Fix #2060: Add support for alternate code patterns in TransformDisplayClassUsage.ValidateConstructor

ICSharpCode.Decompiler/IL/Transforms/TransformDisplayClassUsage.cs

@@ -399,8 +399,19 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				// IL_0000: ldarg.0
 				// IL_0001: call instance void [mscorlib]System.Object::.ctor()
 				// IL_0006: ret
-				if (DecodeOpCodeSkipNop(ref reader) != ILOpCode.Ldarg_0)
-					return false;
+				var opCode = DecodeOpCodeSkipNop(ref reader);
+				switch (opCode) {
+					case ILOpCode.Ldarg:
+					case ILOpCode.Ldarg_s:
+						if (reader.DecodeIndex(opCode) != 0)
+							return false;
+						break;
+					case ILOpCode.Ldarg_0:
+						// OK
+						break;
+					default:
+						return false;
+				}
 				if (DecodeOpCodeSkipNop(ref reader) != ILOpCode.Call)
 					return false;
 				var baseCtorHandle = MetadataTokenHelpers.EntityHandleOrNil(reader.ReadInt32());