[wasm-split] Don't use ParallelFunctionAnalysis in scanModule - #9007
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This removes the use of `ParallelFunctionAnalysis` within `scanModule` (in `computeUsedNames`), which scans `UsedNames` for each module. I'm not 100% sure why but this improves running time at least for Dart applications. I also previously tried to use `ParallelFunctionAnalysis` in other functions but it resulted in slowdown so didn't do it. Maybe cache locality works against the parallelism. This reduces running time of acx_gallery (Jul 2026) by 7.8% (30.6s -> 28.2s) essentials by 4.2% (225.1s -> 215.6s).
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I guess copying all those maps serially is about as expensive as just building them up serially to begin with 🤷
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Given a module element name, many parts of the code queries for its owning modules (where the module element has to be placed) or secondary modules using that module element. This adds `OwnershipTracker`, which precomputes and manages that information. All calls to `getOwner` or `getUsingSecondaries` that required computations iterating on all secondary modules which can be as many as thousands, has been replaced with a call that simply returns prcomputed information. For the Jul 2026 version of the applications received from the Dart team, #9007 and this combined reduce the running time of wasm-split by 25% for acx_gallery (30.6s -> 22.7s) and by 40% for essentials (225.1s -> 134.4s). Suggested in #8832 (comment).
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Previously we removed module elements one by one within a loop. But because `Module` stores a module element in both a map and a vector, removing a single module element using `removeModuleElement` is O(N), because it needs to shift all vector elements after it: https://github.com/WebAssembly/binaryen/blob/302396a676433152a32375a81d71e74687c97a1b/src/wasm/wasm.cpp#L1970-L1979 This removes module elements in bulk using `removeModuleElements`, which does the shifting only once. https://github.com/WebAssembly/binaryen/blob/302396a676433152a32375a81d71e74687c97a1b/src/wasm/wasm.cpp#L2004-L2018 Combined with #8986 and #9007, acx_gallery's running time improved by 55.2% (30.6s -> 13.7s), and essentials by 65% (225.1s -> 78.8s). (for Jul 2026 version) I guess the main reason for the running time increase in #8441 was this O(N) `removeModuleElement` called within a loop after all.
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This removes the use of
ParallelFunctionAnalysiswithinscanModule(incomputeUsedNames), which scansUsedNamesfor each module.I'm not 100% sure why but this improves running time at least for Dart applications. I also previously tried to use
ParallelFunctionAnalysisin other functions but it resulted in slowdown so didn't do it. Maybe cache locality works against the parallelism.This reduces running time of acx_gallery (Jul 2026) by 7.8% (30.6s -> 28.2s) essentials by 4.2% (225.1s -> 215.6s).