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performance is not immediately obvious. One possibility would be the introduction of
a new specialized bytecode to handle reads of integer instance fields. Such a bytecode
would improve the performance of simple Java Virtual Machine’s such as Kaffe by
reducing the number of checks that must be performed during a field access. However,
it is unclear whether the introduction of such a bytecode would have any value in other
virtual machines that perform more aggressive optimizations. The profile distribution
may also be useful because it has identified those types that are encountered with
greatest frequency, and as a result, warrant the greatest amount of attention during
optimization.
6.3 Conclusion
This chapter described some results generated by profiling and analyzing 23 benchmarks.
The information gathered during profiling included both the opcode executed
and its operands. Additional information was also collected for some bytecodes.
Evaluating the profile data revealed many interesting patterns related to the selection
of current specialized bytecode. For example, it was observed that there are many
general purpose load bytecodes executed with greater frequency than the specialized
load bytecodes defined by the Java Virtual Machine Specification. This pattern was
also observed for store bytecodes and constant loading bytecodes. Of these three categories,
the specialized constant loading bytecodes were used with greatest frequency
compared to the general purpose bytecodes in this category. Specialized bytecodes
accounted for half of the 20 most executed bytecodes constant loading bytecodes
compared to only one quarter of the 20 most executed store bytecodes. The analysis
performed revealed that specialized constant loading bytecodes showed the greatest
utility because of design choices made for the Java Virtual Machine that limit the
utility of some specialized load and store bytecodes and the fact that there is asymmetry
in the selection of specialized constant loading bytecodes, allowing them to
more accurately reflect the behaviour of the applications executed.
Based on these results, it is recommended that changes be made to the Java Virtual
Machine Specification in order to improve the utility of specialized bytecodes.
While the work presented in previous chapters showed that specialized bytecodes
appear to have little utility, this is at least in part due to the fact that the values
selected for specialization during the design process are not the values executed with
greatest frequency. Selecting new specialized bytecodes that reflect the behaviour of
the applications being executed could improve their utility considerably. In particu-