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Re: Performance of hand-optimised assembly

From 88888 Dihedral <dihedral88888@googlemail.com>
Newsgroups comp.lang.c
Subject Re: Performance of hand-optimised assembly
Date 2012-01-05 13:39 -0800
Organization http://groups.google.com
Message-ID <17628537.415.1325799572104.JavaMail.geo-discussion-forums@prgi2> (permalink)
References (3 earlier) <jd81e9$qs5$1@speranza.aioe.org> <jdal5r$3n3$1@dont-email.me> <jdalt3$u2b$1@speranza.aioe.org> <je2427$otd$1@dont-email.me> <je28te$g14$1@speranza.aioe.org>

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jacob navia於 2012年1月5日星期四UTC+8上午3時22分25秒寫道：
> Le 04/01/12 18:59, Stephen Sprunk a écrit :
> > On 26-Dec-11 14:36, jacob navia wrote:
> >> Le 26/12/11 21:24, Stephen Sprunk a écrit :
> >>> On 25-Dec-11 14:35, jacob navia wrote:
> >>>> Assembly will always do better than standard C in the above specific
> >>>> code. You can then use the ADDPD and add 2 integers at the same time
> >>>> (under specific loop conditions).
> >>>
> >>> ... unless you have a vectorizing compiler, which will do the exact same
> >>> thing for you without the need for inline assembly.
> >>
> >> Sure. That was a simple example, and no, gcc doesn't do it, at least
> >> in the version I have
> >
> > Like many GCC sub-projects, the work isn't complete, and probably isn't
> > on by default:
> > http://gcc.gnu.org/projects/tree-ssa/vectorization.html
> >
> 
> 
> Note that those instructions are available since at least 10 YEARS
> and still mainstream compilers like MSVC or GCC do not perform any of
> the magic you invoke...
> 
> Sure, maybe ONE DAY IN THE FAR FUTURE they will do it, but until then I
> am using those instructions in my programs now...
> 
> 
> > GCC isn't the only compiler out there, either; I've heard ICC is very
> > good at this, for instance.
> >
> 
> Yes, you need ALLL THE RESOURCES of Intel Corp to build such a compiler,
> no wonder nobody has done that besides Intel.
> 
> >>> Also, when AVX support comes out, that vectorizing compiler will start
> >>> using AVX instructions while your assembly is stuck using SSE.
> >>
> >> Sure, you can recompile your program bu I can't change a few loop
> >> `conditions since I am "stuck" with my old program, poor me.
> >
> > AVX will be different instructions, different registers, etc.
> 
> What?
> 
> Look Stephen, you are surely knowledgable in C but in assembly...
> Take for instance ANDPS (AND NOT PACKED Single precision)
> 
> The corresponding AVX instructions is...
> VANDNPS, with the same syntax same semantics. You just
> add a "V" before the instruction mnemonic.
> 
> All you have to do is use the ymm registers with 256 bits
> instead of the xmm registers with 128 bits. Your loop
> counters must be adjusted (using only half as many loops)
> and that was it, maybe an hour of work for a big program.
> 
> 
> > It won't
> > be a complete rewrite from scratch, but it'll be a lot of work, whereas
> > someone with a vectorizing compiler can just change one option and
> > recompile.
> >
> 
> Yes, but it will be at least 10 years before gcc or MSVC propose that.
> gcc doesn't even propose automatically SSE2 or SSE3 TODAY, 10 years
> after it was announced by Intel...
> 
> 
> >>> Furthermore, there is no guaranteed win for using SEE; early SSE chips
> >>> simply decoded that into two FADDs, so there was no performance benefit
> >>> to all that work you invested in writing SSE assembly.
> >>
> 
> That was in 2000, when it first appeared. Pleeeeeze, we are 2012 now,
> that is no longer relevant at all.
> 
> 
> But let's forget about that. Look at this.
> 
> problem:
> 
> You have a vector of 8 long long integers and you want to shift that
> vector by a given amount left between 1 and 63 bits.
> 
> Interface:
> 
> void ShiftVector(long long *vector, int AmountToShift);
> ; Pointer to vector in %rdi
> ; Amount to shift in %rsi
> ; gcc calling conventions for x86-64
> shiftvector:
>          movq    %rsi,%rcx 
 AmountToShift -> rcx

> 
>          movq (%rdi),%rsi

vector[0] -> rsi
>          movq 8(%rdi),%rax
vector[1] -> rax
>          shldq %cl,%rax,%rsi

Do the shift to the left.  

>          movq %rsi,(%rdi)

Save the rsi part.  Leave the rax part. 
> 
>          movq 16(%rdi),%rsi
vector[2] -> rsi


>          shldq %cl,%rsi,%rax
Do the shift. 
>          movq %rax,8(%rdi)

Save the rax part. Leave the rsi part. 

