[6.0] Significantly improve performance of SyntaxVisitor #2552
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There are two core ideas here: - Before this change, we were allocating `Syntax.Info` for every visited node. We need a heap-allocated object here because `Syntax` can access its parent. In most cases, however, the syntax node was not stored by the visitor and we would just destroy the `Syntax.Info` after finishing the `visit` call. Instead, check if `Syntax.Info` is uniquely referenced, which means that the the node was not stored. In that case, don’t deallocate the memory but place it into a reuse pool. I have seen reductions in `malloc` calls from ~50,000 to ~100 (500x) in `testEmptyVisitorPerformance`. - Now retain and release calls made up a significant portion of the visitor’s performance. Add some annotations to eliminate reference counting. I added comments for the remaining retain calls. I measured that this improves the performance of the `EmptyParametersRule` in SwiftLint by ~35% compared to `509.0.0` (and by ~50% compared to `510.0.0`). Fixes swiftlang#2091 rdar://114330163
This gets us another ~3% performance improvement in SwiftLint listing time.
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@swift-ci Please test |
bnbarham
approved these changes
Mar 20, 2024
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SyntaxVisitorby minimizing the number of memory allocations we need to perform, resulting in a ~35% performance improvement inEmptyParametersRuleof SwiftLint compared to509.0.0(and by ~50% compared to510.0.0).SyntaxVisitorSwiftLintandtestEmptyVisitorPerformanceand verified on the SIL level that we do a minimal amount of ref-counting