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Re: C Compilers QoI

From BartC <bc@freeuk.com>
Newsgroups comp.lang.c
Subject Re: C Compilers QoI
Date 2017-03-18 13:12 +0000
Organization A noiseless patient Spider
Message-ID <oajbig$h38$1@dont-email.me> (permalink)
References (7 earlier) <oaa93r$obp$1@z-news.wcss.wroc.pl> <ed6e2220-879c-4c33-a3e4-fbefc9376fcb@googlegroups.com> <oacq5n$5vs$1@z-news.wcss.wroc.pl> <oacsgf$3qn$1@dont-email.me> <oahvv0$ie0$1@z-news.wcss.wroc.pl>

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On 18/03/2017 00:45, antispam@math.uni.wroc.pl wrote:
> BartC <bc@freeuk.com> wrote:

>> Then I eliminated those extraneous temps to get this:
>>
>>   t2 = c * d
>>   a = b + t2
>>
>> And time reduced to 2.7 seconds. About the same as my own code which
>> doesn't use the t2 temporary.
>>
>> So that would be a worthwhile improvement.
>
> I have implemented it now.  Was easy, 18 extra lines.  However,
> note that each source line generates separate temporary.  So
> your 1 milion lines need 1 milion temporaries, that is 8 MB
> of stack space.  This is going to suffer some slowdown due
> to L2 cache traffic.

I wouldn't worry about it. Don't forget, this is not real code, just a 
compiler test! Besides, the instruction cache will also suffer due to 
using one million copies of the same instructions rather using a loop.

However, in more typical code, there will be some benefit in being able 
to reuse temporaries instead of creating new ones. (I think most are 
used only twice: once to write the value, once more to read it. Repeated 
of course each time a span of code is executed.)

Of course, if there is also an option to somehow output C source code, 
then a normal C compiler can take care of these bothersome details when 
you need the extra performance. I wouldn't try it though when there are 
million line functions, as obviously some have trouble with those...

>> It won't be that much based on your sample code. Probably gcc is
>> eliminated whole swathes of code rather than executing it, so results
>> are misleading.
>
> I did not timing tests so this is just a guess.  But somewhat
> informed guess: for conditions I first compute boolean value
> to a variable and in conditional I test stored value.  Constants
> are stored in memory before use -- one reason is that store
> instruction accepts 64-bit constants while immediates are
> limited to 32-bits.  There is no constant propagation in
> my compiler.  My generator is going to create a lot
> of dependencies between instructions, gcc is resonably good
> at scheduling for parallel execution.  gcc can make creative
> use of addressing modes so that address arithmetic does not
> need separate instuctions.  I have a lot of references to
> memory which may lead to extra latency.
>
> Also, I timed tiny C on somewhat realistic compute intensive
> code and gcc compiled code run 6 times faster.  My code is
> visibly worse than code from tiny C.  OK, now the change I
> made closes part of gap to tiny C, but not all.

On real applications or just benchmarks?

I compiled one of my interpreter projects with both. gcc-O3 was 2.3 
times as fast as Tiny C in 32 bits, 2.1 times as fast in 64 bits (run on 
a small selection of test scripts).

On my half-finished compiler operating on the test code in my OP, gcc-O3 
was 2.15 times as fast as TCC (64 bits). (1.4 seconds/720Klps seconds 
vs. 2.95 seconds; even TCC-compiled code manages 340K lines/second!)

I found that, on real apps, it was switch-statements that slowed down 
TCC further than the usual 2:1 ratio.

Meanwhile, my own clunky code managed 1.7 seconds/590Klps, and that's 
with its weak optimiser turned off completely (actually it made no 
difference here!). That is, with no register variables, no recognising 
values already loaded, no nothing, not even passing parameters in 
registers as the 64-bit ABI stipulates.

1.4 ... 1.7 ... 3.0. I think you will find it easy to get performance 
between TCC and gcc, with the right sort of test application anyway. 
Make sure both TCC and gcc use either 32 or 64 bits to compare timings. 
gcc-m32 is a little faster than -m64.