> 
>          movq 24(%rdi),%rax
>          shldq %cl,%rax,%rsi
>          movq %rsi,16(%rdi)
> 
>          movq 32(%rdi),%rsi
>          shldq %cl,%rsi,%rax
>          movq %rax,24(%rdi)
> 
>          movq 40(%rdi),%rax
>          shldq %cl,%rax,%rsi
>          movq %rsi,32(%rdi)
> 
>          movq 48(%rdi),%rsi
>          shldq %cl,%rsi,%rax
>          movq %rax,40(%rdi)
> 
>          movq 56(%rdi),%rax
>          shldq %cl,%rax,%rsi
>          movq %rsi,48(%rdi)
> 
>          shlq %cl,%rsi
>          movq %rsi,56(%rdi)
> 
>          ret
> 
> 26 instructions, 97 bytes (!!!)
> 
> Write that in C and see how big your procedure is, and how slow :-)

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Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-23 18:43 +0000
  Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-23 19:40 +0000
    Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-23 21:26 +0000
      Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-23 22:02 +0000
        Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-24 02:52 +0000
          Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-23 20:32 -0800
            Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-24 13:09 +0000
              Re: Performance of hand-optimised assembly James Harris <james.harris.1@googlemail.com> - 2011-12-24 05:49 -0800
                Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-24 15:30 +0000
                Re: Performance of hand-optimised assembly James Harris <james.harris.1@googlemail.com> - 2011-12-24 08:15 -0800
                Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-24 17:10 +0000
                Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-24 23:25 +0000
                Re: Performance of hand-optimised assembly jgk@panix.com (Joe keane) - 2012-01-04 03:24 +0000
                Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2012-01-04 09:59 +0100
                Re: Performance of hand-optimised assembly jgk@panix.com (Joe keane) - 2012-01-04 20:57 +0000
                Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2012-01-04 23:04 +0000
                Re: Performance of hand-optimised assembly Noob <root@127.0.0.1> - 2012-01-05 13:32 +0100
              Re: Performance of hand-optimised assembly Philip Lantz <prl@canterey.us> - 2011-12-24 15:29 -0800
          Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-24 12:42 +0000
            Re: Performance of hand-optimised assembly Jens Gustedt <jens.gustedt@loria.fr> - 2011-12-24 16:58 +0100
          Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-24 13:55 +0000
            Re: Performance of hand-optimised assembly Seebs <usenet-nospam@seebs.net> - 2011-12-24 19:24 +0000
              Re: Performance of hand-optimised assembly Geoff <geoff@invalid.invalid> - 2011-12-24 13:44 -0800
            Re: Performance of hand-optimised assembly Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-12-29 02:53 +0200
              Re: Performance of hand-optimised assembly Rui Maciel <rui.maciel@gmail.com> - 2011-12-29 02:11 +0000
  Re: Performance of hand-optimised assembly jgk@panix.com (Joe keane) - 2011-12-24 01:36 +0000
  Re: Performance of hand-optimised assembly "io_x" <a@b.c.invalid> - 2011-12-24 06:44 +0100
    Re: Performance of hand-optimised assembly "io_x" <a@b.c.invalid> - 2011-12-24 09:52 +0100
    Re: Performance of hand-optimised assembly "io_x" <a@b.c.invalid> - 2011-12-26 08:05 +0100
      Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-26 11:52 -0800
        Re: Performance of hand-optimised assembly "io_x" <a@b.c.invalid> - 2011-12-27 07:28 +0100
  Re: Performance of hand-optimised assembly Willem <willem@toad.stack.nl> - 2011-12-24 12:48 +0000
    Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-24 04:56 -0800
    Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-24 23:39 +0000
  Re: Performance of hand-optimised assembly James Harris <james.harris.1@googlemail.com> - 2011-12-24 06:01 -0800
    Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-24 14:55 +0000
      Re: Performance of hand-optimised assembly James Harris <james.harris.1@googlemail.com> - 2011-12-28 03:46 -0800
        Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-28 04:52 -0800
    Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-25 00:07 +0000
      Re: Performance of hand-optimised assembly James Harris <james.harris.1@googlemail.com> - 2011-12-28 03:21 -0800
        Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-28 13:19 +0000
          Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-28 16:01 +0000
            Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-28 17:45 +0000
              Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-28 18:56 -0800
            Re: Performance of hand-optimised assembly Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-12-29 03:32 +0200
            Re: Performance of hand-optimised assembly Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 17:03 -0800
              Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-26 22:08 +0000
                Re: Performance of hand-optimised assembly Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-31 22:20 -0800
        Re: Performance of hand-optimised assembly James Kuyper <jameskuyper@verizon.net> - 2011-12-28 08:24 -0500
        Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-28 14:27 +0000
          Re: Performance of hand-optimised assembly Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 16:50 -0800
            Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-26 21:59 +0000
        Re: Performance of hand-optimised assembly James Harris <james.harris.1@googlemail.com> - 2011-12-28 11:12 -0800
