Fixed 'as' and 'is' operators for value types.

ICSharpCode.Decompiler/Ast/AstMethodBodyBuilder.cs

@@ -447,7 +447,12 @@ namespace ICSharpCode.Decompiler.Ast
 					case ILCode.Conv_Ovf_I_Un:  return arg1.CastTo(typeof(IntPtr));
 					case ILCode.Conv_Ovf_U_Un:  return arg1.CastTo(typeof(UIntPtr));
 					case ILCode.Castclass:      return arg1.CastTo(operandAsTypeRef);
-					case ILCode.Unbox_Any:      return arg1.CastTo(operandAsTypeRef);
+				case ILCode.Unbox_Any:
+					// unboxing does not require a cast if the argument was an isinst instruction
+					if (arg1 is AsExpression && byteCode.Arguments[0].Code == ILCode.Isinst && TypeAnalysis.IsSameType(operand as TypeReference, byteCode.Arguments[0].Operand as TypeReference))
+						return arg1;
+					else
+						return arg1.CastTo(operandAsTypeRef);
 					case ILCode.Isinst:         return arg1.CastAs(operandAsTypeRef);
 					case ILCode.Box:            return arg1;
 					case ILCode.Unbox:          return InlineAssembly(byteCode, args);

ICSharpCode.Decompiler/ILAst/TypeAnalysis.cs

@@ -648,9 +648,15 @@ namespace ICSharpCode.Decompiler.ILAst
 				case ILCode.Conv_R_Un:
 					return (expectedType != null  && expectedType.MetadataType == MetadataType.Single) ? typeSystem.Single : typeSystem.Double;
 				case ILCode.Castclass:
-				case ILCode.Isinst:
 				case ILCode.Unbox_Any:
 					return (TypeReference)expr.Operand;
+				case ILCode.Isinst:
+					{
+						// isinst performs the equivalent of a cast only for reference types;
+						// value types still need to be unboxed after an isinst instruction
+						TypeReference tr = (TypeReference)expr.Operand;
+						return tr.IsValueType ? typeSystem.Object : tr;
+					}
 				case ILCode.Box:
 					if (forceInferChildren)
 						InferTypeForExpression(expr.Arguments.Single(), (TypeReference)expr.Operand);

ICSharpCode.Decompiler/Tests/ValueTypes.cs

@@ -111,4 +111,19 @@ public static class ValueTypes
 	{
 		ValueTypes.MakeArray()[Environment.TickCount]++;
 	}
+	
+	public static bool Is(object obj)
+	{
+		return obj is ValueTypes.S;
+	}
+	
+	public static bool IsNullable(object obj)
+	{
+		return obj is ValueTypes.S?;
+	}
+	
+	public static ValueTypes.S? As(object obj)
+	{
+		return obj as ValueTypes.S?;
+	}
 }