This paper presents a framework for supporting the optimization of Java programs using attributes in Java class les. We show how class le attributes may be used to convey both optimization opportunities and prole information to a variety of Java virtual machines including ahead-of-time compilers and just-in-time compilers. We present our work in the context of Soot, a framework that supports the analysis and transformation of Java bytecode (class les)[21]. We demonstrate the framework with attributes for elimination of array bounds and null pointer checks, and we provide experimental results for the Kae just-in-time compiler, and IBM's High Performance Compiler for Java ahead-of-time compiler. 1 Introduction Java is a clean, portable, object-oriented language that is gaining wide spread acceptance. The target language for Java compilers is Java bytecode which is a platform-independent, stack-based intermediate representation. The bytecode is stored in Java class les, and...

The Java Bytecode language lacks expressiveness for traditional compiler optimizations, making this portable, secure software distribution format inefficient as a program representation for high performance. This inefficiency results from the underlying stack model, as well as the fact that manybytecode operations intrinsically include sub-operations (e.g., iaload includes the address computation, arrayboundschecks and the actual load of the array element). The stack model, with no operand registers and limiting access to the top of the stack, prevents the reuse of values and bytecode reordering. In addition, the bytecodes havenomechanism to indicate which sub-operations in the bytecode stream are redundant or subsumed by previous ones. As a consequence, the Java Bytecode language inhibits the expression of important compiler optimizations, including common sub-expression elimination, register allocation and instruction scheduling. The

Pointer traversals pose significant overhead to the execution of object-oriented programs, since every access to an object?s state requires a pointer dereference. Eliminating redundant pointer traversals reduces both instructions executed as well as redundant memory accesses to relieve pressure on the memory subsystem. We describe an approach to elimination of redundant access expressions that combines partial redundancy elimination (PRE) with type-based alias analysis (TBAA). To explore the potential of this approach we have implemented an optimization framework for Java class files incorporating TBAA-based PRE over pointer access expressions. The framework is implemented as a class-file-to-class-file transformer; optimized classes can then be run in any standard Java execution environment. Our experiments demonstrate improvements in the execution of optimized code for several Java benchmarks running in diverse execution environments: the standard interpreted JDK virtual machine, a virtual machine using ?just-in-time? compilation, and native binaries compiled off-line (?way-ahead-of-time?). Overall, however, our experience is of mixed success with the optimizations, mainly because of the isolation between our optimizer and the underlying execution environments which prevents more effective cooperation between them.We isolate the impact of access path PRE using TBAA, and demonstrate that Java?s requirement of precise exceptions can noticeably impact code-motion optimizations like PRE.

....................................... x 1 INTRODUCTION . . . . . . ........................... 1 1.1 Optimization framework ........................... 1 1.2 Measurements................................. 2 1.3 Overview ................................... 2 2 BACKGROUND .................................. 3 2.1 Controlflowgraphs.............................. 3 2.1.1 Dominators . . . ........................... 3 2.1.2 Loops . . . . . . ........................... 4 2.2 Staticsingleassignmentform......................... 6 2.2.1 Construction . . ........................... 7 2.2.2 Destruction . . . ........................... 11 2.3 Partial redundancy elimination . . . . .................... 12 2.3.1 SSAPRE . . . . ........................... 12 2.4 Other optimizations . . . ........................... 14 2.5 Typebasedaliasanalysis........................... 15 2.5.1 Terminology and notation . . .................... 16 v Page 2.5.2 TBAA . . . . . . ........................

The Javabytecode language lacks expressiveness for traditional compiler optimizations, making this portable, secure software distribution format inefficient as a program representation for high performance. This inefficiency results from the underlying stackmodel,aswell as the fact that manybytecode operations intrinsically include sub-operations (e.g., iaload includes the address computation, array bounds checks and the actual load of the array element). The stack model, with no operand registers and limiting access to the top of the stack, prevents the reuse of values and bytecode reordering. In addition, the language has no mechanism to indicate which sub-operations in the Javabytecode stream are redundant or subsumed by previous ones. As a consequence, the Javabytecode language inhibits the expression of important compiler optimizations, including register allocation and instruction scheduling. The Javabytecode stream generated byaJavabytecode compiler is a significantly under-optimized program representation. The most common solution to overcome this inefficiency is the use of a Just-inTime (JIT) compiler to not only generate native code, but perform optimization as well. However, the latter is a time consuming operation in an already time-constrained translation process. In this paper we present an alternative to an optimizing JIT compiler that makes use of code annotations generated byaJavabytecode compiler. These annotations carry information concerning compiler optimizations. During the translation process, an annotation-aware Java Virtual Machine (JVM) system then uses this information to produce high performance native code without performing much of the necessary analyses or transformations. We describe the implementation of a prototype of...

this document reect the shift towards Java as a primary focus of investigation. At least three of the partners are now engaged in development of parallel or optimizing Java compilers

Recently, there has been a rapidly expanding body of work with the vision of seamlessly integrating idle networked computers into virtual computing environments. This is enabled primarily by the success of research eorts promoting parallel and distributed computing on networks of workstations and the wide acceptance of Java. The proliferation of work in this area has provided new Internet-based infrastructures that harness the power of computing bases comprising hundreds of loosely-connected volunteered machines (i.e., hosts). While many of these systems have proposed the use of non-altruistic market-based schemes for promoting large-scale participation, mechanisms for ensuring that hosts participating in collaborative computing environments perform the work assigned to them have been largely ignored. This paper presents our implementation of one framework that layers a remote audit mechanism on top of an existing distributed computing model, and provides ecient methods for verifying,...

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