Re: Forth-94 vs. Forth-2012 FP data (long)

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: Forth-94 vs. Forth-2012 FP data (long)
Date	2017-05-17 15:02 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2017May17.170216@mips.complang.tuwien.ac.at> (permalink)
References	<2017May13.093451@mips.complang.tuwien.ac.at> <a561c81c-8478-4528-ad63-7c3524bef94c@googlegroups.com> <591c2dab.599913139@news.eternal-september.org>

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stephen@mpeforth.com (Stephen Pelc) writes:
>On Tue, 16 May 2017 22:48:04 -0700 (PDT), Joel Rees
><joel.rees@gmail.com> wrote:
>
>>> daxpy would produce better performance; I show this version to show
>>> what a compiler can do and to get a feeling for how close to the limit
>>> the Forth results are):
>>> 
>>> VFX Forth-2012         VFX Forth-94              gcc (faxpy)
>>> FLD   ST               MOV   EDX, [EBP]          movsd  (%rdi),%xmm1      
>>> MOV   EDX, [EBP]       FLD   TBYTE 0 [EDX]       add    %rsi,%rdi         
>>> FLD   TBYTE 0 [EDX]    FLD   TBYTE [080A3460]    mulsd  %xmm0,%xmm1       
>>> FMULP ST(1), ST        FMULP ST(1), ST           addsd  (%rdx),%xmm1      
>>> FLD   TBYTE 0 [EBX]    FLD   TBYTE 0 [EBX]       movsd  %xmm1,(%rdx)      
>>> FADDP ST(1), ST        FADDP ST(1), ST           add    %rcx,%rdx         
>>> FSTP  TBYTE 0 [EBX]    FSTP  TBYTE 0 [EBX]       sub    $0x1,%r8          
>>> ADD   EBX, 0A          ADD   EBX, 0A             jne    0x4180b8 <faxpy+8>
>>> MOV   EDX, [EBP]       MOV   EDX, [EBP]      
>>> ADD   EDX, 0A          ADD   EDX, 0A         
>>> ADD   [ESP], 01        ADD   [ESP], 01       
>>> ADD   [ESP+04], 01     ADD   [ESP+04], 01    
>>> MOV   [EBP], EDX       MOV   [EBP], EDX      
>>> JNO   080C6D78         JNO   080C6DB8        
>>>
>>> So VFX works nicely for optimizing the PICKs, DUPs etc. away here,
>
>Note also that ?DO ... LOOP is not optimal here as it maintains two
>items in memory. See the last four instructions in the VFX listings.
>A simple BEGIN ... UNTIL may be better.

There is nothing in ?DO...LOOP that prevents a compiler from
generating as good code for it as from BEGIN...WHILE...REPEAT
(BEGIN...UNTIL would be more appropriate for DO...LOOP).  Moreover,
DO...LOOP is a way to reduce stack load, and is therefore usually
preferred by programmers when they program counted loops.  But you can
try to convince me otherwise 

> If you have 16 or more registers
>using two for DO ... LOOP may be more effective.

My suggestion is to use one register (containing the index) and one
memory location (containing the limit) on Intel/AMD CPUs, even with
only 8 registers.  I.e., something like:

inc ecx
cmp ecx, [esp]
jne right-after-do

This means that you can LOOP at up to one iteration per cycle (instead
of 1 per 5 or 6 cycles with the current scheme).  You may worry about
the [esp] memory access, but it does not depend on anything in the
loop, so it can be executed early by out-of-order execution.  And if
you don't put anything else between the cmp and the jne, recent Intel
CPUs will combine (macro-fuse) them, reducing resource consumption,
and maybe increasing performance.

Anyway, as I described in the posting, I unrolled the loop (by a
factor of 4) to reduce the impact of loop overhead.

- 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 2017: http://www.euroforth.org/ef17/

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Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-13 07:34 +0000
  Re: Forth-94 vs. Forth-2012 FP data (long) pahihu <pahihu@gmail.com> - 2017-05-13 11:16 -0700
    Re: Forth-94 vs. Forth-2012 FP data (long) pahihu <pahihu@gmail.com> - 2017-05-13 11:49 -0700
      Re: Forth-94 vs. Forth-2012 FP data (long) pahihu <pahihu@gmail.com> - 2017-05-13 13:38 -0700
        Re: Forth-94 vs. Forth-2012 FP data (long) mhx@iae.nl - 2017-05-13 15:08 -0700
          Re: Forth-94 vs. Forth-2012 FP data (long) pahihu <pahihu@gmail.com> - 2017-05-14 00:51 -0700
          Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-14 07:32 +0000
            Re: Forth-94 vs. Forth-2012 FP data (long) mhx@iae.nl - 2017-05-14 02:46 -0700
              Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-14 14:57 +0000
                Re: Forth-94 vs. Forth-2012 FP data (long) krishna.myneni@ccreweb.org - 2017-05-15 19:11 -0700
    Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-14 08:14 +0000
  Re: Forth-94 vs. Forth-2012 FP data (long) Paul Rubin <no.email@nospam.invalid> - 2017-05-13 15:58 -0700
    Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-14 07:01 +0000
  Re: Forth-94 vs. Forth-2012 FP data (long) krishna.myneni@ccreweb.org - 2017-05-14 19:04 -0700
    Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-15 06:10 +0000
      Re: Forth-94 vs. Forth-2012 FP data (long) krishna.myneni@ccreweb.org - 2017-05-15 01:49 -0700
        Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-15 14:33 +0000
  Re: Forth-94 vs. Forth-2012 FP data (long) "HAA" <someone@microsoft.com> - 2017-05-15 13:44 +1000
    Re: Forth-94 vs. Forth-2012 FP data (long) Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-05-15 04:43 -0500
    Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-15 15:03 +0000
      Re: Forth-94 vs. Forth-2012 FP data (long) "HAA" <someone@microsoft.com> - 2017-05-17 00:10 +1000
  Re: Forth-94 vs. Forth-2012 FP data (long) pahihu <pahihu@gmail.com> - 2017-05-16 09:04 -0700
    Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-17 15:54 +0000
      Re: Forth-94 vs. Forth-2012 FP data (long) mhx@iae.nl - 2017-05-17 10:29 -0700
      Re: Forth-94 vs. Forth-2012 FP data (long) pahihu <pahihu@gmail.com> - 2017-05-17 23:53 -0700
        Re: Forth-94 vs. Forth-2012 FP data (long) pahihu <pahihu@gmail.com> - 2017-05-19 02:34 -0700
  Re: Forth-94 vs. Forth-2012 FP data (long) Joel Rees <joel.rees@gmail.com> - 2017-05-16 22:48 -0700
    Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-17 06:51 +0000
      Re: Forth-94 vs. Forth-2012 FP data (long) Joel Rees <joel.rees@gmail.com> - 2017-05-17 09:29 -0700
    Re: Forth-94 vs. Forth-2012 FP data (long) stephen@mpeforth.com (Stephen Pelc) - 2017-05-17 11:07 +0000
      Re: Forth-94 vs. Forth-2012 FP data (long) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-05-17 15:02 +0000

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