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Date: Thu, 4 Oct 2007 23:53:50 -0700 (PDT)
From: "Pavel Ozhdikhin (JIRA)" <jira@apache.org>
To: commits@harmony.apache.org
Subject: [jira] Updated: (HARMONY-2607) [drlvm][jit][opt][performance]
 improve optimizer to simplify arithmetic calculations involving loops
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     [ https://issues.apache.org/jira/browse/HARMONY-2607?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Pavel Ozhdikhin updated HARMONY-2607:
-------------------------------------

    Attachment: TestInt.java

I was too brief in my previous comment. Actually I did several measurements with a slightly changed test, which uses the return value calculated in the loop, and got an interesting reult on Sun JDK 1.6 "-server" mode:

C:\users\pozhdikh\jira\Harmony-2607>C:\jdk1.6.0\bin\java.exe -server TestInt
1st run: 0, out = 499999
2nd run: 0, out = 499999

Other JREs can not show such a good result:

C:\users\pozhdikh\jira\Harmony-2607>F:\tools\jdk\1.5\win32-bea\bin\java.exe TestInt
1st run: 66861, out = 499999
2nd run: 64392, out = 499999

C:\users\pozhdikh\jira\Harmony-2607>F:\tools\jdk\1.5\win32-bea\bin\java.exe -server TestInt
1st run: 66891, out = 499999
2nd run: 64407, out = 499999

C:\users\pozhdikh\jira\Harmony-2607>C:\jdk1.6.0\bin\java.exe TestInt
1st run: 93829, out = 499999
2nd run: 93845, out = 499999

C:\users\pozhdikh\jira\Harmony-2607>C:\users\pozhdikh\drlvm\trunk\working_vm\build\win_ia32_msvc_release\deploy\jdk\jre\bin\java.exe TestInt
1st run: 11953, out = 499999
2nd run: 11750, out = 499999

C:\users\pozhdikh\jira\Harmony-2607>C:\users\pozhdikh\drlvm\trunk\working_vm\build\win_ia32_msvc_release\deploy\jdk\jre\bin\java.exe -Xem:server TestInt
1st run: 12578, out = 499999
2nd run: 11734, out = 499999

I see 2 ways to achieve a nearly zero execution time:
 - recognize calculation pattern at compile-time, calculate and substitute the result
 - cache return value at run-time and substitute it during re-compilation
More ideas?

BTW, I agree that a dead loop elimination is a good way to optimize silly loops whose result is not used.


> [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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