A region-based compilation technique for a Java just-in-time compiler

Abstract

Method inlining and data flow analysis are two major optimization components for effective program transformations, however they often suffer from the existence of rarely or never executed code contained in the target method. One major problem lies in the assumption that the compilation unit is partitioned at method boundaries. This paper describes the design and implementation of a region-based compilation technique in our dynamic compilation system, in which the compiled regions are selected as code portions without rarely executed code. The key part of this technique is the region selection, partial inlining, and region exit handling. For region selection, we employ both static heuristics and dynamic profiles to identify rare sections of code. The region selection process and method inlining decision are interwoven, so that method inlining exposes other targets for region selection, while the region selection in the inline target conserves the inlining budget, leading to more method inlining. Thus the inlining process can be performed for parts of a method, not for the entire body of the method. When the program attempts to exit from a region boundary, we trigger recompilation and then rely on on-stack replacement to continue the execution from the corresponding entry point in the recompiled code. We have implemented these techniques in our Java JIT compiler, and conducted a comprehensive evaluation. The experimental results show that the approach of region-based compilation achieves approximately 5% performance improvement on average, while reducing the compilation overhead by 20 to 30%, in comparison to the traditional function-based compilation techniques.