OPTIMIZING THE JAVA VIRTUAL MACHINE INSTRUCTION SET BY ...

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these data types in the list of least frequently executed bytecodes is not surprising.
The int data type provides sufficient range for the storage of many of the integer
values used in a program. Long integers are generally avoided unless necessary due
to their increased storage requirements and poorer execution performance on many
platforms.
Many Java programmers elect to use double precision floating point numbers
rather than single precision floating point numbers. This is because single precision
floats offer relatively limited precision and range. Although doubles take twice as
much memory to store, their performance is comparable to single precision floats on
many modern computer architectures.
All of these factors contribute to the infrequent use of float and long data types.
Consequently, few bytecodes are executed to handle values of those types. This
further reinforces the recommendation to consider replacing many of the float and
long load specialized bytecodes with additional specialized integer loads.
The observant reader will also have noticed the presence of iload 0x03 in the
list of least executed load instructions. The presence of this bytecode is surprising in
that it is a despecialized form of what would normally be expressed as iload 3. It
occurs statically in several of the class files used by the symjpack-t benchmark in the
Ashes Suite. These class files were used in their precompiled, as distributed form. It
is not known what compiler was used to create these class files or why the compiler
elected to make use of iload 0x03 rather than the more common iload 3. It was
observed that the iload 3 form is also present within the same class files and that
all occurrences of the iload 0x03 form immediately precede an if icmplt bytecode.
As a result it is possible that the use of iload 0x03 is an artifact of the technique
used by one specific compiler when generating conditional branches.
6.2.2 Local Variable Stores
The distribution of the most frequently utilized store bytecodes was also examined.
It revealed similar patterns to those found for load bytecodes. In particular, it was
observed that general purpose store bytecodes occurred frequently among those store
bytecodes executed with greatest frequency. While the most frequently executed
store bytecode was istore 3, istore 0x04 was a close second. Only 4 of the 10
most frequently executed store bytecodes were specialized. As was the case for load
bytecodes, the proportion worsens as the number of bytecodes considered increases.
When the top 20 store bytecodes are considered only 5 are found to be specialized