[xbuild] Fix bug #676671. Raise AnyEvent .
[mono.git] / mcs / mcs / convert.cs
index 541e92098fec44513d44b9ab04276b6af9caa764..3780fac1b7ba8201e52257103421d54a51abfb6b 100644 (file)
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
-using System.Reflection;
+
+#if STATIC
+using IKVM.Reflection.Emit;
+#else
 using System.Reflection.Emit;
+#endif
 
 namespace Mono.CSharp {
 
@@ -24,8 +27,6 @@ namespace Mono.CSharp {
        static class Convert {
                
                static EmptyExpression MyEmptyExpr;
-               static DoubleHash explicit_conv;
-               static DoubleHash implicit_conv;
                
                static Convert ()
                {
@@ -35,8 +36,6 @@ namespace Mono.CSharp {
                public static void Reset ()
                {
                        MyEmptyExpr = null;
-                       explicit_conv = new DoubleHash (100);
-                       implicit_conv = new DoubleHash (100);
                }
                
                //
@@ -93,43 +92,58 @@ namespace Mono.CSharp {
                        return ImplicitReferenceConversionExists (MyEmptyExpr, arg_type) || ExplicitReferenceConversionExists (array.Element, arg_type);
                }
 
-               static Expression ImplicitTypeParameterConversion (Expression expr, TypeSpec target_type)
+               public static Expression ImplicitTypeParameterConversion (Expression expr, TypeSpec target_type)
                {
                        var expr_type = (TypeParameterSpec) expr.Type;
+
                        //
-                       // From T to a type parameter U
+                       // From T to a type parameter U, provided T depends on U
                        //
                        var ttype = target_type as TypeParameterSpec;
                        if (ttype != null) {
-                               if (expr_type.IsReferenceType && !ttype.IsReferenceType)
-                                       return new BoxedCast (expr, target_type);
+                               if (expr_type.TypeArguments != null) {
+                                       foreach (var targ in expr_type.TypeArguments) {
+                                               if (!TypeSpecComparer.Override.IsEqual (ttype, targ))
+                                                       continue;
+
+                                               if (expr_type.IsReferenceType && !ttype.IsReferenceType)
+                                                       return new BoxedCast (expr, target_type);
+
+                                               return new ClassCast (expr, target_type);
+                                       }
+                               }
+
+                               return null;
+                       }
+
+                       //
+                       // LAMESPEC: From T to dynamic type because it's like T to object
+                       //
+                       if (target_type == InternalType.Dynamic) {
+                               if (expr_type.IsReferenceType)
+                                       return new ClassCast (expr, target_type);
 
-                               return new ClassCast (expr, target_type);
+                               return new BoxedCast (expr, target_type);
                        }
 
                        //
                        // From T to its effective base class C
-                       // From T to any base class of C
+                       // From T to any base class of C (it cannot contain dynamic of be of dynamic type)
                        // From T to any interface implemented by C
                        //
                        var base_type = expr_type.GetEffectiveBase ();
-                       if (base_type == target_type || TypeManager.IsSubclassOf (base_type, target_type) || base_type.ImplementsInterface (target_type)) {
+                       if (base_type == target_type || TypeSpec.IsBaseClass (base_type, target_type, false) || base_type.ImplementsInterface (target_type, true)) {
                                if (expr_type.IsReferenceType)
                                        return new ClassCast (expr, target_type);
 
                                return new BoxedCast (expr, target_type);
                        }
 
-                       var effective_ifaces = expr_type.Interfaces;
-                       if (effective_ifaces != null) {
-                               foreach (var t in effective_ifaces) {
-                                       if (t == target_type || t.ImplementsInterface (target_type)) {
-                                               if (expr_type.IsReferenceType)
-                                                       return new ClassCast (expr, target_type);
+                       if (target_type.IsInterface && expr_type.IsConvertibleToInterface (target_type)) {
+                               if (expr_type.IsReferenceType)
+                                       return new ClassCast (expr, target_type);
 
-                                               return new BoxedCast (expr, target_type);
-                                       }
-                               }
+                               return new BoxedCast (expr, target_type);
                        }
 
                        return null;
@@ -139,6 +153,15 @@ namespace Mono.CSharp {
                {
                        var target_tp = target_type as TypeParameterSpec;
                        if (target_tp != null) {
+                               if (target_tp.TypeArguments != null) {
+                                       foreach (var targ in target_tp.TypeArguments) {
+                                               if (!TypeSpecComparer.Override.IsEqual (source_type, targ))
+                                                       continue;
+
+                                               return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
+                                       }
+                               }
+/*
                                if (target_tp.Interfaces != null) {
                                        foreach (TypeSpec iface in target_tp.Interfaces) {
                                                if (!TypeManager.IsGenericParameter (iface))
@@ -148,7 +171,7 @@ namespace Mono.CSharp {
                                                        return source == null ? EmptyExpression.Null : new ClassCast (source, target_type, true);
                                        }
                                }
-
+*/
                                return null;
                        }
 
@@ -158,7 +181,7 @@ namespace Mono.CSharp {
                        return null;
                }
 
-               static Expression ImplicitReferenceConversion (Expression expr, TypeSpec target_type, bool explicit_cast)
+               public static Expression ImplicitReferenceConversion (Expression expr, TypeSpec target_type, bool explicit_cast)
                {
                        TypeSpec expr_type = expr.Type;
 
@@ -168,9 +191,6 @@ namespace Mono.CSharp {
                                expr.Emit (null);
                        }
 
-                       if (expr_type == TypeManager.void_type)
-                               return null;
-
                        if (expr_type.Kind == MemberKind.TypeParameter)
                                return ImplicitTypeParameterConversion (expr, target_type);
 
@@ -179,7 +199,7 @@ namespace Mono.CSharp {
                        //
                        NullLiteral nl = expr as NullLiteral;
                        if (nl != null) {
-                               return nl.ConvertImplicitly (null, target_type);
+                               return nl.ConvertImplicitly (target_type);
                        }
 
                        if (ImplicitReferenceConversionExists (expr, target_type)) {
@@ -192,15 +212,7 @@ namespace Mono.CSharp {
                                return EmptyCast.Create (expr, target_type);
                        }
 
-                       bool use_class_cast;
-                       if (ImplicitBoxingConversionExists (expr, target_type, out use_class_cast)) {
-                               if (use_class_cast)
-                                       return new ClassCast (expr, target_type);
-                               else
-                                       return new BoxedCast (expr, target_type);
-                       }
-
-                       return null;
+                       return ImplicitBoxingConversion (expr, expr_type, target_type);
                }
 
                //
@@ -214,7 +226,7 @@ namespace Mono.CSharp {
                        TypeSpec expr_type = expr.Type;
 
                        // from the null type to any reference-type.
-                       if (expr_type == TypeManager.null_type)
+                       if (expr_type == InternalType.Null)
                                return target_type != InternalType.AnonymousMethod;
 
                        if (TypeManager.IsGenericParameter (expr_type))
@@ -227,48 +239,31 @@ namespace Mono.CSharp {
 
                        // from any class-type S to any interface-type T.
                        if (target_type.IsInterface) {
-                               if (expr_type.ImplementsInterface (target_type)){
+                               if (expr_type.ImplementsInterface (target_type, true)){
                                        return !TypeManager.IsValueType (expr_type);
                                }
                        }
 
                        //
-                       // notice that it is possible to write "ValueType v = 1", the ValueType here
-                       // is an abstract class, and not really a value type, so we apply the same rules.
+                       // Implicit reference conversions (no-boxing) to object or dynamic
                        //
-                       if (target_type == TypeManager.object_type || target_type == InternalType.Dynamic) {
-                               //
-                               // A pointer type cannot be converted to object
-                               //
-                               if (expr_type.IsPointer)
-                                       return false;
-
-                               if (TypeManager.IsValueType (expr_type))
-                                       return false;
-
-                               if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type || expr_type.IsDelegate) {
-                                       // No mcs internal types are convertible
-                                       return true; // expr_type.MetaInfo.Module != typeof (Convert).Module;
+                       if (target_type.BuildinType == BuildinTypeSpec.Type.Object || target_type.BuildinType == BuildinTypeSpec.Type.Dynamic) {
+                               switch (expr_type.Kind) {
+                               case MemberKind.Class:
+                               case MemberKind.Interface:
+                               case MemberKind.Delegate:
+                               case MemberKind.ArrayType:
+                                       return true;
                                }
 
-                               // From anything to dynamic
-                               if (target_type == InternalType.Dynamic)
-                                       return true;
+                               return expr_type == InternalType.Dynamic;
+                       }
 
-                               // From dynamic to object
-                               if (expr_type == InternalType.Dynamic)
-                                       return true;
+                       if (target_type.BuildinType == BuildinTypeSpec.Type.ValueType)
+                               return expr_type.BuildinType == BuildinTypeSpec.Type.Enum;
 
-                               return false;
-                       } else if (target_type == TypeManager.value_type) {
-                               return expr_type == TypeManager.enum_type;
-                       } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
-                               //
-                               // Special case: enumeration to System.Enum.
-                               // System.Enum is not a value type, it is a class, so we need
-                               // a boxing conversion
-                               //
-                               if (target_type == TypeManager.enum_type || TypeManager.IsGenericParameter (expr_type))
+                       if (expr_type == target_type || TypeSpec.IsBaseClass (expr_type, target_type, true)) {
+                               if (TypeManager.IsGenericParameter (expr_type))
                                        return false;
 
                                if (TypeManager.IsValueType (expr_type))
@@ -307,7 +302,7 @@ namespace Mono.CSharp {
                                }
 
                                // from an array-type to System.Array
-                               if (target_type == TypeManager.array_type)
+                               if (target_type.BuildinType == BuildinTypeSpec.Type.Array)
                                        return true;
 
