2009-07-11 Michael Barker <mike@middlesoft.co.uk>
[mono.git] / mcs / mcs / nullable.cs
index 185dcf46b42b379bbd70413ab9c8771993e8a897..6b109500c0aaab2f1f9e996693f7fada1f4ea563 100644 (file)
@@ -5,10 +5,10 @@
 //          Miguel de Icaza (miguel@ximian.com)
 //          Marek Safar (marek.safar@gmail.com)
 //
-// Licensed under the terms of the GNU GPL
+// Dual licensed under the terms of the MIT X11 or GNU GPL
 //
-// (C) 2001, 2002, 2003 Ximian, Inc (http://www.ximian.com)
-// (C) 2004 Novell, Inc
+// Copyright 2001, 2002, 2003 Ximian, Inc (http://www.ximian.com)
+// Copyright 2004-2008 Novell, Inc
 //
 
 using System;
@@ -20,9 +20,9 @@ namespace Mono.CSharp.Nullable
 {
        public class NullableType : TypeExpr
        {
-               Expression underlying;
+               TypeExpr underlying;
 
-               public NullableType (Expression underlying, Location l)
+               public NullableType (TypeExpr underlying, Location l)
                {
                        this.underlying = underlying;
                        loc = l;
@@ -34,51 +34,46 @@ namespace Mono.CSharp.Nullable
                        : this (new TypeExpression (type, loc), loc)
                { }
 
-               public override string Name {
-                       get { return underlying.ToString () + "?"; }
-               }
-
-               public override string FullName {
-                       get { return underlying.ToString () + "?"; }
-               }
-
                protected override TypeExpr DoResolveAsTypeStep (IResolveContext ec)
                {
-                       TypeArguments args = new TypeArguments (loc);
-                       args.Add (underlying);
-
                        if (TypeManager.generic_nullable_type == null) {
                                TypeManager.generic_nullable_type = TypeManager.CoreLookupType (
                                        "System", "Nullable`1", Kind.Struct, true);
                        }
 
-                       ConstructedType ctype = new ConstructedType (TypeManager.generic_nullable_type, args, loc);
+                       TypeArguments args = new TypeArguments (underlying);
+                       GenericTypeExpr ctype = new GenericTypeExpr (TypeManager.generic_nullable_type, args, loc);
                        return ctype.ResolveAsTypeTerminal (ec, false);
                }
+
+               public override TypeExpr ResolveAsTypeTerminal (IResolveContext ec, bool silent)
+               {
+                       return ResolveAsBaseTerminal (ec, silent);
+               }               
        }
 
        public sealed class NullableInfo
        {
                public readonly Type Type;
                public readonly Type UnderlyingType;
-               public readonly MethodInfo HasValue;
-               public readonly MethodInfo Value;
-               public readonly MethodInfo GetValueOrDefault;
-               public readonly ConstructorInfo Constructor;
+               public MethodInfo HasValue;
+               public MethodInfo Value;
+               public MethodInfo GetValueOrDefault;
+               public ConstructorInfo Constructor;
 
                public NullableInfo (Type type)
                {
                        Type = type;
                        UnderlyingType = TypeManager.GetTypeArguments (type) [0];
 
-                       PropertyInfo has_value_pi = TypeManager.GetPredefinedProperty (type, "HasValue", Location.Null);
-                       PropertyInfo value_pi = TypeManager.GetPredefinedProperty (type, "Value", Location.Null);
+                       PropertyInfo has_value_pi = TypeManager.GetPredefinedProperty (type, "HasValue", Location.Null, Type.EmptyTypes);
+                       PropertyInfo value_pi = TypeManager.GetPredefinedProperty (type, "Value", Location.Null, Type.EmptyTypes);
                        GetValueOrDefault = TypeManager.GetPredefinedMethod (type, "GetValueOrDefault", Location.Null, Type.EmptyTypes);
 
                        HasValue = has_value_pi.GetGetMethod (false);
                        Value = value_pi.GetGetMethod (false);
 #if MS_COMPATIBLE
-                       if (UnderlyingType.Module == CodeGen.Module.Builder) {
+                       if (UnderlyingType.Module == RootContext.ToplevelTypes.Builder) {
                                Type o_type = TypeManager.DropGenericTypeArguments (type);
                                Constructor = TypeBuilder.GetConstructor (type,
                                        TypeManager.GetPredefinedConstructor (o_type, Location.Null, o_type.GetGenericArguments ()));
@@ -88,44 +83,6 @@ namespace Mono.CSharp.Nullable
                        Constructor = type.GetConstructor (new Type[] { UnderlyingType });
                }
        }
-       
-       public class HasValue : Expression
-       {
-               Expression expr;
-               NullableInfo info;
-
-               private HasValue (Expression expr)
-               {
-                       this.expr = expr;
-               }
-               
-               public static Expression Create (Expression expr, EmitContext ec)
-               {
-                       return new HasValue (expr).Resolve (ec);
-               }
-
-               public override void Emit (EmitContext ec)
-               {
-                       IMemoryLocation memory_loc = expr as IMemoryLocation;
-                       if (memory_loc == null) {
-                               LocalTemporary temp = new LocalTemporary (expr.Type);
-                               expr.Emit (ec);
-                               temp.Store (ec);
-                               memory_loc = temp;
-                       }
-                       memory_loc.AddressOf (ec, AddressOp.LoadStore);
-                       ec.ig.EmitCall (OpCodes.Call, info.HasValue, null);
-               }
-
-               public override Expression DoResolve (EmitContext ec)
-               {
-                       this.info = new NullableInfo (expr.Type);
-
-                       type = TypeManager.bool_type;
-                       eclass = expr.eclass;
-                       return this;
-               }
-       }               
 
        public class Unwrap : Expression, IMemoryLocation, IAssignMethod
        {
@@ -133,58 +90,64 @@ namespace Mono.CSharp.Nullable
                NullableInfo info;
 
