IV37329: UNEXPECTED INCOMPATIBLECLASSCHANGEERROR

APAR status

• Closed as program error.

Error description

• Error Message: An unexpected IncompatibleClassChangeError is
  thrown from JIT compiled methods. In a different manifestation,
  an incorrect ArrayIndexOutOfBounds is also thrown.
  .
  Stack Trace: No common stack trace available, it differs from
  application to application.
  .
  Methods with loop in them are susceptible to this problem.
  

Local fix

• Workaround is to exclude the method(s) which throw this
  exception incorrectly. In certain scenarios, it is necessary to
  exclude more than one methods from the top of the failing stack.
  PROBLEM SUMMARY:
  While JIT compiles methods with hot loops in it, an optimizer
  called LoopVersioner incorrectly moves some code parts outside
  of the loop along with some method variables, which are loop
  variants. This caused the method to behave in an unexpected
  manner.
  PROBLEM CONCLUSION:
  This defect will be fixed in:
  6.0 SR13
  5.0 SR16
  The JIT compiler has been modified to correctly identify the
  code parts and variables which qualify for moving outside of the
  loop.
  TEMPORARY FIX:
  -Xjit:disableLoopversioner
  

Problem summary

• While JIT compiles methods with hot loops in it, an optimizer
  called LoopVersioner incorrectly moves some code parts outside
  of the loop along with some method variables, which are loop
  variants. This caused the method to behave in an unexpected
  manner.
  

Problem conclusion

• This defect will be fixed in:
  7.0.0 SR4
  6.0.1 SR5
  6.0.0 SR13
  5.0.0 SR16
  .
  The JIT compiler has been modified to correctly identify the
  code parts and variables which qualify for moving outside of the
  loop.
  

Temporary fix

• -Xjit:disableLoopversioner
  

Comments

APAR Information

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

  IV32630

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

Fix information

• Fixed component name

  JAVA 5 JIT

• Fixed component ID

  620500124

Applicable component levels

• R500 PSY