Rewrite of core coder & decoder functions to fix several bugs and limitations, and...

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

//
// statement.cs: Statement representation for the IL tree.
//
// Authors:
//   Miguel de Icaza (miguel@ximian.com)
//   Martin Baulig (martin@ximian.com)
//   Marek Safar (marek.safar@gmail.com)
//
// Copyright 2001, 2002, 2003 Ximian, Inc.
// Copyright 2003, 2004 Novell, Inc.
// Copyright 2011 Xamarin Inc.
//

using System;
using System.Collections.Generic;

#if STATIC
using IKVM.Reflection.Emit;
#else
using System.Reflection.Emit;
#endif

namespace Mono.CSharp {
        
        public abstract class Statement {
                public Location loc;
                
                /// <summary>
                ///   Resolves the statement, true means that all sub-statements
                ///   did resolve ok.
                //  </summary>
                public virtual bool Resolve (BlockContext bc)
                {
                        return true;
                }

                /// <summary>
                ///   We already know that the statement is unreachable, but we still
                ///   need to resolve it to catch errors.
                /// </summary>
                public virtual bool ResolveUnreachable (BlockContext ec, bool warn)
                {
                        //
                        // This conflicts with csc's way of doing this, but IMHO it's
                        // the right thing to do.
                        //
                        // If something is unreachable, we still check whether it's
                        // correct.  This means that you cannot use unassigned variables
                        // in unreachable code, for instance.
                        //

                        bool unreachable = false;
                        if (warn && !ec.UnreachableReported) {
                                ec.UnreachableReported = true;
                                unreachable = true;
                                ec.Report.Warning (162, 2, loc, "Unreachable code detected");
                        }

                        ec.StartFlowBranching (FlowBranching.BranchingType.Block, loc);
                        bool ok = Resolve (ec);
                        ec.KillFlowBranching ();

                        if (unreachable) {
                                ec.UnreachableReported = false;
                        }

                        return ok;
                }
                                
                /// <summary>
                ///   Return value indicates whether all code paths emitted return.
                /// </summary>
                protected abstract void DoEmit (EmitContext ec);

                public virtual void Emit (EmitContext ec)
                {
                        ec.Mark (loc);
                        DoEmit (ec);

                        if (ec.StatementEpilogue != null) {
                                ec.EmitEpilogue ();
                        }
                }

                //
                // This routine must be overrided in derived classes and make copies
                // of all the data that might be modified if resolved
                // 
                protected abstract void CloneTo (CloneContext clonectx, Statement target);

                public Statement Clone (CloneContext clonectx)
                {
                        Statement s = (Statement) this.MemberwiseClone ();
                        CloneTo (clonectx, s);
                        return s;
                }

                public virtual Expression CreateExpressionTree (ResolveContext ec)
                {
                        ec.Report.Error (834, loc, "A lambda expression with statement body cannot be converted to an expresion tree");
                        return null;
                }
                
                public virtual object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public sealed class EmptyStatement : Statement
        {
                public EmptyStatement (Location loc)
                {
                        this.loc = loc;
                }
                
                public override bool Resolve (BlockContext ec)
                {
                        return true;
                }

                public override bool ResolveUnreachable (BlockContext ec, bool warn)
                {
                        return true;
                }

                public override void Emit (EmitContext ec)
                {
                }

                protected override void DoEmit (EmitContext ec)
                {
                        throw new NotSupportedException ();
                }

                protected override void CloneTo (CloneContext clonectx, Statement target)
                {
                        // nothing needed.
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }
        
        public class If : Statement {
                Expression expr;
                public Statement TrueStatement;
                public Statement FalseStatement;

                bool is_true_ret;

                public If (Expression bool_expr, Statement true_statement, Location l)
                        : this (bool_expr, true_statement, null, l)
                {
                }

                public If (Expression bool_expr,
                           Statement true_statement,
                           Statement false_statement,
                           Location l)
                {
                        this.expr = bool_expr;
                        TrueStatement = true_statement;
                        FalseStatement = false_statement;
                        loc = l;
                }

                public Expression Expr {
                        get {
                                return this.expr;
                        }
                }
                
                public override bool Resolve (BlockContext ec)
                {
                        bool ok = true;

                        expr = expr.Resolve (ec);
                        if (expr == null) {
                                ok = false;
                        } else {
                                //
                                // Dead code elimination
                                //
                                if (expr is Constant) {
                                        bool take = !((Constant) expr).IsDefaultValue;

                                        if (take) {
                                                if (!TrueStatement.Resolve (ec))
                                                        return false;

                                                if ((FalseStatement != null) &&
                                                        !FalseStatement.ResolveUnreachable (ec, true))
                                                        return false;
                                                FalseStatement = null;
                                        } else {
                                                if (!TrueStatement.ResolveUnreachable (ec, true))
                                                        return false;
                                                TrueStatement = null;

                                                if ((FalseStatement != null) &&
                                                        !FalseStatement.Resolve (ec))
                                                        return false;
                                        }

                                        return true;
                                }
                        }

                        ec.StartFlowBranching (FlowBranching.BranchingType.Conditional, loc);
                        
                        ok &= TrueStatement.Resolve (ec);

                        is_true_ret = ec.CurrentBranching.CurrentUsageVector.IsUnreachable;

                        ec.CurrentBranching.CreateSibling ();

                        if (FalseStatement != null)
                                ok &= FalseStatement.Resolve (ec);
                                        
                        ec.EndFlowBranching ();

                        return ok;
                }
                
                protected override void DoEmit (EmitContext ec)
                {
                        Label false_target = ec.DefineLabel ();
                        Label end;

                        //
                        // If we're a boolean constant, Resolve() already
                        // eliminated dead code for us.
                        //
                        Constant c = expr as Constant;
                        if (c != null){
                                c.EmitSideEffect (ec);

                                if (!c.IsDefaultValue)
                                        TrueStatement.Emit (ec);
                                else if (FalseStatement != null)
                                        FalseStatement.Emit (ec);

                                return;
                        }                       
                        
                        expr.EmitBranchable (ec, false_target, false);
                        
                        TrueStatement.Emit (ec);

                        if (FalseStatement != null){
                                bool branch_emitted = false;
                                
                                end = ec.DefineLabel ();
                                if (!is_true_ret){
                                        ec.Emit (OpCodes.Br, end);
                                        branch_emitted = true;
                                }

                                ec.MarkLabel (false_target);
                                FalseStatement.Emit (ec);

                                if (branch_emitted)
                                        ec.MarkLabel (end);
                        } else {
                                ec.MarkLabel (false_target);
                        }
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        If target = (If) t;

                        target.expr = expr.Clone (clonectx);
                        target.TrueStatement = TrueStatement.Clone (clonectx);
                        if (FalseStatement != null)
                                target.FalseStatement = FalseStatement.Clone (clonectx);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class Do : Statement {
                public Expression expr;
                public Statement  EmbeddedStatement;

                public Do (Statement statement, BooleanExpression bool_expr, Location doLocation, Location whileLocation)
                {
                        expr = bool_expr;
                        EmbeddedStatement = statement;
                        loc = doLocation;
                        WhileLocation = whileLocation;
                }

                public Location WhileLocation {
                        get; private set;
                }

                public override bool Resolve (BlockContext ec)
                {
                        bool ok = true;

                        ec.StartFlowBranching (FlowBranching.BranchingType.Loop, loc);

                        bool was_unreachable = ec.CurrentBranching.CurrentUsageVector.IsUnreachable;

                        ec.StartFlowBranching (FlowBranching.BranchingType.Embedded, loc);
                        if (!EmbeddedStatement.Resolve (ec))
                                ok = false;
                        ec.EndFlowBranching ();

                        if (ec.CurrentBranching.CurrentUsageVector.IsUnreachable && !was_unreachable)
                                ec.Report.Warning (162, 2, expr.Location, "Unreachable code detected");

                        expr = expr.Resolve (ec);
                        if (expr == null)
                                ok = false;
                        else if (expr is Constant){
                                bool infinite = !((Constant) expr).IsDefaultValue;
                                if (infinite)
                                        ec.CurrentBranching.CurrentUsageVector.Goto ();
                        }

                        ec.EndFlowBranching ();

                        return ok;
                }
                
                protected override void DoEmit (EmitContext ec)
                {
                        Label loop = ec.DefineLabel ();
                        Label old_begin = ec.LoopBegin;
                        Label old_end = ec.LoopEnd;
                        
                        ec.LoopBegin = ec.DefineLabel ();
                        ec.LoopEnd = ec.DefineLabel ();
                                
                        ec.MarkLabel (loop);
                        EmbeddedStatement.Emit (ec);
                        ec.MarkLabel (ec.LoopBegin);

                        // Mark start of while condition
                        ec.Mark (WhileLocation);

                        //
                        // Dead code elimination
                        //
                        if (expr is Constant) {
                                bool res = !((Constant) expr).IsDefaultValue;

                                expr.EmitSideEffect (ec);
                                if (res)
                                        ec.Emit (OpCodes.Br, loop);
                        } else {
                                expr.EmitBranchable (ec, loop, true);
                        }
                        
                        ec.MarkLabel (ec.LoopEnd);

                        ec.LoopBegin = old_begin;
                        ec.LoopEnd = old_end;
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Do target = (Do) t;

                        target.EmbeddedStatement = EmbeddedStatement.Clone (clonectx);
                        target.expr = expr.Clone (clonectx);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class While : Statement {
                public Expression expr;
                public Statement Statement;
                bool infinite, empty;

                public While (BooleanExpression bool_expr, Statement statement, Location l)
                {
                        this.expr = bool_expr;
                        Statement = statement;
                        loc = l;
                }

                public override bool Resolve (BlockContext ec)
                {
                        bool ok = true;

                        expr = expr.Resolve (ec);
                        if (expr == null)
                                ok = false;

                        //
                        // Inform whether we are infinite or not
                        //
                        if (expr is Constant){
                                bool value = !((Constant) expr).IsDefaultValue;

                                if (value == false){
                                        if (!Statement.ResolveUnreachable (ec, true))
                                                return false;
                                        empty = true;
                                        return true;
                                } else
                                        infinite = true;
                        }

                        ec.StartFlowBranching (FlowBranching.BranchingType.Loop, loc);
                        if (!infinite)
                                ec.CurrentBranching.CreateSibling ();

                        ec.StartFlowBranching (FlowBranching.BranchingType.Embedded, loc);
                        if (!Statement.Resolve (ec))
                                ok = false;
                        ec.EndFlowBranching ();

                        // There's no direct control flow from the end of the embedded statement to the end of the loop
                        ec.CurrentBranching.CurrentUsageVector.Goto ();

                        ec.EndFlowBranching ();

                        return ok;
                }
                
                protected override void DoEmit (EmitContext ec)
                {
                        if (empty) {
                                expr.EmitSideEffect (ec);
                                return;
                        }

                        Label old_begin = ec.LoopBegin;
                        Label old_end = ec.LoopEnd;
                        
                        ec.LoopBegin = ec.DefineLabel ();
                        ec.LoopEnd = ec.DefineLabel ();

                        //
                        // Inform whether we are infinite or not
                        //
                        if (expr is Constant) {
                                // expr is 'true', since the 'empty' case above handles the 'false' case
                                ec.MarkLabel (ec.LoopBegin);

                                if (ec.EmitAccurateDebugInfo)
                                        ec.Emit (OpCodes.Nop);

                                expr.EmitSideEffect (ec);
                                Statement.Emit (ec);
                                ec.Emit (OpCodes.Br, ec.LoopBegin);
                                        
                                //
                                // Inform that we are infinite (ie, `we return'), only
                                // if we do not `break' inside the code.
                                //
                                ec.MarkLabel (ec.LoopEnd);
                        } else {
                                Label while_loop = ec.DefineLabel ();

                                ec.Emit (OpCodes.Br, ec.LoopBegin);
                                ec.MarkLabel (while_loop);

                                Statement.Emit (ec);
                        
                                ec.MarkLabel (ec.LoopBegin);

                                ec.Mark (loc);
                                expr.EmitBranchable (ec, while_loop, true);
                                
                                ec.MarkLabel (ec.LoopEnd);
                        }       

                        ec.LoopBegin = old_begin;
                        ec.LoopEnd = old_end;
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        While target = (While) t;

                        target.expr = expr.Clone (clonectx);
                        target.Statement = Statement.Clone (clonectx);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class For : Statement
        {
                bool infinite, empty;
                
                public For (Location l)
                {
                        loc = l;
                }

                public Statement Initializer {
                        get; set;
                }

                public Expression Condition {
                        get; set;
                }

                public Statement Iterator {
                        get; set;
                }

                public Statement Statement {
                        get; set;
                }

                public override bool Resolve (BlockContext ec)
                {
                        bool ok = true;

                        if (Initializer != null) {
                                if (!Initializer.Resolve (ec))
                                        ok = false;
                        }

                        if (Condition != null) {
                                Condition = Condition.Resolve (ec);
                                if (Condition == null)
                                        ok = false;
                                else if (Condition is Constant) {
                                        bool value = !((Constant) Condition).IsDefaultValue;

                                        if (value == false){
                                                if (!Statement.ResolveUnreachable (ec, true))
                                                        return false;
                                                if ((Iterator != null) &&
                                                        !Iterator.ResolveUnreachable (ec, false))
                                                        return false;
                                                empty = true;
                                                return true;
                                        } else
                                                infinite = true;
                                }
                        } else
                                infinite = true;

                        ec.StartFlowBranching (FlowBranching.BranchingType.Loop, loc);
                        if (!infinite)
                                ec.CurrentBranching.CreateSibling ();

                        bool was_unreachable = ec.CurrentBranching.CurrentUsageVector.IsUnreachable;

                        ec.StartFlowBranching (FlowBranching.BranchingType.Embedded, loc);
                        if (!Statement.Resolve (ec))
                                ok = false;
                        ec.EndFlowBranching ();

