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Re: uninitialized and implicitly initialized locals (was: More ranting)

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Bernd Paysan <bernd.paysan@gmx.de> writes:
>Anton Ertl wrote:
>
>> Hmm, given that he still implements all locals on the in-memory return
>> stack, it should not be that hard to extend his implementation to
>> accept something close to the Gforth-supported usage, with one
>> restriction still remaining: The first locals definition must happen
>> outside any control structure.  When you see another locals
>> definition, you backpatch the return-stack reservation produced by the
>> first locals definition to increase the number of reserved locals, and
>> store the newly defined locals in the new slots.
>
>I don't see any need for this sort of restriction; the only problem of using 
>the return stack for locals is when your code contains >r and r>, and 
>declares the locals in between.

This is not about the return stack.  It would also be relevant with
such an implementation with a separate locals stack (indeed I started
out without specifying on which stack the locals were stored, and then
made it more concrete for easier unterstanding; but apparently also
easier misunderstanding).

This is about words like (from the Gforth tutorial):

: strcmp {: addr1 u1 addr2 u2 -- n :}
 addr1 addr2
 u1 u2 min 0
 ?do {: s1 s2 :}
   s1 c@ s2 c@ -
   ?dup-if
     unloop exit
   then
   s1 char+ s2 char+
 loop
 2drop
 u1 u2 - ;

Because some systems cannot do this, we got the uninitialized locals,
so that code could be rewritten as:

: strcmp {: addr1 u1 addr2 u2 | s1 s2 -- n :}
 addr1 addr2
 u1 u2 min 0
 ?do to s2 to s1
   s1 c@ s2 c@ -
   ?dup-if
     unloop exit
   then
   s1 char+ s2 char+
 loop
 2drop
 u1 u2 - ;

I am claiming that the compiler can do that for the programmer with
relatively little effort.  The restriction I mentioned is to disallow
having the first locals definition inside a control structure, like
here:

: foo ( ... ) \ no locals definition here:
  ... begin {: a b :}
    ... while
    ... repeat
  ... ;

If you allow that, either the backpatching does not just need to
update the space used by locals, but has to insert the locals
allocation in the code before the control structure, or you have to
generate matched allocation and deallocation on every iteration the
way Gforth does it; but the latter option is probably seen as too
inefficient by the implementor (one argument for uninitialized locals
was efficiency).

>Actually, with an analytical compiler, locals could be implemented "right", 
>i.e. it is just a virtual register, assigned to a value on the stack, given 
>a place on a virtual locals stack (which may actually live on the return 
>stack, but allocation of the maximum space needed in a word is moved to the 
>beginning, and deallocation is attached to every compiled EXIT) to be saved 
>when the register allocater runs out of registers (or needs to caller-save 
>registers when calling other words), and that's it - only those locals which 
>need saving in between need to be allocated on that stack, all locals that 
>can be kept in registers and are dead before they need saving don't.  That's 
>what an analytical compiler is for, to take the whole word, and analyze the 
>total dataflow within.  The sequence above { a b } a b + should compile to 
>the same code as a simple +.

Sure, that would be the way to go, but that's a bigger project.  What
I wanted to point out is that it does not take such a big effort to
remove the restrictions that led to uninitialized locals.

- 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 2014: http://www.euroforth.org/ef14/

