OPTIMIZING THE JAVA VIRTUAL MACHINE INSTRUCTION SET BY ...

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Figure 7.1: Two Bytecodes and their Equivalent Multicode
will have n bytes devoted to representing the opcodes. Consequently, n − 1 bytes are
saved for each multicode substitution performed.
This size change is illustrated in Figure 7.1. It shows that a total of 5 bytes (2 opcodes
and 3 operands) were used to represent the bytecode sequence aload getfield
before multicode substitution was performed. When the sequence is replaced with a
multicode, the total number of bytes is reduced to 4 because the number of opcodes
is reduced to one. More significantly, the code will execute more efficiently because
of the removal of a transfer of control, as will be seen in the following sections.
7.2.1 Notation
The symbol x k will be used to denote the codelet for a single Java bytecode. The
symbol k is an integer greater than 0 used to indicate the position of that codelet
within a bytecode sequence or a multicode. The work necessary to transfer control