                        if (Iterator != null){
                                if (ec.CurrentBranching.CurrentUsageVector.IsUnreachable) {
                                        if (!Iterator.ResolveUnreachable (ec, !was_unreachable))
                                                ok = false;
                                } else {
                                        if (!Iterator.Resolve (ec))
                                                ok = false;
                                }
                        }

                        // There's no direct control flow from the end of the embedded statement to the end of the loop
                        ec.CurrentBranching.CurrentUsageVector.Goto ();

                        ec.EndFlowBranching ();

                        return ok;
                }

                protected override void DoEmit (EmitContext ec)
                {
                        if (Initializer != null)
                                Initializer.Emit (ec);

                        if (empty) {
                                Condition.EmitSideEffect (ec);
                                return;
                        }

                        Label old_begin = ec.LoopBegin;
                        Label old_end = ec.LoopEnd;
                        Label loop = ec.DefineLabel ();
                        Label test = ec.DefineLabel ();

                        ec.LoopBegin = ec.DefineLabel ();
                        ec.LoopEnd = ec.DefineLabel ();

                        ec.Emit (OpCodes.Br, test);
                        ec.MarkLabel (loop);
                        Statement.Emit (ec);

                        ec.MarkLabel (ec.LoopBegin);
                        Iterator.Emit (ec);

                        ec.MarkLabel (test);
                        //
                        // If test is null, there is no test, and we are just
                        // an infinite loop
                        //
                        if (Condition != null) {
                                ec.Mark (Condition.Location);

                                //
                                // The Resolve code already catches the case for
                                // Test == Constant (false) so we know that
                                // this is true
                                //
                                if (Condition is Constant) {
                                        Condition.EmitSideEffect (ec);
                                        ec.Emit (OpCodes.Br, loop);
                                } else {
                                        Condition.EmitBranchable (ec, loop, true);
                                }
                                
                        } else
                                ec.Emit (OpCodes.Br, loop);
                        ec.MarkLabel (ec.LoopEnd);

                        ec.LoopBegin = old_begin;
                        ec.LoopEnd = old_end;
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        For target = (For) t;

                        if (Initializer != null)
                                target.Initializer = Initializer.Clone (clonectx);
                        if (Condition != null)
                                target.Condition = Condition.Clone (clonectx);
                        if (Iterator != null)
                                target.Iterator = Iterator.Clone (clonectx);
                        target.Statement = Statement.Clone (clonectx);
                }

                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }
        
        public class StatementExpression : Statement
        {
                ExpressionStatement expr;
                
                public StatementExpression (ExpressionStatement expr)
                {
                        this.expr = expr;
                        loc = expr.StartLocation;
                }

                public StatementExpression (ExpressionStatement expr, Location loc)
                {
                        this.expr = expr;
                        this.loc = loc;
                }

                public ExpressionStatement Expr {
                        get {
                                return this.expr;
                        }
                }
                
                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        StatementExpression target = (StatementExpression) t;
                        target.expr = (ExpressionStatement) expr.Clone (clonectx);
                }
                
                protected override void DoEmit (EmitContext ec)
                {
                        expr.EmitStatement (ec);
                }

                public override bool Resolve (BlockContext ec)
                {
                        expr = expr.ResolveStatement (ec);
                        return expr != null;
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class StatementErrorExpression : Statement
        {
                readonly Expression expr;

                public StatementErrorExpression (Expression expr)
                {
                        this.expr = expr;
                        this.loc = expr.StartLocation;
                }

                public Expression Expr {
                        get {
                                return expr;
                        }
                }

                public override bool Resolve (BlockContext bc)
                {
                        expr.Error_InvalidExpressionStatement (bc);
                        return true;
                }

                protected override void DoEmit (EmitContext ec)
                {
                        throw new NotSupportedException ();
                }

                protected override void CloneTo (CloneContext clonectx, Statement target)
                {
                        throw new NotImplementedException ();
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        //
        // Simple version of statement list not requiring a block
        //
        public class StatementList : Statement
        {
                List<Statement> statements;

                public StatementList (Statement first, Statement second)
                {
                        statements = new List<Statement> () { first, second };
                }

                #region Properties
                public IList<Statement> Statements {
                        get {
                                return statements;
                        }
                }
                #endregion

                public void Add (Statement statement)
                {
                        statements.Add (statement);
                }

                public override bool Resolve (BlockContext ec)
                {
                        foreach (var s in statements)
                                s.Resolve (ec);

                        return true;
                }

                protected override void DoEmit (EmitContext ec)
                {
                        foreach (var s in statements)
                                s.Emit (ec);
                }

                protected override void CloneTo (CloneContext clonectx, Statement target)
                {
                        StatementList t = (StatementList) target;

                        t.statements = new List<Statement> (statements.Count);
                        foreach (Statement s in statements)
                                t.statements.Add (s.Clone (clonectx));
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        // A 'return' or a 'yield break'
        public abstract class ExitStatement : Statement
        {
                protected bool unwind_protect;
                protected abstract bool DoResolve (BlockContext ec);

                public virtual void Error_FinallyClause (Report Report)
                {
                        Report.Error (157, loc, "Control cannot leave the body of a finally clause");
                }

                public sealed override bool Resolve (BlockContext ec)
                {
                        var res = DoResolve (ec);
                        unwind_protect = ec.CurrentBranching.AddReturnOrigin (ec.CurrentBranching.CurrentUsageVector, this);
                        ec.CurrentBranching.CurrentUsageVector.Goto ();
                        return res;
                }
        }

        /// <summary>
        ///   Implements the return statement
        /// </summary>
        public class Return : ExitStatement
        {
                Expression expr;

                public Return (Expression expr, Location l)
                {
                        this.expr = expr;
                        loc = l;
                }

                #region Properties

                public Expression Expr {
                        get {
                                return expr;
                        }
                        protected set {
                                expr = value;
                        }
                }

                #endregion

                protected override bool DoResolve (BlockContext ec)
                {
                        if (expr == null) {
                                if (ec.ReturnType.Kind == MemberKind.Void)
                                        return true;

                                //
                                // Return must not be followed by an expression when
                                // the method return type is Task
                                //
                                if (ec.CurrentAnonymousMethod is AsyncInitializer) {
                                        var storey = (AsyncTaskStorey) ec.CurrentAnonymousMethod.Storey;
                                        if (storey.ReturnType == ec.Module.PredefinedTypes.Task.TypeSpec) {
                                                //
                                                // Extra trick not to emit ret/leave inside awaiter body
                                                //
                                                expr = EmptyExpression.Null;
                                                return true;
                                        }
                                }

                                if (ec.CurrentIterator != null) {
                                        Error_ReturnFromIterator (ec);
                                } else if (ec.ReturnType != InternalType.ErrorType) {
                                        ec.Report.Error (126, loc,
                                                "An object of a type convertible to `{0}' is required for the return statement",
                                                ec.ReturnType.GetSignatureForError ());
                                }

                                return false;
                        }

                        expr = expr.Resolve (ec);
                        TypeSpec block_return_type = ec.ReturnType;

                        AnonymousExpression am = ec.CurrentAnonymousMethod;
                        if (am == null) {
                                if (block_return_type.Kind == MemberKind.Void) {
                                        ec.Report.Error (127, loc,
                                                "`{0}': A return keyword must not be followed by any expression when method returns void",
                                                ec.GetSignatureForError ());

                                        return false;
                                }
                        } else {
                                if (am.IsIterator) {
                                        Error_ReturnFromIterator (ec);
                                        return false;
                                }

                                var async_block = am as AsyncInitializer;
                                if (async_block != null) {
                                        if (expr != null) {
                                                var storey = (AsyncTaskStorey) am.Storey;
                                                var async_type = storey.ReturnType;

                                                if (async_type == null && async_block.ReturnTypeInference != null) {
                                                        async_block.ReturnTypeInference.AddCommonTypeBound (expr.Type);
                                                        return true;
                                                }

                                                if (async_type.Kind == MemberKind.Void) {
                                                        ec.Report.Error (127, loc,
                                                                "`{0}': A return keyword must not be followed by any expression when method returns void",
                                                                ec.GetSignatureForError ());

                                                        return false;
                                                }

                                                if (!async_type.IsGenericTask) {
                                                        if (this is ContextualReturn)
                                                                return true;

                                                        // Same error code as .NET but better error message
                                                        if (async_block.DelegateType != null) {
                                                                ec.Report.Error (1997, loc,
                                                                        "`{0}': A return keyword must not be followed by an expression when async delegate returns `Task'. Consider using `Task<T>' return type",
                                                                        async_block.DelegateType.GetSignatureForError ());
                                                        } else {
                                                                ec.Report.Error (1997, loc,
                                                                        "`{0}': A return keyword must not be followed by an expression when async method returns `Task'. Consider using `Task<T>' return type",
                                                                        ec.GetSignatureForError ());

                                                        }

                                                        return false;
                                                }

                                                //
                                                // The return type is actually Task<T> type argument
                                                //
                                                if (expr.Type == async_type) {
                                                        ec.Report.Error (4016, loc,
                                                                "`{0}': The return expression type of async method must be `{1}' rather than `Task<{1}>'",
                                                                ec.GetSignatureForError (), async_type.TypeArguments[0].GetSignatureForError ());
                                                } else {
                                                        block_return_type = async_type.TypeArguments[0];
                                                }
                                        }
                                } else {
                                        // Same error code as .NET but better error message
                                        if (block_return_type.Kind == MemberKind.Void) {
                                                ec.Report.Error (127, loc,
                                                        "`{0}': A return keyword must not be followed by any expression when delegate returns void",
                                                        am.GetSignatureForError ());

                                                return false;
                                        }

                                        var l = am as AnonymousMethodBody;
                                        if (l != null && expr != null) {
                                                if (l.ReturnTypeInference != null) {
                                                        l.ReturnTypeInference.AddCommonTypeBound (expr.Type);
                                                        return true;
                                                }

                                                //
                                                // Try to optimize simple lambda. Only when optimizations are enabled not to cause
                                                // unexpected debugging experience
                                                //
                                                if (this is ContextualReturn && !ec.IsInProbingMode && ec.Module.Compiler.Settings.Optimize) {
                                                        l.DirectMethodGroupConversion = expr.CanReduceLambda (l);
                                                }
                                        }
                                }
                        }

                        if (expr == null)
                                return false;

                        if (expr.Type != block_return_type && expr.Type != InternalType.ErrorType) {
                                expr = Convert.ImplicitConversionRequired (ec, expr, block_return_type, loc);

                                if (expr == null) {
                                        if (am != null && block_return_type == ec.ReturnType) {
                                                ec.Report.Error (1662, loc,
                                                        "Cannot convert `{0}' to delegate type `{1}' because some of the return types in the block are not implicitly convertible to the delegate return type",
                                                        am.ContainerType, am.GetSignatureForError ());
                                        }
                                        return false;
                                }
                        }

                        return true;                    
                }
                
                protected override void DoEmit (EmitContext ec)
                {
                        if (expr != null) {
                                expr.Emit (ec);

                                var async_body = ec.CurrentAnonymousMethod as AsyncInitializer;
                                if (async_body != null) {
                                        var async_return = ((AsyncTaskStorey) async_body.Storey).HoistedReturn;

                                        // It's null for await without async
                                        if (async_return != null) {
                                                async_return.EmitAssign (ec);

                                                ec.EmitEpilogue ();
                                        }

                                        ec.Emit (unwind_protect ? OpCodes.Leave : OpCodes.Br, async_body.BodyEnd);
                                        return;
                                }

                                ec.EmitEpilogue ();

                                if (unwind_protect || ec.EmitAccurateDebugInfo)
                                        ec.Emit (OpCodes.Stloc, ec.TemporaryReturn ());
                        }

                        if (unwind_protect) {
                                ec.Emit (OpCodes.Leave, ec.CreateReturnLabel ());
                        } else if (ec.EmitAccurateDebugInfo) {
                                ec.Emit (OpCodes.Br, ec.CreateReturnLabel ());
                        } else {
                                ec.Emit (OpCodes.Ret);
                        }
                }

                void Error_ReturnFromIterator (ResolveContext rc)
                {
                        rc.Report.Error (1622, loc,
                                "Cannot return a value from iterators. Use the yield return statement to return a value, or yield break to end the iteration");
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Return target = (Return) t;
                        // It's null for simple return;
                        if (expr != null)
                                target.expr = expr.Clone (clonectx);
                }

                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class Goto : Statement {
                string target;
                LabeledStatement label;
                bool unwind_protect;

                public override bool Resolve (BlockContext ec)
                {
                        unwind_protect = ec.CurrentBranching.AddGotoOrigin (ec.CurrentBranching.CurrentUsageVector, this);
                        ec.CurrentBranching.CurrentUsageVector.Goto ();
                        return true;
                }
                
                public Goto (string label, Location l)
                {
                        loc = l;
                        target = label;
                }

                public string Target {
                        get { return target; }
                }

                public void SetResolvedTarget (LabeledStatement label)
                {
                        this.label = label;
                        label.AddReference ();
                }

                protected override void CloneTo (CloneContext clonectx, Statement target)
                {
                        // Nothing to clone
                }

                protected override void DoEmit (EmitContext ec)
                {
                        if (label == null)
                                throw new InternalErrorException ("goto emitted before target resolved");
                        Label l = label.LabelTarget (ec);
                        ec.Emit (unwind_protect ? OpCodes.Leave : OpCodes.Br, l);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class LabeledStatement : Statement {
                string name;
                bool defined;
                bool referenced;
                Label label;
                Block block;

                FlowBranching.UsageVector vectors;
                
                public LabeledStatement (string name, Block block, Location l)
                {
                        this.name = name;
                        this.block = block;
                        this.loc = l;
                }

                public Label LabelTarget (EmitContext ec)
                {
                        if (defined)
                                return label;