                LocalTemporary temp;
-               bool has_temp;
+               readonly bool useDefaultValue;
 
-               protected Unwrap (Expression expr)
+               Unwrap (Expression expr, bool useDefaultValue)
                {
                        this.expr = expr;
                        this.loc = expr.Location;
+                       this.useDefaultValue = useDefaultValue;
+
+                       info = new NullableInfo (expr.Type);
+                       type = info.UnderlyingType;
+                       eclass = expr.eclass;
                }
 
-               public static Unwrap Create (Expression expr, EmitContext ec)
+               public static Expression Create (Expression expr)
                {
-                       return new Unwrap (expr).Resolve (ec) as Unwrap;
+                       //
+                       // Avoid unwraping and wraping of same type
+                       //
+                       Wrap wrap = expr as Wrap;
+                       if (wrap != null)
+                               return wrap.Child;
+
+                       return Create (expr, false);
+               }
+
+               public static Unwrap Create (Expression expr, bool useDefaultValue)
+               {
+                       return new Unwrap (expr, useDefaultValue);
                }
                
                public override Expression CreateExpressionTree (EmitContext ec)
                {
                        return expr.CreateExpressionTree (ec);
-               }                       
+               }
 
                public override Expression DoResolve (EmitContext ec)
                {
-                       if (expr == null)
-                               return null;
-
-                       temp = new LocalTemporary (expr.Type);
-
-                       info = new NullableInfo (expr.Type);
-                       type = info.UnderlyingType;
-                       eclass = expr.eclass;
                        return this;
                }
-               
+
                public override Expression DoResolveLValue (EmitContext ec, Expression right_side)
                {
                        return DoResolve (ec);
-               }                       
+               }
 
                public override void Emit (EmitContext ec)
                {
-                       AddressOf (ec, AddressOp.LoadStore);
-                       ec.ig.EmitCall (OpCodes.Call, info.Value, null);
+                       Store (ec);
+                       if (useDefaultValue)
+                               Invocation.EmitCall (ec, false, this, info.GetValueOrDefault, null, loc);
+                       else
+                               Invocation.EmitCall (ec, false, this, info.Value, null, loc);
                }
 
                public void EmitCheck (EmitContext ec)
                {
-                       AddressOf (ec, AddressOp.LoadStore);
-                       ec.ig.EmitCall (OpCodes.Call, info.HasValue, null);
-               }
-
-               public void EmitGetValueOrDefault (EmitContext ec)
-               {
-                       AddressOf (ec, AddressOp.LoadStore);
-                       ec.ig.EmitCall (OpCodes.Call, info.GetValueOrDefault, null);
+                       Store (ec);
+                       Invocation.EmitCall (ec, false, this, info.HasValue, null, loc);
                }
 
                public override bool Equals (object obj)
@@ -210,43 +173,59 @@ namespace Mono.CSharp.Nullable
                        }
                }
 
-               public void Store (EmitContext ec)
+               void Store (EmitContext ec)
                {
-                       create_temp (ec);
+                       if (expr is VariableReference)
+                               return;
+
+                       if (temp != null)
+                               return;
+
+                       expr.Emit (ec);
+                       LocalVariable.Store (ec);
                }
 
-               void create_temp (EmitContext ec)
+               public void Load (EmitContext ec)
                {
-                       if ((temp != null) && !has_temp) {
+                       if (expr is VariableReference)
                                expr.Emit (ec);
-                               temp.Store (ec);
-                               has_temp = true;
-                       }
+                       else
+                               LocalVariable.Emit (ec);
                }
 
-               public void LoadTemporary (EmitContext ec)
+               public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
                {
-                       temp.Emit (ec);
+                       type = storey.MutateType (type);
+                       info.Constructor = storey.MutateConstructor (info.Constructor);
+                       info.HasValue = storey.MutateGenericMethod (info.HasValue);
+                       info.GetValueOrDefault = storey.MutateGenericMethod (info.GetValueOrDefault);
+                       info.Value = storey.MutateGenericMethod (info.Value);
                }
 
                public void AddressOf (EmitContext ec, AddressOp mode)
                {
-                       create_temp (ec);
-                       if (temp != null)
-                               temp.AddressOf (ec, AddressOp.LoadStore);
+                       IMemoryLocation ml = expr as VariableReference;
+                       if (ml != null) 
+                               ml.AddressOf (ec, mode);
                        else
-                               ((IMemoryLocation) expr).AddressOf (ec, AddressOp.LoadStore);
+                               LocalVariable.AddressOf (ec, mode);
+               }
+
+               //
+               // Keeps result of non-variable expression
+               //
+               LocalTemporary LocalVariable {
+                       get {
+                               if (temp == null)
+                                       temp = new LocalTemporary (info.Type);
+                               return temp;
+                       }
                }
 
                public void Emit (EmitContext ec, bool leave_copy)
                {
-                       create_temp (ec);
-                       if (leave_copy) {
-                               if (temp != null)
-                                       temp.Emit (ec);
-                               else
-                                       expr.Emit (ec);
-                       }
+                       if (leave_copy)
+                               Load (ec);
 
                        Emit (ec);
                }
@@ -273,6 +252,11 @@ namespace Mono.CSharp.Nullable
                                eclass = ExprClass.Value;
                        }
 
+                       public override Expression CreateExpressionTree (EmitContext ec)
+                       {
+                               throw new NotSupportedException ("ET");
+                       }
+
                        public override Expression DoResolve (EmitContext ec)
                        {
                                return this;
@@ -286,7 +270,7 @@ namespace Mono.CSharp.Nullable
                }
        }
 
-       public class Wrap : EmptyCast
+       public class Wrap : TypeCast
        {
                readonly NullableInfo info;
 
