Inside VOLT: Designing an Open-Source GPU Compiler

TL;DR

VOLT is an open-source GPU compiler framework designed to simplify and standardize the compilation process for emerging open GPU architectures, supporting extensibility and diverse programming models.

Contribution

This paper introduces VOLT, a hierarchical, extensible compiler framework that facilitates SIMT code generation and optimization for open GPU architectures.

Findings

VOLT enables cross-architecture SIMT code generation.

VOLT supports multiple front-end languages and hardware variants.

Case studies demonstrate VOLT's extensibility with ISA extensions and host APIs.

Abstract

Recent efforts in open-source GPU research are opening new avenues in a domain that has long been tightly coupled with a few commercial vendors. Emerging open GPU architectures define SIMT functionality through their own ISAs, but executing existing GPU programs and optimizing performance on these ISAs relies on a compiler framework that is technically complex and often undercounted in open hardware development costs. To address this challenge, the Vortex-Optimized Lightweight Toolchain (VOLT) has been proposed. This paper presents its design principles, overall structure, and the key compiler transformations required to support SIMT execution on Vortex. VOLT enables SIMT code generation and optimization across multiple levels of abstraction through a hierarchical design that accommodates diverse front-end languages and open GPU hardware. To ensure extensibility as GPU architectures evolve, VOLT centralizes fundamental SIMT-related analyses and optimizations in the middle-end, allowing them to be reused across front-ends and easily adapted to emerging open-GPU variants. Through two case studies on ISA extensions and host-runtime API, this paper also demonstrates how VOLT can support extensions