OPTIMIZING THE JAVA VIRTUAL MACHINE INSTRUCTION SET BY ...

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the applications. In addition, because the same constant value may reside
at different locations in different class files, collecting this information
made it possible collect a count for all uses of each unique constant value,
even when those uses were loaded from different constant pool positions.
getfield, putfield, getstatic and putstatic: These bytecodes are
used to access the fields defined within a class. The getfield and putfield
bytecodes are used to read and write instance fields while getstatic
and putstatic are used to access static fields. Two operand
bytes are provided to each of these bytecodes which specify an offset into
the constant pool which contains an element of type CONSTANT Fieldref
info. The information stored in this entry can be used to acquire
the fully qualified name of the field and its type.
6.2 Profile Results
Each of the following subsections examines the operands used by a specific set of
opcodes. The subsections begin by considering load bytecodes, store bytecodes and
constant loading bytecodes. Additional subsections consider the patterns observed in
field accesses and method invocations.
In general, the results presented in the following subsections are averages across all
of the benchmarks considered during this study. These average results were computed
using the technique described in Section 5.1.2 in order to ensure that no one benchmark
was able to skew the distribution of the bytecodes. Some interesting highlights
from specific benchmarks are also included in addition to the average results.
6.2.1 Local Variable Loads
Figure 6.1 presents the most frequently executed load bytecodes. The height of each
bar represents the average percentage of all of the bytecodes executed across the 23
benchmarks tested. Bars on the graph drawn in gray represent specialized bytecodes
while the bars drawn in white represent general purpose bytecodes. Examining the
graph reveals that 6 of the first 10 load bytecodes are specialized. When the first 20
load bytecodes are considered only 8 specialized bytecodes are present. In comparison,
if the selection of specialized load bytecodes was perfect, the first 20 load bytecodes
would be specialized bytecodes.