@@ -297,8 +281,30 @@ namespace Mono.CSharp.Nullable
                        eclass = ExprClass.Value;
                }
 
-               public static new Expression Create (Expression expr, Type type)
+               public Expression Child {
+                       get { return child; }
+               }
+
+               public override Expression CreateExpressionTree (EmitContext ec)
                {
+                       TypeCast child_cast = child as TypeCast;
+                       if (child_cast != null) {
+                               child.Type = type;
+                               return child_cast.CreateExpressionTree (ec);
+                       }
+
+                       return base.CreateExpressionTree (ec);
+               }
+
+               public static Expression Create (Expression expr, Type type)
+               {
+                       //
+                       // Avoid unwraping and wraping of the same type
+                       //
+                       Unwrap unwrap = expr as Unwrap;
+                       if (unwrap != null && TypeManager.IsEqual (expr.Type, TypeManager.GetTypeArguments (type) [0]))
+                               return unwrap.Original;
+               
                        return new Wrap (expr, type);
                }
                
@@ -309,19 +315,6 @@ namespace Mono.CSharp.Nullable
                }
        }
 
-       class LiftedWrap : Wrap
-       {
-               public LiftedWrap (Expression expr, Type type)
-                       : base (expr, type)
-               {
-               }
-
-               public override Expression CreateExpressionTree (EmitContext ec)
-               {
-                       return child.CreateExpressionTree (ec);
-               }
-       }
-
        //
        // Represents null literal lifted to nullable type
        //
@@ -343,12 +336,12 @@ namespace Mono.CSharp.Nullable
                        Report.Warning (458, 2, e.Location, "The result of the expression is always `null' of type `{0}'",
                                TypeManager.CSharpName (e.Type));
 
-                       return ReducedExpression.Create (Create (e.Type, e.Location) , e);
+                       return ReducedExpression.Create (Create (e.Type, e.Location), e);
                }
 
                public override Expression CreateExpressionTree (EmitContext ec)
                {
-                       ArrayList args = new ArrayList (2);
+                       Arguments args = new Arguments (2);
                        args.Add (new Argument (this));
                        args.Add (new Argument (new TypeOf (new TypeExpression (type, loc), loc)));
 
@@ -375,54 +368,47 @@ namespace Mono.CSharp.Nullable
                }
        }
 
-       public abstract class Lifted : Expression, IMemoryLocation
+       public class Lifted : Expression, IMemoryLocation
        {
-               Expression expr, underlying, wrap, null_value;
+               Expression expr, wrap, null_value;
                Unwrap unwrap;
 
-               protected Lifted (Expression expr, Location loc)
+               public Lifted (Expression expr, Unwrap unwrap, Type type)
                {
                        this.expr = expr;
-                       this.loc = loc;
+                       this.unwrap = unwrap;
+                       this.loc = expr.Location;
+                       this.type = type;
+               }
+
+               public Lifted (Expression expr, Expression unwrap, Type type)
+                       : this (expr, unwrap as Unwrap, type)
+               {
                }
                
                public override Expression CreateExpressionTree (EmitContext ec)
                {
-                       return underlying.CreateExpressionTree (ec);
+                       return wrap.CreateExpressionTree (ec);
                }                       
 
                public override Expression DoResolve (EmitContext ec)
                {
-                       expr = expr.Resolve (ec);
-                       if (expr == null)
+                       wrap = Wrap.Create (expr, type);
+                       if (wrap == null)
                                return null;
 
-                       unwrap = Unwrap.Create (expr, ec);
+                       //
+                       // It's null when lifted conversion is transparent
+                       //
                        if (unwrap == null)
-                               return null;
-
-                       underlying = ResolveUnderlying (unwrap, ec);
-                       if (underlying == null)
-                               return null;
+                               return wrap;
 
-                       TypeExpr target_type = new NullableType (underlying.Type, loc);
-                       target_type = target_type.ResolveAsTypeTerminal (ec, false);
-                       if (target_type == null)
-                               return null;
-
-                       wrap = Wrap.Create (underlying, target_type.Type);
-                       if (wrap == null)
-                               return null;
-
-                       null_value = LiftedNull.Create (wrap.Type, loc);
+                       null_value = LiftedNull.Create (type, loc);
 
-                       type = wrap.Type;
                        eclass = ExprClass.Value;
                        return this;
                }
 
-               protected abstract Expression ResolveUnderlying (Expression unwrap, EmitContext ec);
-
                public override void Emit (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;
@@ -447,52 +433,119 @@ namespace Mono.CSharp.Nullable
                }
        }
 
-       public class LiftedConversion : Lifted
+       public class LiftedUnaryOperator : Unary, IMemoryLocation
        {
-               public readonly bool IsUser;
-               public readonly bool IsExplicit;
-               public readonly Type TargetType;
+               Unwrap unwrap;
+               Expression user_operator;
+
+               public LiftedUnaryOperator (Unary.Operator op, Expression expr)
+                       : base (op, expr)
+               {
+               }
 
-               public LiftedConversion (Expression expr, Type target_type, bool is_user,
-                                        bool is_explicit, Location loc)
-                       : base (expr, loc)
+               public void AddressOf (EmitContext ec, AddressOp mode)
                {
-                       this.IsUser = is_user;
-                       this.IsExplicit = is_explicit;
-                       this.TargetType = target_type;
+                       unwrap.AddressOf (ec, mode);
                }
 
-               protected override Expression ResolveUnderlying (Expression unwrap, EmitContext ec)
+               public override Expression CreateExpressionTree (EmitContext ec)
                {
-                       Type type = TypeManager.GetTypeArguments (TargetType) [0];
+                       if (user_operator != null)
+                               return user_operator.CreateExpressionTree (ec);
 
