Avoid decoding all SuppressMessageAttributes up front by 333fred · Pull Request #83087 · dotnet/roslyn

333fred · 2026-04-07T20:44:27Z

Currently, when requesting whether any attribute suppresses a specific diagnostic, we will eagerly decode all SuppressMessageAttributes in the global context. This is potentially a lot of work unrelated to the diagnostic being queried, especially if the compilation then doesn't produce any of the diagnostic that then is resolved. To avoid this, we now only resolve symbols for suppressions of a specific diagnostic ID when that diagnostic ID is requested, and never otherwise. This improves perf of a 1st-party partner team's CI by ~5x.

Microsoft Reviewers: Open in CodeFlow

Currently, when requesting whether any attribute suppresses a specific diagnostic, we will eagerly decode all `SuppressMessageAttribute`s in the global context. This is potentially a lot of work unrelated to the diagnostic being queried, especially if the compilation then doesn't produce any of the diagnostic that then is resolved. To avoid this, we now only resolve symbols for suppressions of a specific diagnostic ID when that diagnostic ID is requested, and never otherwise. This improves perf of a 1st-party partner team's CI by ~5x.

333fred · 2026-04-07T20:49:33Z

@dotnet/roslyn-compiler for review

jjonescz · 2026-04-09T08:23:53Z

@@ -71,12 +59,13 @@ public void AddCompilationWideSuppression(SuppressMessageInfo info)
            public void AddGlobalSymbolSuppression(SuppressMessageInfo info, TargetScope scope)
            {
                Debug.Assert(!_lazyResolvedSuppressionsById.ContainsKey(info.Id));


nit: perhaps we could strengthen the assert and require the resolved suppression dictionary is empty while we construct the unresolved dictionary. #Resolved

333fred · 2026-04-13T17:17:57Z

@dotnet/roslyn-compiler for a second review

jcouv · 2026-04-19T17:37:40Z

Consider adding a test or referencing a test to illustrate the issue. That would make the issue being fixed clearer. Also, such a test could be used as benchmark, to show the impact of the PR.

jcouv · 2026-04-19T18:45:30Z

-            private readonly Dictionary<ISymbol, Dictionary<string, SuppressMessageInfo>> _globalSymbolSuppressions = new Dictionary<ISymbol, Dictionary<string, SuppressMessageInfo>>();
+            // Keep targeted suppressions grouped by diagnostic ID so we only resolve target symbols
+            // for IDs that are actually queried.
+            private readonly Dictionary<string, List<(SuppressMessageInfo Info, TargetScope Scope)>> _unresolvedSuppressionsById = new Dictionary<string, List<(SuppressMessageInfo Info, TargetScope Scope)>>(StringComparer.Ordinal);


(SuppressMessageInfo Info, TargetScope Scope)

It feels like this could be simplified. The SuppressMessageInfo.Scope string is redundant with this TargetScope Scope. I'd be tempted to remove Scope here or store a TargetScope in SuppressMessageInfo (instead of string Scope), unless there's an observable effect on benchmark.
#Closed

jcouv

Done with review pass (commit 2)

…ture * upstream/main: (77 commits) Fix ArgumentNullException in VB Edit and Continue (dotnet#83250) Fix property pattern completion filtering out member being edited (dotnet#83230) Add branch merge skill (dotnet#83229) [main] Source code updates from dotnet/dotnet (dotnet#83215) Support MatchPriority comparison in LSP completion (dotnet#83164) Have CompleteStatement handle EOF statements (dotnet#83205) Minor cleanups related to attributes in VB (dotnet#83206) Simplify Address additional PR feedback Port remaining unit test projects to Linux (dotnet#83153) Unsafe evolution: allow unsafe property accessors (dotnet#83115) Address PR review feedback Allow cohost rename in Razor source-generated docs Refine code review skill (dotnet#82666) Review feedback Allow creation of DocumentUri instances even if System.Uri cannot parse it Improve TextLine and line table performance by packing existing data into unused bits (dotnet#83000) Skip TestFindReferencesAsync_UsingAlias on non-Windows platforms (dotnet#83188) [main] Source code updates from dotnet/dotnet (dotnet#83174) fix comment ...

333fred · 2026-04-21T17:35:05Z

@jcouv for another look please.

jcouv · 2026-04-21T20:06:38Z

+                var resolvedSuppressions = new Dictionary<ISymbol, SuppressMessageInfo>();
+                foreach (var info in suppressions)
+                {
+                    foreach (var target in ResolveTargetSymbols(_compilation, info.Target, info.Scope))


var

nit: type? Also on outer foreach

jcouv · 2026-04-21T20:09:47Z

                }

-                if (TryGetTargetScope(info, out TargetScope scope))
+                if (info.Scope != TargetScope.Invalid)


nit: consider inverting if to decrease nesting (if (invalid) { continue; } if (info is { Scope: ... } ) { continue; }

jcouv · 2026-04-21T20:11:29Z

Gentle ping on this comment

In reply to: 4276450884

jcouv

LGTM Thanks (commit 5) with minor comments to consider. I still think it would be good to include a targeted/stress test

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

333fred · 2026-04-22T22:36:23Z

@jcouv @jjonescz for review

jcouv

LGTM Thanks (commit 8)

333fred requested a review from a team as a code owner April 7, 2026 20:44

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jjonescz reviewed Apr 8, 2026

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jcouv self-assigned this Apr 19, 2026

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Comment thread src/Compilers/Core/Portable/DiagnosticAnalyzer/SuppressMessageAttributeState.cs

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Comment thread src/Compilers/Core/Portable/DiagnosticAnalyzer/SuppressMessageAttributeState.cs

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333fred added 3 commits April 20, 2026 13:08

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333fred and others added 3 commits April 22, 2026 15:16

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Add stress test for many unrelated SuppressMessageAttributes

58b6413

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Clean up added test

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jcouv approved these changes Apr 23, 2026

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Comment thread src/Compilers/CSharp/Test/EndToEnd/EndToEndTests.cs Outdated

Comment thread src/Analyzers/Core/Analyzers/RemoveUnnecessarySuppressions/SuppressMessageAttributeState.cs

jjonescz reviewed Apr 23, 2026

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Comment thread src/Compilers/Core/Portable/DiagnosticAnalyzer/SuppressMessageAttributeState.cs

Sort and clean usings

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333fred enabled auto-merge (squash) April 23, 2026 17:33

build-analysis Bot mentioned this pull request Apr 23, 2026

[Known Build Error] AssemblyLoading_MultipleVersions_AnalyzerDependency set difference #83286

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333fred merged commit f2f83b2 into dotnet:main Apr 23, 2026
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333fred deleted the suppression-restructure branch April 23, 2026 23:09

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[Automated] PRs inserted in VS build main-11724.104 #83340

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[main] Source code updates from dotnet/roslyn dotnet/dotnet#6291

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JoeRobich modified the milestones: Next, 18.7 Apr 28, 2026

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[release/10.0.3xx] Source code updates from dotnet/roslyn dotnet/dotnet#6340

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