A roadmap for extending MicroJIT: a lightweight just-in-time compiler for decreasing startup time

Dynamic compilation is an important technique for improving the performance of interpreted programs during run-time. By replacing code that would normally be interpreted with native machine code, successive executions of code can avoid the interpreter and thus run faster. Eclipse OpenJ9 is an open-source Java Virtual Machine built upon Eclipse OMR components. Eclipse OMR is an open-source collection of components for building run-time environments. The default just-in-time compiler provided by OMR supports multiple levels of compilation and optimizations. MicroJIT is a lightweight, non-optimizing, template based JIT compiler that was previously integrate d into J9, IBM's enterprise JVM that preceded OpenJ9. Previous work showed that MicroJIT, when combined with the default J9 JIT, could improve startup times without reducing the throughput of long running applications. By incorporating MicroJIT into OpenJ9 we hope to offe similar improvements to startup times, while offerin applications in resource constrained environments a lightweight JIT alternative. In this paper we propose four changes for MicroJIT to further improve its fl xibility and performance. First, we will be porting MicroJIT to the 64-bit x86 architecture which will allow the JIT to be used in modern environments. Second, we will extend its bytecode support, which should further reduce the number of required context switches back to the interpreter. Third, we will add support for asynchronous compilation. Lastly, we will add profilin to the generate d code providing the default JIT additional context when it takes over compilation duties from the MicroJIT.