-                       if (IsUser) {
-                               if (IsExplicit)
-                                       return Convert.ExplicitUserConversion (ec, unwrap, type, loc);
-                               else
-                                       return Convert.ImplicitUserConversion (ec, unwrap, type, loc);
+                       if (Oper == Operator.UnaryPlus)
+                               return Expr.CreateExpressionTree (ec);
+
+                       return base.CreateExpressionTree (ec);
+               }
+
+               public override Expression DoResolve (EmitContext ec)
+               {
+                       if (eclass != ExprClass.Invalid)
+                               return this;
+
+                       unwrap = Unwrap.Create (Expr, false);
+                       if (unwrap == null)
+                               return null;
+
+                       Expression res = base.ResolveOperator (ec, unwrap);
+                       if (res != this) {
+                               if (user_operator == null)
+                                       return res;
                        } else {
-                               if (IsExplicit)
-                                       return Convert.ExplicitConversion (ec, unwrap, type, loc);
-                               else
-                                       return Convert.ImplicitConversion (ec, unwrap, type, loc);
+                               res = Expr = LiftExpression (ec, Expr);
                        }
+
+                       if (res == null)
+                               return null;
+
+                       eclass = ExprClass.Value;
+                       type = res.Type;
+                       return this;
                }
-       }
 
-       public class LiftedUnaryOperator : Lifted
-       {
-               public readonly Unary.Operator Oper;
+               public override void Emit (EmitContext ec)
+               {
+                       ILGenerator ig = ec.ig;
+                       Label is_null_label = ig.DefineLabel ();
+                       Label end_label = ig.DefineLabel ();
+
+                       unwrap.EmitCheck (ec);
+                       ig.Emit (OpCodes.Brfalse, is_null_label);
+
+                       NullableInfo ni = new NullableInfo (type);
+
+                       if (user_operator != null) {
+                               user_operator.Emit (ec);
+                       } else {
+                               EmitOperator (ec, ni.UnderlyingType);
+                       }
+
+                       ig.Emit (OpCodes.Newobj, ni.Constructor);
+                       ig.Emit (OpCodes.Br_S, end_label);
+
+                       ig.MarkLabel (is_null_label);
+                       LiftedNull.Create (type, loc).Emit (ec);
+
+                       ig.MarkLabel (end_label);
+               }
+
+               Expression LiftExpression (EmitContext ec, Expression expr)
+               {
+                       TypeExpr lifted_type = new NullableType (expr.Type, expr.Location);
+                       lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
+                       if (lifted_type == null)
+                               return null;
+
+                       expr.Type = lifted_type.Type;
+                       return expr;
+               }
 
-               public LiftedUnaryOperator (Unary.Operator op, Expression expr, Location loc)
-                       : base (expr, loc)
+               protected override Expression ResolveEnumOperator (EmitContext ec, Expression expr)
                {
-                       this.Oper = op;
+                       expr = base.ResolveEnumOperator (ec, expr);
+                       if (expr == null)
+                               return null;
+
+                       Expr = LiftExpression (ec, Expr);
+                       return LiftExpression (ec, expr);
                }
 
-               protected override Expression ResolveUnderlying (Expression unwrap, EmitContext ec)
+               protected override Expression ResolveUserOperator (EmitContext ec, Expression expr)
                {
-                       return new Unary (Oper, unwrap, loc).Resolve (ec);
+                       expr = base.ResolveUserOperator (ec, expr);
+                       if (expr == null)
+                               return null;
+
+                       //
+                       // When a user operator is of non-nullable type
+                       //
+                       if (Expr is Unwrap) {
+                               user_operator = LiftExpression (ec, expr);
+                               return user_operator;
+                       }
+
+                       return expr;
                }
        }
 
@@ -501,6 +554,8 @@ namespace Mono.CSharp.Nullable
                Unwrap left_unwrap, right_unwrap;
                bool left_null_lifted, right_null_lifted;
                Expression left_orig, right_orig;
+               Expression user_operator;
+               ConstructorInfo wrap_ctor;
 
                public LiftedBinaryOperator (Binary.Operator op, Expression left, Expression right,
                                             Location loc)
@@ -509,6 +564,14 @@ namespace Mono.CSharp.Nullable
                        this.loc = loc;
                }
 
+               public override Expression CreateExpressionTree (EmitContext ec)
+               {
+                       if (user_operator != null)
+                               return user_operator.CreateExpressionTree (ec);
+
+                       return base.CreateExpressionTree (ec);
+               }
+
                //
                // CSC 2 has this behavior, it allows structs to be compared
                // with the null literal *outside* of a generics context and
@@ -520,11 +583,10 @@ namespace Mono.CSharp.Nullable
                        Constant c = new BoolConstant (Oper == Operator.Inequality, loc);
 
                        if ((Oper & Operator.EqualityMask) != 0) {
-                               Report.Warning (472, 2, loc, "The result of comparing `{0}' against null is always `{1}'. " +
-                                               "This operation is undocumented and it is temporary supported for compatibility reasons only",
+                               Report.Warning (472, 2, loc, "The result of comparing value type `{0}' with null is `{1}'",
                                                expr.GetSignatureForError (), c.AsString ());
                        } else {
-                               Report.Warning (464, 2, loc, "The result of comparing type `{0}' against null is always `{1}'",
+                               Report.Warning (464, 2, loc, "The result of comparing type `{0}' with null is always `{1}'",
                                                expr.GetSignatureForError (), c.AsString ());
                        }
 
@@ -541,16 +603,17 @@ namespace Mono.CSharp.Nullable
                                return null;
                        }
 
+                       bool use_default_call = (Oper & (Operator.BitwiseMask | Operator.EqualityMask)) != 0;
                        left_orig = left;
                        if (TypeManager.IsNullableType (left.Type)) {
-                               left = left_unwrap = Unwrap.Create (left, ec);
+                               left = left_unwrap = Unwrap.Create (left, use_default_call);
                                if (left == null)
                                        return null;
                        }
 
