Groups > comp.lang.forth > #19314

Re: About stack access profundity

From	Bernd Paysan <bernd.paysan@gmx.de>
Newsgroups	comp.lang.forth
Subject	Re: About stack access profundity
Date	2013-01-31 15:37 +0100
Organization	1&1 Internet AG
Message-ID	<3427167.9fDfFC78xt@sunwukong.fritz.box> (permalink)
References	(8 earlier) <2013Jan29.162133@mips.complang.tuwien.ac.at> <5107ff7c.353609431@192.168.0.50> <2013Jan29.185800@mips.complang.tuwien.ac.at> <1950087.W2tCE9ddpV@sunwukong.fritz.box> <510a62ea.510135172@192.168.0.50>

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Stephen Pelc wrote:
> The code from the LEA up to but not including the SUB is a stack
> shuffle (we ran out of registers) followed by a store. Although it's
> possible to do it without the shuffle, VFX's "rip up and retry"
> rules are not clever enough here.

You need four free registers (including TOS) to fit this code in.  In 
bigForth, I have three free registers, because I have SP, RP, UP, OP 
(object pointer) and an index for loops in a register.  VFX doesn't have 
an OP, and doesn't waste another register for the index, so it should be 
possible to fit it into the available registers.  The main thing you 
need to do is to try hard to eliminate redundancy - all active values 
should only occupy one single register, unless a copy is dearly needed.

> Marcel's iForth version is for 64 bit code with 16 registers. This
> means more registers, so no shuffle, and because there are more
> registers, some can be used for the return stack. Nice code.

Yes, x64 is a much better target, because you have 8 really free 
registers (in x86, there is no register without a special role, though 
EBX is only used in xlat, and xlat is really superfluous - however, you 
can argue that x86 has 8 special purpose registers, and no general 
purpose register at all).

This is also impacting C compilers.  The string instructions use up ECX, 
ESI, and EDI, multiplication uses up EAX and EDX; -fomit-frame-pointer 
gives you EBP, so you have EBP and EBX, no more.  In Gforth, we 
therefore moved all string operations into real subroutines (even though 
that makes them a bit slower), and only then the C compiler is able to 
fit in the most important things.

-- 
Bernd Paysan
"If you want it done right, you have to do it yourself"
http://bernd-paysan.de/

Thread

About stack access profundity Pablo Hugo Reda <pabloreda@gmail.com> - 2013-01-27 12:11 -0800
  Re: About stack access profundity humptydumpty <ouatubi@gmail.com> - 2013-01-28 00:59 -0800
    Re: About stack access profundity Pablo Hugo Reda <pabloreda@gmail.com> - 2013-01-28 07:17 -0800
  Re: About stack access profundity Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-28 03:10 -0600
    Re: About stack access profundity Pablo Hugo Reda <pabloreda@gmail.com> - 2013-01-28 07:23 -0800
      Re: About stack access profundity Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-28 10:46 -0600
        Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-29 08:20 +0000
          Re: About stack access profundity Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-29 03:25 -0600
            Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-29 09:47 +0000
              Re: About stack access profundity Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-29 04:08 -0600
                Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-29 15:21 +0000
                Re: About stack access profundity Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-29 09:57 -0600
                Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-29 17:01 +0000
                Re: About stack access profundity Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-29 12:22 -0600
                Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-30 17:40 +0000
                Re: About stack access profundity Paul Rubin <no.email@nospam.invalid> - 2013-01-30 11:49 -0800
                Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-02-04 16:39 +0000
                Re: About stack access profundity Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-30 16:32 -0600
                Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-31 16:02 +0000
                Re: About stack access profundity stephenXXX@mpeforth.com (Stephen Pelc) - 2013-01-29 17:06 +0000
                Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-29 17:58 +0000
                Re: About stack access profundity Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-01-29 12:29 -0600
                Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-30 17:22 +0000
                Re: About stack access profundity Bernd Paysan <bernd.paysan@gmx.de> - 2013-01-29 20:17 +0100
                Re: About stack access profundity mhx@iae.nl (Marcel Hendrix) - 2013-01-29 21:44 +0200
                Re: About stack access profundity Bernd Paysan <bernd.paysan@gmx.de> - 2013-01-29 22:14 +0100
                Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-30 16:29 +0000
                Re: About stack access profundity Pablo Hugo Reda <pabloreda@gmail.com> - 2013-01-30 09:58 -0800
                Re: About stack access profundity stephenXXX@mpeforth.com (Stephen Pelc) - 2013-01-31 12:32 +0000
                Re: About stack access profundity Bernd Paysan <bernd.paysan@gmx.de> - 2013-01-31 15:37 +0100
                Re: About stack access profundity Mark Wills <forthfreak@gmail.com> - 2013-01-29 23:12 -0800
          Re: About stack access profundity stephenXXX@mpeforth.com (Stephen Pelc) - 2013-01-29 10:08 +0000
            Re: About stack access profundity Pablo Hugo Reda <pabloreda@gmail.com> - 2013-01-29 07:10 -0800
            Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-29 15:17 +0000
      Re: About stack access profundity Mark Wills <forthfreak@gmail.com> - 2013-01-29 00:57 -0800
  Re: About stack access profundity Mark Wills <forthfreak@gmail.com> - 2013-01-28 01:56 -0800
  Re: About stack access profundity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-01-29 15:30 +0000
    Re: About stack access profundity Pablo Hugo Reda <pabloreda@gmail.com> - 2013-01-29 09:06 -0800
  Re: About stack access profundity Pablo Hugo Reda <pabloreda@gmail.com> - 2013-02-03 06:22 -0800
    Re: About stack access profundity Mark Wills <forthfreak@gmail.com> - 2013-02-03 07:25 -0800
      Re: About stack access profundity Pablo Hugo Reda <pabloreda@gmail.com> - 2013-02-03 15:51 -0800
        Re: About stack access profundity Coos Haak <chforth@hccnet.nl> - 2013-02-04 01:12 +0100
    Re: About stack access profundity Mark Wills <forthfreak@gmail.com> - 2013-02-03 23:10 -0800
      Re: About stack access profundity Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-02-04 03:26 -0600
  Re: About stack access profundity humptydumpty <ouatubi@gmail.com> - 2013-02-03 11:26 -0800
    Re: About stack access profundity Pablo Hugo Reda <pabloreda@gmail.com> - 2013-02-03 15:49 -0800

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