libexpr: add nix-expr-benchmarks, add regex optimizations#14827
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xokdvium merged 3 commits intoNixOS:masterfrom Dec 19, 2025
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libexpr: add nix-expr-benchmarks, add regex optimizations#14827xokdvium merged 3 commits intoNixOS:masterfrom
xokdvium merged 3 commits intoNixOS:masterfrom
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Now the CI is failing because of a GitHub API timeout. Some outage, I've just had a similar issue on one of my repos. |
xokdvium
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src/libexpr/primops.cc
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| boost::concurrent_flat_map<std::string, Entry, StringViewHash, std::equal_to<>> cache; | ||
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| std::regex get(std::string_view re) | ||
| std::shared_ptr<const std::regex> get(std::string_view re) |
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Maybe instead of shared_ptr we can use nix::ref, which is non-nunnable shared ptr wrapper. Worth noting in a comment somewhere that putting this behind a shared_ptr is necessary because the flat_map can invalidate pointers pretty easily.
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Provides focused microbenchmarks for expression evaluation hot paths (dynamic attrs, getDerivations attr scanning, and repeated builtins.match).
- RegexCache::get() returned std::regex by value, copying the compiled regex on every cache hit. - Store the compiled regex behind std::shared_ptr<const std::regex> and return the shared pointer instead, so callers reuse the same compiled object. - BM_EvalManyBuiltinsMatchSameRegex_mean improved about 8%
- getDerivations() filters attribute names with std::regex_match, which runs the regex engine for every attribute visited during nixpkgs scanning. - BM_GetDerivationsAttrScan/10000_mean: 3.338 ms → 1.506 ms (≈ -54.9%)
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Instead of reading this PR, please read the individual commits. The latter 2 changes depend on the new benchmark module for libexpr. These are regex oriented optimizations. There is a big performance win for accessing attributes (regex validation engine was heavy).
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