A Simplified Java Compilation System for Resource-Constrained Embedded Processors∗

Embedded platforms are resource-constrained systems in which performance of executed code is of critical importance. However, standard techniques such as full just-in-time(JIT) compilation and/or adaptive optimization (AO) may not be appropriate for this type of systems due to memory and compilation overheads. The research presented in this paper proposes a technique that combines some of the main benefits of JIT compilation, superoperators(SOs) and profile-guided optimization, in order to deliver a lightweight Java compilation system, targeted for resource-constrained environments, that achieves runtime performance similar to that of state-of-the-art JIT/AO systems, while having a minimal impact on runtime memory consumption. The key ideas are to use profiler-selected, extended bytecode basic blocks as superoperators (new bytecode instructions) and to perform few, but very targeted, standard JIT/AO optimizations at compile time only on the superoperators’ bytecode, as directed by compilation “hints” passed on as annotations. As such, our system achieves competitive performance to a JIT/AO system, but with a much lower impact on runtime memory consumption. Moreover, we show that our proposed VM is able to further improve upon the achieved runtime performance by selectively inlining method calls embedded in the chosen superoperators, as directed by runtime profiling data. For experimental evaluation, we developed three incremental Virtual Machines(VMs) that employ the ideas presented above. The customized VMs are first compared (w.r.t. runtime performance) to a simple, fast-to-develop VM (baseline) and then to a VM that employs JIT/AO. Our best-performing system attains speedups ranging from a factor of 1.52 to a factor of 3.07, w.r.t. to the baseline VM. When compared to a state-of-the-art JIT/AO VM, our proposed system performs better for three of the benchmarks and worse for 3 others. However, our SO-extended VM outperforms the JIT/AO system by a factor of 16, on average, w.r.t. runtime memory consumption. We also show that selectively inlining method calls embedded in ∗This work was supported in part by the National Science Foundation under grants NSF CCF-0311738 and CNS-0220069