombs <jenfhaomndgfwutc@murmic.plus.com> - 2016-10-04 08:31 +0100
          Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-04 08:46 +0000
            Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-04 10:38 -0400
            Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-04 11:59 -0700
              Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-05 09:59 +0000
                Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-05 10:16 -0400
                Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-06 08:21 +0000
          Re: Stack Sizes minforth@arcor.de - 2016-10-04 05:00 -0700
          Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-04 08:49 -0400
      Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-03 16:28 -0700
        Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-04 10:36 -0400
          Re: Stack Sizes Rod Pemberton <NoHaveNotOne@zxdehrnyya.cam> - 2016-10-04 16:15 -0400
          Re: Stack Sizes Brad Eckert <hwfwguy@gmail.com> - 2016-11-09 09:56 -0800
            Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-11-12 09:15 -0500
    Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-03 10:35 -0500
    Re: Stack Sizes Bernd Paysan <bernd@net2o.de> - 2016-10-11 01:01 +0000
  Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-03 10:21 -0400
    Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-03 11:06 -0400
      Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-03 15:22 -0400
        Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-03 18:04 -0400
    Re: Stack Sizes Hans Bezemer <the.beez.speaks@gmail.com> - 2016-10-04 20:46 +0200
      Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-04 15:40 -0400
        Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-05 12:26 -0700
          Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-05 15:44 -0500
            Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-05 16:32 -0700
              Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-05 20:01 -0400
                Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-07 07:39 +0000
              Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-05 20:36 -0500
                Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-05 21:28 -0700
          Re: Stack Sizes alex <alex@rivadpm.com> - 2016-10-05 22:07 +0100
            Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-06 00:05 -0700
            Re: Stack Sizes Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-10-06 02:17 -0500
      Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-04 19:27 -0400
        Re: Stack Sizes Hans Bezemer <the.beez.speaks@gmail.com> - 2016-10-05 18:58 +0200
          Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-05 13:17 -0400
            Re: Stack Sizes Hans Bezemer <the.beez.speaks@gmail.com> - 2016-10-22 12:35 +0200
          Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-05 12:18 -0500
            Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-05 16:07 -0400
              Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-05 15:50 -0500
                Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-05 17:36 -0400
                Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-05 17:14 -0500
                Re: Stack Sizes "Elizabeth D. Rather" <erather@forth.com> - 2016-10-05 14:48 -1000
                Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-05 20:49 -0500
  Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-03 16:32 +0000
  Re: Stack Sizes Chris Curl <ccurl609@gmail.com> - 2016-10-03 13:53 -0700
    Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-03 17:54 -0400
  Re: Stack Sizes Rod Pemberton <NoHaveNotOne@zxdehrnyya.cam> - 2016-10-03 23:40 -0400
    Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-04 11:30 -0400
  Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-03 21:47 -0700
    Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-04 11:22 -0400
      Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-04 11:44 -0700
        Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-04 15:53 -0400
          Re: Stack Sizes Rod Pemberton <NoHaveNotOne@zxdehrnyya.cam> - 2016-10-04 16:15 -0400
      Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-05 14:31 -0700
        Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-06 08:48 -0400
          Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-06 13:08 -0700
            Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-06 19:11 -0400
  Re: Stack Sizes jim.brakefield@ieee.org - 2016-10-06 12:08 -0700
    Re: Stack Sizes alex <alex@rivadpm.com> - 2016-10-06 21:47 +0100
    Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-06 19:05 -0400
    Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-06 21:57 -0400
      Re: Stack Sizes jim.brakefield@ieee.org - 2016-10-06 19:21 -0700
        Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-07 00:10 -0400
          Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-06 23:14 -0700
            Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-07 02:26 -0400
              Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-06 23:57 -0700
                Re: Stack Sizes Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-10-07 08:18 -0500
                Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-07 10:52 -0400
                Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-09 16:22 -0700
                Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-10 01:49 -0400
                Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-10 10:21 -0500
                Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-10 22:39 -0400
                Straight Forth Re: Stack Sizes albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-10 12:36 +0200
                Re: Straight Forth Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-13 13:45 -0700
                Re: Straight Forth Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-14 01:16 -0700
                Re: Straight Forth Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-15 20:38 -0700
                Re: Straight Forth Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-16 02:00 -0400
                Re: Straight Forth Re: Stack Sizes lawrencedo99@gmail.com - 2016-10-16 18:38 -0700
                Re: Straight Forth Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-16 22:27 -0400
                Re: Straight Forth Re: Stack Sizes Raimond Dragomir <raimond.dragomir@gmail.com> - 2016-10-16 21:14 -0700
                Re: Straight Forth Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-17 00:35 -0400
                Re: Straight Forth Re: Stack Sizes Raimond Dragomir <raimond.dragomir@gmail.com> - 2016-10-16 23:31 -0700
