Parallel Query Systems : Demand-Driven Incremental Compilers

Abstract: Query systems were recently introduced as an architecture for constructing compilers, and have shown to enable fast and efficient incremental compilation, where results from previous builds is reused to accelerate future builds. With this architecture, a compiler is composed of several queries, each of which extracts a small piece of information about the source program. For example, one query might determine the type of a variable, and another the list of functions defined in some file. The dependencies of a query, which includes other queries or files on disk, are automatically recorded at runtime. With these dependencies, query systems can detect changes in their inputs and incorporate them into the final output, while reusing old results from queries which have not changed. This reduces the amount of work needed to recompile code, which saves both time and energy. We present a new parallel execution model for query systems using work-stealing, which dynamically balances the workload across multiple threads. This is facilitated by various augmentations to existing algorithms to allow concurrent operations. Furthermore, we introduce a novel data structure that accelerates incremental compilation for common use cases. We evaluated the impact of these augmentations by implementing a compiler frontend capable of parsing and type-checking the Go programming language. We demonstrate a 10x reduction in compile times using the parallel execution mode. Finally, under certain common conditions, we show a 5x reduction in incremental compile times compared to the state-of-the-art.