IJ42205: JAVA JIT, INCORRECT RETURN FROM CLASS.ISARRAY()

APAR status

• Closed as program error.

Error description

• Error Message: The return value from Class.isArray() is false
  even when being called against an array class.
  .
  Stack Trace: N/A
  .
  The problem can occur on any platform running the J9 VM.
  The issue must involve a call to Class.isArray()
  The issue is mostly likely to occur when:
  - Using the "Type" interface
  - Casting between "Class" and "Type"
  Other scenarios are possible, but it must involve a variable
  holding a Class where the application is behaving incorrectly
  based on the class type in the variable when calling
  Class.isArray().
  

Local fix

• The problem is caused by the JIT value propagation optimization
  therefore the issue can be avoided by disabling that
  optimization using the following java command line parameter:
  -Xjit:disableLocalVP,disableGlobalVP
  You can also use the following option to target the effects to a
  specific method compilation and therefore minimize the
  performance impact:
  -Xjit{pkg/class.method*}(disableLocalVP,disableGlobalVP)
  Where "pkg/class.method" is the full method name for the method
  which is triggering the issue. Limiting to one method in this
  way will very likely result in no noticeable performance impact.
  

Problem summary

• The JIT would remove some code after incorrectly converting a
  class variable into a constant which would allow the JIT to make
  a incorrect compile time decision that a code path could not
  execute and therefore could be removed.
  

Problem conclusion

• The JIT was modified so that it would not incorrectly convert a
  class variable into a constant.
  .
  This APAR will be fixed in the following Releases:
  .
  IBM SDK, Java Technology Edition
     8    SR7 FP20  (8.0.7.20)
  .
  Contact your IBM Product's Service Team for these Service
  Refreshes and Fix Packs.
  For those running stand-alone, information about the available
  maintenance can be found at:
             https://www.ibm.com/support/pages/java-sdk
  

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