perf: fix FindAll 600x regression for anchored patterns #92
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Problem: FindAll("^HTTP/[12]\.[01]", 6MB) took 346µs instead of <1µs
Root cause: Allocation heuristic make([][2]int, 0, len(haystack)/100+1)
created ~1MB buffer (62k capacity) for a pattern that matches at most once.
Fix:
- Anchored patterns (^...) use cap=1 (max 1 match possible)
- Non-anchored patterns capped at 256 (append grows if needed)
- Added Engine.IsStartAnchored() method for allocation optimization
Result: Now matches stdlib performance (~500ns for anchored patterns)
Benchmarks (6MB input, 1 match):
- Before: coregex 346µs vs stdlib ~0µs (600x slower)
- After: coregex 567ns vs stdlib 566ns (equal performance)
Benchmark ComparisonComparing Summary:
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Summary
FindAllon anchored patterns with large inputs^...) now usecap=1allocation (max 1 match possible)Engine.IsStartAnchored()method for allocation optimizationProblem
FindAll("^HTTP/[12]\.[01]", 6MB_input)took 346µs instead of <1µsRoot cause: Allocation heuristic
make([][2]int, 0, len(haystack)/100+1)created ~1MB buffer (62,915 capacity) for a pattern that matches at most once.Benchmarks (6MB input, 1 match)
Changes
meta/meta.go: Smart allocation infindAllIndicesLoop, newIsStartAnchored()methodregex.go: Smart allocation inFindAllCHANGELOG.md: Document fixTest plan
go test ./...)golangci-lint run)🤖 Generated with Claude Code