Building high-performance virtual machines is a complex and expensive undertaking; many popular languages still have low-performance implementations. We describe a new approach to virtual machine (VM) construction that amortizes much of the effort in initial construction by allowing new languages to be implemented with modest additional effort. The approach relies on abstract syntax tree (AST) interpretation where a node can rewrite itself to a more specialized or more general node, together with an optimizing compiler that exploits the structure of the interpreter. The compiler uses speculative assumptions and deoptimization in order to produce efficient machine code. Our initial experience suggests that high performance is attainable while preserving a modular and layered architecture, and that new highperformance language implementations can be obtained by writing little more than a stylized interpreter.

The Squawk virtual machine is a small Java TM virtual machine (VM) written mostly in Java that runs without an operating system on a wireless sensor platform. Squawk translates standard class file into an internal pre-linked, position independent format that is compact and allows for efficient execution of bytecodes that have been placed into a read-only memory. In addition, Squawk implements an application isolation mechanism whereby applications are represented as object and are therefore treated as first class objects (i.e., they can be reified). Application isolation also enables Squawk to run multiple applications at once with all immutable state being shared between the applications. Mutable state is not shared. The combination of these features reduce the memory footprint of the VM, making it ideal for deployment on small devices.Squawk provides a wireless API that allows developers to write applications for wireless sensor networks (WSNs), this API is an extension of the generic connection framework (GCF). Authentication of deployed files on the wireless device and migration of applications between devices is also performed by the VM. This paper describes the design and implementation of the Squawk VM as applied to the Sun TM Small Programmable Object Technology (SPOT) wireless device; a device developed at Sun Microsystems Laboratories for experimentation with wireless sensor and actuator applications.

No abstract

We present a compiler intermediate representation (IR) that allows dynamic speculative optimizations for high-level languages. The IR is graph-based and contains nodes fixed to control flow as well as floating nodes. Side-effecting nodes include a framestate that maps values back to the original program. Guard nodes dynamically check assumptions and, on failure, deoptimize to the interpreter that continues execution. Guards implicitly use the framestate and program position of the last side-effecting node. Therefore, they can be represented as freely floating nodes in the IR. Exception edges are modeled as explicit control flow and are subject to full optimization. We use profiling and deoptimization to speculatively reduce the number of such edges. The IR is the core of a just-in-time compiler that is integrated with the Java HotSpot VM. We evaluate the design decisions of the IR using major Java benchmark suites.

No abstract