IV77908: NESTED LOOP IN JIT COMPILED METHOD DOES NOT TERMINATE WHEN EXPEC TED

APAR status

• Closed as program error.

Error description

• Error Message: Various error messages are possible, including no
  error message. A known one is an unexpected
  ArrayIndexOutOfBounds Exception.
  .
  Stack Trace: IBM XML Java code is known to trigger the problem
  in the following methods:
  com/ibm/xml/.../SimplePositionHelper.getCurrentPosition10
  and,
  com/ibm/xml/.../DataBufferHelper.computeCoords10
  .
  

Local fix

• The problem can be worked around by either globally disabling
  the loop unrolling optimization with the following Java option:
  -Xjit:disableGLU
  Or, the loop unrolling optimization can be disabled on specific
  methods that are experiencing the problems. Note that if those
  methods get inlined into other methods then the optimization
  will not be disabled on the inlined methods. Disabling inlining
  of the methods can be done with the following Java option:
  -Xjit:dontInline={package/Class.method(signature)}
  Please note that any of these workarounds can affect
  performance.
  

Problem summary

• The problem is caused by the loop unrolling optimization not
  detecting an exit condition in the outer loop of a nested loop
  with a depth of 2. As a result the unrolled version of the loop
  will have copies which do not have the exit condition and thus
  the loop may not terminate as expected.
  

Problem conclusion

• The JIT compiler has been updated to correctly handle nested
  loops which have unique features like the ones which exposed the
  problem in this APAR.
  .
  This APAR will be fixed in the following Java Releases:
     7 R1 SR3 FP20  (7.1.3.20)
     6 R1 SR8 FP15  (6.1.8.15)
     8    SR2       (8.0.2.0)
     7    SR9 FP20  (7.0.9.20)
  .
  Contact your IBM Product's Service Team for these Service
  Refreshes and Fix Packs.
  For those running stand-alone, information about the available
  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:

  PI50631

Fix information

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels

• R130 PSY

     UP

• R260 PSY

     UP