Use SparseSet-like structure for SuffixCache #513
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For simple regexes, allocating and filling 1000 of SuffixCache elements seemed to be quite high on the profile as part of Compiler::new, so I decided to optimise it by using ideas similar to sparse set, but specialised for a hashmap-like structure, instead of a flat array with versioning. In my performance comparisons this gives 8-10% improvement for simple regexes where overhead of Compiler::new is most noticeable.
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FWIW I understand that SuffixCache is meant to be as simple as possible, but I think (hope) this change doesn't make it any more complicated while brings nice performance improvement. |
BurntSushi
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Sep 9, 2018
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Nice, I like it!
FYI, this is definitely one of the areas I plan on putting a lot of focus on. The FSMs for Unicode character classes are way too big currently. RE2 has done some nice work in this area.
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@BurntSushi Seems to pass all the checks? |
This was referenced Oct 13, 2025
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For simple regexes, allocating and filling 1000 of SuffixCache elements seemed to be quite high on the profile as part of Compiler::new, so I decided to optimise it by using ideas similar to sparse set, but specialised for a hashmap-like structure, instead of a flat array with versioning.
In my performance comparisons this gives 8-10% improvement for simple regexes where overhead of Compiler::new is most noticeable.