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[mono.git] / mcs / mcs / ecore.cs

//
// ecore.cs: Core of the Expression representation for the intermediate tree.
//
// Author:
//   Miguel de Icaza (miguel@ximian.com)
//
// (C) 2001 Ximian, Inc.
//
//

namespace Mono.CSharp {
        using System;
        using System.Collections;
        using System.Diagnostics;
        using System.Reflection;
        using System.Reflection.Emit;
        using System.Text;

        /// <remarks>
        ///   The ExprClass class contains the is used to pass the 
        ///   classification of an expression (value, variable, namespace,
        ///   type, method group, property access, event access, indexer access,
        ///   nothing).
        /// </remarks>
        public enum ExprClass : byte {
                Invalid,
                
                Value,
                Variable,
                Namespace,
                Type,
                MethodGroup,
                PropertyAccess,
                EventAccess,
                IndexerAccess,
                Nothing, 
        }

        /// <summary>
        ///   This interface is implemented by variables
        /// </summary>
        public interface IMemoryLocation {
                /// <summary>
                ///   The AddressOf method should generate code that loads
                ///   the address of the object and leaves it on the stack
                /// </summary>
                void AddressOf (EmitContext ec);
        }

        /// <remarks>
        ///   Base class for expressions
        /// </remarks>
        public abstract class Expression {
                public ExprClass eclass;
                protected Type      type;
                
                public Type Type {
                        get {
                                return type;
                        }

                        set {
                                type = value;
                        }
                }

                /// <summary>
                ///   Utility wrapper routine for Error, just to beautify the code
                /// </summary>
                static protected void Error (int error, string s)
                {
                        Report.Error (error, s);
                }

                static protected void Error (int error, Location loc, string s)
                {
                        Report.Error (error, loc, s);
                }
                
                /// <summary>
                ///   Utility wrapper routine for Warning, just to beautify the code
                /// </summary>
                static protected void Warning (int warning, string s)
                {
                        Report.Warning (warning, s);
                }

                static public void error30 (Location loc, Type source, Type target)
                {
                        Report.Error (30, loc, "Cannot convert type '" +
                                      TypeManager.CSharpName (source) + "' to '" +
                                      TypeManager.CSharpName (target) + "'");
                }

                /// <summary>
                ///   Performs semantic analysis on the Expression
                /// </summary>
                ///
                /// <remarks>
                ///   The Resolve method is invoked to perform the semantic analysis
                ///   on the node.
                ///
                ///   The return value is an expression (it can be the
                ///   same expression in some cases) or a new
                ///   expression that better represents this node.
                ///   
                ///   For example, optimizations of Unary (LiteralInt)
                ///   would return a new LiteralInt with a negated
                ///   value.
                ///   
                ///   If there is an error during semantic analysis,
                ///   then an error should be reported (using Report)
                ///   and a null value should be returned.
                ///   
                ///   There are two side effects expected from calling
                ///   Resolve(): the the field variable "eclass" should
                ///   be set to any value of the enumeration
                ///   `ExprClass' and the type variable should be set
                ///   to a valid type (this is the type of the
                ///   expression).
                /// </remarks>
                public abstract Expression DoResolve (EmitContext ec);

                public virtual Expression DoResolveLValue (EmitContext ec, Expression right_side)
                {
                        return DoResolve (ec);
                }
                
                /// <summary>
                ///   Resolves an expression and performs semantic analysis on it.
                /// </summary>
                ///
                /// <remarks>
                ///   Currently Resolve wraps DoResolve to perform sanity
                ///   checking and assertion checking on what we expect from Resolve.
                /// </remarks>
                public Expression Resolve (EmitContext ec)
                {
                        Expression e = DoResolve (ec);

                        if (e != null){
                                if (e is SimpleName){
                                        SimpleName s = (SimpleName) e;
                                        
                                        Report.Error (
                                                103, s.Location,
                                                "The name `" + s.Name + "' could not be found in `" +
                                                ec.TypeContainer.Name + "'");
                                        return null;
                                }
                                
                                if (e.eclass == ExprClass.Invalid)
                                        throw new Exception ("Expression " + e.GetType () +
                                                             " ExprClass is Invalid after resolve");

                                if (e.eclass != ExprClass.MethodGroup)
                                        if (e.type == null)
                                                throw new Exception (
                                                        "Expression " + e.GetType () +
                                                        " did not set its type after Resolve\n" +
                                                        "called from: " + this.GetType ());
                        }

                        return e;
                }

                /// <summary>
                ///   Performs expression resolution and semantic analysis, but
                ///   allows SimpleNames to be returned.
                /// </summary>
                ///
                /// <remarks>
                ///   This is used by MemberAccess to construct long names that can not be
                ///   partially resolved (namespace-qualified names for example).
                /// </remarks>
                public Expression ResolveWithSimpleName (EmitContext ec)
                {
                        Expression e;

                        if (this is SimpleName)
                                e = ((SimpleName) this).DoResolveAllowStatic (ec);
                        else 
                                e = DoResolve (ec);

                        if (e != null){
                                if (e is SimpleName)
                                        return e;

                                if (e.eclass == ExprClass.Invalid)
                                        throw new Exception ("Expression " + e +
                                                             " ExprClass is Invalid after resolve");

                                if (e.eclass != ExprClass.MethodGroup)
                                        if (e.type == null)
                                                throw new Exception ("Expression " + e +
                                                                     " did not set its type after Resolve");
                        }

                        return e;
                }
                
                /// <summary>
                ///   Resolves an expression for LValue assignment
                /// </summary>
                ///
                /// <remarks>
                ///   Currently ResolveLValue wraps DoResolveLValue to perform sanity
                ///   checking and assertion checking on what we expect from Resolve
                /// </remarks>
                public Expression ResolveLValue (EmitContext ec, Expression right_side)
                {
                        Expression e = DoResolveLValue (ec, right_side);

                        if (e != null){
                                if (e is SimpleName){
                                        SimpleName s = (SimpleName) e;
                                        
                                        Report.Error (
                                                103, s.Location,
                                                "The name `" + s.Name + "' could not be found in `" +
                                                ec.TypeContainer.Name + "'");
                                        return null;
                                }

                                if (e.eclass == ExprClass.Invalid)
                                        throw new Exception ("Expression " + e +
                                                             " ExprClass is Invalid after resolve");

                                if (e.eclass != ExprClass.MethodGroup)
                                        if (e.type == null)
                                                throw new Exception ("Expression " + e +
                                                                     " did not set its type after Resolve");
                        }

                        return e;
                }
                
                /// <summary>
                ///   Emits the code for the expression
                /// </summary>
                ///
                /// <remarks>
                ///   The Emit method is invoked to generate the code
                ///   for the expression.  
                /// </remarks>
                public abstract void Emit (EmitContext ec);

                /// <summary>
                ///   Protected constructor.  Only derivate types should
                ///   be able to be created
                /// </summary>

                protected Expression ()
                {
                        eclass = ExprClass.Invalid;
                        type = null;
                }

                /// <summary>
                ///   Returns a literalized version of a literal FieldInfo
                /// </summary>
                ///
                /// <remarks>
                ///   The possible return values are:
                ///      IntConstant, UIntConstant
                ///      LongLiteral, ULongConstant
                ///      FloatConstant, DoubleConstant
                ///      StringConstant
                ///
                ///   The value returned is already resolved.
                /// </remarks>
                public static Constant Constantify (object v, Type t)
                {
                        if (t == TypeManager.int32_type)
                                return new IntConstant ((int) v);
                        else if (t == TypeManager.uint32_type)
                                return new UIntConstant ((uint) v);
                        else if (t == TypeManager.int64_type)
                                return new LongConstant ((long) v);
                        else if (t == TypeManager.uint64_type)
                                return new ULongConstant ((ulong) v);
                        else if (t == TypeManager.float_type)
                                return new FloatConstant ((float) v);
                        else if (t == TypeManager.double_type)
                                return new DoubleConstant ((double) v);
                        else if (t == TypeManager.string_type)
                                return new StringConstant ((string) v);
                        else if (t == TypeManager.short_type)
                                return new ShortConstant ((short)v);
                        else if (t == TypeManager.ushort_type)
                                return new UShortConstant ((ushort)v);
                        else if (t == TypeManager.sbyte_type)
                                return new SByteConstant (((sbyte)v));
                        else if (t == TypeManager.byte_type)
                                return new ByteConstant ((byte)v);
                        else if (t == TypeManager.char_type)
                                return new CharConstant ((char)v);
                        else if (TypeManager.IsEnumType (t)){
                                Expression e = Constantify (v, v.GetType ());

                                return new EnumConstant ((Constant) e, t);
                        } else
                                throw new Exception ("Unknown type for constant (" + t +
                                                     "), details: " + v);
                }

                /// <summary>
                ///   Returns a fully formed expression after a MemberLookup
                /// </summary>
                public static Expression ExprClassFromMemberInfo (EmitContext ec, MemberInfo mi, Location loc)
                {
                        if (mi is EventInfo)
                                return new EventExpr ((EventInfo) mi, loc);
                        else if (mi is FieldInfo)
                                return new FieldExpr ((FieldInfo) mi, loc);
                        else if (mi is PropertyInfo)
                                return new PropertyExpr ((PropertyInfo) mi, loc);
                        else if (mi is Type){
                                return new TypeExpr ((System.Type) mi);
                        }

                        return null;
                }

                //
                // Returns whether the array of memberinfos contains the given method
                //
                static bool ArrayContainsMethod (MemberInfo [] array, MethodBase new_method)
                {
                        Type [] new_args = TypeManager.GetArgumentTypes (new_method);

                        foreach (MethodBase method in array){
                                if (method.Name != new_method.Name)
                                        continue;
                                
                                Type [] old_args = TypeManager.GetArgumentTypes (method);
                                int old_count = old_args.Length;
                                int i;

                                if (new_args.Length != old_count)
                                        continue;
                                
                                for (i = 0; i < old_count; i++){
                                        if (old_args [i] != new_args [i])
                                                break;
                                }
                                if (i != old_count)
                                        continue;

                                if (!(method is MethodInfo && new_method is MethodInfo))
                                        return true;
                                
                                if (((MethodInfo) method).ReturnType == ((MethodInfo) new_method).ReturnType)
                                        return true;
                        }
                        return false;
                }
                
                //
                // We copy methods from `new_members' into `target_list' if the signature
                // for the method from in the new list does not exist in the target_list
                //
                // The name is assumed to be the same.
                //
                public static ArrayList CopyNewMethods (ArrayList target_list, MemberInfo [] new_members)
                {
                        if (target_list == null){
                                target_list = new ArrayList ();

                                target_list.AddRange (new_members);
                                return target_list;
                        }
                        
                        MemberInfo [] target_array = new MemberInfo [target_list.Count];
                        target_list.CopyTo (target_array, 0);
                        
                        foreach (MemberInfo mi in new_members){
                                MethodBase new_method = (MethodBase) mi;

                                if (!ArrayContainsMethod (target_array, new_method))
                                        target_list.Add (new_method);
                        }
                        return target_list;
                }
                
                //
                // FIXME: Probably implement a cache for (t,name,current_access_set)?
                //
                // This code could use some optimizations, but we need to do some
                // measurements.  For example, we could use a delegate to `flag' when
                // something can not any longer be a method-group (because it is something
                // else).
                //
                // Return values:
                //     If the return value is an Array, then it is an array of
                //     MethodBases
                //   
                //     If the return value is an MemberInfo, it is anything, but a Method
                //
                //     null on error.
                //
                // FIXME: When calling MemberLookup inside an `Invocation', we should pass
                // the arguments here and have MemberLookup return only the methods that
                // match the argument count/type, unlike we are doing now (we delay this
                // decision).
                //
                // This is so we can catch correctly attempts to invoke instance methods
                // from a static body (scan for error 120 in ResolveSimpleName).
                //
                //
                // FIXME: Potential optimization, have a static ArrayList
                //

                public static Expression MemberLookup (EmitContext ec, Type t, string name,
                                                       MemberTypes mt, BindingFlags bf, Location loc)
                {
                        Type source_type = ec.ContainerType;

