Concurrency Practice and Experience

Design, implementation, and evaluation of optimizations in a JavaTM just-in-time compiler

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The Java language incurs a runtime overhead for exception checks and object accesses, which are executed without an interior pointer in order to ensure safety. It also requires type inclusion test, dynamic class loading, and dynamic method calls in order to ensure flexibility. A `Just-In-Time' (JIT) compiler generates native code from Java byte code at runtime. It must improve the runtime performance without compromising the safety and flexibility of the Java language. We designed and implemented effective optimizations for a JIT compiler, such as exception check elimination, common subexpression elimination, simple type inclusion test, method inlining, and devirtualization of dynamic method call. We evaluate the performance benefits of these optimizations based on various statistics collected using SPECjvm98, its candidates, and two JavaSoft applications with byte code sizes ranging from 23 000 to 280 000 bytes. Each optimization contributes to an improvement in the performance of the programs.