        Re: Performance of hand-optimised assembly Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-12-29 03:12 +0200
          Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2011-12-29 10:02 +0100
            Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-29 12:06 +0000
            Re: Performance of hand-optimised assembly Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 17:07 -0800
              Re: Performance of hand-optimised assembly Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-13 01:18 +0200
                Re: Performance of hand-optimised assembly Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-08 10:54 -0800
          Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2011-12-29 10:02 +0100
          Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-29 12:06 +0000
            Re: Performance of hand-optimised assembly Keith Thompson <kst-u@mib.org> - 2011-12-29 11:44 -0800
            Re: Performance of hand-optimised assembly Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 17:23 -0800
          Re: Performance of hand-optimised assembly James Harris <james.harris.1@googlemail.com> - 2011-12-29 08:37 -0800
            Re: Performance of hand-optimised assembly Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-01-05 22:19 +0200
  Re: Performance of hand-optimised assembly James Dow Allen <gmail@jamesdowallen.nospam> - 2011-12-24 16:21 +0000
    Re: Performance of hand-optimised assembly Weland <weland@otaku.freeshell.org> - 2011-12-25 10:54 +0000
  Re: Performance of hand-optimised assembly "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2011-12-24 14:52 -0800
  Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2011-12-25 20:12 +0100
    Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-25 11:36 -0800
      Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2011-12-25 21:35 +0100
        Re: Performance of hand-optimised assembly Stephen Sprunk <stephen@sprunk.org> - 2011-12-26 14:24 -0600
          Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2011-12-26 21:36 +0100
            Re: Performance of hand-optimised assembly Stephen Sprunk <stephen@sprunk.org> - 2012-01-04 11:59 -0600
              Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2012-01-04 20:22 +0100
                Re: Performance of hand-optimised assembly Dann Corbit <dcorbit@connx.com> - 2012-01-04 12:59 -0800
                Re: Performance of hand-optimised assembly James Harris <james.harris.1@googlemail.com> - 2012-01-04 15:32 -0800
                Re: Performance of hand-optimised assembly Stephen Sprunk <stephen@sprunk.org> - 2012-01-05 23:47 -0600
                Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-04 22:47 +0000
                Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2012-01-05 00:47 +0100
                Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-05 00:22 +0000
                Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-04 23:44 -0800
                Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2012-01-05 12:16 +0000
                Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2012-01-05 12:49 +0000
                Re: Performance of hand-optimised assembly jgk@panix.com (Joe keane) - 2012-01-05 21:26 +0000
                Re: Performance of hand-optimised assembly "io_x" <a@b.c.invalid> - 2012-01-07 10:32 +0100
                Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2012-01-05 00:58 +0100
                Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-05 13:39 -0800
                Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-07 02:15 -0800
                Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-10 01:07 -0800
                Re: Performance of hand-optimised assembly jgk@panix.com (Joe keane) - 2012-01-07 00:49 +0000
                Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2012-01-07 08:54 +0100
                Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2012-01-07 10:11 +0100
                Re: Performance of hand-optimised assembly "io_x" <a@b.c.invalid> - 2012-01-07 10:51 +0100
                Re: Performance of hand-optimised assembly jgk@panix.com (Joe keane) - 2012-01-07 20:09 +0000
        Re: Performance of hand-optimised assembly Stephen Sprunk <stephen@sprunk.org> - 2012-01-06 23:39 -0600
          Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2012-01-07 10:33 +0100
            Re: Performance of hand-optimised assembly Stephen Sprunk <stephen@sprunk.org> - 2012-01-07 07:36 -0600
              Re: Performance of hand-optimised assembly Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-07 21:03 +0000
                Re: Performance of hand-optimised assembly Stephen Sprunk <stephen@sprunk.org> - 2012-01-07 16:42 -0600
    Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-25 20:23 +0000
      Re: Performance of hand-optimised assembly jacob navia <jacob@spamsink.net> - 2011-12-25 21:50 +0100
        Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-25 22:10 +0000
      Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-25 13:11 -0800
        Re: Performance of hand-optimised assembly "BartC" <bc@freeuk.com> - 2011-12-25 22:07 +0000
          Re: Performance of hand-optimised assembly 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-25 16:39 -0800
  Re: Performance of hand-optimised assembly "io_x" <a@b.c.invalid> - 2011-12-26 05:55 +0100
    Re: Performance of hand-optimised assembly "io_x" <a@b.c.invalid> - 2012-02-17 17:58 +0100
  Re: Performance of hand-optimised assembly "Wolfgang.Draxinger" <Wolfgang.Draxinger@physik.uni-muenchen.de> - 2012-01-10 18:00 +0100

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