                        if (source_type != null){
                                if (source_type == t || source_type.IsSubclassOf (t))
                                        bf |= BindingFlags.NonPublic;
                        }

                        //
                        // Lookup for members starting in the type requested and going
                        // up the hierarchy until a match is found.
                        //
                        // As soon as a non-method match is found, we return.
                        //
                        // If methods are found though, then the search proceeds scanning
                        // for more public methods in the hierarchy with signatures that
                        // do not match any of the signatures found so far.
                        //
                        ArrayList method_list = null;
                        Type current_type = t;
                        bool searching = true;
                        do {
                                MemberInfo [] mi;

                                mi = RootContext.TypeManager.FindMembers (
                                        current_type, mt, bf | BindingFlags.DeclaredOnly,
                                        System.Type.FilterName, name);
                                
                                if (current_type == TypeManager.object_type)
                                        searching = false;
                                else {
                                        current_type = current_type.BaseType;

                                        //
                                        // This happens with interfaces, they have a null
                                        // basetype
                                        //
                                        if (current_type == null)
                                                searching = false;
                                }

                                if (mi == null)
                                        continue;
                                
                                int count = mi.Length;

                                if (count == 0)
                                        continue;
                                
                                if (count == 1 && !(mi [0] is MethodBase))
                                        return Expression.ExprClassFromMemberInfo (ec, mi [0], loc);

                                //
                                // We found methods, turn the search into "method scan"
                                // mode.
                                //
                                method_list = CopyNewMethods (method_list, mi);
                                mt &= (MemberTypes.Method | MemberTypes.Constructor);
                        } while (searching);

                        if (method_list != null && method_list.Count > 0)
                                return new MethodGroupExpr (method_list);

                        return null;
                }

                public const MemberTypes AllMemberTypes =
                        MemberTypes.Constructor |
                        MemberTypes.Event       |
                        MemberTypes.Field       |
                        MemberTypes.Method      |
                        MemberTypes.NestedType  |
                        MemberTypes.Property;
                
                public const BindingFlags AllBindingFlags =
                        BindingFlags.Public |
                        BindingFlags.Static |
                        BindingFlags.Instance;

                public static Expression MemberLookup (EmitContext ec, Type t, string name, Location loc)
                {
                        return MemberLookup (ec, t, name, AllMemberTypes, AllBindingFlags, loc);
                }

                /// <summary>
                ///   This is a wrapper for MemberLookup that is not used to "probe", but
                ///   to find a final definition.  If the final definition is not found, we
                ///   look for private members and display a useful debugging message if we
                ///   find it.
                /// </summary>
                public static Expression MemberLookupFinal (EmitContext ec, Type t, string name, 
                                                            Location loc)
                {
                        Expression e;

                        e = MemberLookup (ec, t, name, AllMemberTypes, AllBindingFlags, loc);

                        if (e != null)
                                return e;
                        
                        e = MemberLookup (ec, t, name, AllMemberTypes,
                                          AllBindingFlags | BindingFlags.NonPublic, loc);
                        if (e == null){
                                Report.Error (
                                        117, loc, "`" + t + "' does not contain a definition " +
                                        "for `" + name + "'");
                        } else {
                                Report.Error (
                                        122, loc, "`" + t + "." + name +
                                        "' is inaccessible due to its protection level");
                        }
                        
                        return null;
                }
                
                static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
                {
                        Type expr_type = expr.Type;

                        if (target_type == TypeManager.object_type) {
                                //
                                // A pointer type cannot be converted to object
                                // 
                                if (expr_type.IsPointer)
                                        return null;
                                
                                if (expr_type.IsClass)
                                        return new EmptyCast (expr, target_type);
                                if (expr_type.IsValueType)
                                        return new BoxedCast (expr);
                        } else if (expr_type.IsSubclassOf (target_type)) {
                                return new EmptyCast (expr, target_type);
                        } else {

                                // This code is kind of mirrored inside StandardConversionExists
                                // with the small distinction that we only probe there
                                //
                                // Always ensure that the code here and there is in sync
                                
                                // from the null type to any reference-type.
                                if (expr is NullLiteral && !target_type.IsValueType)
                                        return new EmptyCast (expr, target_type);

                                // from any class-type S to any interface-type T.
                                if (expr_type.IsClass && target_type.IsInterface) {
                                        if (TypeManager.ImplementsInterface (expr_type, target_type))
                                                return new EmptyCast (expr, target_type);
                                        else
                                                return null;
                                }

                                // from any interface type S to interface-type T.
                                if (expr_type.IsInterface && target_type.IsInterface) {

                                        if (TypeManager.ImplementsInterface (expr_type, target_type))
                                                return new EmptyCast (expr, target_type);
                                        else
                                                return null;
                                }
                                
                                // from an array-type S to an array-type of type T
                                if (expr_type.IsArray && target_type.IsArray) {
                                        if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {

                                                Type expr_element_type = expr_type.GetElementType ();
                                                Type target_element_type = target_type.GetElementType ();

                                                if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
                                                        if (StandardConversionExists (expr_element_type,
                                                                                      target_element_type))
                                                                return new EmptyCast (expr, target_type);
                                        }
                                }
                                
                                
                                // from an array-type to System.Array
                                if (expr_type.IsArray && target_type == TypeManager.array_type)
                                        return new EmptyCast (expr, target_type);
                                
                                // from any delegate type to System.Delegate
                                if (expr_type.IsSubclassOf (TypeManager.delegate_type) &&
                                    target_type == TypeManager.delegate_type)
                                        return new EmptyCast (expr, target_type);
                                        
                                // from any array-type or delegate type into System.ICloneable.
                                if (expr_type.IsArray || expr_type.IsSubclassOf (TypeManager.delegate_type))
                                        if (target_type == TypeManager.icloneable_type)
                                                return new EmptyCast (expr, target_type);
                                
                                return null;

                        }
                        
                        return null;
                }

                /// <summary>
                ///   Handles expressions like this: decimal d; d = 1;
                ///   and changes them into: decimal d; d = new System.Decimal (1);
                /// </summary>
                static Expression InternalTypeConstructor (EmitContext ec, Expression expr, Type target)
                {
                        ArrayList args = new ArrayList ();

                        args.Add (new Argument (expr, Argument.AType.Expression));

                        Expression ne = new New (target.FullName, args,
                                                 new Location (-1));

                        return ne.Resolve (ec);
                }

                /// <summary>
                ///   Implicit Numeric Conversions.
                ///
                ///   expr is the expression to convert, returns a new expression of type
                ///   target_type or null if an implicit conversion is not possible.
                /// </summary>
                static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
                                                                    Type target_type, Location loc)
                {
                        Type expr_type = expr.Type;
                        
                        //
                        // Attempt to do the implicit constant expression conversions

                        if (expr is IntConstant){
                                Expression e;
                                
                                e = TryImplicitIntConversion (target_type, (IntConstant) expr);

                                if (e != null)
                                        return e;
                        } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
                                //
                                // Try the implicit constant expression conversion
                                // from long to ulong, instead of a nice routine,
                                // we just inline it
                                //
                                long v = ((LongConstant) expr).Value;
                                if (v > 0)
                                        return new ULongConstant ((ulong) v);
                        }
                        
                        if (expr_type == TypeManager.sbyte_type){
                                //
                                // From sbyte to short, int, long, float, double.
                                //
                                if (target_type == TypeManager.int32_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (target_type == TypeManager.short_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.byte_type){
                                //
                                // From byte to short, ushort, int, uint, long, ulong, float, double
                                // 
                                if ((target_type == TypeManager.short_type) ||
                                    (target_type == TypeManager.ushort_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.uint32_type))
                                        return new EmptyCast (expr, target_type);

                                if (target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.short_type){
                                //
                                // From short to int, long, float, double
                                // 
                                if (target_type == TypeManager.int32_type)
                                        return new EmptyCast (expr, target_type);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.ushort_type){
                                //
                                // From ushort to int, uint, long, ulong, float, double
                                //
                                if (target_type == TypeManager.uint32_type)
                                        return new EmptyCast (expr, target_type);

                                if (target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (target_type == TypeManager.int32_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.int32_type){
                                //
                                // From int to long, float, double
                                //
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.uint32_type){
                                //
                                // From uint to long, ulong, float, double
                                //
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R4);
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if ((expr_type == TypeManager.uint64_type) ||
                                   (expr_type == TypeManager.int64_type)){
                                //
                                // From long/ulong to float, double
                                //
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
                                                               OpCodes.Conv_R4);        
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.char_type){
                                //
                                // From char to ushort, int, uint, long, ulong, float, double
                                // 
                                if ((target_type == TypeManager.ushort_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.uint32_type))
                                        return new EmptyCast (expr, target_type);
                                if (target_type == TypeManager.uint64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
                                if (target_type == TypeManager.int64_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
                                if (target_type == TypeManager.float_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.float_type){
                                //
                                // float to double
                                //
                                if (target_type == TypeManager.double_type)
                                        return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
                        }

                        return null;
                }

                /// <summary>
                ///  Determines if a standard implicit conversion exists from
                ///  expr_type to target_type
                /// </summary>
                public static bool StandardConversionExists (Type expr_type, Type target_type)
                {
                        if (expr_type == target_type)
                                return true;

                        // First numeric conversions 
                        
                        if (expr_type == TypeManager.sbyte_type){
                                //
                                // From sbyte to short, int, long, float, double.
                                //
                                if ((target_type == TypeManager.int32_type) || 
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type)  ||
                                    (target_type == TypeManager.short_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                
                        } else if (expr_type == TypeManager.byte_type){
                                //
                                // From byte to short, ushort, int, uint, long, ulong, float, double
                                // 
                                if ((target_type == TypeManager.short_type) ||
                                    (target_type == TypeManager.ushort_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.uint32_type) ||
                                    (target_type == TypeManager.uint64_type) ||
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
        
                        } else if (expr_type == TypeManager.short_type){
                                //
                                // From short to int, long, float, double
                                // 
                                if ((target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                        
                        } else if (expr_type == TypeManager.ushort_type){
                                //
                                // From ushort to int, uint, long, ulong, float, double
                                //
                                if ((target_type == TypeManager.uint32_type) ||
                                    (target_type == TypeManager.uint64_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                    
                        } else if (expr_type == TypeManager.int32_type){
                                //
                                // From int to long, float, double
                                //
                                if ((target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                        
                        } else if (expr_type == TypeManager.uint32_type){
                                //
                                // From uint to long, ulong, float, double
                                //
                                if ((target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.uint64_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                        
                        } else if ((expr_type == TypeManager.uint64_type) ||
                                   (expr_type == TypeManager.int64_type)) {
                                //
                                // From long/ulong to float, double
                                //
                                if ((target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;
                                    
                        } else if (expr_type == TypeManager.char_type){
                                //
                                // From char to ushort, int, uint, long, ulong, float, double
                                // 
                                if ((target_type == TypeManager.ushort_type) ||
                                    (target_type == TypeManager.int32_type) ||
                                    (target_type == TypeManager.uint32_type) ||
                                    (target_type == TypeManager.uint64_type) ||
                                    (target_type == TypeManager.int64_type) ||
                                    (target_type == TypeManager.float_type) ||
                                    (target_type == TypeManager.double_type) ||
                                    (target_type == TypeManager.decimal_type))
                                        return true;

                        } else if (expr_type == TypeManager.float_type){
                                //
                                // float to double
                                //
                                if (target_type == TypeManager.double_type)
                                        return true;
                        }       
                        
                        // Next reference conversions

                        if (target_type == TypeManager.object_type) {
                                if ((expr_type.IsClass) ||
                                    (expr_type.IsValueType))
                                        return true;
                                