                                // from an array-type of type T to IList<T>
@@ -317,12 +312,15 @@ namespace Mono.CSharp {
                                return false;
                        }
 
+                       if (TypeSpecComparer.IsEqual (expr_type, target_type))
+                               return true;
+
                        if (TypeSpecComparer.Variant.IsEqual (expr_type, target_type))
                                return true;
 
                        // from any interface type S to interface-type T.
                        if (expr_type.IsInterface && target_type.IsInterface) {
-                               return expr_type.ImplementsInterface (target_type);
+                               return expr_type.ImplementsInterface (target_type, true);
                        }
 
                        // from any delegate type to System.Delegate
@@ -330,58 +328,73 @@ namespace Mono.CSharp {
                                (expr_type == TypeManager.delegate_type || expr_type.IsDelegate))
                                return true;
 
-                       if (TypeManager.IsEqual (expr_type, target_type))
-                               return true;
-
                        return false;
                }
 
-               public static bool ImplicitBoxingConversionExists (Expression expr, TypeSpec target_type,
-                                                                  out bool use_class_cast)
+               public static Expression ImplicitBoxingConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
                {
-                       TypeSpec expr_type = expr.Type;
-                       use_class_cast = false;
-                       
+                       switch (target_type.BuildinType) {
                        //
                        // From any value-type to the type object.
                        //
-                       if (target_type == TypeManager.object_type || target_type == InternalType.Dynamic) {
+                       case BuildinTypeSpec.Type.Object:
+                       case BuildinTypeSpec.Type.Dynamic:
                                //
                                // A pointer type cannot be converted to object
                                //
                                if (expr_type.IsPointer)
-                                       return false;
+                                       return null;
+
+                               if (!TypeManager.IsValueType (expr_type))
+                                       return null;
+
+                               return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 
-                               return TypeManager.IsValueType (expr_type);
-                       }
-                       
                        //
                        // From any value-type to the type System.ValueType.
                        //
-                       if (target_type == TypeManager.value_type)
-                               return TypeManager.IsValueType (expr_type);
+                       case BuildinTypeSpec.Type.ValueType:
+                               if (!TypeManager.IsValueType (expr_type))
+                                       return null;
 
-                       if (target_type == TypeManager.enum_type) {
+                               return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
+
+                       case BuildinTypeSpec.Type.Enum:
                                //
                                // From any enum-type to the type System.Enum.
                                //
                                if (TypeManager.IsEnumType (expr_type))
-                                       return true;
-                               //
-                               // From any nullable-type with an underlying enum-type to the type System.Enum
-                               //
-                               if (TypeManager.IsNullableType (expr_type))
-                                       return TypeManager.IsEnumType (Nullable.NullableInfo.GetUnderlyingType (expr_type));
+                                       return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
+
+                               break;
                        }
 
-                       if (TypeManager.IsSubclassOf (expr_type, target_type)) {
+                       //
+                       // From a nullable-type to a reference type, if a boxing conversion exists from
+                       // the underlying type to the reference type
+                       //
+                       if (TypeManager.IsNullableType (expr_type)) {
+                               if (!TypeManager.IsReferenceType (target_type))
+                                       return null;
+
+                               var res = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
+
+                               // "cast" underlying type to target type to emit correct InvalidCastException when
+                               // underlying hierarchy changes without recompilation
+                               if (res != null && expr != null)
+                                       res = new UnboxCast (res, target_type);
+
+                               return res;
+                       }
+
+                       if (TypeSpec.IsBaseClass (expr_type, target_type, false)) {
                                //
                                // Don't box same type arguments
                                //
                                if (TypeManager.IsGenericParameter (expr_type) && expr_type != target_type)
-                                       return true;
+                                       return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
 
-                               return false;
+                               return null;
                        }
 
                        // This code is kind of mirrored inside ImplicitStandardConversionExists
@@ -391,18 +404,13 @@ namespace Mono.CSharp {
 
                        // from any class-type S to any interface-type T.
                        if (target_type.IsInterface) {
-                               if (expr_type.ImplementsInterface (target_type))
-                                       return TypeManager.IsGenericParameter (expr_type) ||
-                                               TypeManager.IsValueType (expr_type);
-                       }
-
-                       if (TypeManager.IsGenericParameter (expr_type)) {
-                               return ImplicitTypeParameterConversion (expr, target_type) != null;
-//                             return ImplicitTypeParameterBoxingConversion (
-//                                     expr_type, target_type, out use_class_cast);
+                               if (expr_type.ImplementsInterface (target_type, true) &&
+                                       (TypeManager.IsGenericParameter (expr_type) || TypeManager.IsValueType (expr_type))) {
+                                       return expr == null ? EmptyExpression.Null : new BoxedCast (expr, target_type);
+                               }
                        }
 
-                       return false;
+                       return null;
                }
 
                public static Expression ImplicitNulableConversion (ResolveContext ec, Expression expr, TypeSpec target_type)
@@ -412,26 +420,29 @@ namespace Mono.CSharp {
                        //
                        // From null to any nullable type
                        //
-                       if (expr_type == TypeManager.null_type)
+                       if (expr_type == InternalType.Null)
                                return ec == null ? EmptyExpression.Null : Nullable.LiftedNull.Create (target_type, expr.Location);
 
                        // S -> T?
-                       TypeSpec t_el = TypeManager.GetTypeArguments (target_type)[0];
+                       TypeSpec t_el = Nullable.NullableInfo.GetUnderlyingType (target_type);
 
                        // S? -> T?
                        if (TypeManager.IsNullableType (expr_type))
-                               expr_type = TypeManager.GetTypeArguments (expr_type)[0];
+                               expr_type = Nullable.NullableInfo.GetUnderlyingType (expr_type);
 
                        //
                        // Predefined implicit identity or implicit numeric conversion
                        // has to exist between underlying type S and underlying type T
                        //
 
-                       // Handles probing
+                       // conversion exists only mode
                        if (ec == null) {
-                               if (expr_type == t_el)
+                               if (TypeSpecComparer.IsEqual (expr_type, t_el))
                                        return EmptyExpression.Null;
 
+                               if (expr is Constant)
+                                       return ((Constant) expr).ConvertImplicitly (t_el);
+
                                return ImplicitNumericConversion (null, expr_type, t_el);
                        }
 
@@ -441,17 +452,20 @@ namespace Mono.CSharp {
                        else
                                unwrap = expr;
 
-                       Expression conv = expr_type == t_el ? unwrap : ImplicitNumericConversion (unwrap, expr_type, t_el);
-                       if (conv == null)
-                               return null;
+                       Expression conv = unwrap;
+                       if (!TypeSpecComparer.IsEqual (expr_type, t_el)) {
+                               if (conv is Constant)
+                                       conv = ((Constant)conv).ConvertImplicitly (t_el);
+                               else
+                                       conv = ImplicitNumericConversion (conv, expr_type, t_el);
 
+                               if (conv == null)
+                                       return null;
+                       }
+                       
                        if (expr_type != expr.Type)
                                return new Nullable.Lifted (conv, unwrap, target_type).Resolve (ec);
 
-                       // Do constant optimization for S -> T?
-                       if (unwrap is Constant)
-                               conv = ((Constant) unwrap).ConvertImplicitly (ec, t_el);
-
                        return Nullable.Wrap.Create (conv, target_type);
                }
 
