What does such code mean?

[Vincent Ni]

In the Deuce instrumented code, I find that for each read action, the Deuce will instrument the following instructions:

original version: 

  41: getfield      #36    // Field endInfoEntries:[Ljstamp/genome/endInfoEntry;

instrumented version:

  81: getstatic     #88                 // Field jstamp/genome/SequencerDeuceFieldsHolder.endInfoEntries__ADDRESS__:J

  84: lconst_0      

  85: lcmp          

  86: ifge          95

  89: getfield      #38                 // Field endInfoEntries:[Ljstamp/genome/endInfoEntry;

  92: goto          119

  95: dup           

  96: getstatic     #88                 // Field jstamp/genome/SequencerDeuceFieldsHolder.endInfoEntries__ADDRESS__:J

  99: aload         4

  101: invokestatic  #92                 // Method org/deuce/transaction/ContextDelegator.beforeReadAccess:(Ljava/lang/Object;JLorg/deuce/transaction/Context;)V

  104: dup           

  105: getfield      #38                 // Field endInfoEntries:[Ljstamp/genome/endInfoEntry;

  108: getstatic     #88                 // Field jstamp/genome/SequencerDeuceFieldsHolder.endInfoEntries__ADDRESS__:J

  111: aload         4

  113: invokestatic  #96                 // Method org/deuce/transaction/ContextDelegator.onReadAccess:(Ljava/lang/Object;Ljava/lang/Object;JLorg/deuce/transaction/Context;)Ljava/lang/Object;

  116: checkcast     #97                 // class "[Ljstamp/genome/endInfoEntry;"

The question is why Deuce needs to do the comparison (84-89)?

[Guy Korland]

It's kind of  an optimization that if the field is final it doesn't need any transaction logging. 

Deuce marks final fields as such by setting x__ADDRESS__ as negative.

See: https://github.com/DeuceSTM/DeuceSTM/blob/master/src/java/org/deuce/transform/asm/method/DuplicateMethod.java

Guy

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