egg: Fast and extensible equality saturation

An e-graph efficiently represents a congruence relation over many expressions. Although they were originally developed in the late 1970s for use in automated theorem provers, a more recent technique known as equality saturation repurposes e-graphs to implement state-of-the-art, rewrite-driven compil...

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Vydané v:Proceedings of ACM on programming languages Ročník 5; číslo POPL; s. 1 - 29
Hlavní autori: Willsey, Max, Nandi, Chandrakana, Wang, Yisu Remy, Flatt, Oliver, Tatlock, Zachary, Panchekha, Pavel
Médium: Journal Article
Jazyk:English
Vydavateľské údaje: 01.01.2021
ISSN:2475-1421, 2475-1421
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Shrnutí:An e-graph efficiently represents a congruence relation over many expressions. Although they were originally developed in the late 1970s for use in automated theorem provers, a more recent technique known as equality saturation repurposes e-graphs to implement state-of-the-art, rewrite-driven compiler optimizations and program synthesizers. However, e-graphs remain unspecialized for this newer use case. Equality saturation workloads exhibit distinct characteristics and often require ad-hoc e-graph extensions to incorporate transformations beyond purely syntactic rewrites. This work contributes two techniques that make e-graphs fast and extensible, specializing them to equality saturation. A new amortized invariant restoration technique called rebuilding takes advantage of equality saturation's distinct workload, providing asymptotic speedups over current techniques in practice. A general mechanism called e-class analyses integrates domain-specific analyses into the e-graph, reducing the need for ad hoc manipulation. We implemented these techniques in a new open-source library called egg. Our case studies on three previously published applications of equality saturation highlight how egg's performance and flexibility enable state-of-the-art results across diverse domains.
ISSN:2475-1421
2475-1421
DOI:10.1145/3434304