                        right_orig = right;
                        if (TypeManager.IsNullableType (right.Type)) {
-                               right = right_unwrap = Unwrap.Create (right, ec);
+                               right = right_unwrap = Unwrap.Create (right, use_default_call);
                                if (right == null)
                                        return null;
                        }
@@ -560,30 +623,20 @@ namespace Mono.CSharp.Nullable
                        // Arguments can be lifted for equal operators when the return type is bool and both
                        // arguments are of same type
                        //      
-                       if (left is NullLiteral) {
+                       if (left_orig.IsNull) {
                                left = right;
                                left_null_lifted = true;
                                type = TypeManager.bool_type;
                        }
 
-                       if (right is NullLiteral) {
+                       if (right_orig.IsNull) {
                                right = left;
                                right_null_lifted = true;
                                type = TypeManager.bool_type;
                        }
 
                        eclass = ExprClass.Value;
-                       Expression expr = DoResolveCore (ec, left_orig, right_orig);
-                       if (expr != this || (Oper & Operator.ComparisonMask) != 0)
-                               return expr;
-
-                       TypeExpr target_type = new NullableType (type, loc);
-                       target_type = target_type.ResolveAsTypeTerminal (ec, false);
-                       if (target_type == null)
-                               return null;
-
-                       type = target_type.Type;
-                       return this;
+                       return DoResolveCore (ec, left_orig, right_orig);
                }
 
                void EmitBitwiseBoolean (EmitContext ec)
@@ -594,10 +647,10 @@ namespace Mono.CSharp.Nullable
                        Label load_right = ig.DefineLabel ();
                        Label end_label = ig.DefineLabel ();
 
-                       left_unwrap.EmitGetValueOrDefault (ec);
+                       left_unwrap.Emit (ec);
                        ig.Emit (OpCodes.Brtrue_S, load_right);
 
-                       right_unwrap.EmitGetValueOrDefault (ec);
+                       right_unwrap.Emit (ec);
                        ig.Emit (OpCodes.Brtrue_S, load_left);
 
                        left_unwrap.EmitCheck (ec);
@@ -607,115 +660,86 @@ namespace Mono.CSharp.Nullable
                        ig.MarkLabel (load_left);
 
                        if (Oper == Operator.BitwiseAnd) {
-                               left_unwrap.LoadTemporary (ec);
+                               left_unwrap.Load (ec);
                        } else {
-                               right_unwrap.LoadTemporary (ec);
+                               right_unwrap.Load (ec);
                                right_unwrap = left_unwrap;
                        }
                        ig.Emit (OpCodes.Br_S, end_label);
 
                        // load right
                        ig.MarkLabel (load_right);
-                       right_unwrap.LoadTemporary (ec);
+                       right_unwrap.Load (ec);
 
                        ig.MarkLabel (end_label);
                }
 
+               //
+               // Emits optimized equality or inequality operator when possible
+               //
                void EmitEquality (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;
 
-                       Label both_have_value_label = ig.DefineLabel ();
-                       Label end_label = ig.DefineLabel ();
-
                        //
-                       // Both are nullable types
+                       // Either left or right is null
                        //
-                       if (left_unwrap != null && right_unwrap != null && !right.IsNull && !left.IsNull) {
-                               Label dissimilar_label = ig.DefineLabel ();
-
-                               left_unwrap.EmitGetValueOrDefault (ec);
-                               right_unwrap.EmitGetValueOrDefault (ec);
-                               ig.Emit (OpCodes.Bne_Un_S, dissimilar_label);
-
+                       if (left_unwrap != null && (right_null_lifted || right.IsNull)) {
                                left_unwrap.EmitCheck (ec);
-                               right_unwrap.EmitCheck (ec);
-                               if (Oper == Operator.Inequality)
-                                       ig.Emit (OpCodes.Xor);
-                               else
-                                       ig.Emit (OpCodes.Ceq);
-
-                               ig.Emit (OpCodes.Br_S, end_label);
-
-                               ig.MarkLabel (dissimilar_label);
-                               if (Oper == Operator.Inequality)
-                                       ig.Emit (OpCodes.Ldc_I4_1);
-                               else
+                               if (Oper == Binary.Operator.Equality) {
                                        ig.Emit (OpCodes.Ldc_I4_0);
-
-                               ig.MarkLabel (end_label);
+                                       ig.Emit (OpCodes.Ceq);
+                               }
                                return;
                        }
 
-                       //
-                       // Either left or right is nullable
-                       //
-                       if (left_unwrap != null) {
-                               left_unwrap.EmitCheck (ec);
-                               if (right.IsNull) {
-                                       if (Oper == Binary.Operator.Equality) {
-                                               ig.Emit (OpCodes.Ldc_I4_0);
-                                               ig.Emit (OpCodes.Ceq);
-                                       }
-                                       return;
-                               }
-                               ig.Emit (OpCodes.Brtrue_S, both_have_value_label);
-                       } else {
+                       if (right_unwrap != null && (left_null_lifted || left.IsNull)) {
                                right_unwrap.EmitCheck (ec);
-                               if (left.IsNull) {
-                                       if (Oper == Binary.Operator.Equality) {
-                                               ig.Emit (OpCodes.Ldc_I4_0);
-                                               ig.Emit (OpCodes.Ceq);
-                                       }
-                                       return;
+                               if (Oper == Binary.Operator.Equality) {
+                                       ig.Emit (OpCodes.Ldc_I4_0);
+                                       ig.Emit (OpCodes.Ceq);
                                }
-                               ig.Emit (OpCodes.Brtrue_S, both_have_value_label);
+                               return;
                        }
 