                Re: Straight Forth Re: Stack Sizes "Elizabeth D. Rather" <erather@forth.com> - 2016-10-16 20:36 -1000
                Re: Straight Forth Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-17 13:11 -0700
                Re: Straight Forth Re: Stack Sizes Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2016-10-17 19:14 -0400
                Re: Straight Forth Re: Stack Sizes Bernd Paysan <bernd@net2o.de> - 2016-10-17 21:53 +0000
                Re: Straight Forth Re: Stack Sizes lawrencedo99@gmail.com - 2016-10-17 16:54 -0700
                Re: Straight Forth Re: Stack Sizes Bernd Paysan <bernd@net2o.de> - 2016-10-21 22:13 +0000
                Re: Straight Forth Re: Stack Sizes lawrencedo99@gmail.com - 2016-10-21 17:46 -0700
                Re: Straight Forth Re: Stack Sizes Bernd Paysan <bernd@net2o.de> - 2016-10-23 22:26 +0000
                Re: Straight Forth Re: Stack Sizes JUERGEN <epldfpga@aol.com> - 2016-10-24 09:13 -0700
                Re: Straight Forth Re: Stack Sizes lawrencedo99@gmail.com - 2016-10-24 16:28 -0700
                Re: Straight Forth Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-24 17:20 -0700
                Re: Straight Forth Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-24 22:23 -0400
                Re: Straight Forth Re: Stack Sizes Bernd Paysan <bernd@net2o.de> - 2016-11-04 20:39 +0000
                Re: Straight Forth Re: Stack Sizes lawrencedo99@gmail.com - 2016-10-16 22:42 -0700
                Re: Straight Forth Re: Stack Sizes albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-17 11:12 +0200
                Re: Straight Forth Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-17 09:20 -0700
                Re: Straight Forth Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-17 19:11 -0400
                Re: Straight Forth Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-17 16:40 -0700
                Re: Straight Forth Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-17 20:19 -0400
                Re: Straight Forth Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-17 17:25 -0700
                Re: Straight Forth Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-17 20:50 -0400
                Re: Straight Forth Re: Stack Sizes albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-18 02:04 +0200
                Re: Straight Forth Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-18 06:13 +0000
                Re: Straight Forth Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-16 15:21 -0700
                Re: Straight Forth Re: Stack Sizes Doug Hoffman <glidedog@gmail.com> - 2016-10-17 04:09 -0400
                Re: Straight Forth Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-17 13:48 -0700
                Re: Straight Forth Re: Stack Sizes albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-18 02:12 +0200
                Re: Straight Forth Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-18 00:35 -0700
                Re: Straight Forth Re: Stack Sizes albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-18 12:53 +0200
                Re: Straight Forth Re: Stack Sizes hughaguilar96@gmail.com - 2016-10-18 12:12 -0700
                Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-07 16:53 +0000
                Re: Stack Sizes Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-10-09 08:34 -0500
                Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-09 16:03 +0000
                Re: Stack Sizes Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-10-10 03:25 -0500
                Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-10 10:29 -0500
                Re: Stack Sizes Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-10-11 05:19 -0500
                Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-10 14:41 +0000
                Re: Stack Sizes Lars Brinkhoff <lars.spam@nocrew.org> - 2016-10-10 20:23 +0200
                Re: Stack Sizes Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-10-11 05:16 -0500
                Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-12 12:54 +0000
                Re: Stack Sizes albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-12 18:27 +0200
                Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-12 17:06 +0000
                Re: Stack Sizes Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-10-12 13:01 -0500
                Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-12 17:07 -0400
                Re: Stack Sizes albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-13 03:18 +0200
                Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-14 14:26 -0400
                Re: Stack Sizes lawrencedo99@gmail.com - 2016-10-12 20:30 -0700
                Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-13 15:52 +0000
                Re: Stack Sizes lawrencedo99@gmail.com - 2016-10-13 15:05 -0700
                Re: Stack Sizes Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-10-14 03:08 -0500
                Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-14 14:41 -0400
                Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-07 12:33 -0500
                Re: Stack Sizes rickman <gnuarm@gmail.com> - 2016-10-08 01:12 -0400
              Re: Stack Sizes Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2016-10-07 23:05 -0400
                Re: Stack Sizes jim.brakefield@ieee.org - 2016-10-07 21:56 -0700
                Re: Stack Sizes Walter Banks <walter@bytecraft.com> - 2016-10-08 07:23 -0400
                Re: Stack Sizes lawrencedo99@gmail.com - 2016-10-11 22:39 -0700
            Re: Stack Sizes Lars Brinkhoff <lars.spam@nocrew.org> - 2016-10-07 08:21 +0200
            Re: Stack Sizes albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-07 09:22 +0200
              Re: Stack Sizes Lars Brinkhoff <lars.spam@nocrew.org> - 2016-10-07 09:35 +0200
                Re: Stack Sizes jim.brakefield@ieee.org - 2016-10-07 10:51 -0700
                Re: Stack Sizes Cecil Bayona <cbayona@cbayona.com> - 2016-10-07 13:21 -0500
                Re: Stack Sizes Lars Brinkhoff <lars.spam@nocrew.org> - 2016-10-07 20:40 +0200
                Re: Stack Sizes albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-10-07 20:53 +0200
            Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-07 07:35 +0000
              Re: Stack Sizes Paul Rubin <no.email@nospam.invalid> - 2016-10-07 01:09 -0700
                Re: Stack Sizes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-10-07 15:59 +0000
                Re: Stack Sizes Bernd Paysan <bernd@net2o.de> - 2016-10-17 22:05 +0000

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