Overview of the IBM Java Just - in - Time

We present the design and implementation of several optimizations and techniques included in the latest IBM Java Just-in-Time (JIT) Compiler. We first discuss some of the modifications we have applied to Sun Microsystems’ reference implementation of the Java Virtual Machine (JVM) Specification to increase the performance, including a change in the object layout. We then describe each of the optimizations, referring to what had to be taken into account because of both the just-in-time nature of the compiler and the requirements of the Java language specification, such as exception checking. We also present code generation techniques targeting Intel architectures, describing the register allocation schemes, exception handling, and code scheduling. Finally we report on the performance of the IBM JIT compiler, showing both the effectiveness of the individual optimizations and the competitive overall performance of the JIT compiler in comparison with a competitor, using industry-standard benchmarking programs. All the techniques presented here are included in the official product (JIT Compiler version 3.0), which has been integrated into the IBM Developer Kit for Windows, Java Technology Edition, Version 1.1.7.