Elimination of Java array bounds checks in the presence of indirection

Abstract

The Java language specification states that every access to an array needs to be within the bounds of that array, i.e. between 0 and array length − 1. Different techniques for different programming languages have been proposed to eliminate explicit bounds checks. Some of these techniques are implemented in off-the-shelf Java Virtual Machines (JVMs). The underlying principle of these techniques is that bounds checks can be removed when a JVM/compiler has enough information to guarantee that a sequence of accesses (e.g. inside a for-loop) is safe (within the bounds). Most of the techniques for the elimination of array bounds checks have been developed for programming languages that do not support multi-threading and/or enable dynamic class loading. These two characteristics make most of these techniques unsuitable for Java. Techniques developed specifically for Java have not addressed the elimination of array bounds checks in the presence of indirection; that is, when the index is stored in another array (indirection array). With the objective of optimizing applications with array indirection, this paper proposes and evaluates three implementation strategies, each implemented as a Java class. The classes provide the functionality of Java arrays of type int so that objects of the classes can be used instead of indirection arrays. Each strategy enables JVMs, when examining only one of these classes at a time, to obtain enough information to remove array bounds checks. Copyright © 2005 John Wiley & Sons, Ltd.