Karel Driesen           
McGill University, Canada             
karel@cs.mcgill.edu

On the Predictability of Java Byte Codes


Java byte codes are platform-independent. That means that any 
characterization of Java applications at the byte code execution 
level will reveal characteristics that any Java Virtual Machine will 
have to deal with, no matter whether this JVM is a Just-In-Time 
native code optimizing compiler running on a state-of-the-art 
high-performance workstation, or a byte code interpreter running in a 
watch.
We believe that predictability profiles are particularly well-suited 
to capture and visualize program behavior, at a variable level of 
detail, as required by a systems architect interested in control 
flow, data flow, or automatic memory management.

We present predictability profiles for 6 SPECJVM98 programs, for 
three byte code sub traces.
Subtrace:
Invoke (polymorphic call target prediction)
Load (load effective address prediction)
New (new effective type prediction)

For example, for Invoke byte codes, we measured the prediction rate 
achieved by invoke target predictors within every 20000 byte codes of 
the first 2 million byte codes executed using an unlimited, fully 
accurate BTB, and of Two-level predictors of path lengths 1,2,4,8, 
and 16. Prediction profiles for all these predictors are generally 
close together, but usually a BTB performs best in variable program 
phases.