From 5459d6b022087d417f149ec7d67cbb2823d23251 Mon Sep 17 00:00:00 2001
From: Siegfried Pammer <siegfriedpammer@gmail.com>
Date: Sat, 18 Jul 2020 16:55:52 +0200
Subject: [PATCH] #2064: Improve performance of RequiredNamespaceCollector by
 skipping repeated IType.GetAllBaseTypes() calls.

---
 ICSharpCode.Decompiler/CSharp/RequiredNamespaceCollector.cs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/ICSharpCode.Decompiler/CSharp/RequiredNamespaceCollector.cs b/ICSharpCode.Decompiler/CSharp/RequiredNamespaceCollector.cs
index 8e7922292..878edf8fe 100644
--- a/ICSharpCode.Decompiler/CSharp/RequiredNamespaceCollector.cs
+++ b/ICSharpCode.Decompiler/CSharp/RequiredNamespaceCollector.cs
@@ -17,6 +17,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		static readonly Decompiler.TypeSystem.GenericContext genericContext = default;
 
 		readonly HashSet<string> namespaces;
+		readonly HashSet<IType> visitedTypes = new HashSet<IType>();
 
 		public RequiredNamespaceCollector(HashSet<string> namespaces)
 		{
@@ -141,13 +142,15 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		void CollectNamespacesForTypeReference(IType type)
 		{
+			if (!visitedTypes.Add(type))
+				return;
 			switch (type) {
 				case ParameterizedType parameterizedType:
 					namespaces.Add(parameterizedType.Namespace);
 					CollectNamespacesForTypeReference(parameterizedType.GenericType);
 					foreach (var arg in parameterizedType.TypeArguments)
 						CollectNamespacesForTypeReference(arg);
-					break;
+					return; // no need to collect base types again
 				case TypeWithElementType typeWithElementType:
 					CollectNamespacesForTypeReference(typeWithElementType.ElementType);
 					break;