Design and implementation of an optimizing type-centric compiler for a high-level language

Production compilers for programming languages face multiple requirements. They should be correct, as we rely on them to produce code. They should be fast, in order to provide a good developer experience. They should also be easy to maintain and evolve. This thesis shows how an expressive high level type system can be used to simplify the development of a compiler and demonstrates this on a compiler for Scala. First, it shows how expressive types of high level languages can be used to build internal data structures that provide a statically checked API, ensuring that important properties hold at compile time. Second, we also show how high level language features can be used to abstract the components of a compiler. We demonstrate this by introducing a type-safe layer on top of the bytecode emission phase. This makes it possible to abstract away the implementation details of the compiler frontend and run the same bytecode emission phase in two different Scala compilers. Third, it presents MiniPhases, a novel way to organize transformation passes in a compiler. MiniPhases impose constraints on the organization of passes that are beneficial for maintainability, performance, and testability. We include a detailed performance evaluation of MiniPhases which indicates that their speedup is due to improved cache friendliness and to a lower rate of promotions of objects into the old generations of garbage collectors. Finally, we demonstrate how the expressive type system of the language being compiled can be used for static analysis. We present a novel call graph construction algorithm which uses the typing context for context sensitivity. The resulting algorithm is both substantially faster and more precise than existing alternatives. We demonstrate the applicability of this analysis by extending common subexpression elimination to idempotent expression elimination.