@@ -468,143 +482,172 @@ namespace Mono.CSharp {
 
                static Expression ImplicitNumericConversion (Expression expr, TypeSpec expr_type, TypeSpec target_type)
                {
-                       if (expr_type == TypeManager.sbyte_type){
+                       switch (expr_type.BuildinType) {
+                       case BuildinTypeSpec.Type.SByte:
                                //
                                // From sbyte to short, int, long, float, double, decimal
                                //
-                               if (target_type == TypeManager.int32_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.Int:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
-                               if (target_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
-                               if (target_type == TypeManager.double_type)
+                               case BuildinTypeSpec.Type.Double:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
-                               if (target_type == TypeManager.float_type)
+                               case BuildinTypeSpec.Type.Float:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
-                               if (target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
-                               if (target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Decimal:
                                        return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
-                       } else if (expr_type == TypeManager.byte_type){
+                               }
+
+                               break;
+                       case BuildinTypeSpec.Type.Byte:
                                //
                                // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
                                //
-                               if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type ||
-                                   target_type == TypeManager.short_type || target_type == TypeManager.ushort_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.Int:
+                               case BuildinTypeSpec.Type.UInt:
+                               case BuildinTypeSpec.Type.Short:
+                               case BuildinTypeSpec.Type.UShort:
                                        return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
-
-                               if (target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
-                               if (target_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
-                               if (target_type == TypeManager.float_type)
+                               case BuildinTypeSpec.Type.Float:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
-                               if (target_type == TypeManager.double_type)
+                               case BuildinTypeSpec.Type.Double:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
-                               if (target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Decimal:
                                        return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
-
-                       } else if (expr_type == TypeManager.short_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Short:
                                //
                                // From short to int, long, float, double, decimal
                                //
-                               if (target_type == TypeManager.int32_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.Int:
                                        return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
-                               if (target_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
-                               if (target_type == TypeManager.double_type)
+                               case BuildinTypeSpec.Type.Double:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
-                               if (target_type == TypeManager.float_type)
+                               case BuildinTypeSpec.Type.Float:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
-                               if (target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Decimal:
                                        return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
-
-                       } else if (expr_type == TypeManager.ushort_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.UShort:
                                //
                                // From ushort to int, uint, long, ulong, float, double, decimal
                                //
-                               if (target_type == TypeManager.int32_type || target_type == TypeManager.uint32_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.Int:
+                               case BuildinTypeSpec.Type.UInt:
                                        return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
-                               
-                               if (target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
-                               if (target_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
-                               if (target_type == TypeManager.double_type)
+                               case BuildinTypeSpec.Type.Double:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
-                               if (target_type == TypeManager.float_type)
+                               case BuildinTypeSpec.Type.Float:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
-                               if (target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Decimal:
                                        return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
-                       } else if (expr_type == TypeManager.int32_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Int:
                                //
                                // From int to long, float, double, decimal
                                //
-                               if (target_type == TypeManager.int64_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.Long:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
-                               if (target_type == TypeManager.double_type)
+                               case BuildinTypeSpec.Type.Double:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
-                               if (target_type == TypeManager.float_type)
+                               case BuildinTypeSpec.Type.Float:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
-                               if (target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Decimal:
                                        return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
-                       } else if (expr_type == TypeManager.uint32_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.UInt:
                                //
                                // From uint to long, ulong, float, double, decimal
                                //
-                               if (target_type == TypeManager.int64_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.Long:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
-                               if (target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
-                               if (target_type == TypeManager.double_type)
-                                       return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
-                               if (target_type == TypeManager.float_type)
-                                       return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R4);
-                               if (target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Double:
+                                       return expr == null ? EmptyExpression.Null : new OpcodeCastDuplex (expr, target_type, OpCodes.Conv_R_Un, OpCodes.Conv_R8);
+                               case BuildinTypeSpec.Type.Float:
+                                       return expr == null ? EmptyExpression.Null : new OpcodeCastDuplex (expr, target_type, OpCodes.Conv_R_Un, OpCodes.Conv_R4);
+                               case BuildinTypeSpec.Type.Decimal:
                                        return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
-                       } else if (expr_type == TypeManager.int64_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Long:
                                //
-                               // From long/ulong to float, double
+                               // From long to float, double, decimal
                                //
-                               if (target_type == TypeManager.double_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.Double:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
-                               if (target_type == TypeManager.float_type)
+                               case BuildinTypeSpec.Type.Float:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
-                               if (target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Decimal:
                                        return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
-                       } else if (expr_type == TypeManager.uint64_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.ULong:
                                //
-                               // From ulong to float, double
+                               // From ulong to float, double, decimal
                                //
-                               if (target_type == TypeManager.double_type)
-                                       return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R8);
-                               if (target_type == TypeManager.float_type)
-                                       return expr == null ? EmptyExpression.Null : new OpcodeCast (new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un), target_type, OpCodes.Conv_R4);
-                               if (target_type == TypeManager.decimal_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.Double:
+                                       return expr == null ? EmptyExpression.Null : new OpcodeCastDuplex (expr, target_type, OpCodes.Conv_R_Un, OpCodes.Conv_R8);
+                               case BuildinTypeSpec.Type.Float:
+                                       return expr == null ? EmptyExpression.Null : new OpcodeCastDuplex (expr, target_type, OpCodes.Conv_R_Un, OpCodes.Conv_R4);
+                               case BuildinTypeSpec.Type.Decimal:
                                        return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
-                       } else if (expr_type == TypeManager.char_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Char:
                                //
                                // From char to ushort, int, uint, long, ulong, float, double, decimal
                                //
-                               if ((target_type == TypeManager.ushort_type) ||
-                                   (target_type == TypeManager.int32_type) ||
-                                   (target_type == TypeManager.uint32_type))
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.UShort:
+                               case BuildinTypeSpec.Type.Int:
+                               case BuildinTypeSpec.Type.UInt:
                                        return expr == null ? EmptyExpression.Null : EmptyCast.Create (expr, target_type);
-                               if (target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
-                               if (target_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
-                               if (target_type == TypeManager.float_type)
+                               case BuildinTypeSpec.Type.Float:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
-                               if (target_type == TypeManager.double_type)
+                               case BuildinTypeSpec.Type.Double:
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
-                               if (target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Decimal:
                                        return expr == null ? EmptyExpression.Null : new CastToDecimal (expr);
-                       } else if (expr_type == TypeManager.float_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Float:
                                //
                                // float to double
                                //
                                if (target_type == TypeManager.double_type)
                                        return expr == null ? EmptyExpression.Null : new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
+                               break;
                        }
 
                        return null;
@@ -628,7 +671,7 @@ namespace Mono.CSharp {
                        }
                        
                        if (expr.eclass == ExprClass.MethodGroup) {
-                               if (target_type.IsDelegate && RootContext.Version != LanguageVersion.ISO_1) {
+                               if (target_type.IsDelegate && ec.Module.Compiler.Settings.Version != LanguageVersion.ISO_1) {
                                        MethodGroupExpr mg = expr as MethodGroupExpr;
                                        if (mg != null)
                                                return DelegateCreation.ImplicitStandardConversionExists (ec, mg, target_type);
@@ -644,24 +687,38 @@ namespace Mono.CSharp {
                ///  Determines if a standard implicit conversion exists from
                ///  expr_type to target_type
                ///
-               ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
                /// </summary>
                public static bool ImplicitStandardConversionExists (Expression expr, TypeSpec target_type)
                {
                        TypeSpec expr_type = expr.Type;
 
-                       if (expr_type == TypeManager.null_type) {
-                               NullLiteral nl = expr as NullLiteral;
-                               if (nl != null)
-                                       return nl.ConvertImplicitly (null, target_type) != null;
-                       }
-
-                       if (expr_type == TypeManager.void_type)
-                               return false;
+                       NullLiteral nl = expr as NullLiteral;
+                       if (nl != null)
+                               return nl.ConvertImplicitly (target_type) != null;
 
-                       if (TypeManager.IsEqual (expr_type, target_type))
+                       if (expr_type == target_type)
                                return true;
 
+                       // Implicit dynamic conversion
+                       if (expr_type == InternalType.Dynamic) {
+                               switch (target_type.Kind) {
+                               case MemberKind.ArrayType:
+                               case MemberKind.Class:
+                               case MemberKind.Struct:
+                               case MemberKind.Delegate:
+                               case MemberKind.Enum:
+                               case MemberKind.Interface:
+                               case MemberKind.TypeParameter:
+                                       return true;
+                               }
+
+                               // dynamic to __arglist
+                               if (target_type == InternalType.Arglist)
+                                       return true;
+
+                               return false;
+                       }
+
                        if (TypeManager.IsNullableType (target_type)) {
                                return ImplicitNulableConversion (null, expr, target_type) != null;
                        }
@@ -673,32 +730,36 @@ namespace Mono.CSharp {
                        if (ImplicitReferenceConversionExists (expr, target_type))
                                return true;
 
-                       bool use_class_cast;
-                       if (ImplicitBoxingConversionExists (expr, target_type, out use_class_cast))
+                       if (ImplicitBoxingConversion (null, expr_type, target_type) != null)
                                return true;
-
+                       
                        //
                        // Implicit Constant Expression Conversions
                        //
                        if (expr is IntConstant){
                                int value = ((IntConstant) expr).Value;
-
-                               if (target_type == TypeManager.sbyte_type){
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        if (value >= SByte.MinValue && value <= SByte.MaxValue)
                                                return true;
-                               } else if (target_type == TypeManager.byte_type){
+                                       break;
+                               case BuildinTypeSpec.Type.Byte:
                                        if (value >= 0 && value <= Byte.MaxValue)
                                                return true;
-                               } else if (target_type == TypeManager.short_type){
+                                       break;
+                               case BuildinTypeSpec.Type.Short:
                                        if (value >= Int16.MinValue && value <= Int16.MaxValue)
                                                return true;
-                               } else if (target_type == TypeManager.ushort_type){
+                                       break;
+                               case BuildinTypeSpec.Type.UShort:
                                        if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
                                                return true;
-                               } else if (target_type == TypeManager.uint32_type){
+                                       break;
+                               case BuildinTypeSpec.Type.UInt:
                                        if (value >= 0)
                                                return true;
-                               } else if (target_type == TypeManager.uint64_type){
+                                       break;
+                               case BuildinTypeSpec.Type.ULong:
                                         //
                                         // we can optimize this case: a positive int32
                                         // always fits on a uint64.  But we need an opcode
@@ -706,13 +767,12 @@ namespace Mono.CSharp {
                                         //
                                        if (value >= 0)
                                                return true;
-                               }
 
-                               if (value == 0 && target_type.IsEnum)
-                                       return true;
+                                       break;
+                               }
                        }
 
-                       if (expr is LongConstant && target_type == TypeManager.uint64_type){
+                       if (expr is LongConstant && target_type.BuildinType == BuildinTypeSpec.Type.ULong){
                                //
                                // Try the implicit constant expression conversion
                                // from long to ulong, instead of a nice routine,
@@ -723,20 +783,35 @@ namespace Mono.CSharp {
                                        return true;
                        }
 
+                       if (expr is IntegralConstant && TypeManager.IsEnumType (target_type)) {
+                               var i = (IntegralConstant) expr;
+                               //
+                               // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
+                               //
+                               // An implicit enumeration conversion permits the decimal-integer-literal 0
+                               // to be converted to any enum-type and to any nullable-type whose underlying
+                               // type is an enum-type
+                               //
+                               return i.IsZeroInteger;
+                       }
+
                        //
                        // If `expr_type' implements `target_type' (which is an iface)
                        // see TryImplicitIntConversion
                        //
-                       if (target_type.IsInterface && expr_type.ImplementsInterface (target_type))
+                       if (target_type.IsInterface && expr_type.ImplementsInterface (target_type, true))
                                return true;
 
-                       if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
+                       if (target_type.IsPointer && expr_type.IsPointer && ((PointerContainer) target_type).Element.Kind == MemberKind.Void)
                                return true;
 
                        // Conversion from __arglist to System.ArgIterator
                        if (expr_type == InternalType.Arglist)
                                return target_type == TypeManager.arg_iterator_type;
 
