Optimize scope identifiers transformer performance#1417
Open
filipsobol wants to merge 1 commit into
Open
Conversation
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
1 participant
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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
Summary
Optimize identifier renaming performance for large function scopes.
This code change is AI-generated, but the performance improvement was manually verified with an isolated benchmark.
Details
The slowdown appears when a large bundle is wrapped in a UMD factory function. In that shape, most declarations become local variables of one huge function scope.
The same code in ESM form did not show the issue because top-level declarations remain global and are skipped when
renameGlobalsis disabled.The previous implementation could rescan the same lexical scope repeatedly while checking whether
vardeclarations are used by shorthand destructuring assignments. This change caches the relevant destructuring-assignment names per lexical scope, so the scope is scanned once.No output behavior is intended to change.
Performance
Measured on identical, already-prepared input:
7.92s74.51s8.24s7.53s