The Swift Java Compiler: Design and Implementation

We have designed and implemented an optimizing Java compiler called Swift for the Alpha architecture. Swift translates Java bytecodes to optimized Alpha code, and uses static single assignment (SSA) form for its intermediate representation (IR). The Swift IR is relatively simple, but allows for straightforward implementation of all the standard scalar optimizations. The Swift compiler also implements method resolution and inlining, interprocedural alias analysis, elimination of Java run-time checks, object inlining, stack allocation of objects, and synchronization removal. Swift is written completely in Java and installs its generated code into a highperformance JVM that provides all of the necessary run-time facilities. In this paper, we describe the design and implementation of the Swift compiler system. We describe the properties of the intermediate representation, and then give details on many of the useful optimization passes in Swift. We then provide some overall performance results of the Swiftgenerated code for the SpecJVM98 benchmarks, and analyze the performance gains from various optimizations. We find that the Swift design is quite effective in allowing efficient and general implementations of numerous interesting optimizations. The use of SSA form, in particular, has been especially beneficial, and we have found very few optimizations that are difficult to implement in SSA.