-                       if (Oper == Binary.Operator.Equality)
-                               ig.Emit (OpCodes.Ldc_I4_0);
-                       else
-                               ig.Emit (OpCodes.Ldc_I4_1);
-                       ig.Emit (OpCodes.Br, end_label);
-
-                       ig.MarkLabel (both_have_value_label);
-                       EmitOperator (ec);
-
-                       ig.MarkLabel (end_label);
-               }
+                       Label dissimilar_label = ig.DefineLabel ();
+                       Label end_label = ig.DefineLabel ();
 
-               void EmitComparision (EmitContext ec)
-               {
-                       ILGenerator ig = ec.ig;
+                       if (user_operator != null) {
+                               user_operator.Emit (ec);
+                               ig.Emit (Oper == Operator.Equality ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, dissimilar_label);
+                       } else {
+                               left.Emit (ec);
+                               right.Emit (ec);
 
-                       Label is_null_label = ig.DefineLabel ();
-                       Label end_label = ig.DefineLabel ();
+                               ig.Emit (OpCodes.Bne_Un_S, dissimilar_label);
+                       }
 
-                       if (left_unwrap != null) {
+                       if (left_unwrap != null)
                                left_unwrap.EmitCheck (ec);
-                               ig.Emit (OpCodes.Brfalse, is_null_label);
-                       }
 
-                       if (right_unwrap != null) {
+                       if (right_unwrap != null)
                                right_unwrap.EmitCheck (ec);
-                               ig.Emit (OpCodes.Brfalse, is_null_label);
+
+                       if (left_unwrap != null && right_unwrap != null) {
+                               if (Oper == Operator.Inequality)
+                                       ig.Emit (OpCodes.Xor);
+                               else
+                                       ig.Emit (OpCodes.Ceq);
+                       } else {
+                               if (Oper == Operator.Inequality) {
+                                       ig.Emit (OpCodes.Ldc_I4_0);
+                                       ig.Emit (OpCodes.Ceq);
+                               }
                        }
 
-                       EmitOperator (ec);
                        ig.Emit (OpCodes.Br_S, end_label);
 
-                       ig.MarkLabel (is_null_label);
-                       ig.Emit (OpCodes.Ldc_I4_0);
+                       ig.MarkLabel (dissimilar_label);
+                       if (Oper == Operator.Inequality)
+                               ig.Emit (OpCodes.Ldc_I4_1);
+                       else
+                               ig.Emit (OpCodes.Ldc_I4_0);
 
                        ig.MarkLabel (end_label);
                }
@@ -728,12 +752,13 @@ namespace Mono.CSharp.Nullable
 
                public override void Emit (EmitContext ec)
                {
-                       if (left_unwrap != null)
-                               left_unwrap.Store (ec);
-                       if (right_unwrap != null)
-                               right_unwrap.Store (ec);
+                       //
+                       // Optimize same expression operation
+                       //
+                       if (right_unwrap != null && right.Equals (left))
+                               right_unwrap = left_unwrap;
 
-                       if (IsBitwiseBoolean) {
+                       if (user_operator == null && IsBitwiseBoolean) {
                                EmitBitwiseBoolean (ec);
                                return;
                        }
@@ -743,11 +768,6 @@ namespace Mono.CSharp.Nullable
                                return;
                        }
 
-                       if ((Oper & Operator.ComparisonMask) != 0) {
-                               EmitComparision (ec);
-                               return;
-                       }
-
                        ILGenerator ig = ec.ig;
 
                        Label is_null_label = ig.DefineLabel ();
@@ -758,20 +778,44 @@ namespace Mono.CSharp.Nullable
                                ig.Emit (OpCodes.Brfalse, is_null_label);
                        }
 
-                       if (right_unwrap != null) {
+                       //
+                       // Don't emit HasValue check when left and right expressions are same
+                       //
+                       if (right_unwrap != null && !left.Equals (right)) {
                                right_unwrap.EmitCheck (ec);
                                ig.Emit (OpCodes.Brfalse, is_null_label);
                        }
 
-                       base.EmitOperator (ec);
+                       EmitOperator (ec, left.Type);
+
+                       if (wrap_ctor != null)
+                               ig.Emit (OpCodes.Newobj, wrap_ctor);
 
                        ig.Emit (OpCodes.Br_S, end_label);
                        ig.MarkLabel (is_null_label);
-                       LiftedNull.Create (type, loc).Emit (ec);
+
+                       if ((Oper & Operator.ComparisonMask) != 0) {
+                               ig.Emit (OpCodes.Ldc_I4_0);
+                       } else {
+                               LiftedNull.Create (type, loc).Emit (ec);
+                       }
 
                        ig.MarkLabel (end_label);
                }
 
+               protected override void EmitOperator (EmitContext ec, Type l)
+               {
+                       if (user_operator != null) {
+                               user_operator.Emit (ec);
+                               return;
+                       }
+
+                       if (TypeManager.IsNullableType (l))
+                               l = TypeManager.GetTypeArguments (l) [0];
+
+                       base.EmitOperator (ec, l);
+               }
+
                bool IsBitwiseBoolean {
                        get {
                                return (Oper & Operator.BitwiseMask) != 0 && left_unwrap != null && right_unwrap != null &&
@@ -786,38 +830,38 @@ namespace Mono.CSharp.Nullable
                        //
                        // Avoid double conversion
                        //
-                       if (left_unwrap == null || left_null_lifted || !TypeManager.IsEqual (left_unwrap.Type, left.Type)) {
+                       if (left_unwrap == null || left_null_lifted || !TypeManager.IsEqual (left_unwrap.Type, left.Type) || (left_unwrap != null && right_null_lifted)) {
                                lifted_type = new NullableType (left.Type, loc);
                                lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
                                if (lifted_type == null)
                                        return null;
 
-                               if (left is UserCast || left is EmptyCast)
+                               if (left is UserCast || left is TypeCast)
                                        left.Type = lifted_type.Type;
                                else
                                        left = EmptyCast.Create (left, lifted_type.Type);
                        }
 