                        } else if (expr_type.IsSubclassOf (target_type)) {
                                return true;
                                
                        } else {
                                // Please remember that all code below actuall comes
                                // from ImplicitReferenceConversion so make sure code remains in sync
                                
                                // from any class-type S to any interface-type T.
                                if (expr_type.IsClass && target_type.IsInterface) {
                                        if (TypeManager.ImplementsInterface (expr_type, target_type))
                                                return true;
                                }
                                
                                // from any interface type S to interface-type T.
                                // FIXME : Is it right to use IsAssignableFrom ?
                                if (expr_type.IsInterface && target_type.IsInterface)
                                        if (target_type.IsAssignableFrom (expr_type))
                                                return true;
                                
                                // from an array-type S to an array-type of type T
                                if (expr_type.IsArray && target_type.IsArray) {
                                        if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
                                                
                                                Type expr_element_type = expr_type.GetElementType ();
                                                Type target_element_type = target_type.GetElementType ();
                                                
                                                if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
                                                        if (StandardConversionExists (expr_element_type,
                                                                                      target_element_type))
                                                                return true;
                                        }
                                }
                                
                                // from an array-type to System.Array
                                if (expr_type.IsArray && target_type.IsAssignableFrom (expr_type))
                                        return true;
                                
                                // from any delegate type to System.Delegate
                                if (expr_type.IsSubclassOf (TypeManager.delegate_type) &&
                                    target_type == TypeManager.delegate_type)
                                        if (target_type.IsAssignableFrom (expr_type))
                                                return true;
                                        
                                // from any array-type or delegate type into System.ICloneable.
                                if (expr_type.IsArray || expr_type.IsSubclassOf (TypeManager.delegate_type))
                                        if (target_type == TypeManager.icloneable_type)
                                                return true;
                                
                                // from the null type to any reference-type.
                                // FIXME : How do we do this ?

                        }

                        return false;
                }

                static EmptyExpression MyEmptyExpr;
                /// <summary>
                ///   Tells whether an implicit conversion exists from expr_type to
                ///   target_type
                /// </summary>
                public bool ImplicitConversionExists (EmitContext ec, Type expr_type, Type target_type,
                                                      Location l)
                {
                        if (MyEmptyExpr == null)
                                MyEmptyExpr = new EmptyExpression (expr_type);
                        else
                                MyEmptyExpr.SetType (expr_type);

                        return ConvertImplicit (ec, MyEmptyExpr, target_type, l) != null;
                }
                
                /// <summary>
                ///  Finds "most encompassed type" according to the spec (13.4.2)
                ///  amongst the methods in the MethodGroupExpr which convert from a
                ///  type encompassing source_type
                /// </summary>
                static Type FindMostEncompassedType (MethodGroupExpr me, Type source_type)
                {
                        Type best = null;
                        
                        for (int i = me.Methods.Length; i > 0; ) {
                                i--;

                                MethodBase mb = me.Methods [i];
                                ParameterData pd = Invocation.GetParameterData (mb);
                                Type param_type = pd.ParameterType (0);

                                if (StandardConversionExists (source_type, param_type)) {
                                        if (best == null)
                                                best = param_type;
                                        
                                        if (StandardConversionExists (param_type, best))
                                                best = param_type;
                                }
                        }

                        return best;
                }
                
                /// <summary>
                ///  Finds "most encompassing type" according to the spec (13.4.2)
                ///  amongst the methods in the MethodGroupExpr which convert to a
                ///  type encompassed by target_type
                /// </summary>
                static Type FindMostEncompassingType (MethodGroupExpr me, Type target)
                {
                        Type best = null;
                        
                        for (int i = me.Methods.Length; i > 0; ) {
                                i--;
                                
                                MethodInfo mi = (MethodInfo) me.Methods [i];
                                Type ret_type = mi.ReturnType;
                                
                                if (StandardConversionExists (ret_type, target)) {
                                        if (best == null)
                                                best = ret_type;

                                        if (!StandardConversionExists (ret_type, best))
                                                best = ret_type;
                                }
                                
                        }
                        
                        return best;

                }
                

                /// <summary>
                ///  User-defined Implicit conversions
                /// </summary>
                static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
                                                                 Type target, Location loc)
                {
                        return UserDefinedConversion (ec, source, target, loc, false);
                }

                /// <summary>
                ///  User-defined Explicit conversions
                /// </summary>
                static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
                                                                 Type target, Location loc)
                {
                        return UserDefinedConversion (ec, source, target, loc, true);
                }
                
                /// <summary>
                ///   User-defined conversions
                /// </summary>
                static public Expression UserDefinedConversion (EmitContext ec, Expression source,
                                                                Type target, Location loc,
                                                                bool look_for_explicit)
                {
                        Expression mg1 = null, mg2 = null, mg3 = null, mg4 = null;
                        Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
                        Expression e;
                        MethodBase method = null;
                        Type source_type = source.Type;

                        string op_name;
                        
                        // If we have a boolean type, we need to check for the True operator

                        // FIXME : How does the False operator come into the picture ?
                        // FIXME : This doesn't look complete and very correct !
                        if (target == TypeManager.bool_type)
                                op_name = "op_True";
                        else
                                op_name = "op_Implicit";
                        
                        mg1 = MemberLookup (ec, source_type, op_name, loc);

                        if (source_type.BaseType != null)
                                mg2 = MemberLookup (ec, source_type.BaseType, op_name, loc);
                        
                        mg3 = MemberLookup (ec, target, op_name, loc);

                        if (target.BaseType != null)
                                mg4 = MemberLookup (ec, target.BaseType, op_name, loc);

                        MethodGroupExpr union1 = Invocation.MakeUnionSet (mg1, mg2);
                        MethodGroupExpr union2 = Invocation.MakeUnionSet (mg3, mg4);

                        MethodGroupExpr union3 = Invocation.MakeUnionSet (union1, union2);

                        MethodGroupExpr union4 = null;

                        if (look_for_explicit) {

                                op_name = "op_Explicit";
                                
                                mg5 = MemberLookup (ec, source_type, op_name, loc);

                                if (source_type.BaseType != null)
                                        mg6 = MemberLookup (ec, source_type.BaseType, op_name, loc);
                                
                                mg7 = MemberLookup (ec, target, op_name, loc);
                                
                                if (target.BaseType != null)
                                        mg8 = MemberLookup (ec, target.BaseType, op_name, loc);
                                
                                MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6);
                                MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8);

                                union4 = Invocation.MakeUnionSet (union5, union6);
                        }
                        
                        MethodGroupExpr union = Invocation.MakeUnionSet (union3, union4);

                        if (union != null) {

                                Type most_specific_source, most_specific_target;

                                most_specific_source = FindMostEncompassedType (union, source_type);
                                if (most_specific_source == null)
                                        return null;

                                most_specific_target = FindMostEncompassingType (union, target);
                                if (most_specific_target == null) 
                                        return null;
                                
                                int count = 0;
                                
                                for (int i = union.Methods.Length; i > 0;) {
                                        i--;

                                        MethodBase mb = union.Methods [i];
                                        ParameterData pd = Invocation.GetParameterData (mb);
                                        MethodInfo mi = (MethodInfo) union.Methods [i];

                                        if (pd.ParameterType (0) == most_specific_source &&
                                            mi.ReturnType == most_specific_target) {
                                                method = mb;
                                                count++;
                                        }
                                }

                                if (method == null || count > 1) {
                                        Report.Error (-11, loc, "Ambiguous user defined conversion");
                                        return null;
                                }
                                
                                //
                                // 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.
                                //
                                if (look_for_explicit)
                                        source = ConvertExplicitStandard (ec, source, most_specific_source, loc);
                                else
                                        source = ConvertImplicitStandard (ec, source,
                                                                          most_specific_source, loc);

                                if (source == null)
                                        return null;

                                e =  new UserCast ((MethodInfo) method, source);
                                
                                if (e.Type != target){
                                        if (!look_for_explicit)
                                                e = ConvertImplicitStandard (ec, e, target, loc);
                                        else
                                                e = ConvertExplicitStandard (ec, e, target, loc);

                                        return e;
                                } else
                                        return e;
                        }
                        
                        return null;
                }
                
                /// <summary>
                ///   Converts implicitly the resolved expression `expr' into the
                ///   `target_type'.  It returns a new expression that can be used
                ///   in a context that expects a `target_type'. 
                /// </summary>
                static public Expression ConvertImplicit (EmitContext ec, Expression expr,
                                                          Type target_type, Location loc)
                {
                        Type expr_type = expr.Type;
                        Expression e;

                        if (expr_type == target_type)
                                return expr;

                        if (target_type == null)
                                throw new Exception ("Target type is null");

                        e = ConvertImplicitStandard (ec, expr, target_type, loc);
                        if (e != null)
                                return e;

                        e = ImplicitUserConversion (ec, expr, target_type, loc);
                        if (e != null)
                                return e;

                        return null;
                }

                
                /// <summary>
                ///   Attempts to apply the `Standard Implicit
                ///   Conversion' rules to the expression `expr' into
                ///   the `target_type'.  It returns a new expression
                ///   that can be used in a context that expects a
                ///   `target_type'.
                ///
                ///   This is different from `ConvertImplicit' in that the
                ///   user defined implicit conversions are excluded. 
                /// </summary>
                static public Expression ConvertImplicitStandard (EmitContext ec, Expression expr,
                                                                  Type target_type, Location loc)
                {
                        Type expr_type = expr.Type;
                        Expression e;

                        if (expr_type == target_type)
                                return expr;

                        e = ImplicitNumericConversion (ec, expr, target_type, loc);
                        if (e != null)
                                return e;

                        e = ImplicitReferenceConversion (expr, target_type);
                        if (e != null)
                                return e;

                        if (target_type.IsSubclassOf (TypeManager.enum_type) && expr is IntLiteral){
                                IntLiteral i = (IntLiteral) expr;

                                if (i.Value == 0)
                                        return new EmptyCast (expr, target_type);
                        }

                        if (ec.InUnsafe) {
                                if (expr_type.IsPointer){
                                        if (target_type == TypeManager.void_ptr_type)
                                                return new EmptyCast (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 (target_type.GetElementType()==expr_type.GetElementType())
                                                        return expr;
                                        }
                                }
                                
                                if (target_type.IsPointer){
                                        if (expr is NullLiteral)
                                                return new EmptyCast (expr, target_type);
                                }
                        }

                        return null;
                }

                /// <summary>
                ///   Attemps to perform an implict constant conversion of the IntConstant
                ///   into a different data type using casts (See Implicit Constant
                ///   Expression Conversions)
                /// </summary>
                static protected Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
                {
                        int value = ic.Value;

                        //
                        // FIXME: This should really return constants instead of EmptyCasts
                        //
                        if (target_type == TypeManager.sbyte_type){
                                if (value >= SByte.MinValue && value <= SByte.MaxValue)
                                        return new SByteConstant ((sbyte) value);
                        } else if (target_type == TypeManager.byte_type){
                                if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
                                        return new ByteConstant ((byte) value);
                        } else if (target_type == TypeManager.short_type){
                                if (value >= Int16.MinValue && value <= Int16.MaxValue)
                                        return new ShortConstant ((short) value);
                        } else if (target_type == TypeManager.ushort_type){
                                if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
                                        return new UShortConstant ((ushort) value);
                        } else if (target_type == TypeManager.uint32_type){
                                if (value >= 0)
                                        return new UIntConstant ((uint) value);
                        } else if (target_type == TypeManager.uint64_type){
                                //
                                // we can optimize this case: a positive int32
                                // always fits on a uint64.  But we need an opcode
                                // to do it.
                                //
                                if (value >= 0)
                                        return new ULongConstant ((ulong) value);
                        }
                        
                        if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type))
                                return new EnumConstant (ic, target_type);