                        label = ec.DefineLabel ();
                        defined = true;
                        return label;
                }

                public Block Block {
                        get {
                                return block;
                        }
                }

                public string Name {
                        get { return name; }
                }

                public bool IsDefined {
                        get { return defined; }
                }

                public bool HasBeenReferenced {
                        get { return referenced; }
                }

                public FlowBranching.UsageVector JumpOrigins {
                        get { return vectors; }
                }

                public void AddUsageVector (FlowBranching.UsageVector vector)
                {
                        vector = vector.Clone ();
                        vector.Next = vectors;
                        vectors = vector;
                }

                protected override void CloneTo (CloneContext clonectx, Statement target)
                {
                        // nothing to clone
                }

                public override bool Resolve (BlockContext ec)
                {
                        // this flow-branching will be terminated when the surrounding block ends
                        ec.StartFlowBranching (this);
                        return true;
                }

                protected override void DoEmit (EmitContext ec)
                {
                        if (!HasBeenReferenced)
                                ec.Report.Warning (164, 2, loc, "This label has not been referenced");

                        LabelTarget (ec);
                        ec.MarkLabel (label);
                }

                public void AddReference ()
                {
                        referenced = true;
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }
        

        /// <summary>
        ///   `goto default' statement
        /// </summary>
        public class GotoDefault : Statement {
                
                public GotoDefault (Location l)
                {
                        loc = l;
                }

                protected override void CloneTo (CloneContext clonectx, Statement target)
                {
                        // nothing to clone
                }

                public override bool Resolve (BlockContext ec)
                {
                        ec.CurrentBranching.CurrentUsageVector.Goto ();

                        if (ec.Switch == null) {
                                ec.Report.Error (153, loc, "A goto case is only valid inside a switch statement");
                                return false;
                        }

                        if (ec.Switch.DefaultLabel == null) {
                                FlowBranchingBlock.Error_UnknownLabel (loc, "default", ec.Report);
                                return false;
                        }

                        return true;
                }

                protected override void DoEmit (EmitContext ec)
                {
                        ec.Emit (OpCodes.Br, ec.Switch.DefaultLabel.GetILLabel (ec));
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        /// <summary>
        ///   `goto case' statement
        /// </summary>
        public class GotoCase : Statement {
                Expression expr;
                SwitchLabel sl;
                
                public GotoCase (Expression e, Location l)
                {
                        expr = e;
                        loc = l;
                }

                public Expression Expr {
                        get {
                                return this.expr;
                        }
                }
                
                public override bool Resolve (BlockContext ec)
                {
                        if (ec.Switch == null){
                                ec.Report.Error (153, loc, "A goto case is only valid inside a switch statement");
                                return false;
                        }

                        ec.CurrentBranching.CurrentUsageVector.Goto ();

                        expr = expr.Resolve (ec);
                        if (expr == null)
                                return false;

                        Constant c = expr as Constant;
                        if (c == null) {
                                ec.Report.Error (150, expr.Location, "A constant value is expected");
                                return false;
                        }

                        Constant res;
                        if (ec.Switch.IsNullable && c is NullLiteral) {
                                res = c;
                        } else {
                                TypeSpec type = ec.Switch.SwitchType;
                                res = c.Reduce (ec, type);
                                if (res == null) {
                                        c.Error_ValueCannotBeConverted (ec, type, true);
                                        return false;
                                }

                                if (!Convert.ImplicitStandardConversionExists (c, type))
                                        ec.Report.Warning (469, 2, loc,
                                                "The `goto case' value is not implicitly convertible to type `{0}'",
                                                type.GetSignatureForError ());

                        }

                        sl = ec.Switch.ResolveGotoCase (ec, res);
                        return true;
                }

                protected override void DoEmit (EmitContext ec)
                {
                        ec.Emit (OpCodes.Br, sl.GetILLabel (ec));
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        GotoCase target = (GotoCase) t;

                        target.expr = expr.Clone (clonectx);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }
        
        public class Throw : Statement {
                Expression expr;
                
                public Throw (Expression expr, Location l)
                {
                        this.expr = expr;
                        loc = l;
                }

                public Expression Expr {
                        get {
                                return this.expr;
                        }
                }

                public override bool Resolve (BlockContext ec)
                {
                        if (expr == null) {
                                ec.CurrentBranching.CurrentUsageVector.Goto ();
                                return ec.CurrentBranching.CheckRethrow (loc);
                        }

                        expr = expr.Resolve (ec, ResolveFlags.Type | ResolveFlags.VariableOrValue);
                        ec.CurrentBranching.CurrentUsageVector.Goto ();

                        if (expr == null)
                                return false;

                        var et = ec.BuiltinTypes.Exception;
                        if (Convert.ImplicitConversionExists (ec, expr, et))
                                expr = Convert.ImplicitConversion (ec, expr, et, loc);
                        else
                                ec.Report.Error (155, expr.Location, "The type caught or thrown must be derived from System.Exception");

                        return true;
                }
                        
                protected override void DoEmit (EmitContext ec)
                {
                        if (expr == null)
                                ec.Emit (OpCodes.Rethrow);
                        else {
                                expr.Emit (ec);

                                ec.Emit (OpCodes.Throw);
                        }
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Throw target = (Throw) t;

                        if (expr != null)
                                target.expr = expr.Clone (clonectx);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class Break : Statement {
                
                public Break (Location l)
                {
                        loc = l;
                }

                bool unwind_protect;

                public override bool Resolve (BlockContext ec)
                {
                        unwind_protect = ec.CurrentBranching.AddBreakOrigin (ec.CurrentBranching.CurrentUsageVector, loc);
                        ec.CurrentBranching.CurrentUsageVector.Goto ();
                        return true;
                }

                protected override void DoEmit (EmitContext ec)
                {
                        ec.Emit (unwind_protect ? OpCodes.Leave : OpCodes.Br, ec.LoopEnd);
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        // nothing needed
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class Continue : Statement {
                
                public Continue (Location l)
                {
                        loc = l;
                }

                bool unwind_protect;

                public override bool Resolve (BlockContext ec)
                {
                        unwind_protect = ec.CurrentBranching.AddContinueOrigin (ec.CurrentBranching.CurrentUsageVector, loc);
                        ec.CurrentBranching.CurrentUsageVector.Goto ();
                        return true;
                }

                protected override void DoEmit (EmitContext ec)
                {
                        ec.Emit (unwind_protect ? OpCodes.Leave : OpCodes.Br, ec.LoopBegin);
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        // nothing needed.
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public interface ILocalVariable
        {
                void Emit (EmitContext ec);
                void EmitAssign (EmitContext ec);
                void EmitAddressOf (EmitContext ec);
        }

        public interface INamedBlockVariable
        {
                Block Block { get; }
                Expression CreateReferenceExpression (ResolveContext rc, Location loc);
                bool IsDeclared { get; }
                bool IsParameter { get; }
                Location Location { get; }
        }

        public class BlockVariableDeclaration : Statement
        {
                public class Declarator
                {
                        LocalVariable li;
                        Expression initializer;

                        public Declarator (LocalVariable li, Expression initializer)
                        {
                                if (li.Type != null)
                                        throw new ArgumentException ("Expected null variable type");

                                this.li = li;
                                this.initializer = initializer;
                        }

                        public Declarator (Declarator clone, Expression initializer)
                        {
                                this.li = clone.li;
                                this.initializer = initializer;
                        }

                        #region Properties

                        public LocalVariable Variable {
                                get {
                                        return li;
                                }
                        }

                        public Expression Initializer {
                                get {
                                        return initializer;
                                }
                                set {
                                        initializer = value;
                                }
                        }

                        #endregion
                }

                Expression initializer;
                protected FullNamedExpression type_expr;
                protected LocalVariable li;
                protected List<Declarator> declarators;
                TypeSpec type;

                public BlockVariableDeclaration (FullNamedExpression type, LocalVariable li)
                {
                        this.type_expr = type;
                        this.li = li;
                        this.loc = type_expr.Location;
                }

                protected BlockVariableDeclaration (LocalVariable li)
                {
                        this.li = li;
                }

                #region Properties

                public List<Declarator> Declarators {
                        get {
                                return declarators;
                        }
                }

                public Expression Initializer {
                        get {
                                return initializer;
                        }
                        set {
                                initializer = value;
                        }
                }

                public FullNamedExpression TypeExpression {
                        get {
                                return type_expr;
                        }
                }

                public LocalVariable Variable {
                        get {
                                return li;
                        }
                }

                #endregion

                public void AddDeclarator (Declarator decl)
                {
                        if (declarators == null)
                                declarators = new List<Declarator> ();

                        declarators.Add (decl);
                }

                static void CreateEvaluatorVariable (BlockContext bc, LocalVariable li)
                {
                        if (bc.Report.Errors != 0)
                                return;

                        var container = bc.CurrentMemberDefinition.Parent.PartialContainer;

                        Field f = new Field (container, new TypeExpression (li.Type, li.Location), Modifiers.PUBLIC | Modifiers.STATIC,
                                new MemberName (li.Name, li.Location), null);

                        container.AddField (f);
                        f.Define ();

                        li.HoistedVariant = new HoistedEvaluatorVariable (f);
                        li.SetIsUsed ();
                }

                public override bool Resolve (BlockContext bc)
                {
                        return Resolve (bc, true);
                }

                public bool Resolve (BlockContext bc, bool resolveDeclaratorInitializers)
                {
                        if (type == null && !li.IsCompilerGenerated) {
                                var vexpr = type_expr as VarExpr;

                                //
                                // C# 3.0 introduced contextual keywords (var) which behaves like a type if type with
                                // same name exists or as a keyword when no type was found
                                //
                                if (vexpr != null && !vexpr.IsPossibleTypeOrNamespace (bc)) {
                                        if (bc.Module.Compiler.Settings.Version < LanguageVersion.V_3)
                                                bc.Report.FeatureIsNotAvailable (bc.Module.Compiler, loc, "implicitly typed local variable");

                                        if (li.IsFixed) {
                                                bc.Report.Error (821, loc, "A fixed statement cannot use an implicitly typed local variable");
                                                return false;
                                        }

                                        if (li.IsConstant) {
                                                bc.Report.Error (822, loc, "An implicitly typed local variable cannot be a constant");
                                                return false;
                                        }

                                        if (Initializer == null) {
                                                bc.Report.Error (818, loc, "An implicitly typed local variable declarator must include an initializer");
                                                return false;
                                        }

                                        if (declarators != null) {
                                                bc.Report.Error (819, loc, "An implicitly typed local variable declaration cannot include multiple declarators");
                                                declarators = null;
                                        }

                                        Initializer = Initializer.Resolve (bc);
                                        if (Initializer != null) {
                                                ((VarExpr) type_expr).InferType (bc, Initializer);
                                                type = type_expr.Type;
                                        } else {
                                                // Set error type to indicate the var was placed correctly but could
                                                // not be infered
                                                //
                                                // var a = missing ();
                                                //
                                                type = InternalType.ErrorType;
                                        }
                                }

                                if (type == null) {
                                        type = type_expr.ResolveAsType (bc);
                                        if (type == null)
                                                return false;

                                        if (li.IsConstant && !type.IsConstantCompatible) {
                                                Const.Error_InvalidConstantType (type, loc, bc.Report);
                                        }
                                }

                                if (type.IsStatic)
                                        FieldBase.Error_VariableOfStaticClass (loc, li.Name, type, bc.Report);

                                li.Type = type;
                        }

                        bool eval_global = bc.Module.Compiler.Settings.StatementMode && bc.CurrentBlock is ToplevelBlock;
                        if (eval_global) {
                                CreateEvaluatorVariable (bc, li);
                        } else if (type != InternalType.ErrorType) {
                                li.PrepareForFlowAnalysis (bc);
                        }

                        if (initializer != null) {
                                initializer = ResolveInitializer (bc, li, initializer);
                                // li.Variable.DefinitelyAssigned 
                        }

                        if (declarators != null) {
                                foreach (var d in declarators) {
                                        d.Variable.Type = li.Type;
                                        if (eval_global) {
                                                CreateEvaluatorVariable (bc, d.Variable);
                                        } else if (type != InternalType.ErrorType) {
                                                d.Variable.PrepareForFlowAnalysis (bc);
                                        }

                                        if (d.Initializer != null && resolveDeclaratorInitializers) {
                                                d.Initializer = ResolveInitializer (bc, d.Variable, d.Initializer);
                                                // d.Variable.DefinitelyAssigned 
                                        } 
                                }
                        }

                        return true;
                }

                protected virtual Expression ResolveInitializer (BlockContext bc, LocalVariable li, Expression initializer)
                {
                        var a = new SimpleAssign (li.CreateReferenceExpression (bc, li.Location), initializer, li.Location);
                        return a.ResolveStatement (bc);
                }

                protected override void DoEmit (EmitContext ec)
                {
                        li.CreateBuilder (ec);

                        if (Initializer != null)
                                ((ExpressionStatement) Initializer).EmitStatement (ec);

                        if (declarators != null) {
                                foreach (var d in declarators) {
                                        d.Variable.CreateBuilder (ec);
                                        if (d.Initializer != null) {
                                                ec.Mark (d.Variable.Location);
                                                ((ExpressionStatement) d.Initializer).EmitStatement (ec);
                                        }
                                }
                        }
                }

                protected override void CloneTo (CloneContext clonectx, Statement target)
                {
                        BlockVariableDeclaration t = (BlockVariableDeclaration) target;

                        if (type_expr != null)
                                t.type_expr = (FullNamedExpression) type_expr.Clone (clonectx);

                        if (initializer != null)
                                t.initializer = initializer.Clone (clonectx);

                        if (declarators != null) {
                                t.declarators = null;
                                foreach (var d in declarators)
                                        t.AddDeclarator (new Declarator (d, d.Initializer == null ? null : d.Initializer.Clone (clonectx)));
                        }
                }

