Move legacy type remapping code outside of AbstractMaterialGraph and cache the result in a static field

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Graphs/AbstractMaterialGraph.cs

             }
         }
 
-        Dictionary<SerializationHelper.TypeSerializationInfo, SerializationHelper.TypeSerializationInfo> GetLegacyTypeRemapping()
-        {
-            var result = new Dictionary<SerializationHelper.TypeSerializationInfo, SerializationHelper.TypeSerializationInfo>();
-            foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
-            {
-                foreach (var type in assembly.GetTypes())
-                {
-                    if (type.IsAbstract)
-                        continue;
-                    foreach (var attribute in type.GetCustomAttributes(typeof(LegacyAttribute), false))
-                    {
-                        var legacyAttribute = (LegacyAttribute)attribute;
-                        var serializationInfo = new SerializationHelper.TypeSerializationInfo { fullName = legacyAttribute.fullName };
-                        result[serializationInfo] = SerializationHelper.GetTypeSerializableAsString(type);
-                    }
-
-                }
-            }
-
-            return result;
-        }
-
         public void ReplaceWith(IGraph other)
         {
             var otherMg = other as AbstractMaterialGraph;
         {
             // have to deserialize 'globals' before nodes
             m_Properties = SerializationHelper.Deserialize<IShaderProperty>(m_SerializedProperties, null);
-            var nodes = SerializationHelper.Deserialize<INode>(m_SerializableNodes, GetLegacyTypeRemapping());
+            var nodes = SerializationHelper.Deserialize<INode>(m_SerializableNodes, GraphUtil.GetLegacyTypeRemapping());
             m_Nodes = new Dictionary<Guid, INode>(nodes.Count);
             foreach (var node in nodes)
             {

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Util/GraphUtil.cs

         {
             List<PropertyCollector.TextureInfo> configuredTextures;
             FloatShaderProperty outputIdProperty;
-            return graph.GetShader(node, GenerationMode.Preview, string.Format("hidden/preview/{0}", node.GetVariableNameForNode()), out configuredTextures, out previewMode, out outputIdProperty);
+            return graph.GetShader(node, GenerationMode.Preview, String.Format("hidden/preview/{0}", node.GetVariableNameForNode()), out configuredTextures, out previewMode, out outputIdProperty);
         }
 
         public static string GetUberPreviewShader(this AbstractMaterialGraph graph, Dictionary<Guid, int> ids, out FloatShaderProperty outputIdProperty)
             return graph.GetShader(null, GenerationMode.Preview, "hidden/preview", out configuredTextures, out previewMode, out outputIdProperty, ids);
+        }
+
+        static Dictionary<SerializationHelper.TypeSerializationInfo, SerializationHelper.TypeSerializationInfo> s_LegacyTypeRemapping;
+
+        public static Dictionary<SerializationHelper.TypeSerializationInfo, SerializationHelper.TypeSerializationInfo> GetLegacyTypeRemapping()
+        {
+            if (s_LegacyTypeRemapping == null)
+            {
+                s_LegacyTypeRemapping = new Dictionary<SerializationHelper.TypeSerializationInfo, SerializationHelper.TypeSerializationInfo>();
+                foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
+                {
+                    foreach (var type in assembly.GetTypes())
+                    {
+                        if (type.IsAbstract)
+                            continue;
+                        foreach (var attribute in type.GetCustomAttributes(typeof(LegacyAttribute), false))
+                        {
+                            var legacyAttribute = (LegacyAttribute)attribute;
+                            var serializationInfo = new SerializationHelper.TypeSerializationInfo { fullName = legacyAttribute.fullName };
+                            s_LegacyTypeRemapping[serializationInfo] = SerializationHelper.GetTypeSerializableAsString(type);
+                        }
+                    }
+                }
+            }
+
+            return s_LegacyTypeRemapping;
         }
     }
 }