Reduce allocations obtaining classified spans in ClassifierHelper #79856
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ClassifiedSpan[] shows up as 0.7% of total allocations (in LOH) in the completion scenarios in the razor cohosting speedometer test. Surrounding code already uses a custom pool for ClassifiedSpan[] via Classifier.GetPooledList. This PR changes ClassifierHelper.GetClassifiedSpansAsync to take in a SegmentedList<ClassifiedSpan> to populate rather than returning an ImmutableArray<ClassifiedSpan>.
CyrusNajmabadi
approved these changes
Aug 8, 2025
| await AddClassifiedSpansAsync(classifiedSpans, document, [span], options, includeAdditiveSpans, cancellationToken) | ||
| .ConfigureAwait(false); | ||
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|
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| return [.. classifiedSpans]; |
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Should we push the pooling higher?
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I looked into this too, but it doesn't appear the callers to this particular method are high frequency callers (for at least the scenarios I tested). Because of that, I didn't push this change out to that level.
ToddGrun
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CyrusNajmabadi
approved these changes
Aug 19, 2025
This was referenced Aug 29, 2025
JoeRobich
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Aug 29, 2025
46 PRs before and 36 after ```diff + * [Cache diagnostic analyzer computation](dotnet/roslyn#80045) + * [Remove parameter always passed the same value](dotnet/roslyn#80042) * [Update doc for IMethodSymbol.IsExtensionMethod](dotnet/roslyn#80016) * [Don't cache known-broken compositions](dotnet/roslyn#80021) * [Cleanup methods in DiagAnalyzerService](dotnet/roslyn#80013) * [Simplify processing of errors reported by the build](dotnet/roslyn#79964) * [Additional cleanup of the DiagnosticAnalyzerServier](dotnet/roslyn#80005) * [Fix Code Lens around source generated files](dotnet/roslyn#79992) * [Remove superflous DiagService api that can be achieved with existing apis](dotnet/roslyn#80007) * [Generate `init` accessor for required properties inside `readonly struct`s](dotnet/roslyn#80004) * [Remove existing low level diag oop code now that it's all handled at higher levels.](dotnet/roslyn#79994) * [Allow large InlineHint ArrayBuilder pooling](dotnet/roslyn#79857) * [Reduce allocations obtaining classified spans in ClassifierHelper](dotnet/roslyn#79856) * [Compute span diagnostics in oop](dotnet/roslyn#79991) * [Allow Razor cohosting to work with non-Razor SDK projects](dotnet/roslyn#79953) * [Move computation of deprioritized analyzers to oop](dotnet/roslyn#79989) * [EnC: Fix symbol mapping of delegates with indexed name](dotnet/roslyn#79837) * [Emit telemetry 'durations' with known radix point '.'](dotnet/roslyn#79988) * [Move logic up into DiagService](dotnet/roslyn#79985) * [Move the StateManager type up to the DiagnosticService from the DiagnosticIncrementalANalyzer](dotnet/roslyn#79984) * [Immediately remote diagnostics call to OOP](dotnet/roslyn#79983) * [Build Microsoft.CodeAnalysis.SemanticSearch.Extension ref assembly for use in semantic search queries](dotnet/roslyn#79972) * [Only cache compilation if we have the same set of analyzers](dotnet/roslyn#79978) * [Delete unused property](dotnet/roslyn#79963) * [Update 'use expr body' to be a purely syntactic analyzer](dotnet/roslyn#79979) * [Mark 'Use expr body' as a syntax-only fixer](dotnet/roslyn#79971) * [♻️ MSBuildWorkspaceDirectory - Fallback to AppContext.BaseDirectory when Assembly Location is empty](dotnet/roslyn#79934) * [Merge runtime async support into main](dotnet/roslyn#79833) * [Implement "Simplify property accessor" feature](dotnet/roslyn#79754) - * Merge main to runtime async branch (PR: [#79961](dotnet/roslyn#79961)) * [Redo how and when we report source generator telemetry](dotnet/roslyn#79951) * [Allow MEF components to supply assembly path resolvers](dotnet/roslyn#79218) * [Allow Razor to hook up the source generator in misc files](dotnet/roslyn#79891) * [Block ENC for extension blocks](dotnet/roslyn#79883) * [Upgrade servicehub.client to fix test source discovery](dotnet/roslyn#79899) * [Update package restore error message.](dotnet/roslyn#79876) - * Merge main (PR: [#79834](dotnet/roslyn#79834)) - * Merge main (PR: [#79830](dotnet/roslyn#79830)) * [Baseline struct lifting tests](dotnet/roslyn#79505) - * Merge main to runtime async branch (PR: [#79582](dotnet/roslyn#79582)) - * Merge main (PR: [#79424](dotnet/roslyn#79424)) - * Merge main (PR: [#78994](dotnet/roslyn#78994)) - * Merge main to runtime async branch (PR: [#78740](dotnet/roslyn#78740)) - * Merge main to runtime async branch (PR: [#78517](dotnet/roslyn#78517)) - * Merge main to runtime async branch (PR: [#78114](dotnet/roslyn#78114)) - * Merge main to runtime async branch (PR: [#77700](dotnet/roslyn#77700)) - * Merge main to runtime async branch (PR: [#77533](dotnet/roslyn#77533)) - * Merge main to runtime async branch (PR: [#77265](dotnet/roslyn#77265)) ```
This was referenced Sep 8, 2025
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ClassifiedSpan[] shows up as 0.7% of total allocations (in LOH) in the completion scenarios in the razor cohosting speedometer test.
Surrounding code already uses a custom pool for ClassifiedSpan[] via Classifier.GetPooledList. This PR changes ClassifierHelper.GetClassifiedSpansAsync to take in a SegmentedList to populate rather than returning an ImmutableArray.
Test insertion: https://dev.azure.com/devdiv/DevDiv/_git/VS/pullrequest/662555
Speedometer results with this change look good, reduced to around 1.5 MB of allocations from the 37 MB before.