Groups > comp.lang.java.programmer > #15868

Re: Java processors

From	BGB <cr88192@hotmail.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: Java processors
Date	2012-07-08 00:28 -0500
Organization	albasani.net
Message-ID	<jtb5vf$jjd$1@news.albasani.net> (permalink)
References	(7 earlier) <djjev7565b8ctdboqn9t9h7nc0eqdu413m@4ax.com> <89ca24f7-0bf9-4d4b-be91-ef131989c4c9@googlegroups.com> <ma6fv7dr1u82acmp89ti4pjk3srnh3ts92@4ax.com> <jt9hjc$qin$1@news.albasani.net> <ac1iv7lue61ncqckd8dr1vau4oik8a17np@4ax.com>

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On 7/7/2012 11:01 PM, Roedy Green wrote:
> On Sat, 07 Jul 2012 09:34:52 -0500, BGB <cr88192@hotmail.com> wrote,
> quoted or indirectly quoted someone who said :
>
>> in the sequential-consistency case, there is likely to still be a
>> mapping between the bytecode instructions and their equivalent
>> machine-code sequences, so once the JIT does its thing, and any state is
>> copied over, then a jump is made to the analogous location in the
>> machine code.
>
> Now throw in this complication. The JIT decided to convert
> multiplication inside the loop to addition. There potentially needs to
> be a fixup corresponding to each optimisation.
>

there are all sorts of optimizations which could break the simple case, 
but what is to say that the JIT actually uses these optimizations in 
these cases? (rather than limiting itself solely to "reasonably safe" 
optimizations in such cases).

or, alternatively, it could just mark the point where it will jump into 
the code as a "synchronized label" or simiar, so regardless of what 
sorts of optimizations are used elsewhere, everything is "consistent" at 
the location where it will jump into the JITed code (at the potential 
cost of a register spill just before this entry point for all subsequent 
executions, ...).

but, absent more information, it starts to get pointless to speculate.

but, hell, with certain compilers (*cough* MSVC *cough*), it is an 
optimization setting mostly to have it cache the values of variables in 
registers (much less anything much more advanced that this).

caching variables in registers and using basic peephole optimizations 
actually goes a long ways towards generating "optimized" compiler output.

many other (potentially more significant) optimizations are 
higher-level, and don't necessarily actually make much of a difference 
at the lower-levels.

...

Thread

Java processors bob smith <bob@coolfone.comze.com> - 2012-07-05 08:01 -0700
  Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-05 11:28 -0400
    Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-05 13:00 -0500
      Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-05 14:31 -0400
        Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-05 16:42 -0500
        Re: Java processors Arne Vajhøj <arne@vajhoej.dk> - 2012-07-05 20:30 -0400
          Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-05 21:12 -0500
          Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-06 00:13 -0400
            Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 13:26 -0700
              Re: Java processors Gene Wirchenko <genew@ocis.net> - 2012-07-06 13:50 -0700
                Re: Java processors Lew <lewbloch@gmail.com> - 2012-07-06 14:17 -0700
                Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 19:07 -0700
                Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-07 09:34 -0500
                Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-07 21:01 -0700
                Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-08 00:28 -0500
                Re: Java processors Lew <noone@lewscanon.com> - 2012-07-07 23:00 -0700
                Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-08 10:20 -0500
                Re: Java processors Lew <noone@lewscanon.com> - 2012-07-08 09:16 -0700
                Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-08 17:46 +0000
                Re: Java processors Lew <noone@lewscanon.com> - 2012-07-08 11:52 -0700
                Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-08 21:41 +0000
                Re: Java processors Lew <noone@lewscanon.com> - 2012-07-08 17:56 -0700
                Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-08 19:44 -0700
                Re: Java processors Lew <noone@lewscanon.com> - 2012-07-09 23:41 -0700
                Re: Java processors David Lamb <dalamb@cs.queensu.ca> - 2012-07-16 13:22 -0400
                Re: Java processors Lew <lewbloch@gmail.com> - 2012-07-16 14:03 -0700
                Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-08 19:42 -0700
                Re: Java processors Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-07-10 01:13 +0200
                Re: Java processors Lew <lewbloch@gmail.com> - 2012-07-09 16:26 -0700
                Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-11 15:41 -0700
                Re: Java processors Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-07-12 01:02 +0200
                Re: Java processors Wanja Gayk <brixomatic@yahoo.com> - 2012-07-21 18:46 +0200
                Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-21 13:05 -0400
                Re: Java processors Wanja Gayk <brixomatic@yahoo.com> - 2012-07-21 19:23 +0200
                Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-21 14:10 -0400
                Re: Java processors Wanja Gayk <brixomatic@yahoo.com> - 2012-07-23 01:17 +0200
                Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-22 20:15 -0400
                Re: Java processors Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-07-22 15:13 +0200
                Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 19:03 -0700
                Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-08 19:51 -0700
              Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-07 21:17 -0700
                Re: Java processors Lew <noone@lewscanon.com> - 2012-07-07 23:04 -0700
                Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-08 09:29 -0700
                Re: Java processors Lew <noone@lewscanon.com> - 2012-07-08 11:57 -0700
            Re: Java processors Wanja Gayk <brixomatic@yahoo.com> - 2012-07-08 15:40 +0200
              Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-08 10:36 -0500
          Re: Java processors Lew <lewbloch@gmail.com> - 2012-07-06 11:31 -0700
      Re: Java processors Jim Janney <jjanney@shell.xmission.com> - 2012-07-05 13:02 -0600
        Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-05 16:09 -0500
        Re: Java processors Jan Burse <janburse@fastmail.fm> - 2012-07-06 01:29 +0200
          Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-06 00:42 +0000
            Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 13:53 -0700
              Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-06 21:18 +0000
                Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-06 18:17 -0400
                Re: Java processors Martin Gregorie <martin@address-in-sig.invalid> - 2012-07-06 22:29 +0000
                Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 19:10 -0700
                Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-07 09:42 -0500
                Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-07 10:58 -0400
                (OT) Was: Re: Java processors Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-07 11:38 -0400
                Re: (OT) Was: Re: Java processors Gene Wirchenko <genew@ocis.net> - 2012-07-07 21:19 -0700
                Re: (OT) Was: Re: Java processors "Peter J. Holzer" <hjp-usenet2@hjp.at> - 2012-07-08 12:15 +0200
                Re: Java processors Gene Wirchenko <genew@ocis.net> - 2012-07-07 21:17 -0700
          Re: Java processors Jim Janney <jjanney@shell.xmission.com> - 2012-07-05 19:14 -0600
        Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 13:34 -0700
          Re: Java processors Jan Burse <janburse@fastmail.fm> - 2012-07-06 23:04 +0200
            Re: Java processors Silvio Bierman <silvio@moc.com> - 2012-07-07 00:13 +0200
              Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 19:16 -0700
                Re: Java processors "Peter J. Holzer" <hjp-usenet2@hjp.at> - 2012-07-08 11:37 +0200
      Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 13:24 -0700
        Re: Java processors BGB <cr88192@hotmail.com> - 2012-07-07 10:06 -0500
  Re: Java processors Roedy Green <see_website@mindprod.com.invalid> - 2012-07-06 05:22 -0700

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