-                       if (right_unwrap == null || right_null_lifted || !TypeManager.IsEqual (right_unwrap.Type, right.Type)) {
+                       if (right_unwrap == null || right_null_lifted || !TypeManager.IsEqual (right_unwrap.Type, right.Type) || (right_unwrap != null && left_null_lifted)) {
                                lifted_type = new NullableType (right.Type, loc);
                                lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
                                if (lifted_type == null)
                                        return null;
 
-                               if (right is UserCast || right is EmptyCast)
+                               if (right is UserCast || right is TypeCast)
                                        right.Type = lifted_type.Type;
                                else
                                        right = EmptyCast.Create (right, lifted_type.Type);
                        }
 
-                       // TODO: Handle bitwise bool 
-                       if ((Oper & Operator.ComparisonMask) == 0 && !IsBitwiseBoolean) {
+                       if ((Oper & Operator.ComparisonMask) == 0) {
                                lifted_type = new NullableType (res_expr.Type, loc);
                                lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
                                if (lifted_type == null)
                                        return null;
 
-                               res_expr = new LiftedWrap (res_expr, lifted_type.Type).Resolve (ec);
+                               wrap_ctor = new NullableInfo (lifted_type.Type).Constructor;
+                               type = res_expr.Type = lifted_type.Type;
                        }
 
                        if (left_null_lifted) {
@@ -849,11 +893,11 @@ namespace Mono.CSharp.Nullable
                        return res_expr;
                }
 
-               protected override Expression ResolveOperatorPredefined (EmitContext ec, Binary.PredefinedOperator [] operators, bool primitives_only)
+               protected override Expression ResolveOperatorPredefined (EmitContext ec, Binary.PredefinedOperator [] operators, bool primitives_only, Type enum_type)
                {
-                       Expression e = base.ResolveOperatorPredefined (ec, operators, primitives_only);
+                       Expression e = base.ResolveOperatorPredefined (ec, operators, primitives_only, enum_type);
 
-                       if (e == this)
+                       if (e == this || enum_type != null)
                                return LiftResult (ec, e);
 
                        //
@@ -877,13 +921,13 @@ namespace Mono.CSharp.Nullable
                        if (expr == null)
                                return null;
 
-                       //
-                       // When lifting null literal and user operator exists, no call is made
-                       //
-                       if (left_null_lifted || right_null_lifted)
-                               expr = ReducedExpression.Create (this, expr).Resolve (ec);
+                       expr = LiftResult (ec, expr);
+                       if (expr is Constant)
+                               return expr;
 
-                       return LiftResult (ec, expr);
+                       type = expr.Type;
+                       user_operator = expr;
+                       return this;
                }
        }
 
@@ -901,87 +945,121 @@ namespace Mono.CSharp.Nullable
                
                public override Expression CreateExpressionTree (EmitContext ec)
                {
+                       if (left.Type == TypeManager.null_type)
+                               Report.Error (845, loc, "An expression tree cannot contain a coalescing operator with null left side");
+
                        UserCast uc = left as UserCast;
                        Expression conversion = null;
                        if (uc != null) {
                                left = uc.Source;
 
-                               ArrayList c_args = new ArrayList (2);
+                               Arguments c_args = new Arguments (2);
                                c_args.Add (new Argument (uc.CreateExpressionTree (ec)));
                                c_args.Add (new Argument (left.CreateExpressionTree (ec)));
                                conversion = CreateExpressionFactoryCall ("Lambda", c_args);
                        }
 
-                       ArrayList args = new ArrayList (3);
+                       Arguments args = new Arguments (3);
                        args.Add (new Argument (left.CreateExpressionTree (ec)));
                        args.Add (new Argument (right.CreateExpressionTree (ec)));
                        if (conversion != null)
                                args.Add (new Argument (conversion));
                        
                        return CreateExpressionFactoryCall ("Coalesce", args);
-               }                       
+               }
 
-               public override Expression DoResolve (EmitContext ec)
+               Expression ConvertExpression (EmitContext ec)
                {
-                       if (type != null)
-                               return this;
-
-                       left = left.Resolve (ec);
-                       right = right.Resolve (ec);
-
-                       if (left == null || right == null)
+                       // TODO: ImplicitConversionExists should take care of this
+                       if (left.eclass == ExprClass.MethodGroup)
                                return null;
 
-                       eclass = ExprClass.Value;
-                       Type ltype = left.Type, rtype = right.Type;
-                       Expression expr;
+                       Type ltype = left.Type;
 
+                       //
+                       // If left is a nullable type and an implicit conversion exists from right to underlying type of left,
+                       // the result is underlying type of left
+                       //
                        if (TypeManager.IsNullableType (ltype)) {
-                               NullableInfo info = new NullableInfo (ltype);
-
-                               unwrap = Unwrap.Create (left, ec);
+                               unwrap = Unwrap.Create (left, false);
                                if (unwrap == null)
                                        return null;
 
-                               expr = Convert.ImplicitConversion (ec, right, info.UnderlyingType, loc);
-                               if (expr != null) {
+                               if (Convert.ImplicitConversionExists (ec, right, unwrap.Type)) {
                                        left = unwrap;
-                                       right = expr;
-                                       type = expr.Type;
+                                       type = left.Type;
+                                       right = Convert.ImplicitConversion (ec, right, type, loc);
+                                       return this;
+                               }
+                       } else if (TypeManager.IsReferenceType (ltype)) {
+                               if (Convert.ImplicitConversionExists (ec, right, ltype)) {
+                                       //
+                                       // Reduce (constant ?? expr) to constant
+                                       //
+                                       Constant lc = left as Constant;
+                                       if (lc != null && !lc.IsDefaultValue)
+                                               return new SideEffectConstant (lc, right, loc).Resolve (ec);
+
+                                       //
+                                       // Reduce (left ?? null) to left OR (null-constant ?? right) to right
+                                       //
+                                       if (right.IsNull || lc != null)
+                                               return ReducedExpression.Create (lc != null ? right : left, this).Resolve (ec);
+
+                                       right = Convert.ImplicitConversion (ec, right, ltype, loc);
+                                       type = left.Type;
                                        return this;
                                }
-                       } else if (!TypeManager.IsReferenceType (ltype)) {
-                               Binary.Error_OperatorCannotBeApplied (loc, "??", ltype, rtype);
+                       } else {
                                return null;
                        }
 