                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class BlockConstantDeclaration : BlockVariableDeclaration
        {
                public BlockConstantDeclaration (FullNamedExpression type, LocalVariable li)
                        : base (type, li)
                {
                }

                public override void Emit (EmitContext ec)
                {
                        // Nothing to emit, not even sequence point
                }

                protected override Expression ResolveInitializer (BlockContext bc, LocalVariable li, Expression initializer)
                {
                        initializer = initializer.Resolve (bc);
                        if (initializer == null)
                                return null;

                        var c = initializer as Constant;
                        if (c == null) {
                                initializer.Error_ExpressionMustBeConstant (bc, initializer.Location, li.Name);
                                return null;
                        }

                        c = c.ConvertImplicitly (li.Type);
                        if (c == null) {
                                if (TypeSpec.IsReferenceType (li.Type))
                                        initializer.Error_ConstantCanBeInitializedWithNullOnly (bc, li.Type, initializer.Location, li.Name);
                                else
                                        initializer.Error_ValueCannotBeConverted (bc, li.Type, false);

                                return null;
                        }

                        li.ConstantValue = c;
                        return initializer;
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        //
        // The information about a user-perceived local variable
        //
        public class LocalVariable : INamedBlockVariable, ILocalVariable
        {
                [Flags]
                public enum Flags
                {
                        Used = 1,
                        IsThis = 1 << 1,
                        AddressTaken = 1 << 2,
                        CompilerGenerated = 1 << 3,
                        Constant = 1 << 4,
                        ForeachVariable = 1 << 5,
                        FixedVariable = 1 << 6,
                        UsingVariable = 1 << 7,
//                      DefinitelyAssigned = 1 << 8,
                        IsLocked = 1 << 9,

                        ReadonlyMask = ForeachVariable | FixedVariable | UsingVariable
                }

                TypeSpec type;
                readonly string name;
                readonly Location loc;
                readonly Block block;
                Flags flags;
                Constant const_value;

                public VariableInfo VariableInfo;
                HoistedVariable hoisted_variant;

                LocalBuilder builder;

                public LocalVariable (Block block, string name, Location loc)
                {
                        this.block = block;
                        this.name = name;
                        this.loc = loc;
                }

                public LocalVariable (Block block, string name, Flags flags, Location loc)
                        : this (block, name, loc)
                {
                        this.flags = flags;
                }

                //
                // Used by variable declarators
                //
                public LocalVariable (LocalVariable li, string name, Location loc)
                        : this (li.block, name, li.flags, loc)
                {
                }

                #region Properties

                public bool AddressTaken {
                        get {
                                return (flags & Flags.AddressTaken) != 0;
                        }
                }

                public Block Block {
                        get {
                                return block;
                        }
                }

                public Constant ConstantValue {
                        get {
                                return const_value;
                        }
                        set {
                                const_value = value;
                        }
                }

                //
                // Hoisted local variable variant
                //
                public HoistedVariable HoistedVariant {
                        get {
                                return hoisted_variant;
                        }
                        set {
                                hoisted_variant = value;
                        }
                }

                public bool IsDeclared {
                        get {
                                return type != null;
                        }
                }

                public bool IsCompilerGenerated {
                        get {
                                return (flags & Flags.CompilerGenerated) != 0;
                        }
                }

                public bool IsConstant {
                        get {
                                return (flags & Flags.Constant) != 0;
                        }
                }

                public bool IsLocked {
                        get {
                                return (flags & Flags.IsLocked) != 0;
                        }
                        set {
                                flags = value ? flags | Flags.IsLocked : flags & ~Flags.IsLocked;
                        }
                }

                public bool IsThis {
                        get {
                                return (flags & Flags.IsThis) != 0;
                        }
                }

                public bool IsFixed {
                        get {
                                return (flags & Flags.FixedVariable) != 0;
                        }
                }

                bool INamedBlockVariable.IsParameter {
                        get {
                                return false;
                        }
                }

                public bool IsReadonly {
                        get {
                                return (flags & Flags.ReadonlyMask) != 0;
                        }
                }

                public Location Location {
                        get {
                                return loc;
                        }
                }

                public string Name {
                        get {
                                return name;
                        }
                }

                public TypeSpec Type {
                    get {
                                return type;
                        }
                    set {
                                type = value;
                        }
                }

                #endregion

                public void CreateBuilder (EmitContext ec)
                {
                        if ((flags & Flags.Used) == 0) {
                                if (VariableInfo == null) {
                                        // Missing flow analysis or wrong variable flags
                                        throw new InternalErrorException ("VariableInfo is null and the variable `{0}' is not used", name);
                                }

                                if (VariableInfo.IsEverAssigned)
                                        ec.Report.Warning (219, 3, Location, "The variable `{0}' is assigned but its value is never used", Name);
                                else
                                        ec.Report.Warning (168, 3, Location, "The variable `{0}' is declared but never used", Name);
                        }

                        if (HoistedVariant != null)
                                return;

                        if (builder != null) {
                                if ((flags & Flags.CompilerGenerated) != 0)
                                        return;

                                // To avoid Used warning duplicates
                                throw new InternalErrorException ("Already created variable `{0}'", name);
                        }

                        //
                        // All fixed variabled are pinned, a slot has to be alocated
                        //
                        builder = ec.DeclareLocal (Type, IsFixed);
                        if (!ec.HasSet (BuilderContext.Options.OmitDebugInfo) && (flags & Flags.CompilerGenerated) == 0)
                                ec.DefineLocalVariable (name, builder);
                }

                public static LocalVariable CreateCompilerGenerated (TypeSpec type, Block block, Location loc)
                {
                        LocalVariable li = new LocalVariable (block, GetCompilerGeneratedName (block), Flags.CompilerGenerated | Flags.Used, loc);
                        li.Type = type;
                        return li;
                }

                public Expression CreateReferenceExpression (ResolveContext rc, Location loc)
                {
                        if (IsConstant && const_value != null)
                                return Constant.CreateConstantFromValue (Type, const_value.GetValue (), loc);

                        return new LocalVariableReference (this, loc);
                }

                public void Emit (EmitContext ec)
                {
                        // TODO: Need something better for temporary variables
                        if ((flags & Flags.CompilerGenerated) != 0)
                                CreateBuilder (ec);

                        ec.Emit (OpCodes.Ldloc, builder);
                }

                public void EmitAssign (EmitContext ec)
                {
                        // TODO: Need something better for temporary variables
                        if ((flags & Flags.CompilerGenerated) != 0)
                                CreateBuilder (ec);

                        ec.Emit (OpCodes.Stloc, builder);
                }

                public void EmitAddressOf (EmitContext ec)
                {
                        ec.Emit (OpCodes.Ldloca, builder);
                }

                public static string GetCompilerGeneratedName (Block block)
                {
                        // HACK: Debugger depends on the name semantics
                        return "$locvar" + block.ParametersBlock.TemporaryLocalsCount++.ToString ("X");
                }

                public string GetReadOnlyContext ()
                {
                        switch (flags & Flags.ReadonlyMask) {
                        case Flags.FixedVariable:
                                return "fixed variable";
                        case Flags.ForeachVariable:
                                return "foreach iteration variable";
                        case Flags.UsingVariable:
                                return "using variable";
                        }

                        throw new InternalErrorException ("Variable is not readonly");
                }

                public bool IsThisAssigned (BlockContext ec, Block block)
                {
                        if (VariableInfo == null)
                                throw new Exception ();

                        if (!ec.DoFlowAnalysis || ec.CurrentBranching.IsAssigned (VariableInfo))
                                return true;

                        return VariableInfo.IsFullyInitialized (ec, block.StartLocation);
                }

                public bool IsAssigned (BlockContext ec)
                {
                        if (VariableInfo == null)
                                throw new Exception ();

                        return !ec.DoFlowAnalysis || ec.CurrentBranching.IsAssigned (VariableInfo);
                }

                public void PrepareForFlowAnalysis (BlockContext bc)
                {
                        //
                        // No need for definitely assigned check for these guys
                        //
                        if ((flags & (Flags.Constant | Flags.ReadonlyMask | Flags.CompilerGenerated)) != 0)
                                return;

                        VariableInfo = new VariableInfo (this, bc.FlowOffset);
                        bc.FlowOffset += VariableInfo.Length;
                }

                //
                // Mark the variables as referenced in the user code
                //
                public void SetIsUsed ()
                {
                        flags |= Flags.Used;
                }

                public void SetHasAddressTaken ()
                {
                        flags |= (Flags.AddressTaken | Flags.Used);
                }

                public override string ToString ()
                {
                        return string.Format ("LocalInfo ({0},{1},{2},{3})", name, type, VariableInfo, Location);
                }
        }

        /// <summary>
        ///   Block represents a C# block.
        /// </summary>
        ///
        /// <remarks>
        ///   This class is used in a number of places: either to represent
        ///   explicit blocks that the programmer places or implicit blocks.
        ///
        ///   Implicit blocks are used as labels or to introduce variable
        ///   declarations.
        ///
        ///   Top-level blocks derive from Block, and they are called ToplevelBlock
        ///   they contain extra information that is not necessary on normal blocks.
        /// </remarks>
        public class Block : Statement {
                [Flags]
                public enum Flags
                {
                        Unchecked = 1,
                        HasRet = 8,
                        Unsafe = 16,
                        HasCapturedVariable = 64,
                        HasCapturedThis = 1 << 7,
                        IsExpressionTree = 1 << 8,
                        CompilerGenerated = 1 << 9,
                        HasAsyncModifier = 1 << 10,
                        Resolved = 1 << 11,
                        YieldBlock = 1 << 12,
                        AwaitBlock = 1 << 13,
                        Iterator = 1 << 14
                }

                public Block Parent;
                public Location StartLocation;
                public Location EndLocation;

                public ExplicitBlock Explicit;
                public ParametersBlock ParametersBlock;

                protected Flags flags;

                //
                // The statements in this block
                //
                protected List<Statement> statements;

                protected List<Statement> scope_initializers;

                int? resolving_init_idx;

                Block original;

#if DEBUG
                static int id;
                public int ID = id++;

                static int clone_id_counter;
                int clone_id;
#endif

//              int assignable_slots;

                public Block (Block parent, Location start, Location end)
                        : this (parent, 0, start, end)
                {
                }

                public Block (Block parent, Flags flags, Location start, Location end)
                {
                        if (parent != null) {
                                // the appropriate constructors will fixup these fields
                                ParametersBlock = parent.ParametersBlock;
                                Explicit = parent.Explicit;
                        }
                        
                        this.Parent = parent;
                        this.flags = flags;
                        this.StartLocation = start;
                        this.EndLocation = end;
                        this.loc = start;
                        statements = new List<Statement> (4);

                        this.original = this;
                }

                #region Properties

                public bool HasUnreachableClosingBrace {
                        get {
                                return (flags & Flags.HasRet) != 0;
                        }
                        set {
                                flags = value ? flags | Flags.HasRet : flags & ~Flags.HasRet;
                        }
                }

                public Block Original {
                        get {
                                return original;
                        }
                        protected set {
                                original = value;
                        }
                }

                public bool IsCompilerGenerated {
                        get { return (flags & Flags.CompilerGenerated) != 0; }
                        set { flags = value ? flags | Flags.CompilerGenerated : flags & ~Flags.CompilerGenerated; }
                }

                public bool Unchecked {
                        get { return (flags & Flags.Unchecked) != 0; }
                        set { flags = value ? flags | Flags.Unchecked : flags & ~Flags.Unchecked; }
                }

                public bool Unsafe {
                        get { return (flags & Flags.Unsafe) != 0; }
                        set { flags |= Flags.Unsafe; }
                }

                public List<Statement> Statements {
                        get { return statements; }
                }

                #endregion

                public void SetEndLocation (Location loc)
                {
                        EndLocation = loc;
                }

                public void AddLabel (LabeledStatement target)
                {
                        ParametersBlock.TopBlock.AddLabel (target.Name, target);
                }

                public void AddLocalName (LocalVariable li)
                {
                        AddLocalName (li.Name, li);
                }

                public void AddLocalName (string name, INamedBlockVariable li)
                {
                        ParametersBlock.TopBlock.AddLocalName (name, li, false);
                }

                public virtual void Error_AlreadyDeclared (string name, INamedBlockVariable variable, string reason)
                {
                        if (reason == null) {
                                Error_AlreadyDeclared (name, variable);
                                return;
                        }

                        ParametersBlock.TopBlock.Report.Error (136, variable.Location,
                                "A local variable named `{0}' cannot be declared in this scope because it would give a different meaning " +
                                "to `{0}', which is already used in a `{1}' scope to denote something else",
                                name, reason);
                }

                public virtual void Error_AlreadyDeclared (string name, INamedBlockVariable variable)
                {
                        var pi = variable as ParametersBlock.ParameterInfo;
                        if (pi != null) {
                                pi.Parameter.Error_DuplicateName (ParametersBlock.TopBlock.Report);
                        } else {
                                ParametersBlock.TopBlock.Report.Error (128, variable.Location,
                                        "A local variable named `{0}' is already defined in this scope", name);
                        }
                }
                                        
                public virtual void Error_AlreadyDeclaredTypeParameter (string name, Location loc)
                {
                        ParametersBlock.TopBlock.Report.Error (412, loc,
                                "The type parameter name `{0}' is the same as local variable or parameter name",
                                name);
                }

                //
                // It should be used by expressions which require to
                // register a statement during resolve process.
                //
                public void AddScopeStatement (Statement s)
                {
                        if (scope_initializers == null)
                                scope_initializers = new List<Statement> ();

                        //
                        // Simple recursive helper, when resolve scope initializer another
                        // new scope initializer can be added, this ensures it's initialized
                        // before existing one. For now this can happen with expression trees
                        // in base ctor initializer only
                        //
                        if (resolving_init_idx.HasValue) {
                                scope_initializers.Insert (resolving_init_idx.Value, s);
                                ++resolving_init_idx;
                        } else {
                                scope_initializers.Add (s);
                        }
                }
                
                public void AddStatement (Statement s)
                {
                        statements.Add (s);
                }

                public int AssignableSlots {
                        get {
                                // FIXME: HACK, we don't know the block available variables count now, so set this high enough
                                return 4096;
//                              return assignable_slots;
                        }
                }

                public LabeledStatement LookupLabel (string name)
                {
                        return ParametersBlock.TopBlock.GetLabel (name, this);
                }

                public override bool Resolve (BlockContext ec)
                {
                        if ((flags & Flags.Resolved) != 0)
                                return true;

