[wasm-split] Deduplicate loops in shareImportableItems (NFC) - #8992
Open
aheejin wants to merge 20 commits into
Open
[wasm-split] Deduplicate loops in shareImportableItems (NFC)#8992aheejin wants to merge 20 commits into
aheejin wants to merge 20 commits into
Conversation
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, this reduces the running time of wasm-split by 17% for acx_gallery (30s -> 25s) and by 33% for essentials (230s -> 153s). Suggested in #8832 (comment).
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 Combining with #8986, acx_gallery's running time improved by 50.3% (30s -> 15s), and essentials by 60.8% (230s -> 90s). (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.
We have six mostly identical loops in `shareImportableItems`, each for memories, tables, globals, tags, data segments, and element segments. This factors the core logic out as a generic lambda function.
tlively
approved these changes
Aug 13, 2026
tlively
left a comment
tlively
left a comment
Member
There was a problem hiding this comment.
Nice! LGTM once the preliminaries land.
Co-authored-by: Thomas Lively <tlively@google.com>
Co-authored-by: Thomas Lively <tlively123@gmail.com>
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).
Co-authored-by: Thomas Lively <tlively@google.com>
aheejin
force-pushed
the
wasm_split_remove_opt
branch
from
August 17, 2026 23:38
e802ede to
485abf9
Compare
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
We have six mostly identical loops in
shareImportableItems, each for memories, tables, globals, tags, data segments, and element segments. This factors the core logic out as a generic lambda function.