+                       if (TypeSpecComparer.IsEqual (expr_type, target_type))
+                               return true;
+
                        return false;
                }
 
@@ -817,27 +892,25 @@ namespace Mono.CSharp {
                        return best;
                }
 
-               /// <summary>
-               ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
-               ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
-               ///   for explicit and implicit conversion operators.
-               /// </summary>
-               static public TypeSpec FindMostSpecificSource (IList<MethodSpec> list,
-                                                          Expression source, bool apply_explicit_conv_rules)
+               //
+               // Finds the most specific source Sx according to the rules of the spec (13.4.4)
+               // by making use of FindMostEncomp* methods. Applies the correct rules separately
+               // for explicit and implicit conversion operators.
+               //
+               static TypeSpec FindMostSpecificSource (List<MethodSpec> list, TypeSpec sourceType, Expression source, bool apply_explicit_conv_rules)
                {
-                       var src_types_set = new List<TypeSpec> ();
+                       var src_types_set = new TypeSpec [list.Count];
 
                        //
-                       // If any operator converts from S then Sx = S
+                       // Try exact match first, if any operator converts from S then Sx = S
                        //
-                       TypeSpec source_type = source.Type;
-                       foreach (var mb in list){
-                               TypeSpec param_type = mb.Parameters.Types [0];
+                       for (int i = 0; i < src_types_set.Length; ++i) {
+                               TypeSpec param_type = list [i].Parameters.Types [0];
 
-                               if (param_type == source_type)
+                               if (param_type == sourceType)
                                        return param_type;
 
-                               src_types_set.Add (param_type);
+                               src_types_set [i] = param_type;
                        }
 
                        //
@@ -916,241 +989,251 @@ namespace Mono.CSharp {
                /// <summary>
                ///  User-defined Implicit conversions
                /// </summary>
-               static public Expression ImplicitUserConversion (ResolveContext ec, Expression source,
-                                                                TypeSpec target, Location loc)
+               static public Expression ImplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
                {
-                       return UserDefinedConversion (ec, source, target, loc, false, true);
+                       return UserDefinedConversion (ec, source, target, true, loc);
                }
 
                /// <summary>
                ///  User-defined Explicit conversions
                /// </summary>
-               static Expression ExplicitUserConversion (ResolveContext ec, Expression source,
-                                                                TypeSpec target, Location loc)
+               static Expression ExplicitUserConversion (ResolveContext ec, Expression source, TypeSpec target, Location loc)
                {
-                       return UserDefinedConversion (ec, source, target, loc, true, true);
+                       return UserDefinedConversion (ec, source, target, false, loc);
                }
 
-               static void AddConversionOperators (List<MethodSpec> list,
-                                                   Expression source, TypeSpec target_type,
-                                                   bool look_for_explicit,
-                                                   MethodGroupExpr mg)
+               static void FindApplicableUserDefinedConversionOperators (IList<MemberSpec> operators, Expression source, TypeSpec target, bool implicitOnly, ref List<MethodSpec> candidates)
                {
-                       if (mg == null)
-                               return;
-
-                       TypeSpec source_type = source.Type;
-                       EmptyExpression expr = EmptyExpression.Grab ();
-
                        //
                        // LAMESPEC: Undocumented IntPtr/UIntPtr conversions
                        // IntPtr -> uint uses int
                        // UIntPtr -> long uses ulong
                        //
-                       if (source_type == TypeManager.intptr_type) {
-                               if (target_type == TypeManager.uint32_type)
-                                       target_type = TypeManager.int32_type;
-                       } else if (source_type == TypeManager.uintptr_type) {
-                               if (target_type == TypeManager.int64_type)
-                                       target_type = TypeManager.uint64_type;
+                       if (source.Type.BuildinType == BuildinTypeSpec.Type.IntPtr) {
+                               if (target.BuildinType == BuildinTypeSpec.Type.UInt)
+                                       target = TypeManager.int32_type;
+                       } else if (source.Type.BuildinType == BuildinTypeSpec.Type.UIntPtr) {
+                               if (target.BuildinType == BuildinTypeSpec.Type.Long)
+                                       target = TypeManager.uint64_type;
+                       } else if (source.Type.IsInterface) {
+                               // Neither A nor B are interface-types
+                               return;
                        }
 
-                       foreach (MethodSpec m in mg.Methods) {
-                               AParametersCollection pd = m.Parameters;
-                               TypeSpec return_type = m.ReturnType;
-                               TypeSpec arg_type = pd.Types [0];
+                       // For a conversion operator to be applicable, it must be possible
+                       // to perform a standard conversion from the source type to
+                       // the operand type of the operator, and it must be possible
+                       // to perform a standard conversion from the result type of
+                       // the operator to the target type.
 
-                               if (source_type != arg_type) {
-                                       if (!ImplicitStandardConversionExists (source, arg_type)) {
-                                               if (!look_for_explicit)
-                                                       continue;
-                                               expr.SetType (arg_type);
-                                               if (!ImplicitStandardConversionExists (expr, source_type))
-                                                       continue;
-                                       }
+                       Expression texpr = null;
+
+                       foreach (MethodSpec op in operators) {
+                               
+                               // Can be null because MemberCache.GetUserOperator does not resize the array
+                               if (op == null)
+                                       continue;
+
+                               var t = op.Parameters.Types[0];
+                               if (source.Type != t && !ImplicitStandardConversionExists (source, t)) {
+                                       if (implicitOnly)
+                                               continue;
+
+                                       if (!ImplicitStandardConversionExists (new EmptyExpression (t), source.Type))
+                                               continue;
                                }
 
-                               if (target_type != return_type) {
-                                       expr.SetType (return_type);
-                                       if (!ImplicitStandardConversionExists (expr, target_type)) {
-                                               if (!look_for_explicit)
+                               t = op.ReturnType;
+
+                               // LAMESPEC: Exclude UIntPtr -> int conversion
+                               if (t.BuildinType == BuildinTypeSpec.Type.UInt && source.Type.BuildinType == BuildinTypeSpec.Type.UIntPtr)
+                                       continue;
+
+                               if (t.IsInterface)
+                                       continue;
+
+                               if (target != t) {
+                                       if (TypeManager.IsNullableType (t))
+                                               t = Nullable.NullableInfo.GetUnderlyingType (t);
+
+                                       if (!ImplicitStandardConversionExists (new EmptyExpression (t), target)) {
+                                               if (implicitOnly)
                                                        continue;
-                                               expr.SetType (target_type);
-                                               if (!ImplicitStandardConversionExists (expr, return_type))
+
+                                               if (texpr == null)
+                                                       texpr = new EmptyExpression (target);
+
+                                               if (!ImplicitStandardConversionExists (texpr, t))
                                                        continue;
                                        }
                                }
 
-                               // See LAMESPEC: Exclude IntPtr -> int conversion
-                               if (source_type == TypeManager.uintptr_type && return_type == TypeManager.uint32_type)
-                                       continue;
+                               if (candidates == null)
+                                       candidates = new List<MethodSpec> ();
 
-                               list.Add (m);
+                               candidates.Add (op);
                        }
-
-                       EmptyExpression.Release (expr);
                }
 
-               /// <summary>
-               ///   Compute the user-defined conversion operator from source_type to target_type.
-               ///   `look_for_explicit' controls whether we should also include the list of explicit operators
-               /// </summary>
-               static MethodSpec GetConversionOperator (CompilerContext ctx, TypeSpec container_type, Expression source, TypeSpec target_type, bool look_for_explicit)
+               //
+               // User-defined conversions
+               //
+               static Expression UserDefinedConversion (ResolveContext ec, Expression source, TypeSpec target, bool implicitOnly, Location loc)
                {
-                       var ops = new List<MethodSpec> (4);
+                       List<MethodSpec> candidates = null;
 
+                       //
+                       // If S or T are nullable types, source_type and target_type are their underlying types
+                       // otherwise source_type and target_type are equal to S and T respectively.
+                       //
                        TypeSpec source_type = source.Type;
+                       TypeSpec target_type = target;
+                       Expression source_type_expr;
 
-                       if (source_type != TypeManager.decimal_type) {
-                               AddConversionOperators (ops, source, target_type, look_for_explicit,
-                                       Expression.MethodLookup (ctx, container_type, source_type, MemberKind.Operator, "op_Implicit", 0, Location.Null));
-                               if (look_for_explicit) {
-                                       AddConversionOperators (ops, source, target_type, look_for_explicit,
-                                               Expression.MethodLookup (ctx,
-                                                       container_type, source_type, MemberKind.Operator, "op_Explicit", 0, Location.Null));
-                               }
-                       }
+                       if (TypeManager.IsNullableType (source_type)) {
+                               // No implicit conversion S? -> T for non-reference types
+                               if (implicitOnly && !TypeManager.IsReferenceType (target_type) && !TypeManager.IsNullableType (target_type))
+                                       return null;
 
-                       if (target_type != TypeManager.decimal_type) {
-                               AddConversionOperators (ops, source, target_type, look_for_explicit,
-                                       Expression.MethodLookup (ctx, container_type, target_type, MemberKind.Operator, "op_Implicit", 0, Location.Null));
-                               if (look_for_explicit) {
-                                       AddConversionOperators (ops, source, target_type, look_for_explicit,
-                                               Expression.MethodLookup (ctx,
-                                                       container_type, target_type, MemberKind.Operator, "op_Explicit", 0, Location.Null));
-                               }
+                               source_type_expr = Nullable.Unwrap.Create (source);
+                               source_type = source_type_expr.Type;
+                       } else {
+                               source_type_expr = source;
                        }
 