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Re: Why smudge? hughaguilar96@yahoo.com - 2014-09-30 19:25 -0700
  Re: Why smudge? november.nihal@gmail.com - 2014-10-01 08:54 -0700
    Re: Why smudge? albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-01 19:09 +0000
  Re: Why smudge? november.nihal@gmail.com - 2014-10-01 10:16 -0700
    Re: Why smudge? hughaguilar96@yahoo.com - 2014-10-01 18:54 -0700
  Re: Why smudge? hughaguilar96@yahoo.com - 2014-10-02 15:31 -0700
    Re: Why smudge? Michael Barry <barrym95838@yahoo.com> - 2014-10-02 16:35 -0700
      Re: Why smudge? hughaguilar96@yahoo.com - 2014-10-02 17:02 -0700
        Re: Why smudge? Michael Barry <barrym95838@yahoo.com> - 2014-10-02 17:51 -0700
          Re: Why smudge? hughaguilar96@yahoo.com - 2014-10-02 18:50 -0700
        Re: Why smudge? Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2014-10-04 00:30 +0100
          Re: Why smudge? hughaguilar96@yahoo.com - 2014-10-03 17:40 -0700
            Re: Why smudge? Raimond Dragomir <raimond.dragomir@gmail.com> - 2014-10-03 23:00 -0700
              Pelc's effort to sabotage cross-compiler writing has a work-around now! hughaguilar96@yahoo.com - 2014-10-04 21:14 -0700
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-05 03:42 -0500
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! Enoch <emc.consultants@gmail.com> - 2014-10-05 10:43 -0700
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! hughaguilar96@yahoo.com - 2014-10-05 20:21 -0700
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-06 03:58 -0500
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! hughaguilar96@yahoo.com - 2014-10-05 17:09 -0700
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! Michael Barry <barrym95838@yahoo.com> - 2014-10-06 11:15 -0700
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! hughaguilar96@yahoo.com - 2014-10-06 18:52 -0700
                More ranting Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-07 03:48 -0500
                Re: More ranting albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-07 12:43 +0000
                Re: More ranting Bernd Paysan <bernd.paysan@gmx.de> - 2014-10-07 16:23 +0200
                Re: More ranting "Rod Pemberton" <buzzoff@nonamewhichexists.cmm> - 2014-10-16 01:03 -0400
                Re: More ranting Just Ian <superian@gmail.com> - 2014-10-16 07:14 -0700
                Re: More ranting Michael Barry <barrym95838@yahoo.com> - 2014-10-16 13:23 -0700
                uninitialized and implicitly initialized locals (was: More ranting) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-07 15:36 +0000
                Re: uninitialized and implicitly initialized locals (was: More ranting) Bernd Paysan <bernd.paysan@gmx.de> - 2014-10-07 22:15 +0200
                Re: uninitialized and implicitly initialized locals (was: More ranting) mhx@iae.nl - 2014-10-07 15:07 -0700
                Re: uninitialized and implicitly initialized locals (was: More ranting) Bernd Paysan <bernd.paysan@gmx.de> - 2014-10-08 03:11 +0200
                Re: uninitialized and implicitly initialized locals (was: More ranting) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-08 13:25 +0000
                Re: uninitialized and implicitly initialized locals (was: More ranting) hughaguilar96@yahoo.com - 2014-10-09 16:22 -0700
                Re: uninitialized and implicitly initialized locals (was: More ranting) "Rod Pemberton" <buzzoff@nonamewhichexists.cmm> - 2014-10-17 21:58 -0400
                Re: uninitialized and implicitly initialized locals (was: More ranting) mhx@iae.nl (Marcel Hendrix) - 2014-10-12 11:18 +0200
                Re: uninitialized and implicitly initialized locals (was: More ranting) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-08 12:35 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-07 15:27 -0500
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-08 12:56 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-08 08:24 -0500
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-08 15:32 +0000
                Simplified automatic scoping (was: uninitialized ...) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-08 16:06 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-08 11:57 -0500
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-08 12:18 -0500
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-09 14:19 +0000
                Re: uninitialized and implicitly initialized locals hughaguilar96@yahoo.com - 2014-10-09 14:42 -0700
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-09 14:07 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-09 10:44 -0500
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-10 16:03 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-10 13:35 -0500
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-11 10:53 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-12 11:34 -0500
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-15 12:44 +0000
                Re: uninitialized and implicitly initialized locals albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-15 14:34 +0000
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-15 15:03 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-15 11:10 -0500
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-16 12:19 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-17 03:56 -0500
                Re: uninitialized and implicitly initialized locals "Elizabeth D. Rather" <erather@forth.com> - 2014-10-17 07:48 -1000
                Re: uninitialized and implicitly initialized locals hughaguilar96@yahoo.com - 2014-10-17 19:26 -0700
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-18 12:55 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-18 13:21 -0500
                Re: uninitialized and implicitly initialized locals "Elizabeth D. Rather" <erather@forth.com> - 2014-10-18 08:44 -1000
                Re: uninitialized and implicitly initialized locals albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-19 09:53 +0000
                Re: uninitialized and implicitly initialized locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-20 12:48 +0000
                Re: uninitialized and implicitly initialized locals "Rod Pemberton" <buzzoff@nonamewhichexists.cmm> - 2014-10-20 16:24 -0400
                Re: uninitialized and implicitly initialized locals "Elizabeth D. Rather" <erather@forth.com> - 2014-10-20 10:30 -1000
                Re: uninitialized and implicitly initialized locals hughaguilar96@yahoo.com - 2014-10-20 16:23 -0700
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 04:16 -0500
                Re: uninitialized and implicitly initialized locals mhx@iae.nl (Marcel Hendrix) - 2014-10-26 11:32 +0200
                Re: uninitialized and implicitly initialized locals stephenXXX@mpeforth.com (Stephen Pelc) - 2014-10-26 14:27 +0000
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 13:56 -0500
                Re: uninitialized and implicitly initialized locals mhx@iae.nl (Marcel Hendrix) - 2014-10-26 20:32 +0200
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 16:18 -0500
                Re: uninitialized and implicitly initialized locals hughaguilar96@yahoo.com - 2014-10-26 15:05 -0700
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 17:53 -0500
                Re: uninitialized and implicitly initialized locals hughaguilar96@yahoo.com - 2014-10-26 16:30 -0700
                Re: uninitialized and implicitly initialized locals "Rod Pemberton" <buzzoff@nonamewhichexists.cmm> - 2014-10-27 01:45 -0400
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-27 12:21 -0500
                Re: uninitialized and implicitly initialized locals Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 17:57 -0500
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2014-10-06 20:55 +0100
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! hughaguilar96@yahoo.com - 2014-10-06 16:05 -0700
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2014-10-09 07:36 +0100
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! stephenXXX@mpeforth.com (Stephen Pelc) - 2014-10-10 01:52 +0000
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! hughaguilar96@yahoo.com - 2014-10-09 19:56 -0700
                Re: Pelc's effort to sabotage cross-compiler writing has a work-around now! "Rod Pemberton" <buzzoff@nonamewhichexists.cmm> - 2014-10-17 23:11 -0400
            Re: Why smudge? Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2014-10-05 11:05 +0100
              Re: Why smudge? hughaguilar96@yahoo.com - 2014-10-05 19:48 -0700
                Re: Why smudge? Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2014-10-06 07:53 +0100
                Re: Why smudge? "Elizabeth D. Rather" <erather@forth.com> - 2014-10-05 21:29 -1000
              Re: Why smudge? hughaguilar96@yahoo.com - 2014-10-09 15:16 -0700
              Re: Why smudge? "Rod Pemberton" <buzzoff@nonamewhichexists.cmm> - 2014-10-16 01:03 -0400

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