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Groups > comp.lang.forth > #13208

Re: SEE in gforth 7.0.0 64 bits

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"Anton Ertl" <anton@mips.complang.tuwien.ac.at> wrote in message
news:2012Jun23.155121@mips.complang.tuwien.ac.at...
> "Rod Pemberton" <do_not_have@notemailnot.cmm> writes:
...

> >What code for DUP is being used to generate the assembly
> >sequences you posted?  I thought it was supposed to be C
> >code.  If it's C code, I'd like to see the code.
>
> Actually the source code is:
>
> dup ( w -- w w ) core dupe
>
> This is translated into the following C code (after macro
> expansion, on AMD64, debugging version):
>
> H_dupe: asm(""); I_dupe:
> { saved_ip=ip; asm(""); }
> {
> Cell w;
> ;
> ((w)=(Cell)(sp[0]));
> sp += -1;
> {
> # 1323 "prim"
> # 6744 "prim.i"
> }
> (ip++);
> ((sp[0])=(Cell)(w));
> K_dupe: asm("");
> do {asm("":"=X"(cfa)); do {(real_ca=(*(ip-1)));} while(0);} while(0);
> J_dupe: asm("");
> goto *real_ca;
> }
>

Things I see.

They may be of no real consequence since it seems much of the emitted code
is unused by DUP, i.e., macro's, code template, generic pattern code, etc.

a) unused label's and empty asm's.  If gforth "knows" to not emit asm code,
why doesn't it "know" to not emit unused labels and empty asm directives?

b) unneeded do-while's.  If gforth "knows" it doesn't need to use a break or
continue within the do-while as goto's, why does it emit do-while's?  From
the many label's, it seems gforth is mostly using goto's.  So, why is
do-while being used?  E.g., macro's?  Or, vice-versa, if you can use
do-while's with break and continue as goto's, why use actual goto's and
label's elsewhere?  The do-while's might optimize better.

c) using an increment ++ operator for ip, but using += for sp ...  Even if
there is a need to adjust sp by multiple cells, it seems likely the stack
adjustments or operations would be done one cell at a time.

d) ip is incremented, then later, one is subtracted from ip for the
dereference ...  Should or could the decrement be relocated?

e) the code is incrementing sp as if it's pointer to cell, but not
dereferencing sp to access the object sp points to.  Instead of
dereferencing sp, e.g., *sp, the subscript operator [], e.g., sp[0], is
being used for accessing what sp points to.  If the code is directly
adjusting sp, one has to ask if the index is being used.  I.e., is the index
in sp[index] _always_ zero ... ?  If so, there is no need for the subscript
operator.  The subscript operator will also typically add an additional
addition operation on x86 versus a pointer dereference.  However, gcc is
good with constants, so zero likely optimizes away here, but other values
won't.  I.e., if the index is non-zero sometimes, adjust sp by the index,
then eliminate the index and subscript operator.  Dereferencing sp may also
eliminate the ' Cell' casts, depending on how sp is declared.


Rod Pemberton

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SEE in gforth 7.0.0 64 bits Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-06-21 21:05 +0000
  Re: SEE in gforth 7.0.0 64 bits Josh Grams <josh@qualdan.com> - 2012-06-21 22:52 +0000
    Re: SEE in gforth 7.0.0 64 bits Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-06-22 11:25 +0000
    Re: SEE in gforth 7.0.0 64 bits Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-06-22 12:23 +0000
      Re: SEE in gforth 7.0.0 64 bits anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-06-22 11:57 +0000
        Re: SEE in gforth 7.0.0 64 bits Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-06-22 20:42 +0000
          Re: SEE in gforth 7.0.0 64 bits rugxulo@gmail.com - 2012-06-24 05:28 -0700
  Re: SEE in gforth 7.0.0 64 bits Paul Rubin <no.email@nospam.invalid> - 2012-06-21 19:31 -0700
    Re: SEE in gforth 7.0.0 64 bits Mark Wills <markrobertwills@yahoo.co.uk> - 2012-06-22 00:54 -0700
      Re: SEE in gforth 7.0.0 64 bits anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-06-22 11:16 +0000
        Re: SEE in gforth 7.0.0 64 bits "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-06-22 16:17 -0400
          Re: SEE in gforth 7.0.0 64 bits anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-06-23 13:51 +0000
            Re: SEE in gforth 7.0.0 64 bits "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-06-24 04:06 -0400
              Re: SEE in gforth 7.0.0 64 bits Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-06-24 06:55 -0500
              Re: SEE in gforth 7.0.0 64 bits anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-06-24 13:24 +0000
                Re: SEE in gforth 7.0.0 64 bits "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-06-24 18:44 -0400
                Re: SEE in gforth 7.0.0 64 bits Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-06-25 05:00 -0500
                Re: SEE in gforth 7.0.0 64 bits "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-06-25 17:54 -0400
                Re: SEE in gforth 7.0.0 64 bits Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-06-26 03:41 -0500
            Re: SEE in gforth 7.0.0 64 bits rugxulo@gmail.com - 2012-06-24 05:25 -0700
              Re: SEE in gforth 7.0.0 64 bits anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-06-24 14:08 +0000
                Re: SEE in gforth 7.0.0 64 bits rugxulo@gmail.com - 2012-06-25 07:56 -0700
        OT: fixing Mark's A0's, was [Re: SEE in gforth 7.0.0 64 bits] "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-06-22 16:18 -0400
          Re: OT: fixing Mark's A0's, was [Re: SEE in gforth 7.0.0 64 bits] Marc Olschok <nobody@nowhere.invalid> - 2012-06-25 12:42 +0000
            Re: OT: fixing Mark's A0's, was [Re: SEE in gforth 7.0.0 64 bits] Mark Wills <markrobertwills@yahoo.co.uk> - 2012-06-25 06:30 -0700
              Re: OT: fixing Mark's A0's, was [Re: SEE in gforth 7.0.0 64 bits] rugxulo@gmail.com - 2012-06-25 08:04 -0700
                Re: OT: fixing Mark's A0's, was [Re: SEE in gforth 7.0.0 64 bits] Mark Wills <markrobertwills@yahoo.co.uk> - 2012-06-25 11:00 -0700
                Re: OT: fixing Mark's A0's, was [Re: SEE in gforth 7.0.0 64 bits] "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-06-25 17:47 -0400
      Re: SEE in gforth 7.0.0 64 bits "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-06-22 16:01 -0400
  Re: SEE in gforth 7.0.0 64 bits Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2012-06-24 15:15 +0100

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