                        return null;
                }

                /// <summary>
                ///   Attemptes to implicityly convert `target' into `type', using
                ///   ConvertImplicit.  If there is no implicit conversion, then
                ///   an error is signaled
                /// </summary>
                static public Expression ConvertImplicitRequired (EmitContext ec, Expression source,
                                                                  Type target_type, Location loc)
                {
                        Expression e;
                        
                        e = ConvertImplicit (ec, source, target_type, loc);
                        if (e != null)
                                return e;

                        if (source is DoubleLiteral && target_type == TypeManager.float_type){
                                Error (664, loc,
                                       "Double literal cannot be implicitly converted to " +
                                       "float type, use F suffix to create a float literal");
                        }
                        
                        string msg = "Cannot convert implicitly from `"+
                                TypeManager.CSharpName (source.Type) + "' to `" +
                                TypeManager.CSharpName (target_type) + "'";

                        Error (29, loc, msg);

                        return null;
                }

                /// <summary>
                ///   Performs the explicit numeric conversions
                /// </summary>
                static Expression ConvertNumericExplicit (EmitContext ec, Expression expr,
                                                          Type target_type)
                {
                        Type expr_type = expr.Type;
                        
                        if (expr_type == TypeManager.sbyte_type){
                                //
                                // From sbyte to byte, ushort, uint, ulong, char
                                //
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
                                if (target_type == TypeManager.ushort_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
                                if (target_type == TypeManager.uint32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
                                if (target_type == TypeManager.uint64_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
                        } else if (expr_type == TypeManager.byte_type){
                                //
                                // From byte to sbyte and char
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
                        } else if (expr_type == TypeManager.short_type){
                                //
                                // From short to sbyte, byte, ushort, uint, ulong, char
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
                                if (target_type == TypeManager.ushort_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
                                if (target_type == TypeManager.uint32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
                                if (target_type == TypeManager.uint64_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
                        } else if (expr_type == TypeManager.ushort_type){
                                //
                                // From ushort to sbyte, byte, short, char
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
                                if (target_type == TypeManager.short_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
                        } else if (expr_type == TypeManager.int32_type){
                                //
                                // From int to sbyte, byte, short, ushort, uint, ulong, char
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
                                if (target_type == TypeManager.short_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
                                if (target_type == TypeManager.ushort_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
                                if (target_type == TypeManager.uint32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
                                if (target_type == TypeManager.uint64_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
                        } else if (expr_type == TypeManager.uint32_type){
                                //
                                // From uint to sbyte, byte, short, ushort, int, char
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
                                if (target_type == TypeManager.short_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
                                if (target_type == TypeManager.ushort_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
                                if (target_type == TypeManager.int32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
                        } else if (expr_type == TypeManager.int64_type){
                                //
                                // From long to sbyte, byte, short, ushort, int, uint, ulong, char
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
                                if (target_type == TypeManager.short_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
                                if (target_type == TypeManager.ushort_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
                                if (target_type == TypeManager.int32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
                                if (target_type == TypeManager.uint32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
                                if (target_type == TypeManager.uint64_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
                        } else if (expr_type == TypeManager.uint64_type){
                                //
                                // From ulong to sbyte, byte, short, ushort, int, uint, long, char
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
                                if (target_type == TypeManager.short_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
                                if (target_type == TypeManager.ushort_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
                                if (target_type == TypeManager.int32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
                                if (target_type == TypeManager.uint32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
                                if (target_type == TypeManager.int64_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
                        } else if (expr_type == TypeManager.char_type){
                                //
                                // From char to sbyte, byte, short
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
                                if (target_type == TypeManager.short_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
                        } else if (expr_type == TypeManager.float_type){
                                //
                                // From float to sbyte, byte, short,
                                // ushort, int, uint, long, ulong, char
                                // or decimal
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
                                if (target_type == TypeManager.short_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
                                if (target_type == TypeManager.ushort_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
                                if (target_type == TypeManager.int32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
                                if (target_type == TypeManager.uint32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
                                if (target_type == TypeManager.int64_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
                                if (target_type == TypeManager.uint64_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } else if (expr_type == TypeManager.double_type){
                                //
                                // From double to byte, byte, short,
                                // ushort, int, uint, long, ulong,
                                // char, float or decimal
                                //
                                if (target_type == TypeManager.sbyte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
                                if (target_type == TypeManager.byte_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
                                if (target_type == TypeManager.short_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
                                if (target_type == TypeManager.ushort_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
                                if (target_type == TypeManager.int32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
                                if (target_type == TypeManager.uint32_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
                                if (target_type == TypeManager.int64_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
                                if (target_type == TypeManager.uint64_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
                                if (target_type == TypeManager.char_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
                                if (target_type == TypeManager.float_type)
                                        return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
                                if (target_type == TypeManager.decimal_type)
                                        return InternalTypeConstructor (ec, expr, target_type);
                        } 

                        // decimal is taken care of by the op_Explicit methods.

                        return null;
                }

                /// <summary>
                ///  Returns whether an explicit reference conversion can be performed
                ///  from source_type to target_type
                /// </summary>
                static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
                {
                        bool target_is_value_type = target_type.IsValueType;
                        
                        if (source_type == target_type)
                                return true;
                        
                        //
                        // From object to any reference type
                        //
                        if (source_type == TypeManager.object_type && !target_is_value_type)
                                return true;
                                        
                        //
                        // From any class S to any class-type T, provided S is a base class of T
                        //
                        if (target_type.IsSubclassOf (source_type))
                                return true;

                        //
                        // From any interface type S to any interface T provided S is not derived from T
                        //
                        if (source_type.IsInterface && target_type.IsInterface){
                                if (!target_type.IsSubclassOf (source_type))
                                        return true;
                        }
                            
                        //
                        // 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 &&
                            !target_type.IsAssignableFrom (source_type))
                                return true;

                        //
                        // 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 &&
                            (!target_type.IsSealed || source_type.IsAssignableFrom (target_type)))
                                return true;

                        // From an array type S with an element type Se to an array type T with an 
                        // element type Te provided all the following are true:
                        //     * S and T differe only in element type, in other words, S and T
                        //       have the same number of dimensions.
                        //     * Both Se and Te are reference types
                        //     * An explicit referenc conversions exist from Se to Te
                        //
                        if (source_type.IsArray && target_type.IsArray) {
                                if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
                                        
                                        Type source_element_type = source_type.GetElementType ();
                                        Type target_element_type = target_type.GetElementType ();
                                        
                                        if (!source_element_type.IsValueType && !target_element_type.IsValueType)
                                                if (ExplicitReferenceConversionExists (source_element_type,
                                                                                       target_element_type))
                                                        return true;
                                }
                        }
                        

                        // From System.Array to any array-type
                        if (source_type == TypeManager.array_type &&
                            target_type.IsSubclassOf (TypeManager.array_type)){
                                return true;
                        }

                        //
                        // From System delegate to any delegate-type
                        //
                        if (source_type == TypeManager.delegate_type &&
                            target_type.IsSubclassOf (TypeManager.delegate_type))
                                return true;

                        //
                        // From ICloneable to Array or Delegate types
                        //
                        if (source_type == TypeManager.icloneable_type &&
                            (target_type == TypeManager.array_type ||
                             target_type == TypeManager.delegate_type))
                                return true;
                        
                        return false;
                }

                /// <summary>
                ///   Implements Explicit Reference conversions
                /// </summary>
                static Expression ConvertReferenceExplicit (Expression source, Type target_type)
                {
                        Type source_type = source.Type;
                        bool target_is_value_type = target_type.IsValueType;
                        
                        //
                        // From object to any reference type
                        //
                        if (source_type == TypeManager.object_type && !target_is_value_type)
                                return new ClassCast (source, target_type);


                        //
                        // From any class S to any class-type T, provided S is a base class of T
                        //
                        if (target_type.IsSubclassOf (source_type))
                                return new ClassCast (source, target_type);

                        //
                        // From any interface type S to any interface T provided S is not derived from T
                        //
                        if (source_type.IsInterface && target_type.IsInterface){

                                Type [] ifaces = source_type.GetInterfaces ();

                                if (TypeManager.ImplementsInterface (source_type, target_type))
                                        return null;
                                else
                                        return new ClassCast (source, target_type);
                        }
                            
                        //
                        // 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) {
                                
                                if (TypeManager.ImplementsInterface (source_type, target_type))
                                        return null;
                                else
                                        return 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)
                                        return null;
                                
                                if (TypeManager.ImplementsInterface (target_type, source_type))
                                        return new ClassCast (source, target_type);
                                else
                                        return null;
                        }
                        
                        // From an array type S with an element type Se to an array type T with an 
                        // element type Te provided all the following are true:
                        //     * S and T differe only in element type, in other words, S and T
                        //       have the same number of dimensions.
                        //     * Both Se and Te are reference types
                        //     * An explicit referenc conversions exist from Se to Te
                        //
                        if (source_type.IsArray && target_type.IsArray) {
                                if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
                                        
                                        Type source_element_type = source_type.GetElementType ();
                                        Type target_element_type = target_type.GetElementType ();
                                        
                                        if (!source_element_type.IsValueType && !target_element_type.IsValueType)
                                                if (ExplicitReferenceConversionExists (source_element_type,
                                                                                       target_element_type))
                                                        return new ClassCast (source, target_type);
                                }
                        }
                        

                        // From System.Array to any array-type
                        if (source_type == TypeManager.array_type &&
                            target_type.IsSubclassOf (TypeManager.array_type)){
                                return new ClassCast (source, target_type);
                        }

                        //
                        // From System delegate to any delegate-type
                        //
                        if (source_type == TypeManager.delegate_type &&
                            target_type.IsSubclassOf (TypeManager.delegate_type))
                                return new ClassCast (source, target_type);

                        //
                        // From ICloneable to Array or Delegate types
                        //
                        if (source_type == TypeManager.icloneable_type &&
                            (target_type == TypeManager.array_type ||
                             target_type == TypeManager.delegate_type))
                                return new ClassCast (source, target_type);
                        
                        return null;
                }
                
                /// <summary>
                ///   Performs an explicit conversion of the expression `expr' whose
                ///   type is expr.Type to `target_type'.
                /// </summary>
                static public Expression ConvertExplicit (EmitContext ec, Expression expr,
                                                          Type target_type, Location loc)
                {
                        Type expr_type = expr.Type;
                        Expression ne = ConvertImplicitStandard (ec, expr, target_type, loc);

                        if (ne != null)
                                return ne;

                        ne = ConvertNumericExplicit (ec, expr, target_type);
                        if (ne != null)
                                return ne;

                        //
                        // Unboxing conversion.
                        //
                        if (expr_type == TypeManager.object_type && target_type.IsValueType)
                                return new UnboxCast (expr, target_type);

                        //
                        // Enum types
                        //
                        if (expr_type.IsSubclassOf (TypeManager.enum_type)) {
                                Expression e;

                                //
                                // FIXME: Is there any reason we should have EnumConstant
                                // dealt with here instead of just using always the
                                // UnderlyingSystemType to wrap the type?
                                //
                                if (expr is EnumConstant)
                                        e = ((EnumConstant) expr).Child;
                                else {
                                        e = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
                                }
                                
                                e = ConvertImplicit (ec, e, target_type, loc);
                                if (e != null)
                                        return e;
                                
                                return ConvertNumericExplicit (ec, e, target_type);
                        }
                        
                        ne = ConvertReferenceExplicit (expr, target_type);
                        if (ne != null)
                                return ne;

                        if (ec.InUnsafe){
                                if (target_type.IsPointer){
                                        if (expr_type.IsPointer)
                                                return new EmptyCast (expr, target_type);
                                        
