rewrite followSets() to drastically improve compile performance #408
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cosmicexplorer
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Nov 24, 2024
- see zaach/jison#408 for a discussion of the changes
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Problem
I am looking to introduce some changes to the CoffeeScript Jison grammar. In doing so, I found that it took surprisingly long to generate. I added some grammar compile performance measurements to the CoffeeScript build system in jashkenas/coffeescript#5473, and was wondering if there was a way to improve them.
Solution
I spent quite a while rewriting a lot of the code (see e.g. https://github.com/zaach/jison/compare/master...cosmicexplorer:jison:performance-work-for-coffeescript?expand=1), and while I think a lot of that would be useful to the project, I found that the performance could be vastly improved by modifying a single method:
followSets(), which performs a fixed-point calculation.Result
There should be no change in functionality or compatibility, but many compiles should run much faster. The CoffeeScript parser build time goes from ~12 seconds down to ~4 seconds on my laptop with this change (3x improvement).