OPTIMIZING THE JAVA VIRTUAL MACHINE INSTRUCTION SET BY ...

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Chapter 7
Multicodes
This chapter introduces multicodes, an optimization technique designed to improve
the performance of Java interpreters. A multicode is a new bytecode that performs
the same behaviour as a collection of two or more existing bytecodes, when they
are found in a contiguous sequence. The optimization technique works by reducing
the amount of overhead imposed by the Java Virtual Machine, resulting in reduced
application run time. Identifying commonly occurring bytecode sequences is the
first step in the multicode optimization process. Once the sequences are identified,
occurrences of those sequences within the class files that make up the application and
the Java library are replaced with the multicode, reducing the number of fetch-decodeexecute
operations that must be performed, and opening up additional optimization
opportunities. Multicodes are not defined by a static specification like bytecodes are.
Instead, they are more dynamic entities that can vary from application to application,
which are automatically identified by the techniques described in this thesis.
7.1 Definitions
The following terms will be used throughout the remainder of the thesis.
Codelet: The set of statements within the Java interpreter that implement
the task specified by a Java bytecode (or multicode).
Basic Block: “A sequence of consecutive statements in which flow of
control enters at the beginning and leaves at the end without halt or
possibility of branching except at the end” [12].
Multicode Block: The notion of a multicode block is similar to that of
a basic block. However, there are several distinctions. In particular, a