                                        if (expr_type == TypeManager.sbyte_type ||
                                            expr_type == TypeManager.byte_type ||
                                            expr_type == TypeManager.short_type ||
                                            expr_type == TypeManager.ushort_type ||
                                            expr_type == TypeManager.int32_type ||
                                            expr_type == TypeManager.uint32_type ||
                                            expr_type == TypeManager.uint64_type ||
                                            expr_type == TypeManager.int64_type)
                                                return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
                                }
                                if (expr_type.IsPointer){
                                        if (target_type == TypeManager.sbyte_type ||
                                            target_type == TypeManager.byte_type ||
                                            target_type == TypeManager.short_type ||
                                            target_type == TypeManager.ushort_type ||
                                            target_type == TypeManager.int32_type ||
                                            target_type == TypeManager.uint32_type ||
                                            target_type == TypeManager.uint64_type ||
                                            target_type == TypeManager.int64_type){
                                                Expression e = new EmptyCast (expr, TypeManager.uint32_type);
                                                Expression ci, ce;

                                                ci = ConvertImplicitStandard (ec, e, target_type, loc);

                                                if (ci != null)
                                                        return ci;

                                                ce = ConvertNumericExplicit (ec, e, target_type);
                                                if (ce != null)
                                                        return ce;
                                                //
                                                // We should always be able to go from an uint32
                                                // implicitly or explicitly to the other integral
                                                // types
                                                //
                                                throw new Exception ("Internal compiler error");
                                        }
                                }
                        }
                        
                        ne = ExplicitUserConversion (ec, expr, target_type, loc);
                        if (ne != null)
                                return ne;

                        error30 (loc, expr_type, target_type);
                        return null;
                }

                /// <summary>
                ///   Same as ConverExplicit, only it doesn't include user defined conversions
                /// </summary>
                static public Expression ConvertExplicitStandard (EmitContext ec, Expression expr,
                                                                  Type target_type, Location l)
                {
                        Expression ne = ConvertImplicitStandard (ec, expr, target_type, l);

                        if (ne != null)
                                return ne;

                        ne = ConvertNumericExplicit (ec, expr, target_type);
                        if (ne != null)
                                return ne;

                        ne = ConvertReferenceExplicit (expr, target_type);
                        if (ne != null)
                                return ne;

                        error30 (l, expr.Type, target_type);
                        return null;
                }

                static string ExprClassName (ExprClass c)
                {
                        switch (c){
                        case ExprClass.Invalid:
                                return "Invalid";
                        case ExprClass.Value:
                                return "value";
                        case ExprClass.Variable:
                                return "variable";
                        case ExprClass.Namespace:
                                return "namespace";
                        case ExprClass.Type:
                                return "type";
                        case ExprClass.MethodGroup:
                                return "method group";
                        case ExprClass.PropertyAccess:
                                return "property access";
                        case ExprClass.EventAccess:
                                return "event access";
                        case ExprClass.IndexerAccess:
                                return "indexer access";
                        case ExprClass.Nothing:
                                return "null";
                        }
                        throw new Exception ("Should not happen");
                }
                
                /// <summary>
                ///   Reports that we were expecting `expr' to be of class `expected'
                /// </summary>
                protected void report118 (Location loc, Expression expr, string expected)
                {
                        string kind = "Unknown";
                        
                        if (expr != null)
                                kind = ExprClassName (expr.eclass);

                        Error (118, loc, "Expression denotes a `" + kind +
                               "' where a `" + expected + "' was expected");
                }

                static void error31 (Location l, string val, Type t)
                {
                        Report.Error (31, l, "Constant value `" + val + "' cannot be converted to " +
                                      TypeManager.CSharpName (t));
                }

                public static void UnsafeError (Location loc)
                {
                        Report.Error (214, loc, "Pointers may only be used in an unsafe context");
                }
                
                /// <summary>
                ///   Converts the IntConstant, UIntConstant, LongConstant or
                ///   ULongConstant into the integral target_type.   Notice
                ///   that we do not return an `Expression' we do return
                ///   a boxed integral type.
                ///
                ///   FIXME: Since I added the new constants, we need to
                ///   also support conversions from CharConstant, ByteConstant,
                ///   SByteConstant, UShortConstant, ShortConstant
                ///
                ///   This is used by the switch statement, so the domain
                ///   of work is restricted to the literals above, and the
                ///   targets are int32, uint32, char, byte, sbyte, ushort,
                ///   short, uint64 and int64
                /// </summary>
                public static object ConvertIntLiteral (Constant c, Type target_type, Location loc)
                {
                        string s = "";

                        if (c.Type == target_type)
                                return ((Constant) c).GetValue ();

                        //
                        // Make into one of the literals we handle, we dont really care
                        // about this value as we will just return a few limited types
                        // 
                        if (c is EnumConstant)
                                c = ((EnumConstant)c).WidenToCompilerConstant ();

                        if (c is IntConstant){
                                int v = ((IntConstant) c).Value;
                                
                                if (target_type == TypeManager.uint32_type){
                                        if (v >= 0)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v >= SByte.MinValue && v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v >= Int16.MinValue && v <= UInt16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v >= UInt16.MinValue && v <= UInt16.MaxValue)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type){
                                        if (v > 0)
                                                return (ulong) v;
                                }

                                s = v.ToString ();
                        } else if (c is UIntConstant){
                                uint v = ((UIntConstant) c).Value;

                                if (target_type == TypeManager.int32_type){
                                        if (v <= Int32.MaxValue)
                                                return (int) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v <= UInt16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v <= UInt16.MaxValue)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;
                                s = v.ToString ();
                        } else if (c is LongConstant){ 
                                long v = ((LongConstant) c).Value;

                                if (target_type == TypeManager.int32_type){
                                        if (v >= UInt32.MinValue && v <= UInt32.MaxValue)
                                                return (int) v;
                                } else if (target_type == TypeManager.uint32_type){
                                        if (v >= 0 && v <= UInt32.MaxValue)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v >= SByte.MinValue && v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v >= Int16.MinValue && v <= UInt16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v >= UInt16.MinValue && v <= UInt16.MaxValue)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.uint64_type){
                                        if (v > 0)
                                                return (ulong) v;
                                }
                                s = v.ToString ();
                        } else if (c is ULongConstant){
                                ulong v = ((ULongConstant) c).Value;

                                if (target_type == TypeManager.int32_type){
                                        if (v <= Int32.MaxValue)
                                                return (int) v;
                                } else if (target_type == TypeManager.uint32_type){
                                        if (v <= UInt32.MaxValue)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v <= (int) SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v <= UInt16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v <= UInt16.MaxValue)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type){
                                        if (v <= Int64.MaxValue)
                                                return (long) v;
                                }
                                s = v.ToString ();
                        } else if (c is ByteConstant){
                                byte v = ((ByteConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type)
                                        return (int) v;
                                else if (target_type == TypeManager.uint32_type)
                                        return (uint) v;
                                else if (target_type == TypeManager.char_type)
                                        return (char) v;
                                else if (target_type == TypeManager.sbyte_type){
                                        if (v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type)
                                        return (short) v;
                                else if (target_type == TypeManager.ushort_type)
                                        return (ushort) v;
                                else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;
                                s = v.ToString ();
                        } else if (c is SByteConstant){
                                sbyte v = ((SByteConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type)
                                        return (int) v;
                                else if (target_type == TypeManager.uint32_type){
                                        if (v >= 0)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= 0)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= 0)
                                                return (byte) v;
                                } else if (target_type == TypeManager.short_type)
                                        return (short) v;
                                else if (target_type == TypeManager.ushort_type){
                                        if (v >= 0)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type){
                                        if (v >= 0)
                                                return (ulong) v;
                                }
                                s = v.ToString ();
                        } else if (c is ShortConstant){
                                short v = ((ShortConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type){
                                        return (int) v;
                                } else if (target_type == TypeManager.uint32_type){
                                        if (v >= 0)
                                                return (uint) v;
                                } else if (target_type == TypeManager.char_type){
                                        if (v >= 0)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v >= SByte.MinValue && v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.ushort_type){
                                        if (v >= 0)
                                                return (ushort) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;

                                s = v.ToString ();
                        } else if (c is UShortConstant){
                                ushort v = ((UShortConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type)
                                        return (int) v;
                                else if (target_type == TypeManager.uint32_type)
                                        return (uint) v;
                                else if (target_type == TypeManager.char_type){
                                        if (v >= Char.MinValue && v <= Char.MaxValue)
                                                return (char) v;
                                } else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v <= SByte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v <= Int16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;

                                s = v.ToString ();
                        } else if (c is CharConstant){
                                char v = ((CharConstant) c).Value;
                                
                                if (target_type == TypeManager.int32_type)
                                        return (int) v;
                                else if (target_type == TypeManager.uint32_type)
                                        return (uint) v;
                                else if (target_type == TypeManager.byte_type){
                                        if (v >= Byte.MinValue && v <= Byte.MaxValue)
                                                return (byte) v;
                                } else if (target_type == TypeManager.sbyte_type){
                                        if (v <= SByte.MaxValue)
                                                return (sbyte) v;
                                } else if (target_type == TypeManager.short_type){
                                        if (v <= Int16.MaxValue)
                                                return (short) v;
                                } else if (target_type == TypeManager.ushort_type)
                                        return (short) v;
                                else if (target_type == TypeManager.int64_type)
                                        return (long) v;
                                else if (target_type == TypeManager.uint64_type)
                                        return (ulong) v;

                                s = v.ToString ();
                        }
                        error31 (loc, s, target_type);
                        return null;
                }

                //
                // Load the object from the pointer.  The `IsReference' is used
                // to control whether we should use Ldind_Ref or LdObj if the
                // value is not a `core' type.
                //
                // Maybe we should try to extract this infromation form the type?
                // TODO: Maybe this is a bug.  The reason we have this flag is because
                // I had almost identical code in ParameterReference (for handling
                // references) and in UnboxCast.
                //
                public static void LoadFromPtr (ILGenerator ig, Type t, bool IsReference)
                {
                        if (t == TypeManager.int32_type)
                                ig.Emit (OpCodes.Ldind_I4);
                        else if (t == TypeManager.uint32_type)
                                ig.Emit (OpCodes.Ldind_U4);
                        else if (t == TypeManager.short_type)
                                ig.Emit (OpCodes.Ldind_I2);
                        else if (t == TypeManager.ushort_type)
                                ig.Emit (OpCodes.Ldind_U2);
                        else if (t == TypeManager.char_type)
                                ig.Emit (OpCodes.Ldind_U2);
                        else if (t == TypeManager.byte_type)
                                ig.Emit (OpCodes.Ldind_U1);
                        else if (t == TypeManager.sbyte_type)
                                ig.Emit (OpCodes.Ldind_I1);
                        else if (t == TypeManager.uint64_type)
                                ig.Emit (OpCodes.Ldind_I8);
                        else if (t == TypeManager.int64_type)
                                ig.Emit (OpCodes.Ldind_I8);
                        else if (t == TypeManager.float_type)
                                ig.Emit (OpCodes.Ldind_R4);
                        else if (t == TypeManager.double_type)
                                ig.Emit (OpCodes.Ldind_R8);
                        else if (t == TypeManager.bool_type)
                                ig.Emit (OpCodes.Ldind_I1);
                        else if (t == TypeManager.intptr_type)
                                ig.Emit (OpCodes.Ldind_I);
                        else if (TypeManager.IsEnumType (t)){
                                LoadFromPtr (ig, TypeManager.EnumToUnderlying (t), IsReference);
                        } else {
                                if (IsReference)
                                        ig.Emit (OpCodes.Ldind_Ref);
                                else 
                                        ig.Emit (OpCodes.Ldobj, t);
                        }
                }

