roslyn: Very slow IntelliSense on relatively small code base

I’m not sure which process should be looked into for this case, devenv or ServiceHub.RoslynCodeAnalysisService.

GetSymbolInfo is commonly showing up as expensive in both:

• ServiceHub.RoslynCodeAnalysisService: GetSymbolInfo is called by NameSyntaxClassifier.AddClassification
• devenv: GetSymbolInfo is called by CSharpSyntaxContext.CreateContext and CSharpTypeInferenceService+TypeInferrer.InferTypesWorker_DoNotCallDirectly.

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If I clear GroupPats and FoldPats (which I read somewhere, but I don’t understand what they actually do), I see GetUseSiteInfo starts showing up.