-                       if (ops.Count == 0)
-                               return null;
+                       if (TypeManager.IsNullableType (target_type))
+                               target_type = Nullable.NullableInfo.GetUnderlyingType (target_type);
 
-                       TypeSpec most_specific_source = FindMostSpecificSource (ops, source, look_for_explicit);
-                       if (most_specific_source == null)
-                               return null;
+                       // Only these containers can contain a user defined implicit or explicit operators
+                       const MemberKind user_conversion_kinds = MemberKind.Class | MemberKind.Struct | MemberKind.TypeParameter;
 
-                       TypeSpec most_specific_target = FindMostSpecificTarget (ops, target_type, look_for_explicit);
-                       if (most_specific_target == null)
-                               return null;
+                       if ((source_type.Kind & user_conversion_kinds) != 0 && source_type != TypeManager.decimal_type) {
+                               bool declared_only = source_type.IsStruct;
 
-                       MethodSpec method = null;
+                               var operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Implicit, declared_only);
+                               if (operators != null) {
+                                       FindApplicableUserDefinedConversionOperators (operators, source_type_expr, target_type, implicitOnly, ref candidates);
+                               }
 
-                       foreach (var m in ops) {
-                               if (m.ReturnType != most_specific_target)
-                                       continue;
-                               if (m.Parameters.Types [0] != most_specific_source)
-                                       continue;
-                               // Ambiguous: more than one conversion operator satisfies the signature.
-                               if (method != null)
-                                       return null;
-                               method = m;
+                               if (!implicitOnly) {
+                                       operators = MemberCache.GetUserOperator (source_type, Operator.OpType.Explicit, declared_only);
+                                       if (operators != null) {
+                                               FindApplicableUserDefinedConversionOperators (operators, source_type_expr, target_type, false, ref candidates);
+                                       }
+                               }
                        }
 
-                       return method;
-               }
+                       if ((target.Kind & user_conversion_kinds) != 0 && target_type != TypeManager.decimal_type) {
+                               bool declared_only = target.IsStruct || implicitOnly;
 
-               /// <summary>
-               ///   User-defined conversions
-               /// </summary>
-               public static Expression UserDefinedConversion (ResolveContext ec, Expression source,
-                                                               TypeSpec target, Location loc,
-                                                               bool look_for_explicit, bool return_convert)
-               {
-                       TypeSpec source_type = source.Type;
-                       MethodSpec method = null;
-                       Expression expr = null;
-
-                       object o;
-                       DoubleHash hash;
-                       if (look_for_explicit) {
-                               hash = explicit_conv;
-                       } else {
-                               // Implicit user operators cannot convert to interfaces
-                               if (target.IsInterface)
-                                       return null;
-
-                               hash = implicit_conv;
-                       }                       
-
-                       if (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
-                               method = (MethodSpec) o;
-                       } else {
-                               if (source_type == InternalType.Dynamic)
-                                       return null;
+                               var operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Implicit, declared_only);
+                               if (operators != null) {
+                                       FindApplicableUserDefinedConversionOperators (operators, source_type_expr, target_type, implicitOnly, ref candidates);
+                               }
 
-                               method = GetConversionOperator (ec.Compiler, null, source, target, look_for_explicit);
+                               if (!implicitOnly) {
+                                       operators = MemberCache.GetUserOperator (target_type, Operator.OpType.Explicit, declared_only);
+                                       if (operators != null) {
+                                               FindApplicableUserDefinedConversionOperators (operators, source_type_expr, target_type, false, ref candidates);
+                                       }
+                               }
                        }
 
-                       if (method != null) {
-                               TypeSpec most_specific_source = method.Parameters.Types[0];
+                       if (candidates == null)
+                               return null;
 
+                       //
+                       // Find the most specific conversion operator
+                       //
+                       MethodSpec most_specific_operator;
+                       TypeSpec s_x, t_x;
+                       if (candidates.Count == 1) {
+                               most_specific_operator = candidates[0];
+                               s_x = most_specific_operator.Parameters.Types[0];
+                               t_x = most_specific_operator.ReturnType;
+                       } else {
                                //
-                               // This will do the conversion to the best match that we
-                               // found.  Now we need to perform an implict standard conversion
-                               // if the best match was not the type that we were requested
-                               // by target.
+                               // Pass original source type to find the best match against input type and
+                               // not the unwrapped expression
                                //
-                               if (look_for_explicit) {
-                                       ReportPrinter temp = new SessionReportPrinter ();
-                                       ReportPrinter prev = ec.Report.SetPrinter (temp);
+                               s_x = FindMostSpecificSource (candidates, source.Type, source_type_expr, !implicitOnly);
+                               if (s_x == null)
+                                       return null;
 
-                                       expr = ExplicitConversionStandard (ec, source, most_specific_source, loc);
+                               t_x = FindMostSpecificTarget (candidates, target, !implicitOnly);
+                               if (t_x == null)
+                                       return null;
 
-                                       ec.Report.SetPrinter (prev);
-                                       if (temp.ErrorsCount != 0)
-                                               expr = null;
-                               } else {
-                                       if (ImplicitStandardConversionExists (source, most_specific_source))
-                                               expr = ImplicitConversionStandard (ec, source, most_specific_source, loc);
-                                       else
-                                               expr = null;
+                               most_specific_operator = null;
+                               for (int i = 0; i < candidates.Count; ++i) {
+                                       if (candidates[i].ReturnType == t_x && candidates[i].Parameters.Types[0] == s_x) {
+                                               most_specific_operator = candidates[i];
+                                               break;
+                                       }
                                }
-                       }
 
-                       if (expr == null) {
-                               bool nullable = false;
+                               if (most_specific_operator == null) {
+                                       MethodSpec ambig_arg = null;
+                                       foreach (var candidate in candidates) {
+                                               if (candidate.ReturnType == t_x)
+                                                       most_specific_operator = candidate;
+                                               else if (candidate.Parameters.Types[0] == s_x)
+                                                       ambig_arg = candidate;
+                                       }
 
-                               if (TypeManager.IsNullableType (source_type)) {
-                                       source = Nullable.Unwrap.Create (source);
-                                       nullable = true;
+                                       ec.Report.Error (457, loc,
+                                               "Ambiguous user defined operators `{0}' and `{1}' when converting from `{2}' to `{3}'",
+                                               ambig_arg.GetSignatureForError (), most_specific_operator.GetSignatureForError (),
+                                               source.Type.GetSignatureForError (), target.GetSignatureForError ());
                                }
+                       }
 
-                               TypeSpec target_underlying;
-                               if (TypeManager.IsNullableType (target)) {
-                                       target_underlying = TypeManager.GetTypeArguments (target)[0];
-                                       nullable = true;
+                       //
+                       // Convert input type when it's different to best operator argument
+                       //
+                       if (s_x != source_type) {
+                               var c = source as Constant;
+                               if (c != null) {
+                                       source = c.TryReduce (ec, s_x, loc);
                                } else {
-                                       // No implicit conversion S? -> T for non-reference type T
-                                       if (!look_for_explicit && !TypeManager.IsReferenceType (target))
-                                               nullable = false;
-
-                                       target_underlying = target;
+                                       source = implicitOnly ?
+                                               ImplicitConversionStandard (ec, source_type_expr, s_x, loc) :
+                                               ExplicitConversionStandard (ec, source_type_expr, s_x, loc);
                                }
+                       } else {
+                               source = source_type_expr;
+                       }
 
-                               if (nullable) {
-                                       expr = UserDefinedConversion (ec, source, target_underlying, loc, look_for_explicit, return_convert);
+                       source = new UserCast (most_specific_operator, source, loc).Resolve (ec);
 
-                                       // Do result expression lifting only when it's needed
-                                       if (expr != null && (!look_for_explicit || TypeManager.IsReferenceType (target)))
-                                               expr = new Nullable.Lifted (expr, source, target).Resolve (ec);
+                       //
+                       // Convert result type when it's different to best operator return type
+                       //
+                       if (t_x != target_type) {
+                               //
+                               // User operator is of T?, no need to lift it
+                               //
+                               if (TypeManager.IsNullableType (t_x) && t_x == target)
+                                       return source;
 
-                                       return expr;
-                               }
-                       } else {
-                               expr = new UserCast (method, expr, loc).Resolve (ec);
+                               source = implicitOnly ?
+                                       ImplicitConversionStandard (ec, source, target_type, loc) :
+                                       ExplicitConversionStandard (ec, source, target_type, loc);
 
-                               if (return_convert && !TypeManager.IsEqual (expr.Type, target)) {
-                                       if (look_for_explicit) {
-                                               expr = ExplicitConversionStandard (ec, expr, target, loc);
-                                       } else {
-                                               expr = ImplicitConversionStandard (ec, expr, target, loc);
-                                       }
-                               }
+                               if (source == null)
+                                       return null;
                        }
 
-                       if (!(source is Constant))
-                               hash.Insert (source_type, target, method);
+                       //
+                       // Source expression is of nullable type, lift the result in the case it's null and
+                       // not nullable/lifted user operator is used
+                       //
+                       if (source_type_expr is Nullable.Unwrap && !TypeManager.IsNullableType (s_x) && (TypeManager.IsReferenceType (target) || target_type != target))
+                               source = new Nullable.Lifted (source, source_type_expr, target).Resolve (ec);
+                       else if (target_type != target)
+                               source = Nullable.Wrap.Create (source, target);
 
-                       return expr;
+                       return source;
                }
 
                /// <summary>
@@ -1204,7 +1287,7 @@ namespace Mono.CSharp {
                                //
                                // Only allow anonymous method conversions on post ISO_1
                                //
-                               if (RootContext.Version != LanguageVersion.ISO_1){
+                               if (ec.Module.Compiler.Settings.Version != LanguageVersion.ISO_1){
                                        MethodGroupExpr mg = expr as MethodGroupExpr;
                                        if (mg != null)
                                                return ImplicitDelegateCreation.Create (
@@ -1215,14 +1298,31 @@ namespace Mono.CSharp {
                        TypeSpec expr_type = expr.Type;
                        Expression e;
 
