OPTIMIZING THE JAVA VIRTUAL MACHINE INSTRUCTION SET BY ...

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multicode block is defined to be a sequence of one or more bytecodes such
that the following conditions are met:
• The bytecodes within the sequence are adjacent to each other within
the code stream.
• A bytecode within the sequence is the target of a branch if and only
if it is the first bytecode in the sequence.
• Excluding exceptions, if the first bytecode within the block executes
then all bytecodes within the sequence execute.
• An exception handler covers a bytecode within the sequence if and
only if that exception handler covers all bytecodes within the sequence.
A multicode block is distinct from a basic block in two ways.
1. It is possible for a basic block to include some instructions that reside
outside of an exception handler and some instructions that reside
within an exception handler. A multicode block does not permit
this, requiring all bytecodes within the sequence to be handled by
the same exception handlers.
2. A basic block only permits a change in the flow of control at the
end of the block. A multicode block is less restrictive, permitting a
change in the flow of control to occur within the block provided that
it occurs as the result of an exception.
Multicode: A new Java Virtual Machine bytecode which provides functionality
that is equivalent to a sequence of two or more existing Java
bytecodes.
Candidate Sequence: A sequence of adjacent bytecodes within a multicode
block that is being considered for replacement with a multicode.
7.2 An Overview of Multicodes
Section 2.2 described several techniques that can be used to implement a Java interpreter.
While these techniques represent increasingly efficient implementations, each