IV44071: UNEXPECTED EXCEPTION CAUSED BY INCORRECT LOOP OPTIMIZATION IN THE JIT COMPILER

APAR status

• Closed as program error.

Error description

• Error Message: JRuby throws an unexpected RangeError. This
  problem could affect other Java programs too, and the most
  likely symptom is an ArrayIndexOutOfBoundsException.
  .
  Stack Trace:
  RangeError: 256 out of char range
      org/jruby/RubyInteger.java:272:in `chr'
      test_digest_extend.rb:43:in `test_digest_s_hexencode'
      org/jruby/RubyArray.java:2336:in `collect'
      test_digest_extend.rb:43:in `test_digest_s_hexencode'
      org/jruby/RubyKernel.java:1944:in `send'
      org/jruby/RubyArray.java:1603:in `each'
      org/jruby/RubyArray.java:1603:in `each'
  .
  

Local fix

• -Xjit:disableLoopStrider
  Note that the use of this option may have a small performance
  impact. In most cases the performance will be reduced by 1% or
  less.
  

Problem summary

• The problem is caused by the loop striding optimization in the
  JIT compiler. The optimization is designed to reduce the amount
  of computation needed to derive the value of induction variables
  in each iteration of a loop, by replacing the computation with
  simpler arithmetics. When a variable is used in the loop
  termination condition, and the variable is the result of a
  type conversion, and the variable is referenced in multiple
  expressions, then the optimization may incorrectly replace the
  variable in the wrong expression (e.g. in an array index),
  causing the loop to misbehave or an array operation to go out
  of bounds.
  

Problem conclusion

• This defect will be fixed in:
  7.0.0 SR5
  6.0.1 SR6
  6.0.0 SR14
  5.0.0 SR16 FP3
  .
  The JIT compiler has been modified to correct the optimization.
  

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:

  IV44072

Fix information

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels

• R260 PSY

     UP

• R600 PSY

     UP