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From "Egor Pasko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-2607) [drlvm][jit][opt][performance] improve optimizer to simplify arithmetic calculations involving loops
Date Fri, 05 Oct 2007 09:59:50 GMT

    [ https://issues.apache.org/jira/browse/HARMONY-2607?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12532614
] 

Egor Pasko commented on HARMONY-2607:
-------------------------------------

there is a big question whether we want to optimize silly loops..

for example, GCC does NOT optimize for (i=0; i<N; i++) { x = x + 1; } that is because users
do not expect it to be optimized. So why bother?

another point is that recognizing patterns might turn into a longer investigation and less
optimal code than traditional data flow analysis. So, I am not very impressed on optimizing
such patterns, but I do not mind a couple of such hacks if you want :)

> [drlvm][jit][opt][performance] improve optimizer to simplify arithmetic calculations
involving loops
> ----------------------------------------------------------------------------------------------------
>
>                 Key: HARMONY-2607
>                 URL: https://issues.apache.org/jira/browse/HARMONY-2607
>             Project: Harmony
>          Issue Type: Improvement
>          Components: DRLVM
>         Environment: Windows/IA32
>            Reporter: Pavel Ozhdikhin
>            Priority: Minor
>         Attachments: DoubleTest.java, Test.java, TestInt.java
>
>
> In the attached test arithmetical calculations and loops may be safely eliminated in
both methods test1() and test2().
> Indeed , the results below show that JRockit 1.5 can eliminate them - it faster executes
the first run and don't spend time at all for a second:
> ================================
> JRockit 1.5 results:
> >C:\jrockit-jdk1.5.0\bin\java.exe -version
> java version "1.5.0"
> Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-b64)
> BEA WebLogic JRockit(R) (build dra-38972-20041208-2001-win-ia32, R25.0.0-75, GC: System
optimized over throughput (initial strategy single
> parpar))
> >C:\jrockit-jdk1.5.0\bin\java.exe Test
> 1st run: 203
> 2nd run: 0
> ================================
> DRLVM results:
> >C:\win_ia32_msvc_release\deploy\jre\bin\java.exe -version
> Apache Harmony Launcher : (c) Copyright 1991, 2006 The Apache Software Foundation or
its licensors, as applicable.
> java version "1.5.0"
> pre-alpha : not complete or compatible
> svn = r483842, (Dec 11 2006), Windows/ia32/msvc 1310, release build
> http://incubator.apache.org/harmony
> C:\win_ia32_msvc_release\deploy\jre\bin\java.exe Test
> 1st run: 19734
> 2nd run: 14828
> ================================
> The optimizer should be able to eliminate such code if it does not have ane side-effect.

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