Don't unnecessarily default-initialize variables prior to a call with out-parameter.

ICSharpCode.Decompiler/FlowAnalysis/DefiniteAssignmentVisitor.cs

@@ -183,7 +183,17 @@ namespace ICSharpCode.Decompiler.FlowAnalysis
 		
 		protected internal override void VisitLdLoca(LdLoca inst)
 		{
+			// A variable needs to be initialized before we can take it by reference.
+			// The exception is if the variable is passed to an out parameter.
+			if (!IsOutArgument(inst)) {
 				EnsureInitialized(inst.Variable);
 			}
 		}
+
+		static bool IsOutArgument(ILInstruction inst)
+		{
+			return inst.Parent is CallInstruction call
+				&& call.GetParameter(inst.ChildIndex)?.IsOut == true;
+		}
+	}
 }

ICSharpCode.Decompiler/IL/Instructions/CallInstruction.cs

@@ -65,6 +65,19 @@ namespace ICSharpCode.Decompiler.IL
 			this.Arguments = new InstructionCollection<ILInstruction>(this, 0);
 		}
 
+		/// <summary>
+		/// Gets the parameter for the argument with the specified index.
+		/// Returns null for the <c>this</c> parameter.
+		/// </summary>
+		public IParameter GetParameter(int argumentIndex)
+		{
+			int firstParamIndex = (Method.IsStatic || OpCode == OpCode.NewObj) ? 0 : 1;
+			if (argumentIndex < firstParamIndex) {
+				return null; // asking for 'this' parameter
+			}
+			return Method.Parameters[argumentIndex - firstParamIndex];
+		}
+		
 		public override StackType ResultType {
 			get {
 				if (OpCode == OpCode.NewObj)

ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs

@@ -338,7 +338,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 							return CleanUpVariableName(m.Name.Substring(3));
 						}
 					}
-					var p = m.Parameters.ElementAtOrDefault((!(call is NewObj) && !m.IsStatic) ? i - 1 : i);
+					var p = call.GetParameter(i);
 					if (p != null && !string.IsNullOrEmpty(p.Name))
 						return CleanUpVariableName(p.Name);
 					break;