                        Block prev_block = ec.CurrentBlock;
                        bool ok = true;
                        bool unreachable = ec.IsUnreachable;
                        bool prev_unreachable = unreachable;

                        ec.CurrentBlock = this;
                        ec.StartFlowBranching (this);

                        //
                        // Compiler generated scope statements
                        //
                        if (scope_initializers != null) {
                                for (resolving_init_idx = 0; resolving_init_idx < scope_initializers.Count; ++resolving_init_idx) {
                                        scope_initializers[resolving_init_idx.Value].Resolve (ec);
                                }

                                resolving_init_idx = null;
                        }

                        //
                        // This flag is used to notate nested statements as unreachable from the beginning of this block.
                        // For the purposes of this resolution, it doesn't matter that the whole block is unreachable 
                        // from the beginning of the function.  The outer Resolve() that detected the unreachability is
                        // responsible for handling the situation.
                        //
                        int statement_count = statements.Count;
                        for (int ix = 0; ix < statement_count; ix++){
                                Statement s = statements [ix];

                                //
                                // Warn if we detect unreachable code.
                                //
                                if (unreachable) {
                                        if (s is EmptyStatement)
                                                continue;

                                        if (!ec.UnreachableReported && !(s is LabeledStatement) && !(s is SwitchLabel)) {
                                                ec.Report.Warning (162, 2, s.loc, "Unreachable code detected");
                                                ec.UnreachableReported = true;
                                        }
                                }

                                //
                                // Note that we're not using ResolveUnreachable() for unreachable
                                // statements here.  ResolveUnreachable() creates a temporary
                                // flow branching and kills it afterwards.  This leads to problems
                                // if you have two unreachable statements where the first one
                                // assigns a variable and the second one tries to access it.
                                //

                                if (!s.Resolve (ec)) {
                                        ok = false;
                                        if (!ec.IsInProbingMode)
                                                statements [ix] = new EmptyStatement (s.loc);

                                        continue;
                                }

                                if (unreachable && !(s is LabeledStatement) && !(s is SwitchLabel) && !(s is Block))
                                        statements [ix] = new EmptyStatement (s.loc);

                                unreachable = ec.CurrentBranching.CurrentUsageVector.IsUnreachable;
                                if (unreachable) {
                                        ec.IsUnreachable = true;
                                } else if (ec.IsUnreachable)
                                        ec.IsUnreachable = false;
                        }

                        if (unreachable != prev_unreachable) {
                                ec.IsUnreachable = prev_unreachable;
                                ec.UnreachableReported = false;
                        }

                        while (ec.CurrentBranching is FlowBranchingLabeled)
                                ec.EndFlowBranching ();

                        bool flow_unreachable = ec.EndFlowBranching ();

                        ec.CurrentBlock = prev_block;

                        if (flow_unreachable)
                                flags |= Flags.HasRet;

                        // If we're a non-static `struct' constructor which doesn't have an
                        // initializer, then we must initialize all of the struct's fields.
                        if (this == ParametersBlock.TopBlock && !ParametersBlock.TopBlock.IsThisAssigned (ec) && !flow_unreachable)
                                ok = false;

                        flags |= Flags.Resolved;
                        return ok;
                }

                public override bool ResolveUnreachable (BlockContext ec, bool warn)
                {
                        bool unreachable = false;
                        if (warn && !ec.UnreachableReported) {
                                ec.UnreachableReported = true;
                                unreachable = true;
                                ec.Report.Warning (162, 2, loc, "Unreachable code detected");
                        }

                        var fb = ec.StartFlowBranching (FlowBranching.BranchingType.Block, loc);
                        fb.CurrentUsageVector.IsUnreachable = true;
                        bool ok = Resolve (ec);
                        ec.KillFlowBranching ();

                        if (unreachable)
                                ec.UnreachableReported = false;

                        return ok;
                }
                
                protected override void DoEmit (EmitContext ec)
                {
                        for (int ix = 0; ix < statements.Count; ix++){
                                statements [ix].Emit (ec);
                        }
                }

                public override void Emit (EmitContext ec)
                {
                        if (scope_initializers != null)
                                EmitScopeInitializers (ec);

                        DoEmit (ec);
                }

                protected void EmitScopeInitializers (EmitContext ec)
                {
                        foreach (Statement s in scope_initializers)
                                s.Emit (ec);
                }

#if DEBUG
                public override string ToString ()
                {
                        return String.Format ("{0} ({1}:{2})", GetType (), ID, StartLocation);
                }
#endif

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Block target = (Block) t;
#if DEBUG
                        target.clone_id = clone_id_counter++;
#endif

                        clonectx.AddBlockMap (this, target);
                        if (original != this)
                                clonectx.AddBlockMap (original, target);

                        target.ParametersBlock = (ParametersBlock) (ParametersBlock == this ? target : clonectx.RemapBlockCopy (ParametersBlock));
                        target.Explicit = (ExplicitBlock) (Explicit == this ? target : clonectx.LookupBlock (Explicit));

                        if (Parent != null)
                                target.Parent = clonectx.RemapBlockCopy (Parent);

                        target.statements = new List<Statement> (statements.Count);
                        foreach (Statement s in statements)
                                target.statements.Add (s.Clone (clonectx));
                }

                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class ExplicitBlock : Block
        {
                protected AnonymousMethodStorey am_storey;

                public ExplicitBlock (Block parent, Location start, Location end)
                        : this (parent, (Flags) 0, start, end)
                {
                }

                public ExplicitBlock (Block parent, Flags flags, Location start, Location end)
                        : base (parent, flags, start, end)
                {
                        this.Explicit = this;
                }

                #region Properties

                public AnonymousMethodStorey AnonymousMethodStorey {
                        get {
                                return am_storey;
                        }
                }

                public bool HasAwait {
                        get {
                                return (flags & Flags.AwaitBlock) != 0;
                        }
                }

                public bool HasCapturedThis {
                        set {
                                flags = value ? flags | Flags.HasCapturedThis : flags & ~Flags.HasCapturedThis;
                        }
                        get {
                                return (flags & Flags.HasCapturedThis) != 0;
                        }
                }

                //
                // Used to indicate that the block has reference to parent
                // block and cannot be made static when defining anonymous method
                //
                public bool HasCapturedVariable {
                        set {
                                flags = value ? flags | Flags.HasCapturedVariable : flags & ~Flags.HasCapturedVariable;
                        }
                        get {
                                return (flags & Flags.HasCapturedVariable) != 0;
                        }
                }

                public bool HasYield {
                        get {
                                return (flags & Flags.YieldBlock) != 0;
                        }
                }

                #endregion

                //
                // Creates anonymous method storey in current block
                //
                public AnonymousMethodStorey CreateAnonymousMethodStorey (ResolveContext ec)
                {
                        //
                        // Return same story for iterator and async blocks unless we are
                        // in nested anonymous method
                        //
                        if (ec.CurrentAnonymousMethod is StateMachineInitializer && ParametersBlock.Original == ec.CurrentAnonymousMethod.Block.Original)
                                return ec.CurrentAnonymousMethod.Storey;

                        if (am_storey == null) {
                                MemberBase mc = ec.MemberContext as MemberBase;

                                //
                                // Creates anonymous method storey for this block
                                //
                                am_storey = new AnonymousMethodStorey (this, ec.CurrentMemberDefinition.Parent.PartialContainer, mc, ec.CurrentTypeParameters, "AnonStorey", MemberKind.Class);
                        }

                        return am_storey;
                }

                public override void Emit (EmitContext ec)
                {
                        if (am_storey != null) {
                                DefineStoreyContainer (ec, am_storey);
                                am_storey.EmitStoreyInstantiation (ec, this);
                        }

                        if (scope_initializers != null)
                                EmitScopeInitializers (ec);

                        if (ec.EmitAccurateDebugInfo && !IsCompilerGenerated && ec.Mark (StartLocation)) {
                                ec.Emit (OpCodes.Nop);
                        }

                        if (Parent != null)
                                ec.BeginScope ();

                        DoEmit (ec);

                        if (Parent != null)
                                ec.EndScope ();

                        if (ec.EmitAccurateDebugInfo && !HasUnreachableClosingBrace && !IsCompilerGenerated && ec.Mark (EndLocation)) {
                                ec.Emit (OpCodes.Nop);
                        }
                }

                protected void DefineStoreyContainer (EmitContext ec, AnonymousMethodStorey storey)
                {
                        if (ec.CurrentAnonymousMethod != null && ec.CurrentAnonymousMethod.Storey != null) {
                                storey.SetNestedStoryParent (ec.CurrentAnonymousMethod.Storey);
                                storey.Mutator = ec.CurrentAnonymousMethod.Storey.Mutator;
                        }

                        //
                        // Creates anonymous method storey
                        //
                        storey.CreateContainer ();
                        storey.DefineContainer ();

                        if (Original.Explicit.HasCapturedThis && Original.ParametersBlock.TopBlock.ThisReferencesFromChildrenBlock != null) {

                                //
                                // Only first storey in path will hold this reference. All children blocks will
                                // reference it indirectly using $ref field
                                //
                                for (Block b = Original.Explicit; b != null; b = b.Parent) {
                                        if (b.Parent != null) {
                                                var s = b.Parent.Explicit.AnonymousMethodStorey;
                                                if (s != null) {
                                                        storey.HoistedThis = s.HoistedThis;
                                                        break;
                                                }
                                        }

                                        if (b.Explicit == b.Explicit.ParametersBlock && b.Explicit.ParametersBlock.StateMachine != null) {
                                                storey.HoistedThis = b.Explicit.ParametersBlock.StateMachine.HoistedThis;

                                                if (storey.HoistedThis != null)
                                                        break;
                                        }
                                }
                                
                                //
                                // We are the first storey on path and 'this' has to be hoisted
                                //
                                if (storey.HoistedThis == null) {
                                        foreach (ExplicitBlock ref_block in Original.ParametersBlock.TopBlock.ThisReferencesFromChildrenBlock) {
                                                //
                                                // ThisReferencesFromChildrenBlock holds all reference even if they
                                                // are not on this path. It saves some memory otherwise it'd have to
                                                // be in every explicit block. We run this check to see if the reference
                                                // is valid for this storey
                                                //
                                                Block block_on_path = ref_block;
                                                for (; block_on_path != null && block_on_path != Original; block_on_path = block_on_path.Parent);

                                                if (block_on_path == null)
                                                        continue;

                                                if (storey.HoistedThis == null) {
                                                        storey.AddCapturedThisField (ec);
                                                }

                                                for (ExplicitBlock b = ref_block; b.AnonymousMethodStorey != storey; b = b.Parent.Explicit) {
                                                        if (b.AnonymousMethodStorey != null) {
                                                                b.AnonymousMethodStorey.AddParentStoreyReference (ec, storey);
                                                                b.AnonymousMethodStorey.HoistedThis = storey.HoistedThis;

                                                                //
                                                                // Stop propagation inside same top block
                                                                //
                                                                if (b.ParametersBlock == ParametersBlock.Original)
                                                                        break;

                                                                b = b.ParametersBlock;
                                                        }

                                                        var pb = b as ParametersBlock;
                                                        if (pb != null && pb.StateMachine != null) {
                                                                if (pb.StateMachine == storey)
                                                                        break;

                                                                pb.StateMachine.AddParentStoreyReference (ec, storey);
                                                        }
                                                        
                                                        b.HasCapturedVariable = true;
                                                }
                                        }
                                }
                        }

                        var ref_blocks = storey.ReferencesFromChildrenBlock;
                        if (ref_blocks != null) {
                                foreach (ExplicitBlock ref_block in ref_blocks) {
                                        for (ExplicitBlock b = ref_block; b.AnonymousMethodStorey != storey; b = b.Parent.Explicit) {
                                                if (b.AnonymousMethodStorey != null) {
                                                        b.AnonymousMethodStorey.AddParentStoreyReference (ec, storey);

                                                        //
                                                        // Stop propagation inside same top block
                                                        //
                                                        if (b.ParametersBlock == ParametersBlock.Original)
                                                                break;

                                                        b = b.ParametersBlock;
                                                }

                                                var pb = b as ParametersBlock;
                                                if (pb != null && pb.StateMachine != null) {
                                                        if (pb.StateMachine == storey)
                                                                break;

                                                        pb.StateMachine.AddParentStoreyReference (ec, storey);
                                                }

                                                b.HasCapturedVariable = true;
                                        }
                                }
                        }

                        storey.Define ();
                        storey.Parent.PartialContainer.AddCompilerGeneratedClass (storey);
                }

                public void RegisterAsyncAwait ()
                {
                        var block = this;
                        while ((block.flags & Flags.AwaitBlock) == 0) {
                                block.flags |= Flags.AwaitBlock;

                                if (block is ParametersBlock)
                                        return;

                                block = block.Parent.Explicit;
                        }
                }

                public void RegisterIteratorYield ()
                {
                        ParametersBlock.TopBlock.IsIterator = true;

                        var block = this;
                        while ((block.flags & Flags.YieldBlock) == 0) {
                                block.flags |= Flags.YieldBlock;

                                if (block.Parent == null)
                                        return;

                                block = block.Parent.Explicit;
                        }
                }

                public void WrapIntoDestructor (TryFinally tf, ExplicitBlock tryBlock)
                {
                        tryBlock.statements = statements;
                        statements = new List<Statement> (1);
                        statements.Add (tf);
                }
        }