-                       expr = Convert.ImplicitConversion (ec, right, ltype, loc);
-                       if (expr != null) {
-                               type = expr.Type;
-                               right = expr;
-                               return this;
-                       }
+                       Type rtype = right.Type;
+                       if (!Convert.ImplicitConversionExists (ec, unwrap != null ? unwrap : left, rtype) || right.eclass == ExprClass.MethodGroup)
+                               return null;
 
-                       Expression left_null = unwrap != null ? unwrap : left;
-                       expr = Convert.ImplicitConversion (ec, left_null, rtype, loc);
-                       if (expr != null) {
-                               left = expr;
-                               type = rtype;
+                       //
+                       // Reduce (null ?? right) to right
+                       //
+                       if (left.IsNull)
+                               return ReducedExpression.Create (right, this).Resolve (ec);
+
+                       left = Convert.ImplicitConversion (ec, unwrap != null ? unwrap : left, rtype, loc);
+                       type = rtype;
+                       return this;
+               }
+
+               public override Expression DoResolve (EmitContext ec)
+               {
+                       if (eclass != ExprClass.Invalid)
                                return this;
+
+                       left = left.Resolve (ec);
+                       right = right.Resolve (ec);
+
+                       if (left == null || right == null)
+                               return null;
+
+                       eclass = ExprClass.Value;
+
+                       Expression e = ConvertExpression (ec);
+                       if (e == null) {
+                               Binary.Error_OperatorCannotBeApplied (left, right, "??", loc);
+                               return null;
                        }
 
-                       Binary.Error_OperatorCannotBeApplied (loc, "??", ltype, rtype);
-                       return null;
+                       return e;
                }
 
                public override void Emit (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;
 
-                       Label is_null_label = ig.DefineLabel ();
                        Label end_label = ig.DefineLabel ();
 
                        if (unwrap != null) {
+                               Label is_null_label = ig.DefineLabel ();
+
                                unwrap.EmitCheck (ec);
                                ig.Emit (OpCodes.Brfalse, is_null_label);
 
@@ -992,19 +1070,27 @@ namespace Mono.CSharp.Nullable
                                right.Emit (ec);
 
                                ig.MarkLabel (end_label);
-                       } else {
-                               left.Emit (ec);
-                               ig.Emit (OpCodes.Dup);
-                               ig.Emit (OpCodes.Brtrue, end_label);
+                               return;
+                       }
 
-                               ig.MarkLabel (is_null_label);
+                       left.Emit (ec);
 
-                               ig.Emit (OpCodes.Pop);
-                               right.Emit (ec);
+                       ig.Emit (OpCodes.Dup);
+                       ig.Emit (OpCodes.Brtrue, end_label);
 
-                               ig.MarkLabel (end_label);
-                       }
+                       ig.Emit (OpCodes.Pop);
+                       right.Emit (ec);
+
+                       ig.MarkLabel (end_label);
                }
+
+               public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
+               {
+                       left.MutateHoistedGenericType (storey);
+                       right.MutateHoistedGenericType (storey);
+                       type = storey.MutateType (type);
+               }
+
                protected override void CloneTo (CloneContext clonectx, Expression t)
                {
                        NullCoalescingOperator target = (NullCoalescingOperator) t;
@@ -1017,7 +1103,7 @@ namespace Mono.CSharp.Nullable
        public class LiftedUnaryMutator : ExpressionStatement
        {
                public readonly UnaryMutator.Mode Mode;
-               Expression expr, null_value;
+               Expression expr;
                UnaryMutator underlying;
                Unwrap unwrap;
 
@@ -1030,22 +1116,26 @@ namespace Mono.CSharp.Nullable
                        eclass = ExprClass.Value;
                }
 
+               public override Expression CreateExpressionTree (EmitContext ec)
+               {
+                       return new SimpleAssign (this, this).CreateExpressionTree (ec);
+               }
+
                public override Expression DoResolve (EmitContext ec)
                {
                        expr = expr.Resolve (ec);
                        if (expr == null)
                                return null;
 
-                       unwrap = Unwrap.Create (expr, ec);
+                       unwrap = Unwrap.Create (expr, false);
                        if (unwrap == null)
                                return null;
 
-                       underlying = (UnaryMutator) new UnaryMutator (Mode, unwrap, loc).Resolve (ec);
+                       underlying = (UnaryMutator) new UnaryMutator (Mode, unwrap).Resolve (ec);
                        if (underlying == null)
                                return null;
 
                        type = expr.Type;
-                       null_value = LiftedNull.Create (type, loc);
                        return this;
                }
 
@@ -1058,15 +1148,16 @@ namespace Mono.CSharp.Nullable
                        unwrap.EmitCheck (ec);
                        ig.Emit (OpCodes.Brfalse, is_null_label);
 
-                       if (is_expr)
+                       if (is_expr) {
                                underlying.Emit (ec);
-                       else
+                               ig.Emit (OpCodes.Br_S, end_label);
+                       } else {
                                underlying.EmitStatement (ec);
-                       ig.Emit (OpCodes.Br, end_label);
+                       }
 
                        ig.MarkLabel (is_null_label);
                        if (is_expr)
-                               null_value.Emit (ec);
+                               LiftedNull.Create (type, loc).Emit (ec);
 
                        ig.MarkLabel (end_label);
                }