                //
                // The stack contains the pointer and the value of type `type'
                //
                public static void StoreFromPtr (ILGenerator ig, Type type)
                {
                        if (type == TypeManager.int32_type || type == TypeManager.uint32_type)
                                ig.Emit (OpCodes.Stind_I4);
                        else if (type == TypeManager.int64_type || type == TypeManager.uint64_type)
                                ig.Emit (OpCodes.Stind_I8);
                        else if (type == TypeManager.char_type || type == TypeManager.short_type ||
                                 type == TypeManager.ushort_type)
                                ig.Emit (OpCodes.Stind_I2);
                        else if (type == TypeManager.float_type)
                                ig.Emit (OpCodes.Stind_R4);
                        else if (type == TypeManager.double_type)
                                ig.Emit (OpCodes.Stind_R8);
                        else if (type == TypeManager.byte_type || type == TypeManager.sbyte_type ||
                                 type == TypeManager.bool_type)
                                ig.Emit (OpCodes.Stind_I1);
                        else if (type == TypeManager.intptr_type)
                                ig.Emit (OpCodes.Stind_I);
                        else
                                ig.Emit (OpCodes.Stind_Ref);
                }
                
                //
                // Returns the size of type `t' if known, otherwise, 0
                //
                public static int GetTypeSize (Type t)
                {
                        if (t == TypeManager.int32_type ||
                            t == TypeManager.uint32_type ||
                            t == TypeManager.float_type)
                                return 4;
                        else if (t == TypeManager.int64_type ||
                                 t == TypeManager.uint64_type ||
                                 t == TypeManager.double_type)
                                return 8;
                        else if (t == TypeManager.byte_type ||
                                 t == TypeManager.sbyte_type ||
                                 t == TypeManager.bool_type)    
                                return 1;
                        else if (t == TypeManager.short_type ||
                                 t == TypeManager.char_type ||
                                 t == TypeManager.ushort_type)
                                return 2;
                        else
                                return 0;
                }
        }

        /// <summary>
        ///   This is just a base class for expressions that can
        ///   appear on statements (invocations, object creation,
        ///   assignments, post/pre increment and decrement).  The idea
        ///   being that they would support an extra Emition interface that
        ///   does not leave a result on the stack.
        /// </summary>
        public abstract class ExpressionStatement : Expression {

                /// <summary>
                ///   Requests the expression to be emitted in a `statement'
                ///   context.  This means that no new value is left on the
                ///   stack after invoking this method (constrasted with
                ///   Emit that will always leave a value on the stack).
                /// </summary>
                public abstract void EmitStatement (EmitContext ec);
        }

        /// <summary>
        ///   This kind of cast is used to encapsulate the child
        ///   whose type is child.Type into an expression that is
        ///   reported to return "return_type".  This is used to encapsulate
        ///   expressions which have compatible types, but need to be dealt
        ///   at higher levels with.
        ///
        ///   For example, a "byte" expression could be encapsulated in one
        ///   of these as an "unsigned int".  The type for the expression
        ///   would be "unsigned int".
        ///
        /// </summary>
        public class EmptyCast : Expression {
                protected Expression child;

                public EmptyCast (Expression child, Type return_type)
                {
                        eclass = child.eclass;
                        type = return_type;
                        this.child = child;
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        child.Emit (ec);
                }
        }

        /// <summary>
        ///  This class is used to wrap literals which belong inside Enums
        /// </summary>
        public class EnumConstant : Constant {
                public Constant Child;

                public EnumConstant (Constant child, Type enum_type)
                {
                        eclass = child.eclass;
                        this.Child = child;
                        type = enum_type;
                }
                
                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        Child.Emit (ec);
                }

                public override object GetValue ()
                {
                        return Child.GetValue ();
                }

                //
                // Converts from one of the valid underlying types for an enumeration
                // (int32, uint32, int64, uint64, short, ushort, byte, sbyte) to
                // one of the internal compiler literals: Int/UInt/Long/ULong Literals.
                //
                public Constant WidenToCompilerConstant ()
                {
                        Type t = TypeManager.EnumToUnderlying (Child.Type);
                        object v = ((Constant) Child).GetValue ();;
                        
                        if (t == TypeManager.int32_type)
                                return new IntConstant ((int) v);
                        if (t == TypeManager.uint32_type)
                                return new UIntConstant ((uint) v);
                        if (t == TypeManager.int64_type)
                                return new LongConstant ((long) v);
                        if (t == TypeManager.uint64_type)
                                return new ULongConstant ((ulong) v);
                        if (t == TypeManager.short_type)
                                return new ShortConstant ((short) v);
                        if (t == TypeManager.ushort_type)
                                return new UShortConstant ((ushort) v);
                        if (t == TypeManager.byte_type)
                                return new ByteConstant ((byte) v);
                        if (t == TypeManager.sbyte_type)
                                return new SByteConstant ((sbyte) v);

                        throw new Exception ("Invalid enumeration underlying type: " + t);
                }

                //
                // Extracts the value in the enumeration on its native representation
                //
                public object GetPlainValue ()
                {
                        Type t = TypeManager.EnumToUnderlying (Child.Type);
                        object v = ((Constant) Child).GetValue ();;
                        
                        if (t == TypeManager.int32_type)
                                return (int) v;
                        if (t == TypeManager.uint32_type)
                                return (uint) v;
                        if (t == TypeManager.int64_type)
                                return (long) v;
                        if (t == TypeManager.uint64_type)
                                return (ulong) v;
                        if (t == TypeManager.short_type)
                                return (short) v;
                        if (t == TypeManager.ushort_type)
                                return (ushort) v;
                        if (t == TypeManager.byte_type)
                                return (byte) v;
                        if (t == TypeManager.sbyte_type)
                                return (sbyte) v;

                        return null;
                }
                
                public override string AsString ()
                {
                        return Child.AsString ();
                }
        }

        /// <summary>
        ///   This kind of cast is used to encapsulate Value Types in objects.
        ///
        ///   The effect of it is to box the value type emitted by the previous
        ///   operation.
        /// </summary>
        public class BoxedCast : EmptyCast {

                public BoxedCast (Expression expr)
                        : base (expr, TypeManager.object_type)
                {
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        base.Emit (ec);
                        ec.ig.Emit (OpCodes.Box, child.Type);
                }
        }

        public class UnboxCast : EmptyCast {
                public UnboxCast (Expression expr, Type return_type)
                        : base (expr, return_type)
                {
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        Type t = type;
                        ILGenerator ig = ec.ig;
                        
                        base.Emit (ec);
                        ig.Emit (OpCodes.Unbox, t);

                        LoadFromPtr (ig, t, false);
                }
        }
        
        /// <summary>
        ///   This is used to perform explicit numeric conversions.
        ///
        ///   Explicit numeric conversions might trigger exceptions in a checked
        ///   context, so they should generate the conv.ovf opcodes instead of
        ///   conv opcodes.
        /// </summary>
        public class ConvCast : EmptyCast {
                public enum Mode : byte {
                        I1_U1, I1_U2, I1_U4, I1_U8, I1_CH,
                        U1_I1, U1_CH,
                        I2_I1, I2_U1, I2_U2, I2_U4, I2_U8, I2_CH,
                        U2_I1, U2_U1, U2_I2, U2_CH,
                        I4_I1, I4_U1, I4_I2, I4_U2, I4_U4, I4_U8, I4_CH,
                        U4_I1, U4_U1, U4_I2, U4_U2, U4_I4, U4_CH,
                        I8_I1, I8_U1, I8_I2, I8_U2, I8_I4, I8_U4, I8_U8, I8_CH,
                        U8_I1, U8_U1, U8_I2, U8_U2, U8_I4, U8_U4, U8_I8, U8_CH,
                        CH_I1, CH_U1, CH_I2,
                        R4_I1, R4_U1, R4_I2, R4_U2, R4_I4, R4_U4, R4_I8, R4_U8, R4_CH,
                        R8_I1, R8_U1, R8_I2, R8_U2, R8_I4, R8_U4, R8_I8, R8_U8, R8_CH, R8_R4
                }

                Mode mode;
                
                public ConvCast (Expression child, Type return_type, Mode m)
                        : base (child, return_type)
                {
                        mode = m;
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;
                        
                        base.Emit (ec);

                        if (ec.CheckState){
                                switch (mode){
                                case Mode.I1_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.I1_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.I1_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.I1_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.I1_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.U1_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.U1_CH: /* nothing */ break;

                                case Mode.I2_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.I2_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.I2_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.I2_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.I2_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.I2_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.U2_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.U2_U1: ig.Emit (OpCodes.Conv_Ovf_U1_Un); break;
                                case Mode.U2_I2: ig.Emit (OpCodes.Conv_Ovf_I2_Un); break;
                                case Mode.U2_CH: /* nothing */ break;

                                case Mode.I4_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.I4_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.I4_I2: ig.Emit (OpCodes.Conv_Ovf_I2); break;
                                case Mode.I4_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.I4_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.I4_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.I4_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.U4_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.U4_U1: ig.Emit (OpCodes.Conv_Ovf_U1_Un); break;
                                case Mode.U4_I2: ig.Emit (OpCodes.Conv_Ovf_I2_Un); break;
                                case Mode.U4_U2: ig.Emit (OpCodes.Conv_Ovf_U2_Un); break;
                                case Mode.U4_I4: ig.Emit (OpCodes.Conv_Ovf_I4_Un); break;
                                case Mode.U4_CH: ig.Emit (OpCodes.Conv_Ovf_U2_Un); break;

                                case Mode.I8_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.I8_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.I8_I2: ig.Emit (OpCodes.Conv_Ovf_I2); break;
                                case Mode.I8_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.I8_I4: ig.Emit (OpCodes.Conv_Ovf_I4); break;
                                case Mode.I8_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.I8_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.I8_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.U8_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.U8_U1: ig.Emit (OpCodes.Conv_Ovf_U1_Un); break;
                                case Mode.U8_I2: ig.Emit (OpCodes.Conv_Ovf_I2_Un); break;
                                case Mode.U8_U2: ig.Emit (OpCodes.Conv_Ovf_U2_Un); break;
                                case Mode.U8_I4: ig.Emit (OpCodes.Conv_Ovf_I4_Un); break;
                                case Mode.U8_U4: ig.Emit (OpCodes.Conv_Ovf_U4_Un); break;
                                case Mode.U8_I8: ig.Emit (OpCodes.Conv_Ovf_I8_Un); break;
                                case Mode.U8_CH: ig.Emit (OpCodes.Conv_Ovf_U2_Un); break;

                                case Mode.CH_I1: ig.Emit (OpCodes.Conv_Ovf_I1_Un); break;
                                case Mode.CH_U1: ig.Emit (OpCodes.Conv_Ovf_U1_Un); break;
                                case Mode.CH_I2: ig.Emit (OpCodes.Conv_Ovf_I2_Un); break;

                                case Mode.R4_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.R4_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.R4_I2: ig.Emit (OpCodes.Conv_Ovf_I2); break;
                                case Mode.R4_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.R4_I4: ig.Emit (OpCodes.Conv_Ovf_I4); break;
                                case Mode.R4_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.R4_I8: ig.Emit (OpCodes.Conv_Ovf_I8); break;
                                case Mode.R4_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.R4_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;

                                case Mode.R8_I1: ig.Emit (OpCodes.Conv_Ovf_I1); break;
                                case Mode.R8_U1: ig.Emit (OpCodes.Conv_Ovf_U1); break;
                                case Mode.R8_I2: ig.Emit (OpCodes.Conv_Ovf_I2); break;
                                case Mode.R8_U2: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.R8_I4: ig.Emit (OpCodes.Conv_Ovf_I4); break;
                                case Mode.R8_U4: ig.Emit (OpCodes.Conv_Ovf_U4); break;
                                case Mode.R8_I8: ig.Emit (OpCodes.Conv_Ovf_I8); break;
                                case Mode.R8_U8: ig.Emit (OpCodes.Conv_Ovf_U8); break;
                                case Mode.R8_CH: ig.Emit (OpCodes.Conv_Ovf_U2); break;
                                case Mode.R8_R4: ig.Emit (OpCodes.Conv_R4); break;
                                }
                        } else {
                                switch (mode){
                                case Mode.I1_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.I1_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.I1_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.I1_U8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.I1_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.U1_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.U1_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.I2_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.I2_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.I2_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.I2_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.I2_U8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.I2_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.U2_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.U2_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.U2_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.U2_CH: /* nothing */ break;

