perf: ArraySet.add returns index — drop trailing indexOf in hot paths#65
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Three per-mapping hot paths followed `add()` with `indexOf()` to grab the inserted/existing index. Both call into the same Map: `add` does a has+set+get-equivalent, `indexOf` does a redundant get. Returning the index from `add` lets callers get the result for free — one Map op per source/name instead of two. Affected: * SourceMapGenerator.addMapping * SourceMapGenerator.applySourceMap * IndexedSourceMapConsumer._parseMappings Bench (SOLO=1 PHASES=adding generate vs main, two-process): addMapping mean +21.4% across jridgewell fixtures (preact +30.3%, react +21.4%, amp +20.5%, issue-41 +34.8%, vscode +21.1%, babel.min +0.2% — flat, very few unique sources) API: ArraySet.add gains a return value. Existing callers ignoring it keep working unchanged.
This was referenced May 10, 2026
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Summary
ArraySet.addnow returns the string's index in the set (existing or new). Three per-mapping hot paths previously pairedadd()withindexOf()to grab that index — that's two Map operations where one suffices. Lettingaddreturn it cuts the redundantMap.get.Affected hot paths:
SourceMapGenerator.addMapping— once per added mapping (source + name)SourceMapGenerator.applySourceMap— once per rebuilt mapping (source + name)IndexedSourceMapConsumer._parseMappings— once per section mapping (source + name)Bench
SOLO=1 PHASES=adding scripts/bench-diff.sh main generate(two-process, ops/sec via benchmark.js):Sample sizes 24–100 runs per cell, error bars ≤3%. Mean +21.4%. babel.min is flat because it has very few unique sources/names — the saved
Map.getis amortized away.API
ArraySet.addgains a return value (the index). Existing callers that ignore the return value continue to work unchanged — no breaking change.Test plan