Verifying and improving Halide’s term rewriting system with program synthesis

Halide is a domain-specific language for high-performance image processing and tensor computations, widely adopted in industry. Internally, the Halide compiler relies on a term rewriting system to prove properties of code required for efficient and correct compilation. This rewrite system is a colle...

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Bibliographic Details
Published in:Proceedings of ACM on programming languages Vol. 4; no. OOPSLA; pp. 1 - 28
Main Authors: Newcomb, Julie L., Adams, Andrew, Johnson, Steven, Bodik, Rastislav, Kamil, Shoaib
Format: Journal Article
Language:English
Published: New York, NY, USA ACM 13.11.2020
Subjects:
General programming languages
History of computing
History of programming languages
Professional topics
Social and professional topics
Software and its engineering
Software notations and tools
synthesis
term rewriting system
verification
ISSN:2475-1421, 2475-1421
Online Access:Get full text
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Summary:Halide is a domain-specific language for high-performance image processing and tensor computations, widely adopted in industry. Internally, the Halide compiler relies on a term rewriting system to prove properties of code required for efficient and correct compilation. This rewrite system is a collection of handwritten transformation rules that incrementally rewrite expressions into simpler forms; the system requires high performance in both time and memory usage to keep compile times low, while operating over the undecidable theory of integers. In this work, we apply formal techniques to prove the correctness of existing rewrite rules and provide a guarantee of termination. Then, we build an automatic program synthesis system in order to craft new, provably correct rules from failure cases where the compiler was unable to prove properties. We identify and fix 4 incorrect rules as well as 8 rules which could give rise to infinite rewriting loops. We demonstrate that the synthesizer can produce better rules than hand-authored ones in five bug fixes, and describe four cases in which it has served as an assistant to a human compiler engineer. We further show that it can proactively improve weaknesses in the compiler by synthesizing a large number of rules without human supervision and showing that the enhanced ruleset lowers peak memory usage of compiled code without appreciably increasing compilation times.
ISSN:2475-1421
2475-1421
DOI:10.1145/3428234