                                case Mode.I4_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.I4_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.I4_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.I4_U4: /* nothing */ break;
                                case Mode.I4_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.I4_U8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.I4_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.U4_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.U4_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.U4_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.U4_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.U4_I4: /* nothing */ break;
                                case Mode.U4_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.I8_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.I8_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.I8_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.I8_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.I8_I4: ig.Emit (OpCodes.Conv_I4); break;
                                case Mode.I8_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.I8_U8: /* nothing */ break;
                                case Mode.I8_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.U8_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.U8_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.U8_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.U8_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.U8_I4: ig.Emit (OpCodes.Conv_I4); break;
                                case Mode.U8_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.U8_I8: /* nothing */ break;
                                case Mode.U8_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.CH_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.CH_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.CH_I2: ig.Emit (OpCodes.Conv_I2); break;

                                case Mode.R4_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.R4_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.R4_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.R4_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.R4_I4: ig.Emit (OpCodes.Conv_I4); break;
                                case Mode.R4_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.R4_I8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.R4_U8: ig.Emit (OpCodes.Conv_U8); break;
                                case Mode.R4_CH: ig.Emit (OpCodes.Conv_U2); break;

                                case Mode.R8_I1: ig.Emit (OpCodes.Conv_I1); break;
                                case Mode.R8_U1: ig.Emit (OpCodes.Conv_U1); break;
                                case Mode.R8_I2: ig.Emit (OpCodes.Conv_I2); break;
                                case Mode.R8_U2: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.R8_I4: ig.Emit (OpCodes.Conv_I4); break;
                                case Mode.R8_U4: ig.Emit (OpCodes.Conv_U4); break;
                                case Mode.R8_I8: ig.Emit (OpCodes.Conv_I8); break;
                                case Mode.R8_U8: ig.Emit (OpCodes.Conv_U8); break;
                                case Mode.R8_CH: ig.Emit (OpCodes.Conv_U2); break;
                                case Mode.R8_R4: ig.Emit (OpCodes.Conv_R4); break;
                                }
                        }
                }
        }
        
        public class OpcodeCast : EmptyCast {
                OpCode op, op2;
                bool second_valid;
                
                public OpcodeCast (Expression child, Type return_type, OpCode op)
                        : base (child, return_type)
                        
                {
                        this.op = op;
                        second_valid = false;
                }

                public OpcodeCast (Expression child, Type return_type, OpCode op, OpCode op2)
                        : base (child, return_type)
                        
                {
                        this.op = op;
                        this.op2 = op2;
                        second_valid = true;
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        base.Emit (ec);
                        ec.ig.Emit (op);

                        if (second_valid)
                                ec.ig.Emit (op2);
                }                       
        }

        /// <summary>
        ///   This kind of cast is used to encapsulate a child and cast it
        ///   to the class requested
        /// </summary>
        public class ClassCast : EmptyCast {
                public ClassCast (Expression child, Type return_type)
                        : base (child, return_type)
                        
                {
                }

                public override Expression DoResolve (EmitContext ec)
                {
                        // This should never be invoked, we are born in fully
                        // initialized state.

                        return this;
                }

                public override void Emit (EmitContext ec)
                {
                        base.Emit (ec);

                        ec.ig.Emit (OpCodes.Castclass, type);
                }                       
                
        }
        
        /// <summary>
        ///   SimpleName expressions are initially formed of a single
        ///   word and it only happens at the beginning of the expression.
        /// </summary>
        ///
        /// <remarks>
        ///   The expression will try to be bound to a Field, a Method
        ///   group or a Property.  If those fail we pass the name to our
        ///   caller and the SimpleName is compounded to perform a type
        ///   lookup.  The idea behind this process is that we want to avoid
        ///   creating a namespace map from the assemblies, as that requires
        ///   the GetExportedTypes function to be called and a hashtable to
        ///   be constructed which reduces startup time.  If later we find
        ///   that this is slower, we should create a `NamespaceExpr' expression
        ///   that fully participates in the resolution process. 
        ///   
        ///   For example `System.Console.WriteLine' is decomposed into
        ///   MemberAccess (MemberAccess (SimpleName ("System"), "Console"), "WriteLine")
        ///   
        ///   The first SimpleName wont produce a match on its own, so it will
        ///   be turned into:
        ///   MemberAccess (SimpleName ("System.Console"), "WriteLine").
        ///   
        ///   System.Console will produce a TypeExpr match.
        ///   
        ///   The downside of this is that we might be hitting `LookupType' too many
        ///   times with this scheme.
        /// </remarks>
        public class SimpleName : Expression {
                public readonly string Name;
                public readonly Location Location;
                
                public SimpleName (string name, Location l)
                {
                        Name = name;
                        Location = l;
                }

                public static void Error120 (Location l, string name)
                {
                        Report.Error (
                                120, l,
                                "An object reference is required " +
                                "for the non-static field `"+name+"'");
                }
                
                //
                // Checks whether we are trying to access an instance
                // property, method or field from a static body.
                //
                Expression MemberStaticCheck (Expression e)
                {
                        if (e is FieldExpr){
                                FieldInfo fi = ((FieldExpr) e).FieldInfo;
                                
                                if (!fi.IsStatic){
                                        Error120 (Location, Name);
                                        return null;
                                }
                        } else if (e is MethodGroupExpr){
                                MethodGroupExpr mg = (MethodGroupExpr) e;

                                if (!mg.RemoveInstanceMethods ()){
                                        Error120 (Location, mg.Methods [0].Name);
                                        return null;
                                }
                                return e;
                        } else if (e is PropertyExpr){
                                if (!((PropertyExpr) e).IsStatic){
                                        Error120 (Location, Name);
                                        return null;
                                }
                        } else if (e is EventExpr) {
                                if (!((EventExpr) e).IsStatic) {
                                        Error120 (Location, Name);
                                        return null;
                                }
                        }

                        return e;
                }
                
                public override Expression DoResolve (EmitContext ec)
                {
                        return SimpleNameResolve (ec, false);
                }

                public Expression DoResolveAllowStatic (EmitContext ec)
                {
                        return SimpleNameResolve (ec, true);
                }

                /// <remarks>
                ///   7.5.2: Simple Names. 
                ///
                ///   Local Variables and Parameters are handled at
                ///   parse time, so they never occur as SimpleNames.
                ///
                ///   The `allow_static' flag is used by MemberAccess only
                ///   and it is used to inform us that it is ok for us to 
                ///   avoid the static check, because MemberAccess might end
                ///   up resolving the Name as a Type name and the access as
                ///   a static type access.
                ///
                ///   ie: Type Type; .... { Type.GetType (""); }
                ///
                ///   Type is both an instance variable and a Type;  Type.GetType
                ///   is the static method not an instance method of type.
                /// </remarks>
                Expression SimpleNameResolve (EmitContext ec, bool allow_static)
                {
                        Expression e;

                        //
                        // Stage 1: Performed by the parser (binding to locals or parameters).
                        //

                        //
                        // Stage 2: Lookup members 
                        //
                        e = MemberLookup (ec, ec.TypeContainer.TypeBuilder, Name, Location);
                        if (e == null){
                                //
                                // Stage 3: Lookup symbol in the various namespaces. 
                                //
                                DeclSpace ds = ec.TypeContainer;
                                Type t;
                                string alias_value;
                                
                                if ((t = RootContext.LookupType (ds, Name, true, Location)) != null)
                                        return new TypeExpr (t);
                                
                                //
                                // Stage 2 part b: Lookup up if we are an alias to a type
                                // or a namespace.
                                //
                                // Since we are cheating: we only do the Alias lookup for
                                // namespaces if the name does not include any dots in it
                                //
                                
                                if (Name.IndexOf ('.') == -1 && (alias_value = ec.TypeContainer.LookupAlias (Name)) != null) {
                                // System.Console.WriteLine (Name + " --> " + alias_value);
                                        if ((t = RootContext.LookupType (ds, alias_value, true, Location))
                                            != null)
                                                return new TypeExpr (t);
                                        
                                // we have alias value, but it isn't Type, so try if it's namespace
                                        return new SimpleName (alias_value, Location);
                                }
                                
                                // No match, maybe our parent can compose us
                                // into something meaningful.
                                return this;
                        }
                        
                        //
                        // Stage 2 continues here. 
                        // 
                        if (e is TypeExpr)
                                return e;

                        if (e is FieldExpr){
                                FieldExpr fe = (FieldExpr) e;
                                FieldInfo fi = fe.FieldInfo;

                                if (fi.FieldType.IsPointer && !ec.InUnsafe){
                                        UnsafeError (Location);
                                }
                                
                                if (ec.IsStatic){
                                        if (!allow_static && !fi.IsStatic){
                                                Error120 (Location, Name);
                                                return null;
                                        }
                                } else {
                                        // If we are not in static code and this
                                        // field is not static, set the instance to `this'.

                                        if (!fi.IsStatic)
                                                fe.InstanceExpression = ec.This;
                                }

                                
                                if (fi is FieldBuilder) {
                                        Const c = TypeManager.LookupConstant ((FieldBuilder) fi);
                                        
                                        if (c != null) {
                                                object o = c.LookupConstantValue (ec);
                                                object real_value = ((Constant)c.Expr).GetValue ();
                                                return Constantify (real_value, fi.FieldType);
                                        }
                                }

                                return e;
                        }                               

                        if (e is EventExpr) {
                                //
                                // If the event is local to this class, we transform ourselves into
                                // a FieldExpr
                                //
                                EventExpr ee = (EventExpr) e;

                                Expression ml = MemberLookup (
                                        ec, ec.TypeContainer.TypeBuilder, ee.EventInfo.Name,
                                        MemberTypes.Event, AllBindingFlags, Location);

                                if (ml != null) {
                                        MemberInfo mi = ec.TypeContainer.GetFieldFromEvent ((EventExpr) ml);

                                        if (mi == null) {
                                                //
                                                // If this happens, then we have an event with its own
                                                // accessors and private field etc so there's no need
                                                // to transform ourselves : we should instead flag an error
                                                //
                                                Assign.error70 (ee.EventInfo, Location);
                                                return null;
                                        }

                                        ml = ExprClassFromMemberInfo (ec, mi, Location);
                                        
                                        if (ml == null) {
                                                Report.Error (-200, Location, "Internal error!!");
                                                return null;
                                        }

                                        Expression instance_expr;
                                        
                                        FieldInfo fi = ((FieldExpr) ml).FieldInfo;

                                        if (fi.IsStatic)
                                                instance_expr = null;
                                        else
                                                instance_expr = ec.This;

                                        instance_expr = instance_expr.Resolve (ec);

                                        if (instance_expr != null)
                                                instance_expr = instance_expr.Resolve (ec);
                                        
                                        return MemberAccess.ResolveMemberAccess (ec, ml, instance_expr, Location, null);
                                }
                        }
                                
                        
                        if (ec.IsStatic){
                                if (allow_static)
                                        return e;

                                return MemberStaticCheck (e);
                        } else
                                return e;
                }

                public override void Emit (EmitContext ec)
                {
                        //
                        // If this is ever reached, then we failed to
                        // find the name as a namespace
                        //

                        Error (103, Location, "The name `" + Name +
                               "' does not exist in the class `" +
                               ec.TypeContainer.Name + "'");
                }
        }
        
        /// <summary>
        ///   Fully resolved expression that evaluates to a type
        /// </summary>
        public class TypeExpr : Expression {
                public TypeExpr (Type t)
                {
                        Type = t;
                        eclass = ExprClass.Type;
                }

                override public Expression DoResolve (EmitContext ec)
                {
                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        throw new Exception ("Implement me");
                }
        }

