Overview of the IBM Java just-in-time compiler

We present the design and implementation of several optimizations and techn iques included in the latest IBM Java(TM) Just-in-Time (JIT) Compiler. We f irst discuss some of the modifications we have applied to Sun Microsystems' reference implementation of the Java Virtual Machine (JVM(TM)) Specificati on 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 th e requirements of the Java language specification, such as exception checki ng. We also present code generation techniques targeting Intel architecture s, 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 comp etitive overall performance of the JIT compiler in comparison with a compet itor using industry-standard benchmarking programs. All the techniques pres ented here are included in the official product (JIT Compiler version 3.0), which has been integrated into the ISM Developer Kit for Windows(TM), Java Technology Edition, Version 1.1.7.