Unboxing Virgil ADTs for Fun and Profit

TL;DR

This paper introduces annotation-guided optimizations for algebraic data types in Virgil, enabling more efficient memory use and hardware-specific data manipulation through unboxing and packing annotations.

Contribution

It extends Virgil with #unboxed and #packed annotations, allowing automatic transformation to scalar representations and programmer-controlled bit layouts.

Findings

Reduced memory usage in various workloads

Improved data manipulation aligned with hardware formats

Demonstrated performance benefits of annotations

Abstract

Algebraic Data Types (ADTs) are an increasingly common feature in modern programming languages. In many implementations, values of non-nullary, multi-case ADTs are allocated on the heap, which may reduce performance and increase memory usage. This work explores annotation-guided optimizations to ADT representation in Virgil, a systems-level programming language that compiles to x86, x86-64, Wasm and the Java Virtual Machine. We extend Virgil with annotations: #unboxed to eliminate the overhead of heap allocation via automatic compiler transformation to a scalar representation, and #packed, to enable programmer-expressed bit-layouts. These annotations allow programmers to both save memory and manipulate data in formats dictated by hardware. We dedicate this work as an homage and echo of work done in collaboration with Jens in the work entitled "A Declarative Approach to Generating Machine Code Tools", an unpublished manuscript from 2005. In fact, this work inherits some syntactic conventions from that prior work. The performance impact of these representation changes was evaluated on a variety of workloads in terms of execution time and memory usage, but we don't include it because Jens like semantics and type systems better!