Better Living through Operational Semantics: An Optimizing Compiler for Radio Protocols

Geoffrey Mainland (Drexel University, USA) gives the fourth talk in the first panel, Low-level and Systems Programming, on the 2nd day of the ICFP conference. Software-defined radio (SDR) promises to bring the flexibility and rapid iterative workflow of software to radio protocol design. Many factors make achieving this promise challenging, not least of which are the high data rates and timing requirements of real-world radio protocols. The Ziria language and accompanying compiler demonstrated that a high-level language can compete in this demanding space, but extracting reusable lessons from this success is difficult due to Ziria's lack of a formal semantics. Our first contribution is a core language, operational semantics, and type system for Ziria. The insight we gained through developing this operational semantics led to our second contribution, consisting of two program transformations. The first is fusion, which can eliminate intermediate queues in Ziria programs. Fusion subsumes many one-off optimizations performed by the original Ziria compiler. The second transformation is pipeline coalescing, which reduces execution overhead by batching IO. Pipeline coalescing relies critically on fusion and provides a much simpler story for the original Ziria compiler's "vectorization" transformation. These developments serve as the basis of our third contribution, a new compiler for Ziria that produces significantly faster code than the original compiler. The new compiler leverages our intermediate language to help eliminate unnecessary memory traffic. As well as providing a firm foundation for the Ziria language, our work on an operational semantics resulted in very real software engineering benefits. These benefits need not be limited to SDR--the core language and accompanying transformations we present are applicable to other domains that require processing streaming data at high speed.