        //
        // ParametersBlock was introduced to support anonymous methods
        // and lambda expressions
        // 
        public class ParametersBlock : ExplicitBlock
        {
                public class ParameterInfo : INamedBlockVariable
                {
                        readonly ParametersBlock block;
                        readonly int index;
                        public VariableInfo VariableInfo;
                        bool is_locked;

                        public ParameterInfo (ParametersBlock block, int index)
                        {
                                this.block = block;
                                this.index = index;
                        }

                        #region Properties

                        public ParametersBlock Block {
                                get {
                                        return block;
                                }
                        }

                        Block INamedBlockVariable.Block {
                                get {
                                        return block;
                                }
                        }

                        public bool IsDeclared {
                                get {
                                        return true;
                                }
                        }

                        public bool IsParameter {
                                get {
                                        return true;
                                }
                        }

                        public bool IsLocked {
                                get {
                                        return is_locked;
                                }
                                set {
                                        is_locked = value;
                                }
                        }

                        public Location Location {
                                get {
                                        return Parameter.Location;
                                }
                        }

                        public Parameter Parameter {
                                get {
                                        return block.Parameters [index];
                                }
                        }

                        public TypeSpec ParameterType {
                                get {
                                        return Parameter.Type;
                                }
                        }

                        #endregion

                        public Expression CreateReferenceExpression (ResolveContext rc, Location loc)
                        {
                                return new ParameterReference (this, loc);
                        }
                }

                // 
                // Block is converted into an expression
                //
                sealed class BlockScopeExpression : Expression
                {
                        Expression child;
                        readonly ParametersBlock block;

                        public BlockScopeExpression (Expression child, ParametersBlock block)
                        {
                                this.child = child;
                                this.block = block;
                        }

                        public override bool ContainsEmitWithAwait ()
                        {
                                return child.ContainsEmitWithAwait ();
                        }

                        public override Expression CreateExpressionTree (ResolveContext ec)
                        {
                                throw new NotSupportedException ();
                        }

                        protected override Expression DoResolve (ResolveContext ec)
                        {
                                if (child == null)
                                        return null;

                                child = child.Resolve (ec);
                                if (child == null)
                                        return null;

                                eclass = child.eclass;
                                type = child.Type;
                                return this;
                        }

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

                protected ParametersCompiled parameters;
                protected ParameterInfo[] parameter_info;
                bool resolved;
                protected bool unreachable;
                protected ToplevelBlock top_block;
                protected StateMachine state_machine;

                public ParametersBlock (Block parent, ParametersCompiled parameters, Location start)
                        : base (parent, 0, start, start)
                {
                        if (parameters == null)
                                throw new ArgumentNullException ("parameters");

                        this.parameters = parameters;
                        ParametersBlock = this;

                        flags |= (parent.ParametersBlock.flags & (Flags.YieldBlock | Flags.AwaitBlock));

                        this.top_block = parent.ParametersBlock.top_block;
                        ProcessParameters ();
                }

                protected ParametersBlock (ParametersCompiled parameters, Location start)
                        : base (null, 0, start, start)
                {
                        if (parameters == null)
                                throw new ArgumentNullException ("parameters");

                        this.parameters = parameters;
                        ParametersBlock = this;
                }

                //
                // It's supposed to be used by method body implementation of anonymous methods
                //
                protected ParametersBlock (ParametersBlock source, ParametersCompiled parameters)
                        : base (null, 0, source.StartLocation, source.EndLocation)
                {
                        this.parameters = parameters;
                        this.statements = source.statements;
                        this.scope_initializers = source.scope_initializers;

                        this.resolved = true;
                        this.unreachable = source.unreachable;
                        this.am_storey = source.am_storey;
                        this.state_machine = source.state_machine;

                        ParametersBlock = this;

                        //
                        // Overwrite original for comparison purposes when linking cross references
                        // between anonymous methods
                        //
                        Original = source.Original;
                }

                #region Properties

                public bool IsAsync {
                        get {
                                return (flags & Flags.HasAsyncModifier) != 0;
                        }
                        set {
                                flags = value ? flags | Flags.HasAsyncModifier : flags & ~Flags.HasAsyncModifier;
                        }
                }

                //
                // Block has been converted to expression tree
                //
                public bool IsExpressionTree {
                        get {
                                return (flags & Flags.IsExpressionTree) != 0;
                        }
                }

                //
                // The parameters for the block.
                //
                public ParametersCompiled Parameters {
                        get {
                                return parameters;
                        }
                }

                public StateMachine StateMachine {
                        get {
                                return state_machine;
                        }
                }

                public ToplevelBlock TopBlock {
                        get {
                                return top_block;
                        }
                }

                public bool Resolved {
                        get {
                                return (flags & Flags.Resolved) != 0;
                        }
                }

                public int TemporaryLocalsCount { get; set; }

                #endregion

                // <summary>
                //   Check whether all `out' parameters have been assigned.
                // </summary>
                public void CheckOutParameters (FlowBranching.UsageVector vector)
                {
                        if (vector.IsUnreachable)
                                return;

                        int n = parameter_info == null ? 0 : parameter_info.Length;

                        for (int i = 0; i < n; i++) {
                                VariableInfo var = parameter_info[i].VariableInfo;

                                if (var == null)
                                        continue;

                                if (vector.IsAssigned (var, false))
                                        continue;

                                var p = parameter_info[i].Parameter;
                                TopBlock.Report.Error (177, p.Location,
                                        "The out parameter `{0}' must be assigned to before control leaves the current method",
                                        p.Name);
                        }
                }

                public override Expression CreateExpressionTree (ResolveContext ec)
                {
                        if (statements.Count == 1) {
                                Expression expr = ((Statement) statements[0]).CreateExpressionTree (ec);
                                if (scope_initializers != null)
                                        expr = new BlockScopeExpression (expr, this);

                                return expr;
                        }

                        return base.CreateExpressionTree (ec);
                }

                public override void Emit (EmitContext ec)
                {
                        if (state_machine != null && state_machine.OriginalSourceBlock != this) {
                                DefineStoreyContainer (ec, state_machine);
                                state_machine.EmitStoreyInstantiation (ec, this);
                        }

                        base.Emit (ec);
                }

                public void EmitEmbedded (EmitContext ec)
                {
                        if (state_machine != null && state_machine.OriginalSourceBlock != this) {
                                DefineStoreyContainer (ec, state_machine);
                                state_machine.EmitStoreyInstantiation (ec, this);
                        }

                        base.Emit (ec);
                }

                public ParameterInfo GetParameterInfo (Parameter p)
                {
                        for (int i = 0; i < parameters.Count; ++i) {
                                if (parameters[i] == p)
                                        return parameter_info[i];
                        }

                        throw new ArgumentException ("Invalid parameter");
                }

                public ParameterReference GetParameterReference (int index, Location loc)
                {
                        return new ParameterReference (parameter_info[index], loc);
                }

                public Statement PerformClone ()
                {
                        CloneContext clonectx = new CloneContext ();
                        return Clone (clonectx);
                }

                protected void ProcessParameters ()
                {
                        if (parameters.Count == 0)
                                return;

                        parameter_info = new ParameterInfo[parameters.Count];
                        for (int i = 0; i < parameter_info.Length; ++i) {
                                var p = parameters.FixedParameters[i];
                                if (p == null)
                                        continue;

                                // TODO: Should use Parameter only and more block there
                                parameter_info[i] = new ParameterInfo (this, i);
                                if (p.Name != null)
                                        AddLocalName (p.Name, parameter_info[i]);
                        }
                }

                public bool Resolve (FlowBranching parent, BlockContext rc, IMethodData md)
                {
                        if (resolved)
                                return true;

                        resolved = true;

                        if (rc.HasSet (ResolveContext.Options.ExpressionTreeConversion))
                                flags |= Flags.IsExpressionTree;

                        try {
                                ResolveMeta (rc);

                                using (rc.With (ResolveContext.Options.DoFlowAnalysis, true)) {
                                        FlowBranchingToplevel top_level = rc.StartFlowBranching (this, parent);

                                        if (!Resolve (rc))
                                                return false;

                                        unreachable = top_level.End ();
                                }
                        } catch (Exception e) {
                                if (e is CompletionResult || rc.Report.IsDisabled || e is FatalException)
                                        throw;

                                if (rc.CurrentBlock != null) {
                                        rc.Report.Error (584, rc.CurrentBlock.StartLocation, "Internal compiler error: {0}", e.Message);
                                } else {
                                        rc.Report.Error (587, "Internal compiler error: {0}", e.Message);
                                }

                                if (rc.Module.Compiler.Settings.DebugFlags > 0)
                                        throw;
                        }

                        if (rc.ReturnType.Kind != MemberKind.Void && !unreachable) {
                                if (rc.CurrentAnonymousMethod == null) {
                                        // FIXME: Missing FlowAnalysis for generated iterator MoveNext method
                                        if (md is StateMachineMethod) {
                                                unreachable = true;
                                        } else {
                                                rc.Report.Error (161, md.Location, "`{0}': not all code paths return a value", md.GetSignatureForError ());
                                                return false;
                                        }
                                } else {
                                        //
                                        // If an asynchronous body of F is either an expression classified as nothing, or a 
                                        // statement block where no return statements have expressions, the inferred return type is Task
                                        //
                                        if (IsAsync) {
                                                var am = rc.CurrentAnonymousMethod as AnonymousMethodBody;
                                                if (am != null && am.ReturnTypeInference != null && !am.ReturnTypeInference.HasBounds (0)) {
                                                        am.ReturnTypeInference = null;
                                                        am.ReturnType = rc.Module.PredefinedTypes.Task.TypeSpec;
                                                        return true;
                                                }
                                        }

                                        rc.Report.Error (1643, rc.CurrentAnonymousMethod.Location, "Not all code paths return a value in anonymous method of type `{0}'",
                                                          rc.CurrentAnonymousMethod.GetSignatureForError ());
                                        return false;
                                }
                        }

                        return true;
                }

                void ResolveMeta (BlockContext ec)
                {
                        int orig_count = parameters.Count;

                        for (int i = 0; i < orig_count; ++i) {
                                Parameter.Modifier mod = parameters.FixedParameters[i].ModFlags;

                                if ((mod & Parameter.Modifier.OUT) == 0)
                                        continue;

                                VariableInfo vi = new VariableInfo (parameters, i, ec.FlowOffset);
                                parameter_info[i].VariableInfo = vi;
                                ec.FlowOffset += vi.Length;
                        }
                }

                public ToplevelBlock ConvertToIterator (IMethodData method, TypeDefinition host, TypeSpec iterator_type, bool is_enumerable)
                {
                        var iterator = new Iterator (this, method, host, iterator_type, is_enumerable);
                        var stateMachine = new IteratorStorey (iterator);

                        state_machine = stateMachine;
                        iterator.SetStateMachine (stateMachine);

                        var tlb = new ToplevelBlock (host.Compiler, Parameters, Location.Null);
                        tlb.Original = this;
                        tlb.IsCompilerGenerated = true;
                        tlb.state_machine = stateMachine;
                        tlb.AddStatement (new Return (iterator, iterator.Location));
                        return tlb;
                }

                public ParametersBlock ConvertToAsyncTask (IMemberContext context, TypeDefinition host, ParametersCompiled parameters, TypeSpec returnType, TypeSpec delegateType, Location loc)
                {
                        for (int i = 0; i < parameters.Count; i++) {
                                Parameter p = parameters[i];
                                Parameter.Modifier mod = p.ModFlags;
                                if ((mod & Parameter.Modifier.RefOutMask) != 0) {
                                        host.Compiler.Report.Error (1988, p.Location,
                                                "Async methods cannot have ref or out parameters");
                                        return this;
                                }

                                if (p is ArglistParameter) {
                                        host.Compiler.Report.Error (4006, p.Location,
                                                "__arglist is not allowed in parameter list of async methods");
                                        return this;
                                }

                                if (parameters.Types[i].IsPointer) {
                                        host.Compiler.Report.Error (4005, p.Location,
                                                "Async methods cannot have unsafe parameters");
                                        return this;
                                }
                        }

                        if (!HasAwait) {
                                host.Compiler.Report.Warning (1998, 1, loc,
                                        "Async block lacks `await' operator and will run synchronously");
                        }

                        var block_type = host.Module.Compiler.BuiltinTypes.Void;
                        var initializer = new AsyncInitializer (this, host, block_type);
                        initializer.Type = block_type;
                        initializer.DelegateType = delegateType;

                        var stateMachine = new AsyncTaskStorey (this, context, initializer, returnType);

                        state_machine = stateMachine;
                        initializer.SetStateMachine (stateMachine);

                        var b = this is ToplevelBlock ?
                                new ToplevelBlock (host.Compiler, Parameters, Location.Null) :
                                new ParametersBlock (Parent, parameters, Location.Null) {
                                        IsAsync = true,
                                };

                        b.Original = this;
                        b.IsCompilerGenerated = true;
                        b.state_machine = stateMachine;
                        b.AddStatement (new StatementExpression (initializer));
                        return b;
                }
        }

        //
        //
        //
        public class ToplevelBlock : ParametersBlock
        {
                LocalVariable this_variable;
                CompilerContext compiler;
                Dictionary<string, object> names;
                Dictionary<string, object> labels;

                List<ExplicitBlock> this_references;

                public ToplevelBlock (CompilerContext ctx, Location loc)
                        : this (ctx, ParametersCompiled.EmptyReadOnlyParameters, loc)
                {
                }

                public ToplevelBlock (CompilerContext ctx, ParametersCompiled parameters, Location start)
                        : base (parameters, start)
                {
                        this.compiler = ctx;
                        top_block = this;
                        flags |= Flags.HasRet;

