egg: egraphs good

Are you using egg? Please cite using the BibTeX below and add your project to the egg website!

BibTeX

@article{2021-egg,
  author = {Willsey, Max and Nandi, Chandrakana and Wang, Yisu Remy and Flatt, Oliver and Tatlock, Zachary and Panchekha, Pavel},
  title = {egg: Fast and Extensible Equality Saturation},
  year = {2021},
  issue_date = {January 2021},
  publisher = {Association for Computing Machinery},
  address = {New York, NY, USA},
  volume = {5},
  number = {POPL},
  url = {https://doi.org/10.1145/3434304},
  doi = {10.1145/3434304},
  abstract = {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.},
  journal = {Proc. ACM Program. Lang.},
  month = jan,
  articleno = {23},
  numpages = {29},
  keywords = {equality saturation, e-graphs}
}

Check out the web demo for some quick e-graph action!

Using egg

Add egg to your Cargo.toml like this:

[dependencies]
egg = "0.9.1"

Make sure to compile with --release if you are measuring performance!

Developing

It's written in Rust. Typically, you install Rust using rustup.

Run cargo doc --open to build and open the documentation in a browser.

Before committing/pushing, make sure to run make, which runs all the tests and lints that CI will (including those under feature flags). This requires the cbc solver due to the lp feature.

Tests

Running cargo test will run the tests. Some tests may time out; try cargo test --release if that happens.

There are a couple interesting tests in the tests directory:

• prop.rs implements propositional logic and proves some simple theorems.
• math.rs implements real arithmetic, with a little bit of symbolic differentiation.
• lambda.rs implements a small lambda calculus, using egg as a partial evaluator.

Benchmarking

To get a simple csv of the runtime of each test, you set the environment variable EGG_BENCH_CSV to something to append a row per test to a csv.

Example:

EGG_BENCH_CSV=math.csv cargo test --test math --release -- --nocapture --test --test-threads=1