-                       if (expr_type.Equals (target_type)) {
-                               if (expr_type != TypeManager.null_type && expr_type != InternalType.AnonymousMethod)
+                       if (expr_type == target_type) {
+                               if (expr_type != InternalType.Null && expr_type != InternalType.AnonymousMethod)
                                        return expr;
                                return null;
                        }
 
-                       if (TypeSpecComparer.Variant.IsEqual (expr_type, target_type)) {
-                               return expr;
+                       if (expr_type == InternalType.Dynamic) {
+                               switch (target_type.Kind) {
+                               case MemberKind.ArrayType:
+                               case MemberKind.Class:
+                                       if (target_type.BuildinType == BuildinTypeSpec.Type.Object)
+                                               return EmptyCast.Create (expr, target_type);
+
+                                       goto case MemberKind.Struct;
+                               case MemberKind.Struct:
+                               case MemberKind.Delegate:
+                               case MemberKind.Enum:
+                               case MemberKind.Interface:
+                               case MemberKind.TypeParameter:
+                                       Arguments args = new Arguments (1);
+                                       args.Add (new Argument (expr));
+                                       return new DynamicConversion (target_type, explicit_cast ? CSharpBinderFlags.ConvertExplicit : 0, args, loc).Resolve (ec);
+                               }
+
+                               return null;
                        }
 
                        if (TypeManager.IsNullableType (target_type))
@@ -1234,7 +1334,7 @@ namespace Mono.CSharp {
                        Constant c = expr as Constant;
                        if (c != null) {
                                try {
-                                       c = c.ConvertImplicitly (ec, target_type);
+                                       c = c.ConvertImplicitly (target_type);
                                } catch {
                                        Console.WriteLine ("Conversion error happened in line {0}", loc);
                                        throw;
@@ -1251,38 +1351,40 @@ namespace Mono.CSharp {
                        if (e != null)
                                return e;
 
-                       if (expr is IntConstant && TypeManager.IsEnumType (target_type)){
-                               Constant i = (Constant) expr;
+                       if (expr is IntegralConstant && TypeManager.IsEnumType (target_type)){
+                               var i = (IntegralConstant) expr;
                                //
-                               // LAMESPEC: Conversion from any 0 constant is allowed
+                               // LAMESPEC: csc allows any constant like 0 values to be converted, including const float f = 0.0
                                //
                                // An implicit enumeration conversion permits the decimal-integer-literal 0
                                // to be converted to any enum-type and to any nullable-type whose underlying
                                // type is an enum-type
                                //
-                               if (i.IsDefaultValue)
-                                       return new EnumConstant (i, target_type).Resolve (ec);
+                               if (i.IsZeroInteger) {
+                                       // Recreate 0 literal to remove any collected conversions
+                                       return new EnumConstant (new IntLiteral (ec.BuildinTypes, 0, i.Location), target_type);
+                               }
                        }
 
                        if (ec.IsUnsafe) {
-                               if (expr_type.IsPointer){
-                                       if (target_type == TypeManager.void_ptr_type)
-                                               return EmptyCast.Create (expr, target_type);
-
-                                       //
-                                       // yep, comparing pointer types cant be done with
-                                       // t1 == t2, we have to compare their element types.
-                                       //
-                                       if (target_type.IsPointer){
-                                               if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
+                               var target_pc = target_type as PointerContainer;
+                               if (target_pc != null) {
+                                       if (expr_type.IsPointer) {
+                                               //
+                                               // Pointer types are same when they have same element types
+                                               //
+                                               if (expr_type == target_pc)
                                                        return expr;
 
+                                               if (target_pc.Element.Kind == MemberKind.Void)
+                                                       return EmptyCast.Create (expr, target_type);
+
                                                //return null;
                                        }
-                               }
 
-                               if (expr_type == TypeManager.null_type && target_type.IsPointer)
-                                       return EmptyCast.Create (new NullPointer (loc), target_type);
+                                       if (expr_type == InternalType.Null)
+                                               return EmptyCast.Create (new NullPointer (loc), target_type);
+                               }
                        }
 
                        if (expr_type == InternalType.AnonymousMethod){
@@ -1295,6 +1397,13 @@ namespace Mono.CSharp {
                        if (expr_type == InternalType.Arglist && target_type == TypeManager.arg_iterator_type)
                                return expr;
 
+                       if (TypeSpecComparer.IsEqual (expr_type, target_type)) {
+                               if (expr_type == target_type)
+                                       return expr;
+
+                               return EmptyCast.Create (expr, target_type);
+                       }
+
                        return null;
                }
 
@@ -1310,12 +1419,6 @@ namespace Mono.CSharp {
                        if (e != null)
                                return e;
 
-                       if (source.Type == InternalType.Dynamic) {
-                               Arguments args = new Arguments (1);
-                               args.Add (new Argument (source));
-                               return new DynamicConversion (target_type, 0, args, loc).Resolve (ec);
-                       }
-
                        source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
                        return null;
                }
@@ -1344,249 +1447,271 @@ namespace Mono.CSharp {
                public static Expression ExplicitNumericConversion (Expression expr, TypeSpec target_type)
                {
                        TypeSpec expr_type = expr.Type;
-                       TypeSpec real_target_type = target_type;
-
-                       if (expr_type == TypeManager.sbyte_type){
+                       switch (expr_type.BuildinType) {
+                       case BuildinTypeSpec.Type.SByte:
                                //
                                // From sbyte to byte, ushort, uint, ulong, char, uintptr
                                //
-                               if (real_target_type == TypeManager.byte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
-                               if (real_target_type == TypeManager.ushort_type)
+                               case BuildinTypeSpec.Type.UShort:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
-                               if (real_target_type == TypeManager.uint32_type)
+                               case BuildinTypeSpec.Type.UInt:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
-                               if (real_target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
 
                                // One of the built-in conversions that belonged in the class library
-                               if (real_target_type == TypeManager.uintptr_type){
+                               case BuildinTypeSpec.Type.UIntPtr:
                                        Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I1_U8);
-
-                                       return new OperatorCast (u8e, TypeManager.uintptr_type, true);
+                                       return new OperatorCast (u8e, target_type, true);
                                }
-                       } else if (expr_type == TypeManager.byte_type){
+                               break;
+                       case BuildinTypeSpec.Type.Byte:
                                //
                                // From byte to sbyte and char
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
-                       } else if (expr_type == TypeManager.short_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Short:
                                //
                                // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
-                               if (real_target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
-                               if (real_target_type == TypeManager.ushort_type)
+                               case BuildinTypeSpec.Type.UShort:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
-                               if (real_target_type == TypeManager.uint32_type)
+                               case BuildinTypeSpec.Type.UInt:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
-                               if (real_target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
 
                                // One of the built-in conversions that belonged in the class library
-                               if (real_target_type == TypeManager.uintptr_type){
+                               case BuildinTypeSpec.Type.UIntPtr:
                                        Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
-
-                                       return new OperatorCast (u8e, TypeManager.uintptr_type, true);
+                                       return new OperatorCast (u8e, target_type, true);
                                }
-                       } else if (expr_type == TypeManager.ushort_type){
+                               break;
+                       case BuildinTypeSpec.Type.UShort:
                                //
                                // From ushort to sbyte, byte, short, char
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
-                               if (real_target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
-                               if (real_target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
-                       } else if (expr_type == TypeManager.int32_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Int:
                                //
                                // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
-                               if (real_target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
-                               if (real_target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
-                               if (real_target_type == TypeManager.ushort_type)
+                               case BuildinTypeSpec.Type.UShort:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
-                               if (real_target_type == TypeManager.uint32_type)
+                               case BuildinTypeSpec.Type.UInt:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
-                               if (real_target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
 
                                // One of the built-in conversions that belonged in the class library
-                               if (real_target_type == TypeManager.uintptr_type){
+                               case BuildinTypeSpec.Type.UIntPtr:
                                        Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
-
-                                       return new OperatorCast (u8e, TypeManager.uintptr_type, true);
+                                       return new OperatorCast (u8e, target_type, true);
                                }
-                       } else if (expr_type == TypeManager.uint32_type){
+                               break;
+                       case BuildinTypeSpec.Type.UInt:
                                //
                                // From uint to sbyte, byte, short, ushort, int, char
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
-                               if (real_target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
-                               if (real_target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
-                               if (real_target_type == TypeManager.ushort_type)
+                               case BuildinTypeSpec.Type.UShort:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
-                               if (real_target_type == TypeManager.int32_type)
+                               case BuildinTypeSpec.Type.Int:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
-                       } else if (expr_type == TypeManager.int64_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Long:
                                //
                                // From long to sbyte, byte, short, ushort, int, uint, ulong, char
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
-                               if (real_target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
-                               if (real_target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
-                               if (real_target_type == TypeManager.ushort_type)
+                               case BuildinTypeSpec.Type.UShort:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
-                               if (real_target_type == TypeManager.int32_type)
+                               case BuildinTypeSpec.Type.Int:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
-                               if (real_target_type == TypeManager.uint32_type)
+                               case BuildinTypeSpec.Type.UInt:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
-                               if (real_target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
-                       } else if (expr_type == TypeManager.uint64_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.ULong:
                                //
                                // From ulong to sbyte, byte, short, ushort, int, uint, long, char
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
-                               if (real_target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
-                               if (real_target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
-                               if (real_target_type == TypeManager.ushort_type)
+                               case BuildinTypeSpec.Type.UShort:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
-                               if (real_target_type == TypeManager.int32_type)
+                               case BuildinTypeSpec.Type.Int:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
-                               if (real_target_type == TypeManager.uint32_type)
+                               case BuildinTypeSpec.Type.UInt:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
-                               if (real_target_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
 
