Java Annotation - Aware Just - In - Time ( AJIT ) Compilation

The Java Bytecode language lacks expressiveness for traditional compiler optimizations, making this portable, secure software distribution format ineecient as a program representation for high performance. This inee-ciency results from the underlying stack model, as well as the fact that many bytecode 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 bytecodes have no mechanism 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 bytecode stream generated by the Java front-end is a signiicantly under-optimized program representation. The most common solution to overcome this aspect of the language is the use of a Just-in-Time (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 by the Java front-end. These annotations carry information concerning compiler optimization. During the translation process, an annotation-aware JIT (AJIT) 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 the rst prototype of our annotation-aware JIT system and show performance results comparing our system with other Java Virtual Machines (JVMs) running on SPARC architecture .