        /// <summary>
        ///   MethodGroup Expression.
        ///  
        ///   This is a fully resolved expression that evaluates to a type
        /// </summary>
        public class MethodGroupExpr : Expression {
                public MethodBase [] Methods;
                Expression instance_expression = null;
                
                public MethodGroupExpr (MemberInfo [] mi)
                {
                        Methods = new MethodBase [mi.Length];
                        mi.CopyTo (Methods, 0);
                        eclass = ExprClass.MethodGroup;
                }

                public MethodGroupExpr (ArrayList l)
                {
                        Methods = new MethodBase [l.Count];

                        l.CopyTo (Methods, 0);
                        eclass = ExprClass.MethodGroup;
                }
                
                //
                // `A method group may have associated an instance expression' 
                // 
                public Expression InstanceExpression {
                        get {
                                return instance_expression;
                        }

                        set {
                                instance_expression = value;
                        }
                }
                
                override public Expression DoResolve (EmitContext ec)
                {
                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        throw new Exception ("This should never be reached");
                }

                bool RemoveMethods (bool keep_static)
                {
                        ArrayList smethods = new ArrayList ();
                        int top = Methods.Length;
                        int i;
                        
                        for (i = 0; i < top; i++){
                                MethodBase mb = Methods [i];

                                if (mb.IsStatic == keep_static)
                                        smethods.Add (mb);
                        }

                        if (smethods.Count == 0)
                                return false;

                        Methods = new MethodBase [smethods.Count];
                        smethods.CopyTo (Methods, 0);

                        return true;
                }
                
                /// <summary>
                ///   Removes any instance methods from the MethodGroup, returns
                ///   false if the resulting set is empty.
                /// </summary>
                public bool RemoveInstanceMethods ()
                {
                        return RemoveMethods (true);
                }

                /// <summary>
                ///   Removes any static methods from the MethodGroup, returns
                ///   false if the resulting set is empty.
                /// </summary>
                public bool RemoveStaticMethods ()
                {
                        return RemoveMethods (false);
                }
        }

        /// <summary>
        ///   Fully resolved expression that evaluates to a Field
        /// </summary>
        public class FieldExpr : Expression, IAssignMethod, IMemoryLocation {
                public readonly FieldInfo FieldInfo;
                public Expression InstanceExpression;
                Location loc;
                
                public FieldExpr (FieldInfo fi, Location l)
                {
                        FieldInfo = fi;
                        eclass = ExprClass.Variable;
                        type = fi.FieldType;
                        loc = l;
                }

                override public Expression DoResolve (EmitContext ec)
                {
                        if (!FieldInfo.IsStatic){
                                if (InstanceExpression == null){
                                        throw new Exception ("non-static FieldExpr without instance var\n" +
                                                             "You have to assign the Instance variable\n" +
                                                             "Of the FieldExpr to set this\n");
                                }

                                InstanceExpression = InstanceExpression.Resolve (ec);
                                if (InstanceExpression == null)
                                        return null;
                        }

                        return this;
                }

                override public Expression DoResolveLValue (EmitContext ec, Expression right_side)
                {
                        Expression e = DoResolve (ec);

                        if (e == null)
                                return null;
                        
                        if (!FieldInfo.IsInitOnly)
                                return this;

                        //
                        // InitOnly fields can only be assigned in constructors
                        //

                        if (ec.IsConstructor)
                                return this;

                        Report.Error (191, loc,
                                      "Readonly field can not be assigned outside " +
                                      "of constructor or variable initializer");
                        
                        return null;
                }

                override public void Emit (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;
                        bool is_volatile = false;
                                
                        if (FieldInfo is FieldBuilder){
                                Field f = TypeManager.GetField (FieldInfo);
                                if (f != null && (f.ModFlags & Modifiers.VOLATILE) != 0)
                                        is_volatile = true;
                                
                                f.status |= Field.Status.USED;
                        }
                        
                        if (FieldInfo.IsStatic){
                                if (is_volatile)
                                        ig.Emit (OpCodes.Volatile);
                                
                                ig.Emit (OpCodes.Ldsfld, FieldInfo);
                        } else {
                                if (InstanceExpression.Type.IsValueType){
                                        IMemoryLocation ml;
                                        LocalTemporary tempo = null;
                                        
                                        if (!(InstanceExpression is IMemoryLocation)){
                                                tempo = new LocalTemporary (
                                                        ec, InstanceExpression.Type);

                                                InstanceExpression.Emit (ec);
                                                tempo.Store (ec);
                                                ml = tempo;
                                        } else
                                                ml = (IMemoryLocation) InstanceExpression;

                                        ml.AddressOf (ec);
                                } else 
                                        InstanceExpression.Emit (ec);

                                if (is_volatile)
                                        ig.Emit (OpCodes.Volatile);
                                
                                ig.Emit (OpCodes.Ldfld, FieldInfo);
                        }
                }

                public void EmitAssign (EmitContext ec, Expression source)
                {
                        bool is_static = FieldInfo.IsStatic;
                        ILGenerator ig = ec.ig;
                        
                        if (!is_static){
                                Expression instance = InstanceExpression;

                                if (instance.Type.IsValueType){
                                        if (instance is IMemoryLocation){
                                                IMemoryLocation ml = (IMemoryLocation) instance;

                                                ml.AddressOf (ec);
                                        } else
                                                throw new Exception ("The " + instance + " of type " +
                                                                     instance.Type +
                                                                     " represents a ValueType and does " +
                                                                     "not implement IMemoryLocation");
                                } else
                                        instance.Emit (ec);
                        }
                        source.Emit (ec);

                        if (FieldInfo is FieldBuilder){
                                Field f = TypeManager.GetField (FieldInfo);
                                if (f != null && (f.ModFlags & Modifiers.VOLATILE) != 0)
                                        ig.Emit (OpCodes.Volatile);
                        }
                        
                        if (is_static)
                                ig.Emit (OpCodes.Stsfld, FieldInfo);
                        else 
                                ig.Emit (OpCodes.Stfld, FieldInfo);

                        if (FieldInfo is FieldBuilder){
                                Field f = TypeManager.GetField (FieldInfo);

                                f.status |= Field.Status.ASSIGNED;
                        }
                }
                
                public void AddressOf (EmitContext ec)
                {
                        ILGenerator ig = ec.ig;
                        
                        if (FieldInfo is FieldBuilder){
                                Field f = TypeManager.GetField (FieldInfo);
                                if (f != null && (f.ModFlags & Modifiers.VOLATILE) != 0)
                                        ig.Emit (OpCodes.Volatile);
                        }

                        //
                        // FIXME:
                        //
                        // Mhm.  We do not know what we are being used for:
                        // READING or WRITING the field.
                        //
                        // I think we want an extra argument to AddressOf to pass
                        // this semantic information.
                        //
                        // For now: just flag both assigned and used.
                        //
                        if (FieldInfo is FieldBuilder){
                                Field f = TypeManager.GetField (FieldInfo);

                                f.status |= Field.Status.ASSIGNED | Field.Status.USED;
                        }

                        //
                        // Handle initonly fields specially: make a copy and then
                        // get the address of the copy.
                        //
                        if (FieldInfo.IsInitOnly){
                                LocalBuilder local;
                                
                                Emit (ec);
                                local = ig.DeclareLocal (type);
                                ig.Emit (OpCodes.Stloc, local);
                                ig.Emit (OpCodes.Ldloca, local);
                                return;
                        } 

                        if (FieldInfo.IsStatic)
                                ig.Emit (OpCodes.Ldsflda, FieldInfo);
                        else {
                                InstanceExpression.Emit (ec);
                                ig.Emit (OpCodes.Ldflda, FieldInfo);
                        }
                }
        }
        
        /// <summary>
        ///   Expression that evaluates to a Property.  The Assign class
        ///   might set the `Value' expression if we are in an assignment.
        ///
        ///   This is not an LValue because we need to re-write the expression, we
        ///   can not take data from the stack and store it.  
        /// </summary>
        public class PropertyExpr : ExpressionStatement, IAssignMethod {
                public readonly PropertyInfo PropertyInfo;
                public readonly bool IsStatic;
                public bool IsBase;
                MethodInfo [] Accessors;
                Location loc;
                
                Expression instance_expr;
                
                public PropertyExpr (PropertyInfo pi, Location l)
                {
                        PropertyInfo = pi;
                        eclass = ExprClass.PropertyAccess;
                        IsStatic = false;
                        loc = l;
                        Accessors = TypeManager.GetAccessors (pi);

                        if (Accessors != null)
                                for (int i = 0; i < Accessors.Length; i++){
                                        if (Accessors [i] != null)
                                                if (Accessors [i].IsStatic)
                                                        IsStatic = true;
                                }
                        else
                                Accessors = new MethodInfo [2];
                        
                        type = pi.PropertyType;
                }

                //
                // The instance expression associated with this expression
                //
                public Expression InstanceExpression {
                        set {
                                instance_expr = value;
                        }

                        get {
                                return instance_expr;
                        }
                }

                public bool VerifyAssignable ()
                {
                        if (!PropertyInfo.CanWrite){
                                Report.Error (200, loc, 
                                              "The property `" + PropertyInfo.Name +
                                              "' can not be assigned to, as it has not set accessor");
                                return false;
                        }

                        return true;
                }

                override public Expression DoResolve (EmitContext ec)
                {
                        if (!PropertyInfo.CanRead){
                                Report.Error (154, loc, 
                                              "The property `" + PropertyInfo.Name +
                                              "' can not be used in " +
                                              "this context because it lacks a get accessor");
                                return null;
                        }

                        type = PropertyInfo.PropertyType;

                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        Invocation.EmitCall (ec, IsBase, IsStatic, instance_expr, Accessors [0], null);
                        
                }

                //
                // Implements the IAssignMethod interface for assignments
                //
                public void EmitAssign (EmitContext ec, Expression source)
                {
                        Argument arg = new Argument (source, Argument.AType.Expression);
                        ArrayList args = new ArrayList ();

                        args.Add (arg);
                        Invocation.EmitCall (ec, false, IsStatic, instance_expr, Accessors [1], args);
                }

                override public void EmitStatement (EmitContext ec)
                {
                        Emit (ec);
                        ec.ig.Emit (OpCodes.Pop);
                }
        }

        /// <summary>
        ///   Fully resolved expression that evaluates to an Event
        /// </summary>
        public class EventExpr : Expression {
                public readonly EventInfo EventInfo;
                Location loc;
                public Expression InstanceExpression;

                public readonly bool IsStatic;

                MethodInfo add_accessor, remove_accessor;
                
                public EventExpr (EventInfo ei, Location loc)
                {
                        EventInfo = ei;
                        this.loc = loc;
                        eclass = ExprClass.EventAccess;

                        add_accessor = TypeManager.GetAddMethod (ei);
                        remove_accessor = TypeManager.GetRemoveMethod (ei);
                        
                        if (add_accessor.IsStatic || remove_accessor.IsStatic)
                                        IsStatic = true;

                        if (EventInfo is MyEventBuilder)
                                type = ((MyEventBuilder) EventInfo).EventType;
                        else
                                type = EventInfo.EventHandlerType;
                }

                override public Expression DoResolve (EmitContext ec)
                {
                        // We are born fully resolved
                        return this;
                }

                override public void Emit (EmitContext ec)
                {
                        throw new Exception ("Should not happen I think");
                }

                public void EmitAddOrRemove (EmitContext ec, Expression source)
                {
                        Expression handler = ((Binary) source).Right;
                        
                        Argument arg = new Argument (handler, Argument.AType.Expression);
                        ArrayList args = new ArrayList ();
                                
                        args.Add (arg);
                        
                        if (((Binary) source).Oper == Binary.Operator.Addition)
                                Invocation.EmitCall (
                                        ec, false, IsStatic, InstanceExpression, add_accessor, args);
                        else
                                Invocation.EmitCall (
                                        ec, false, IsStatic, InstanceExpression, remove_accessor, args);
                }
        }
}