-- 
bartc

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C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 13:01 +0000
  Re: C Compilers QoI mark.bluemel@gmail.com - 2017-03-14 06:16 -0700
  Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 06:42 -0700
  Re: C Compilers QoI "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-03-14 06:56 -0700
    Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 15:58 +0000
      Re: C Compilers QoI "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-03-14 09:22 -0700
      Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-14 16:54 +0000
        Re: C Compilers QoI supercat@casperkitty.com - 2017-03-14 10:24 -0700
          Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-14 17:58 +0000
            Re: C Compilers QoI supercat@casperkitty.com - 2017-03-14 14:12 -0700
              Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-14 16:34 -0500
              Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-14 17:36 -0500
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 23:06 +0000
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-14 16:20 -0700
              Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-15 02:32 +0000
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-15 12:49 +0000
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-15 11:56 -0700
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-15 23:09 +0000
                Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-16 18:17 +0000
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 11:47 -0700
                Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 07:50 +1300
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 12:59 -0700
                Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-16 21:24 +0100
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 14:23 -0700
                Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 11:30 +1300
                Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 11:38 +1300
                Re: C Compilers QoI Gareth Owen <gwowen@gmail.com> - 2017-03-17 05:07 +0000
                Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 20:26 +1300
                Re: C Compilers QoI Gareth Owen <gwowen@gmail.com> - 2017-03-17 07:59 +0000
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 16:14 -0700
                Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-16 22:54 -0500
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-17 09:01 -0700
                Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-26 14:16 +1300
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-26 14:19 -0700
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-26 22:43 +0100
                Re: C Compilers QoI GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-27 01:28 +0200
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-26 22:07 -0700
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-27 11:28 +0100
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 07:38 -0700
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-27 16:23 +0100
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 08:55 -0700
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-27 17:01 +0100
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 10:03 -0700
                Re: C Compilers QoI GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-27 17:58 +0200
                Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-27 03:54 -0700
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 08:46 -0700
                Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-27 17:47 +0000
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 11:48 -0700
                Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-27 15:37 -0500
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 14:46 -0700
                Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-27 20:28 -0500
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-28 01:18 -0700
                Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-28 18:24 -0500
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-29 07:40 -0700
                Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-29 17:05 +0200
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-29 11:07 -0700
                Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-31 04:04 +0000
                Re: C Compilers QoI bartc <bc@freeuk.com> - 2017-03-31 10:53 +0100
                Re: C Compilers QoI Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-03-31 07:35 -0700
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-31 08:07 -0700
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-31 07:54 -0700
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-31 07:43 -0700
                Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 11:21 +1300
                Re: C Compilers QoI Ian Collins <ian-news@hotmail.com> - 2017-03-17 11:24 +1300
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-16 22:15 +0000
                Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-17 12:31 +0000
                Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-16 15:24 -0700
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 16:03 -0700
                Re: C Compilers QoI scott@slp53.sl.home (Scott Lurndal) - 2017-03-17 12:39 +0000
                Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-17 08:27 -0700
                Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-16 01:35 +0000
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-16 02:18 +0000
                Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-18 00:45 +0000
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-18 13:12 +0000
                Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-18 20:31 +0000
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-18 17:31 -0700
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-16 09:22 -0700
          Re: C Compilers QoI Nick Bowler <nbowler@draconx.ca> - 2017-03-24 16:13 +0000
            Re: C Compilers QoI supercat@casperkitty.com - 2017-03-24 12:32 -0700
              Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-24 22:13 -0500
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-25 13:05 -0700
                Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-27 15:44 -0500
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-27 14:51 -0700
                Re: C Compilers QoI Robert Wessel <robertwessel2@yahoo.com> - 2017-03-27 20:31 -0500
        Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 17:26 +0000
          Re: C Compilers QoI Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-03-15 12:02 -0500
  Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-14 15:00 +0100
    Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 07:36 -0700
      Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-14 15:57 +0100
      Re: C Compilers QoI Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-03-14 08:11 -0700
        Re: C Compilers QoI BGB <cr88192@hotmail.com> - 2017-03-29 23:51 -0500
    Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 15:28 +0000
      Re: C Compilers QoI David Brown <david.brown@hesbynett.no> - 2017-03-14 21:41 +0100
  Re: C Compilers QoI Keith Thompson <kst-u@mib.org> - 2017-03-14 09:26 -0700
    Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 18:23 +0000
      Re: C Compilers QoI Keith Thompson <kst-u@mib.org> - 2017-03-14 12:05 -0700
  Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 09:35 -0700
    Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 17:08 +0000
      Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 10:24 -0700
        Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 17:34 +0000
        Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 11:55 -0700
          Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 19:03 +0000
            Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 19:06 +0000
            Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 12:10 -0700
              Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 21:14 +0000
                Re: C Compilers QoI already5chosen@yahoo.com - 2017-03-14 14:42 -0700
                Re: C Compilers QoI supercat@casperkitty.com - 2017-03-14 14:53 -0700
                Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 23:20 +0000
                Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-15 02:43 +0000
  Re: C Compilers QoI jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-14 19:39 +0100
    Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-14 19:10 +0000
  Re: C Compilers QoI antispam@math.uni.wroc.pl - 2017-03-14 19:29 +0000
  Re: C Compilers QoI Noob <root@127.0.0.1> - 2017-03-15 09:27 +0100
  Re: C Compilers QoI ed_davis2@yahoo.com - 2017-03-16 15:10 -0700
    Re: C Compilers QoI BartC <bc@freeuk.com> - 2017-03-16 23:19 +0000

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