                                // One of the built-in conversions that belonged in the class library
-                               if (real_target_type == TypeManager.intptr_type){
-                                       return new OperatorCast (EmptyCast.Create (expr, TypeManager.int64_type),
-                                                                TypeManager.intptr_type, true);
+                               case BuildinTypeSpec.Type.IntPtr:
+                                       return new OperatorCast (EmptyCast.Create (expr, TypeManager.int64_type), target_type, true);
                                }
-                       } else if (expr_type == TypeManager.char_type){
+                               break;
+                       case BuildinTypeSpec.Type.Char:
                                //
                                // From char to sbyte, byte, short
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
-                               if (real_target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
-                               if (real_target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
-                       } else if (expr_type == TypeManager.float_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Float:
                                //
                                // From float to sbyte, byte, short,
                                // ushort, int, uint, long, ulong, char
                                // or decimal
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
-                               if (real_target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
-                               if (real_target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
-                               if (real_target_type == TypeManager.ushort_type)
+                               case BuildinTypeSpec.Type.UShort:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
-                               if (real_target_type == TypeManager.int32_type)
+                               case BuildinTypeSpec.Type.Int:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
-                               if (real_target_type == TypeManager.uint32_type)
+                               case BuildinTypeSpec.Type.UInt:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
-                               if (real_target_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
-                               if (real_target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
-                               if (real_target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Decimal:
                                        return new CastToDecimal (expr, true);
-                       } else if (expr_type == TypeManager.double_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.Double:
                                //
                                // From double to sbyte, byte, short,
                                // ushort, int, uint, long, ulong,
                                // char, float or decimal
                                //
-                               if (real_target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
-                               if (real_target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
-                               if (real_target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
-                               if (real_target_type == TypeManager.ushort_type)
+                               case BuildinTypeSpec.Type.UShort:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
-                               if (real_target_type == TypeManager.int32_type)
+                               case BuildinTypeSpec.Type.Int:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
-                               if (real_target_type == TypeManager.uint32_type)
+                               case BuildinTypeSpec.Type.UInt:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
-                               if (real_target_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
-                               if (real_target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
-                               if (real_target_type == TypeManager.char_type)
+                               case BuildinTypeSpec.Type.Char:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
-                               if (real_target_type == TypeManager.float_type)
+                               case BuildinTypeSpec.Type.Float:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
-                               if (real_target_type == TypeManager.decimal_type)
+                               case BuildinTypeSpec.Type.Decimal:
                                        return new CastToDecimal (expr, true);
-                       } else if (expr_type == TypeManager.uintptr_type){
+                               }
+                               break;
+                       case BuildinTypeSpec.Type.UIntPtr:
                                //
                                // Various built-in conversions that belonged in the class library
                                //
                                // from uintptr to sbyte, short, int32
                                //
-                               if (real_target_type == TypeManager.sbyte_type){
-                                       Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
-                                       return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I1);
-                               }
-                               if (real_target_type == TypeManager.short_type){
-                                       Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
-                                       return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I2);
-                               }
-                               if (real_target_type == TypeManager.int32_type){
-                                       return EmptyCast.Create (new OperatorCast (expr, TypeManager.uint32_type, true),
-                                                             TypeManager.int32_type);
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
+                                       return new ConvCast (new OperatorCast (expr, TypeManager.uint32_type, true), target_type, ConvCast.Mode.U4_I1);
+                               case BuildinTypeSpec.Type.Short:
+                                       return new ConvCast (new OperatorCast (expr, TypeManager.uint32_type, true), target_type, ConvCast.Mode.U4_I2);
+                               case BuildinTypeSpec.Type.Int:
+                                       return EmptyCast.Create (new OperatorCast (expr, TypeManager.uint32_type, true), target_type);
                                }
-                       } else if (expr_type == TypeManager.intptr_type){
-                               if (real_target_type == TypeManager.uint64_type){
-                                       return EmptyCast.Create (new OperatorCast (expr, TypeManager.int64_type, true),
-                                                             TypeManager.uint64_type);
+                               break;
+                       case BuildinTypeSpec.Type.IntPtr:
+                               if (target_type.BuildinType == BuildinTypeSpec.Type.ULong) {
+                                       return EmptyCast.Create (new OperatorCast (expr, TypeManager.int64_type, true), target_type);
                                }
-                       } else if (expr_type == TypeManager.decimal_type) {
+                               break;
+                       case BuildinTypeSpec.Type.Decimal:
                                return new CastFromDecimal (expr, target_type).Resolve ();
                        }
+
                        return null;
                }
 
@@ -1611,53 +1736,60 @@ namespace Mono.CSharp {
                /// </summary>
                static Expression ExplicitReferenceConversion (Expression source, TypeSpec source_type, TypeSpec target_type)
                {
-                       bool target_is_value_type = TypeManager.IsStruct (target_type);
-
                        //
                        // From object to a generic parameter
                        //
-                       if (source_type == TypeManager.object_type && TypeManager.IsGenericParameter (target_type))
+                       if (source_type.BuildinType == BuildinTypeSpec.Type.Object && TypeManager.IsGenericParameter (target_type))
                                return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
 
                        //
                        // Explicit type parameter conversion.
                        //
-                       if (TypeManager.IsGenericParameter (source_type))
+                       if (source_type.Kind == MemberKind.TypeParameter)
                                return ExplicitTypeParameterConversion (source, source_type, target_type);
 
+                       bool target_is_value_type = TypeManager.IsStruct (target_type) || TypeManager.IsEnumType (target_type);
+
                        //
-                       // From object to any reference type or value type (unboxing)
+                       // Unboxing conversion from System.ValueType to any non-nullable-value-type
                        //
-                       if (source_type == TypeManager.object_type)
-                               return source == null ? EmptyExpression.Null :
-                                       target_is_value_type ? (Expression) new UnboxCast (source, target_type) : new ClassCast (source, target_type);
+                       if (source_type.BuildinType == BuildinTypeSpec.Type.ValueType && target_is_value_type)
+                               return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
 
                        //
-                       // Unboxing conversion from the types object and System.ValueType to any non-nullable-value-type
+                       // From object or dynamic to any reference type or value type (unboxing)
                        //
-                       if (source_type == TypeManager.value_type && target_is_value_type)
-                               return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
+                       if (source_type.BuildinType == BuildinTypeSpec.Type.Object || source_type == InternalType.Dynamic) {
+                               if (target_type.IsPointer)
+                                       return null;
+
+                               return
+                                       source == null ? EmptyExpression.Null :
+                                       target_is_value_type ? new UnboxCast (source, target_type) :
+                                       source is Constant ? (Expression) new EmptyConstantCast ((Constant) source, target_type) :
+                                       new ClassCast (source, target_type);
+                       }
 
                        //
                        // From any class S to any class-type T, provided S is a base class of T
                        //
-                       if (TypeManager.IsSubclassOf (target_type, source_type))
+                       if (source_type.Kind == MemberKind.Class && TypeSpec.IsBaseClass (target_type, source_type, true))
                                return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
 
                        //
                        // From any interface-type S to to any class type T, provided T is not
                        // sealed, or provided T implements S.
                        //
-                       if (source_type.IsInterface) {
-                               if (!target_type.IsSealed || target_type.ImplementsInterface (source_type)) {
-                                       if (target_type.IsClass)
-                                               return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
+                       if (source_type.Kind == MemberKind.Interface) {
+                               if (!target_type.IsSealed || target_type.ImplementsInterface (source_type, true)) {
+                                       if (source == null)
+                                               return EmptyExpression.Null;
 
                                        //
                                        // Unboxing conversion from any interface-type to any non-nullable-value-type that
                                        // implements the interface-type
                                        //
-                                       return source == null ? EmptyExpression.Null : new UnboxCast (source, target_type);
+                                       return target_is_value_type ? new UnboxCast (source, target_type) : (Expression) new ClassCast (source, target_type);
                                }
 
                                //
@@ -1678,7 +1810,7 @@ namespace Mono.CSharp {
                                        //
                                        // From System.Array to any array-type
                                        //
-                                       if (source_type == TypeManager.array_type)
+                                       if (source_type.BuildinType == BuildinTypeSpec.Type.Array)
                                                return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
 
                                        //
@@ -1720,7 +1852,7 @@ namespace Mono.CSharp {
                        // From any class type S to any interface T, provides S is not sealed
                        // and provided S does not implement T.
                        //
-                       if (target_type.IsInterface && !source_type.IsSealed && !source_type.ImplementsInterface (target_type)) {
+                       if (target_type.IsInterface && !source_type.IsSealed && !source_type.ImplementsInterface (target_type, true)) {
                                return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
                        }
 
@@ -1730,6 +1862,46 @@ namespace Mono.CSharp {
                        if (source_type == TypeManager.delegate_type && TypeManager.IsDelegateType (target_type))
                                return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
 
