IV68132: JAVA JIT - MERGING BOUND-CHECKS CAN PREVENT CODE FROM BEING EXEC UTED.

APAR status

• Closed as program error.

Error description

• Error Message: Unexpected behaviour when executing catch blocks
  handling IndexOutOfBoundsException.
  .
  Stack Trace: N/A
  .
  The problem could occur on all platforms and all releases of the
  J9 VM, but given that it only effects IndexOutOfBoundsException
  exception paths, it's very unlikely to be encountered.
  

Local fix

• -Xjit:disableAndSimplificationNote: Use of this option will have
  a very small effect on the performance of some JIT generated
  code. The over all effect of a applications performance will be
  less then 1% in almost all cases.
  

Problem summary

• Two near by bound-checks are merged allowing for code that
  should have been executed to be skipped when the exception path
  is taken. The side-effects of this skipped code could only be
  used in the catcher, all other side effects would be spotted and
  prevent the bound-checks from being merged in the first place.
  

Problem conclusion

• The JIT was modified such that bound-check merging is prevented
  when there is code between the two bound-checks that would
  modify variables used in the exception path.
  .
  This APAR will be fixed in the following Java Releases:
     7    SR9       (7.0.9.0)
     6    SR17      (6.0.17.0)
     6 R1 SR9       (6.1.9.0)
     7 R1 SR3       (7.1.3.0)
     8    SR1       (8.0.1.0)
  .
  Contact your IBM Product's Service Team for these Service
  Refreshes and Fix Packs.
  For those running stand-alone, information about the Service
  Refreshes and Fix Packs can be found at:
             https://www.ibm.com/developerworks/java/jdk/
  

Temporary fix

Comments

APAR Information

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

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

Fix information

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels

• R260 PSY

     UP

• R600 PSY

     UP

• R130 PSY

     UP