                        ProcessParameters ();
                }

                //
                // Recreates a top level block from parameters block. Used for
                // compiler generated methods where the original block comes from
                // explicit child block. This works for already resolved blocks
                // only to ensure we resolve them in the correct flow order
                //
                public ToplevelBlock (ParametersBlock source, ParametersCompiled parameters)
                        : base (source, parameters)
                {
                        this.compiler = source.TopBlock.compiler;
                        top_block = this;
                        flags |= Flags.HasRet;
                }

                public bool IsIterator {
                        get {
                                return (flags & Flags.Iterator) != 0;
                        }
                        set {
                                flags = value ? flags | Flags.Iterator : flags & ~Flags.Iterator;
                        }
                }

                public Report Report {
                        get {
                                return compiler.Report;
                        }
                }

                //
                // Used by anonymous blocks to track references of `this' variable
                //
                public List<ExplicitBlock> ThisReferencesFromChildrenBlock {
                        get {
                                return this_references;
                        }
                }

                //
                // Returns the "this" instance variable of this block.
                // See AddThisVariable() for more information.
                //
                public LocalVariable ThisVariable {
                        get {
                                return this_variable;
                        }
                }

                public void AddLocalName (string name, INamedBlockVariable li, bool ignoreChildrenBlocks)
                {
                        if (names == null)
                                names = new Dictionary<string, object> ();

                        object value;
                        if (!names.TryGetValue (name, out value)) {
                                names.Add (name, li);
                                return;
                        }

                        INamedBlockVariable existing = value as INamedBlockVariable;
                        List<INamedBlockVariable> existing_list;
                        if (existing != null) {
                                existing_list = new List<INamedBlockVariable> ();
                                existing_list.Add (existing);
                                names[name] = existing_list;
                        } else {
                                existing_list = (List<INamedBlockVariable>) value;
                        }

                        //
                        // A collision checking between local names
                        //
                        var variable_block = li.Block.Explicit;
                        for (int i = 0; i < existing_list.Count; ++i) {
                                existing = existing_list[i];
                                Block b = existing.Block.Explicit;

                                // Collision at same level
                                if (variable_block == b) {
                                        li.Block.Error_AlreadyDeclared (name, li);
                                        break;
                                }

                                // Collision with parent
                                Block parent = variable_block;
                                while ((parent = parent.Parent) != null) {
                                        if (parent == b) {
                                                li.Block.Error_AlreadyDeclared (name, li, "parent or current");
                                                i = existing_list.Count;
                                                break;
                                        }
                                }

                                if (!ignoreChildrenBlocks && variable_block.Parent != b.Parent) {
                                        // Collision with children
                                        while ((b = b.Parent) != null) {
                                                if (variable_block == b) {
                                                        li.Block.Error_AlreadyDeclared (name, li, "child");
                                                        i = existing_list.Count;
                                                        break;
                                                }
                                        }
                                }
                        }

                        existing_list.Add (li);
                }

                public void AddLabel (string name, LabeledStatement label)
                {
                        if (labels == null)
                                labels = new Dictionary<string, object> ();

                        object value;
                        if (!labels.TryGetValue (name, out value)) {
                                labels.Add (name, label);
                                return;
                        }

                        LabeledStatement existing = value as LabeledStatement;
                        List<LabeledStatement> existing_list;
                        if (existing != null) {
                                existing_list = new List<LabeledStatement> ();
                                existing_list.Add (existing);
                                labels[name] = existing_list;
                        } else {
                                existing_list = (List<LabeledStatement>) value;
                        }

                        //
                        // A collision checking between labels
                        //
                        for (int i = 0; i < existing_list.Count; ++i) {
                                existing = existing_list[i];
                                Block b = existing.Block;

                                // Collision at same level
                                if (label.Block == b) {
                                        Report.SymbolRelatedToPreviousError (existing.loc, name);
                                        Report.Error (140, label.loc, "The label `{0}' is a duplicate", name);
                                        break;
                                }

                                // Collision with parent
                                b = label.Block;
                                while ((b = b.Parent) != null) {
                                        if (existing.Block == b) {
                                                Report.Error (158, label.loc,
                                                        "The label `{0}' shadows another label by the same name in a contained scope", name);
                                                i = existing_list.Count;
                                                break;
                                        }
                                }

                                // Collision with with children
                                b = existing.Block;
                                while ((b = b.Parent) != null) {
                                        if (label.Block == b) {
                                                Report.Error (158, label.loc,
                                                        "The label `{0}' shadows another label by the same name in a contained scope", name);
                                                i = existing_list.Count;
                                                break;
                                        }
                                }
                        }

                        existing_list.Add (label);
                }

                public void AddThisReferenceFromChildrenBlock (ExplicitBlock block)
                {
                        if (this_references == null)
                                this_references = new List<ExplicitBlock> ();

                        if (!this_references.Contains (block))
                                this_references.Add (block);
                }

                public void RemoveThisReferenceFromChildrenBlock (ExplicitBlock block)
                {
                        this_references.Remove (block);
                }

                //
                // Creates an arguments set from all parameters, useful for method proxy calls
                //
                public Arguments GetAllParametersArguments ()
                {
                        int count = parameters.Count;
                        Arguments args = new Arguments (count);
                        for (int i = 0; i < count; ++i) {
                                var arg_expr = GetParameterReference (i, parameter_info[i].Location);
                                args.Add (new Argument (arg_expr));
                        }

                        return args;
                }

                //
                // Lookup inside a block, the returned value can represent 3 states
                //
                // true+variable: A local name was found and it's valid
                // false+variable: A local name was found in a child block only
                // false+null: No local name was found
                //
                public bool GetLocalName (string name, Block block, ref INamedBlockVariable variable)
                {
                        if (names == null)
                                return false;

                        object value;
                        if (!names.TryGetValue (name, out value))
                                return false;

                        variable = value as INamedBlockVariable;
                        Block b = block;
                        if (variable != null) {
                                do {
                                        if (variable.Block == b.Original)
                                                return true;

                                        b = b.Parent;
                                } while (b != null);

                                b = variable.Block;
                                do {
                                        if (block == b)
                                                return false;

                                        b = b.Parent;
                                } while (b != null);
                        } else {
                                List<INamedBlockVariable> list = (List<INamedBlockVariable>) value;
                                for (int i = 0; i < list.Count; ++i) {
                                        variable = list[i];
                                        do {
                                                if (variable.Block == b.Original)
                                                        return true;

                                                b = b.Parent;
                                        } while (b != null);

                                        b = variable.Block;
                                        do {
                                                if (block == b)
                                                        return false;

                                                b = b.Parent;
                                        } while (b != null);

                                        b = block;
                                }
                        }

                        variable = null;
                        return false;
                }

                public LabeledStatement GetLabel (string name, Block block)
                {
                        if (labels == null)
                                return null;

                        object value;
                        if (!labels.TryGetValue (name, out value)) {
                                return null;
                        }

                        var label = value as LabeledStatement;
                        Block b = block;
                        if (label != null) {
                                if (label.Block == b.Original)
                                        return label;
                        } else {
                                List<LabeledStatement> list = (List<LabeledStatement>) value;
                                for (int i = 0; i < list.Count; ++i) {
                                        label = list[i];
                                        if (label.Block == b.Original)
                                                return label;
                                }
                        }
                                
                        return null;
                }

                // <summary>
                //   This is used by non-static `struct' constructors which do not have an
                //   initializer - in this case, the constructor must initialize all of the
                //   struct's fields.  To do this, we add a "this" variable and use the flow
                //   analysis code to ensure that it's been fully initialized before control
                //   leaves the constructor.
                // </summary>
                public void AddThisVariable (BlockContext bc)
                {
                        if (this_variable != null)
                                throw new InternalErrorException (StartLocation.ToString ());

                        this_variable = new LocalVariable (this, "this", LocalVariable.Flags.IsThis | LocalVariable.Flags.Used, StartLocation);
                        this_variable.Type = bc.CurrentType;
                        this_variable.PrepareForFlowAnalysis (bc);
                }

                public bool IsThisAssigned (BlockContext ec)
                {
                        return this_variable == null || this_variable.IsThisAssigned (ec, this);
                }

                public override void Emit (EmitContext ec)
                {
                        if (Report.Errors > 0)
                                return;

                        try {
                        if (IsCompilerGenerated) {
                                using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
                                        base.Emit (ec);
                                }
                        } else {
                                base.Emit (ec);
                        }

                        //
                        // If `HasReturnLabel' is set, then we already emitted a
                        // jump to the end of the method, so we must emit a `ret'
                        // there.
                        //
                        // Unfortunately, System.Reflection.Emit automatically emits
                        // a leave to the end of a finally block.  This is a problem
                        // if no code is following the try/finally block since we may
                        // jump to a point after the end of the method.
                        // As a workaround, we're always creating a return label in
                        // this case.
                        //
                        if (ec.HasReturnLabel || !unreachable) {
                                if (ec.HasReturnLabel)
                                        ec.MarkLabel (ec.ReturnLabel);

                                if (ec.EmitAccurateDebugInfo && !IsCompilerGenerated)
                                        ec.Mark (EndLocation);

                                if (ec.ReturnType.Kind != MemberKind.Void)
                                        ec.Emit (OpCodes.Ldloc, ec.TemporaryReturn ());

                                ec.Emit (OpCodes.Ret);
                        }

                        } catch (Exception e) {
                                throw new InternalErrorException (e, StartLocation);
                        }
                }
        }
        
        public class SwitchLabel : Statement
        {
                Expression label;
                Constant converted;

                Label? il_label;

                //
                // if expr == null, then it is the default case.
                //
                public SwitchLabel (Expression expr, Location l)
                {
                        label = expr;
                        loc = l;
                }

                public bool IsDefault {
                        get {
                                return label == null;
                        }
                }

                public Expression Label {
                        get {
                                return label;
                        }
                }

                public Location Location {
                        get {
                                return loc;
                        }
                }

                public Constant Converted {
                        get {
                                return converted;
                        }
                        set {
                                converted = value;
                        }
                }

                public bool SectionStart { get; set; }

                public Label GetILLabel (EmitContext ec)
                {
                        if (il_label == null){
                                il_label = ec.DefineLabel ();
                        }

                        return il_label.Value;
                }

                protected override void DoEmit (EmitContext ec)
                {
                        ec.MarkLabel (GetILLabel (ec));
                }

                public override bool Resolve (BlockContext bc)
                {
                        bc.CurrentBranching.CurrentUsageVector.ResetBarrier ();

                        return base.Resolve (bc);
                }

                //
                // Resolves the expression, reduces it to a literal if possible
                // and then converts it to the requested type.
                //
                public bool ResolveAndReduce (ResolveContext ec, TypeSpec required_type, bool allow_nullable)
                {       
                        Expression e = label.Resolve (ec);

                        if (e == null)
                                return false;

                        Constant c = e as Constant;
                        if (c == null){
                                ec.Report.Error (150, loc, "A constant value is expected");
                                return false;
                        }

                        if (allow_nullable && c is NullLiteral) {
                                converted = c;
                                return true;
                        }

                        converted = c.ImplicitConversionRequired (ec, required_type, loc);
                        return converted != null;
                }

                public void Error_AlreadyOccurs (ResolveContext ec, TypeSpec switch_type, SwitchLabel collision_with)
                {
                        string label;
                        if (converted == null)
                                label = "default";
                        else
                                label = converted.GetValueAsLiteral ();
                        
                        ec.Report.SymbolRelatedToPreviousError (collision_with.loc, null);
                        ec.Report.Error (152, loc, "The label `case {0}:' already occurs in this switch statement", label);
                }

                protected override void CloneTo (CloneContext clonectx, Statement target)
                {
                        var t = (SwitchLabel) target;
                        if (label != null)
                                t.label = label.Clone (clonectx);
                }

                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class Switch : Statement
        {
                // structure used to hold blocks of keys while calculating table switch
                sealed class LabelsRange : IComparable<LabelsRange>
                {
                        public readonly long min;
                        public long max;
                        public readonly List<long> label_values;

                        public LabelsRange (long value)
                        {
                                min = max = value;
                                label_values = new List<long> ();
                                label_values.Add (value);
                        }

                        public LabelsRange (long min, long max, ICollection<long> values)
                        {
                                this.min = min;
                                this.max = max;
                                this.label_values = new List<long> (values);
                        }

                        public long Range {
                                get {
                                        return max - min + 1;
                                }
                        }

                        public bool AddValue (long value)
                        {
                                var gap = value - min + 1;
                                // Ensure the range has > 50% occupancy
                                if (gap > 2 * (label_values.Count + 1) || gap <= 0)
                                        return false;

                                max = value;
                                label_values.Add (value);
                                return true;
                        }

                        public int CompareTo (LabelsRange other)
                        {
                                int nLength = label_values.Count;
                                int nLengthOther = other.label_values.Count;
                                if (nLengthOther == nLength)
                                        return (int) (other.min - min);

                                return nLength - nLengthOther;
                        }
                }

                sealed class DispatchStatement : Statement
                {
                        readonly Switch body;

                        public DispatchStatement (Switch body)
                        {
                                this.body = body;
                        }

                        protected override void CloneTo (CloneContext clonectx, Statement target)
                        {
                                throw new NotImplementedException ();
                        }

                        protected override void DoEmit (EmitContext ec)
                        {
                                body.EmitDispatch (ec);
                        }
                }

                public Expression Expr;

                //
                // Mapping of all labels to their SwitchLabels
                //
                Dictionary<long, SwitchLabel> labels;
                Dictionary<string, SwitchLabel> string_labels;
                List<SwitchLabel> case_labels;

                /// <summary>
                ///   The governing switch type
                /// </summary>
                public TypeSpec SwitchType;

                Expression new_expr;

                SwitchLabel case_null;
                SwitchLabel case_default;

                Label defaultLabel, nullLabel;
                VariableReference value;
                ExpressionStatement string_dictionary;
                FieldExpr switch_cache_field;
                ExplicitBlock block;

                //
                // Nullable Types support
                //
                Nullable.Unwrap unwrap;

                public Switch (Expression e, ExplicitBlock block, Location l)
                {
                        Expr = e;
                        this.block = block;
                        loc = l;
                }

                public ExplicitBlock Block {
                        get {
                                return block;
                        }
                }

                public SwitchLabel DefaultLabel {
                        get {
                                return case_default;
                        }
                }

                public bool IsNullable {
                        get {
                                return unwrap != null;
                        }
                }