+                       //
+                       // From variant generic delegate to same variant generic delegate type
+                       //
+                       if (source_type.IsDelegate && target_type.IsDelegate && source_type.MemberDefinition == target_type.MemberDefinition) {
+                               var tparams = source_type.MemberDefinition.TypeParameters;
+                               var targs_src = source_type.TypeArguments;
+                               var targs_dst = target_type.TypeArguments;
+                               int i;
+                               for (i = 0; i < tparams.Length; ++i) {
+                                       //
+                                       // If TP is invariant, types have to be identical
+                                       //
+                                       if (TypeSpecComparer.IsEqual (targs_src[i], targs_dst[i]))
+                                               continue;
+
+                                       if (tparams[i].Variance == Variance.Covariant) {
+                                               //
+                                               //If TP is covariant, an implicit or explicit identity or reference conversion is required
+                                               //
+                                               if (ImplicitReferenceConversionExists (new EmptyExpression (targs_src[i]), targs_dst[i]))
+                                                       continue;
+
+                                               if (ExplicitReferenceConversionExists (targs_src[i], targs_dst[i]))
+                                                       continue;
+
+                                       } else if (tparams[i].Variance == Variance.Contravariant) {
+                                               //
+                                               //If TP is contravariant, both are either identical or reference types
+                                               //
+                                               if (TypeManager.IsReferenceType (targs_src[i]) && TypeManager.IsReferenceType (targs_dst[i]))
+                                                       continue;
+                                       }
+
+                                       break;
+                               }
+
+                               if (i == tparams.Length)
+                                       return source == null ? EmptyExpression.Null : new ClassCast (source, target_type);
+                       }
+
                        return null;
                }
 
@@ -1748,47 +1920,66 @@ namespace Mono.CSharp {
                                return ne;
 
                        if (TypeManager.IsEnumType (expr_type)) {
+                               TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
                                Expression underlying = EmptyCast.Create (expr, EnumSpec.GetUnderlyingType (expr_type));
-                               expr = ExplicitConversionCore (ec, underlying, target_type, loc);
-                               if (expr != null)
-                                       return expr;
+                               if (underlying.Type == real_target)
+                                       ne = underlying;
+
+                               if (ne == null)
+                                       ne = ImplicitNumericConversion (underlying, real_target);
+
+                               if (ne == null)
+                                       ne = ExplicitNumericConversion (underlying, real_target);
 
-                               return ExplicitUserConversion (ec, underlying, target_type, loc);                               
+                               //
+                               // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
+                               //
+                               if (ne == null && (real_target.BuildinType == BuildinTypeSpec.Type.IntPtr || real_target.BuildinType == BuildinTypeSpec.Type.UIntPtr))
+                                       ne = ExplicitUserConversion (ec, underlying, real_target, loc);
+
+                               return ne != null ? EmptyCast.Create (ne, target_type) : null;
                        }
 
-                       if (TypeManager.IsEnumType (target_type)){
+                       if (TypeManager.IsEnumType (target_type)) {
                                //
-                               // Type System.Enum can be unboxed to any enum-type
+                               // System.Enum can be unboxed to any enum-type
                                //
-                               if (expr_type == TypeManager.enum_type)
+                               if (expr_type.BuildinType == BuildinTypeSpec.Type.Enum)
                                        return new UnboxCast (expr, target_type);
 
-                               Expression ce = ExplicitConversionCore (ec, expr, EnumSpec.GetUnderlyingType (target_type), loc);
-                               if (ce != null)
-                                       return EmptyCast.Create (ce, target_type);
-                               
+                               TypeSpec real_target = TypeManager.IsEnumType (target_type) ? EnumSpec.GetUnderlyingType (target_type) : target_type;
+
+                               if (expr_type == real_target)
+                                       return EmptyCast.Create (expr, target_type);
+
+                               ne = ImplicitNumericConversion (expr, real_target);
+                               if (ne != null)
+                                       return EmptyCast.Create (ne, target_type);
+
+                               ne = ExplicitNumericConversion (expr, real_target);
+                               if (ne != null)
+                                       return EmptyCast.Create (ne, target_type);
+
                                //
                                // LAMESPEC: IntPtr and UIntPtr conversion to any Enum is allowed
                                //
-                               if (expr_type == TypeManager.intptr_type || expr_type == TypeManager.uintptr_type) {
-                                       ne = ExplicitUserConversion (ec, expr, EnumSpec.GetUnderlyingType (target_type), loc);
+                               if (expr_type.BuildinType == BuildinTypeSpec.Type.IntPtr || expr_type.BuildinType == BuildinTypeSpec.Type.UIntPtr) {
+                                       ne = ExplicitUserConversion (ec, expr, real_target, loc);
                                        if (ne != null)
                                                return ExplicitConversionCore (ec, ne, target_type, loc);
                                }
-                               
-                               return null;
+                       } else {
+                               ne = ExplicitNumericConversion (expr, target_type);
+                               if (ne != null)
+                                       return ne;
                        }
 
-                       ne = ExplicitNumericConversion (expr, target_type);
-                       if (ne != null)
-                               return ne;
-
                        //
                        // Skip the ExplicitReferenceConversion because we can not convert
                        // from Null to a ValueType, and ExplicitReference wont check against
                        // null literal explicitly
                        //
-                       if (expr_type != TypeManager.null_type){
+                       if (expr_type != InternalType.Null) {
                                ne = ExplicitReferenceConversion (expr, expr_type, target_type);
                                if (ne != null)
                                        return ne;
@@ -1811,40 +2002,44 @@ namespace Mono.CSharp {
                                if (expr_type.IsPointer)
                                        return EmptyCast.Create (expr, target_type);
 
-                               if (expr_type == TypeManager.sbyte_type ||
-                                       expr_type == TypeManager.short_type ||
-                                       expr_type == TypeManager.int32_type)
+                               switch (expr_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
+                               case BuildinTypeSpec.Type.Short:
+                               case BuildinTypeSpec.Type.Int:
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
 
-                               if (expr_type == TypeManager.ushort_type ||
-                                       expr_type == TypeManager.uint32_type ||
-                                       expr_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.UShort:
+                               case BuildinTypeSpec.Type.UInt:
+                               case BuildinTypeSpec.Type.Byte:
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
 
-                               if (expr_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_I);
 
-                               if (expr_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_I);
+                               }
                        }
 
                        if (expr_type.IsPointer){
-                               if (target_type == TypeManager.sbyte_type)
+                               switch (target_type.BuildinType) {
+                               case BuildinTypeSpec.Type.SByte:
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
-                               if (target_type == TypeManager.byte_type)
+                               case BuildinTypeSpec.Type.Byte:
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
-                               if (target_type == TypeManager.short_type)
+                               case BuildinTypeSpec.Type.Short:
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
-                               if (target_type == TypeManager.ushort_type)
+                               case BuildinTypeSpec.Type.UShort:
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
-                               if (target_type == TypeManager.int32_type)
+                               case BuildinTypeSpec.Type.Int:
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
-                               if (target_type == TypeManager.uint32_type)
+                               case BuildinTypeSpec.Type.UInt:
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
-                               if (target_type == TypeManager.int64_type)
+                               case BuildinTypeSpec.Type.Long:
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I_I8);
-                               if (target_type == TypeManager.uint64_type)
+                               case BuildinTypeSpec.Type.ULong:
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
+                               }
                        }
                        return null;
                }
@@ -1871,7 +2066,7 @@ namespace Mono.CSharp {
                        if (ne != null)
                                return ne;
 
-                       if (ec.IsUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
+                       if (ec.IsUnsafe && expr.Type.IsPointer && target_type.IsPointer && ((PointerContainer)expr.Type).Element.Kind == MemberKind.Void)
                                return EmptyCast.Create (expr, target_type);
 
                        expr.Error_ValueCannotBeConverted (ec, l, target_type, true);
@@ -1891,10 +2086,10 @@ namespace Mono.CSharp {
                                // Don't eliminate explicit precission casts
                                //
                                if (e == expr) {
-                                       if (target_type == TypeManager.float_type)
+                                       if (target_type.BuildinType == BuildinTypeSpec.Type.Float)
                                                return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                        
-                                       if (target_type == TypeManager.double_type)
+                                       if (target_type.BuildinType == BuildinTypeSpec.Type.Double)
                                                return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                }
                                        
@@ -1903,30 +2098,31 @@ namespace Mono.CSharp {
 
                        TypeSpec expr_type = expr.Type;
                        if (TypeManager.IsNullableType (target_type)) {
+                               TypeSpec target;
+
                                if (TypeManager.IsNullableType (expr_type)) {
-                                       TypeSpec target = TypeManager.GetTypeArguments (target_type)[0];
+                                       target = Nullable.NullableInfo.GetUnderlyingType (target_type);
                                        Expression unwrap = Nullable.Unwrap.Create (expr);
                                        e = ExplicitConversion (ec, unwrap, target, expr.Location);
                                        if (e == null)
                                                return null;
 
                                        return new Nullable.Lifted (e, unwrap, target_type).Resolve (ec);
-                               } else if (expr_type == TypeManager.object_type) {
+                               }
+                               if (expr_type.BuildinType == BuildinTypeSpec.Type.Object) {
                                        return new UnboxCast (expr, target_type);
-                               } else {
-                                       TypeSpec target = TypeManager.GetTypeArguments (target_type) [0];
-
-                                       e = ExplicitConversionCore (ec, expr, target, loc);
-                                       if (e != null)
-                                               return Nullable.Wrap.Create (e, target_type);
                                }
+
+                               target = TypeManager.GetTypeArguments (target_type) [0];
+                               e = ExplicitConversionCore (ec, expr, target, loc);
+                               if (e != null)
+                                       return Nullable.Wrap.Create (e, target_type);
                        } else if (TypeManager.IsNullableType (expr_type)) {
-                               e = Nullable.Unwrap.Create (expr, false);
+                               e = ImplicitBoxingConversion (expr, Nullable.NullableInfo.GetUnderlyingType (expr_type), target_type);
+                               if (e != null)
+                                       return e;
 
-                               bool use_class_cast;
-                               if (ImplicitBoxingConversionExists (e, target_type, out use_class_cast))
-                                       return new BoxedCast (expr, target_type);
-                               
+                               e = Nullable.Unwrap.Create (expr, false);                       
                                e = ExplicitConversionCore (ec, e, target_type, loc);
                                if (e != null)
                                        return EmptyCast.Create (e, target_type);