IV26973: BAD LOOP VERSIONER TEST LEADS TO POOR PERFORMANCE, OR TO A CRASH IN JITTED CODE

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APAR status

  • Closed as program error.

Error description

  • Error Message: This could be a performance problem, or it could
    appear as a crash with vmState=0x00000000.
    .
    Stack Trace:
    .
    

Local fix

  • -Xjit:disableLoopVersioner
    

Problem summary

  • The jit optimization "loop versioner" attempts to make a fast
    version of a loop that omits certain checks in the loop by
    performing equivalent checks before the loop starts.  If the
    loop contains an array access using an indexing expression that
    changes every loop iteration, the optimization can erroneously
    try to pull that indexing expression out of the loop, resulting
    in a nonsense check before the loop.  This corrupt check can
    cause control to flow to the slow version of the loop, thereby
    harming performance; or else the corruption could be so severe
    that the generated code crashes.
    

Problem conclusion

  • This defect will be fixed in:
    6.0.1 SR3
    7.0.0 SR2
    6.0.0 SR11
    5.0.0 SR14
    .
    The loop versioner optimization was fixed so it doesn't try to
    emit checks based on the array indexing expression under these
    circumstances.
    

Temporary fix

Comments

APAR Information

  • APAR number

    IV26973

  • Reported component name

    JIT

  • Reported component ID

    620700124

  • Reported release

    260

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-08-24

  • Closed date

    2012-08-24

  • Last modified date

    2012-08-24

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

    IV26974

Fix information

  • Fixed component name

    JIT

  • Fixed component ID

    620700124

Applicable component levels

  • R260 PSY

       UP

  • R600 PSY

       UP



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Document information


More support for:

Runtimes for Java Technology
Just In Time (JIT) Compiler

Software version:

260

Reference #:

IV26973

Modified date:

2012-08-24

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