IV19965: JVM INCORRECTLY REMOVED A CONDITION CHECK WHEN COMPARING TO MIN OR MAX INTEGER

APAR status

• Closed as program error.

Error description

• Error Message: The Java JIT compiler might remove a comparison
  of an integer variable by mistake if it dominates (or is
  dominated by) a comparison of the same integer variable
  against the minimum or maximum integer value. This leads to
  incorrect control flow in the program and could result in a
  variety of associated symptoms such as segmentation fault,
  incorrect output, or hang.
  .
  Stack Trace: N/A
  .
  The following Java code illustrates the problem:
  
  if (i <= 0x7fffffff)  // always true
    {
    if (i < 0)          // sometimes removed by the JIT
      System.out.print("input < 0");
    }
  else
    System.out.print("should never get here");
  
  When the JIT compiler malfunctions in this case, it could remove
  the (i < 0) check, and cause the program to always print "input
  < 0" even if the variable i is positive.
  

Local fix

• The -Xjit:disableAndSimplification option can be used as a
  workaround. Note that a small performance degradation might
  occur as this disables some compiler optimizations.
  

Problem summary

• The problem is caused by an incorrect overflow/underflow check
  in the Java  JIT compiler.
  

Problem conclusion

• This defect will be fixed in:
  6.0.1 SR2
  7.0.0 SR1
  .
  The JIT compiler has been updated to resolve the problem
  

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

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