                //
                // Determines the governing type for a switch.  The returned
                // expression might be the expression from the switch, or an
                // expression that includes any potential conversions to
                //
                Expression SwitchGoverningType (ResolveContext ec, Expression expr)
                {
                        switch (expr.Type.BuiltinType) {
                        case BuiltinTypeSpec.Type.Byte:
                        case BuiltinTypeSpec.Type.SByte:
                        case BuiltinTypeSpec.Type.UShort:
                        case BuiltinTypeSpec.Type.Short:
                        case BuiltinTypeSpec.Type.UInt:
                        case BuiltinTypeSpec.Type.Int:
                        case BuiltinTypeSpec.Type.ULong:
                        case BuiltinTypeSpec.Type.Long:
                        case BuiltinTypeSpec.Type.Char:
                        case BuiltinTypeSpec.Type.String:
                        case BuiltinTypeSpec.Type.Bool:
                                return expr;
                        }

                        if (expr.Type.IsEnum)
                                return expr;

                        //
                        // Try to find a *user* defined implicit conversion.
                        //
                        // If there is no implicit conversion, or if there are multiple
                        // conversions, we have to report an error
                        //
                        Expression converted = null;
                        foreach (TypeSpec tt in ec.BuiltinTypes.SwitchUserTypes) {
                                Expression e;
                                
                                e = Convert.ImplicitUserConversion (ec, expr, tt, loc);
                                if (e == null)
                                        continue;

                                //
                                // Ignore over-worked ImplicitUserConversions that do
                                // an implicit conversion in addition to the user conversion.
                                // 
                                if (!(e is UserCast))
                                        continue;

                                if (converted != null){
                                        ec.Report.ExtraInformation (loc, "(Ambiguous implicit user defined conversion in previous ");
                                        return null;
                                }

                                converted = e;
                        }
                        return converted;
                }

                public static TypeSpec[] CreateSwitchUserTypes (BuiltinTypes types)
                {
                        // LAMESPEC: For some reason it does not contain bool which looks like csc bug
                        return new[] {
                                types.SByte,
                                types.Byte,
                                types.Short,
                                types.UShort,
                                types.Int,
                                types.UInt,
                                types.Long,
                                types.ULong,
                                types.Char,
                                types.String
                        };
                }

                //
                // Performs the basic sanity checks on the switch statement
                // (looks for duplicate keys and non-constant expressions).
                //
                // It also returns a hashtable with the keys that we will later
                // use to compute the switch tables
                //
                bool ResolveLabels (ResolveContext ec, Constant value)
                {
                        bool error = false;
                        if (SwitchType.BuiltinType == BuiltinTypeSpec.Type.String) {
                                string_labels = new Dictionary<string, SwitchLabel> ();
                        } else {
                                labels = new Dictionary<long, SwitchLabel> ();
                        }

                        case_labels = new List<SwitchLabel> ();
                        int default_label_index = -1;
                        bool constant_label_found = false;

                        for (int i = 0; i < block.Statements.Count; ++i) {
                                var s = block.Statements[i];

                                var sl = s as SwitchLabel;
                                if (sl == null) {
                                        continue;
                                }

                                case_labels.Add (sl);

                                if (sl.IsDefault) {
                                        if (case_default != null) {
                                                sl.Error_AlreadyOccurs (ec, SwitchType, case_default);
                                                error = true;
                                        }

                                        default_label_index = i;
                                        case_default = sl;
                                        continue;
                                }

                                if (!sl.ResolveAndReduce (ec, SwitchType, IsNullable)) {
                                        error = true;
                                        continue;
                                }

                                try {
                                        if (string_labels != null) {
                                                string string_value = sl.Converted.GetValue () as string;
                                                if (string_value == null)
                                                        case_null = sl;
                                                else
                                                        string_labels.Add (string_value, sl);
                                        } else {
                                                if (sl.Converted is NullLiteral) {
                                                        case_null = sl;
                                                } else {
                                                        labels.Add (sl.Converted.GetValueAsLong (), sl);
                                                }
                                        }
                                } catch (ArgumentException) {
                                        if (string_labels != null)
                                                sl.Error_AlreadyOccurs (ec, SwitchType, string_labels[(string) sl.Converted.GetValue ()]);
                                        else
                                                sl.Error_AlreadyOccurs (ec, SwitchType, labels[sl.Converted.GetValueAsLong ()]);

                                        error = true;
                                }

                                if (value != null) {
                                        var constant_label = constant_label_found ? null : FindLabel (value);
                                        if (constant_label == null || constant_label != sl)
                                                block.Statements[i] = new EmptyStatement (s.loc);
                                        else
                                                constant_label_found = true;
                                }
                        }

                        if (value != null && constant_label_found && default_label_index >= 0)
                                block.Statements[default_label_index] = new EmptyStatement (case_default.loc);

                        return !error;
                }
                
                //
                // This method emits code for a lookup-based switch statement (non-string)
                // Basically it groups the cases into blocks that are at least half full,
                // and then spits out individual lookup opcodes for each block.
                // It emits the longest blocks first, and short blocks are just
                // handled with direct compares.
                //
                void EmitTableSwitch (EmitContext ec, Expression val)
                {
                        if (labels != null && labels.Count > 0) {
                                List<LabelsRange> ranges;
                                if (string_labels != null) {
                                        // We have done all hard work for string already
                                        // setup single range only
                                        ranges = new List<LabelsRange> (1);
                                        ranges.Add (new LabelsRange (0, labels.Count - 1, labels.Keys));
                                } else {
                                        var element_keys = new long[labels.Count];
                                        labels.Keys.CopyTo (element_keys, 0);
                                        Array.Sort (element_keys);

                                        //
                                        // Build possible ranges of switch labes to reduce number
                                        // of comparisons
                                        //
                                        ranges = new List<LabelsRange> (element_keys.Length);
                                        var range = new LabelsRange (element_keys[0]);
                                        ranges.Add (range);
                                        for (int i = 1; i < element_keys.Length; ++i) {
                                                var l = element_keys[i];
                                                if (range.AddValue (l))
                                                        continue;

                                                range = new LabelsRange (l);
                                                ranges.Add (range);
                                        }

                                        // sort the blocks so we can tackle the largest ones first
                                        ranges.Sort ();
                                }

                                Label lbl_default = defaultLabel;
                                TypeSpec compare_type = SwitchType.IsEnum ? EnumSpec.GetUnderlyingType (SwitchType) : SwitchType;

                                for (int range_index = ranges.Count - 1; range_index >= 0; --range_index) {
                                        LabelsRange kb = ranges[range_index];
                                        lbl_default = (range_index == 0) ? defaultLabel : ec.DefineLabel ();

                                        // Optimize small ranges using simple equality check
                                        if (kb.Range <= 2) {
                                                foreach (var key in kb.label_values) {
                                                        SwitchLabel sl = labels[key];
                                                        if (sl == case_default || sl == case_null)
                                                                continue;

                                                        if (sl.Converted.IsZeroInteger) {
                                                                val.EmitBranchable (ec, sl.GetILLabel (ec), false);
                                                        } else {
                                                                val.Emit (ec);
                                                                sl.Converted.Emit (ec);
                                                                ec.Emit (OpCodes.Beq, sl.GetILLabel (ec));
                                                        }
                                                }
                                        } else {
                                                // TODO: if all the keys in the block are the same and there are
                                                //       no gaps/defaults then just use a range-check.
                                                if (compare_type.BuiltinType == BuiltinTypeSpec.Type.Long || compare_type.BuiltinType == BuiltinTypeSpec.Type.ULong) {
                                                        // TODO: optimize constant/I4 cases

                                                        // check block range (could be > 2^31)
                                                        val.Emit (ec);
                                                        ec.EmitLong (kb.min);
                                                        ec.Emit (OpCodes.Blt, lbl_default);

                                                        val.Emit (ec);
                                                        ec.EmitLong (kb.max);
                                                        ec.Emit (OpCodes.Bgt, lbl_default);

                                                        // normalize range
                                                        val.Emit (ec);
                                                        if (kb.min != 0) {
                                                                ec.EmitLong (kb.min);
                                                                ec.Emit (OpCodes.Sub);
                                                        }

                                                        ec.Emit (OpCodes.Conv_I4);      // assumes < 2^31 labels!
                                                } else {
                                                        // normalize range
                                                        val.Emit (ec);
                                                        int first = (int) kb.min;
                                                        if (first > 0) {
                                                                ec.EmitInt (first);
                                                                ec.Emit (OpCodes.Sub);
                                                        } else if (first < 0) {
                                                                ec.EmitInt (-first);
                                                                ec.Emit (OpCodes.Add);
                                                        }
                                                }

                                                // first, build the list of labels for the switch
                                                int iKey = 0;
                                                long cJumps = kb.Range;
                                                Label[] switch_labels = new Label[cJumps];
                                                for (int iJump = 0; iJump < cJumps; iJump++) {
                                                        var key = kb.label_values[iKey];
                                                        if (key == kb.min + iJump) {
                                                                switch_labels[iJump] = labels[key].GetILLabel (ec);
                                                                iKey++;
                                                        } else {
                                                                switch_labels[iJump] = lbl_default;
                                                        }
                                                }

                                                // emit the switch opcode
                                                ec.Emit (OpCodes.Switch, switch_labels);
                                        }

                                        // mark the default for this block
                                        if (range_index != 0)
                                                ec.MarkLabel (lbl_default);
                                }

                                // the last default just goes to the end
                                if (ranges.Count > 0)
                                        ec.Emit (OpCodes.Br, lbl_default);
                        }
                }
                
                SwitchLabel FindLabel (Constant value)
                {
                        SwitchLabel sl = null;

                        if (string_labels != null) {
                                string s = value.GetValue () as string;
                                if (s == null) {
                                        if (case_null != null)
                                                sl = case_null;
                                        else if (case_default != null)
                                                sl = case_default;
                                } else {
                                        string_labels.TryGetValue (s, out sl);
                                }
                        } else {
                                if (value is NullLiteral) {
                                        sl = case_null;
                                } else {
                                        labels.TryGetValue (value.GetValueAsLong (), out sl);
                                }
                        }

                        return sl;
                }

                public override bool Resolve (BlockContext ec)
                {
                        Expr = Expr.Resolve (ec);
                        if (Expr == null)
                                return false;

                        new_expr = SwitchGoverningType (ec, Expr);

                        if (new_expr == null && Expr.Type.IsNullableType) {
                                unwrap = Nullable.Unwrap.Create (Expr, false);
                                if (unwrap == null)
                                        return false;

                                new_expr = SwitchGoverningType (ec, unwrap);
                        }

                        if (new_expr == null) {
                                if (Expr.Type != InternalType.ErrorType) {
                                        ec.Report.Error (151, loc,
                                                "A switch expression of type `{0}' cannot be converted to an integral type, bool, char, string, enum or nullable type",
                                                Expr.Type.GetSignatureForError ());
                                }

                                return false;
                        }

                        // Validate switch.
                        SwitchType = new_expr.Type;

                        if (SwitchType.BuiltinType == BuiltinTypeSpec.Type.Bool && ec.Module.Compiler.Settings.Version == LanguageVersion.ISO_1) {
                                ec.Report.FeatureIsNotAvailable (ec.Module.Compiler, loc, "switch expression of boolean type");
                                return false;
                        }

                        if (block.Statements.Count == 0)
                                return true;

                        var constant = new_expr as Constant;

                        if (!ResolveLabels (ec, constant))
                                return false;

                        //
                        // Don't need extra variable for constant switch or switch with
                        // only default case
                        //
                        if (constant == null && (case_labels.Count - (case_default != null ? 1 : 0)) != 0) {
                                //
                                // Store switch expression for comparison purposes
                                //
                                value = new_expr as VariableReference;
                                if (value == null) {
                                        // Create temporary variable inside switch scope
                                        var current_block = ec.CurrentBlock;
                                        ec.CurrentBlock = Block;
                                        value = TemporaryVariableReference.Create (SwitchType, ec.CurrentBlock, loc);
                                        value.Resolve (ec);
                                        ec.CurrentBlock = current_block;
                                }
                        }

                        Switch old_switch = ec.Switch;
                        ec.Switch = this;
                        ec.Switch.SwitchType = SwitchType;

                        ec.StartFlowBranching (FlowBranching.BranchingType.Switch, loc);

                        ec.CurrentBranching.CurrentUsageVector.Goto ();

                        var ok = block.Resolve (ec);

                        if (case_default == null)
                                ec.CurrentBranching.CurrentUsageVector.ResetBarrier ();

                        ec.EndFlowBranching ();
                        ec.Switch = old_switch;

                        if (!ok)
                                return false;

                        if (constant == null && SwitchType.BuiltinType == BuiltinTypeSpec.Type.String && string_labels.Count > 6) {
                                ResolveStringSwitchMap (ec);
                        }

                        //
                        // Needed to emit anonymous storey initialization before
                        // any generated switch dispatch
                        //
                        block.AddScopeStatement (new DispatchStatement (this));

                        return true;
                }

                public SwitchLabel ResolveGotoCase (ResolveContext rc, Constant value)
                {
                        var sl = FindLabel (value);

                        if (sl == null) {
                                FlowBranchingBlock.Error_UnknownLabel (loc, "case " + value.GetValueAsLiteral (), rc.Report);
                        }

                        return sl;
                }

                //
                // Converts string switch into string hashtable
                //
                void ResolveStringSwitchMap (ResolveContext ec)
                {
                        FullNamedExpression string_dictionary_type;
                        if (ec.Module.PredefinedTypes.Dictionary.Define ()) {
                                string_dictionary_type = new TypeExpression (
                                        ec.Module.PredefinedTypes.Dictionary.TypeSpec.MakeGenericType (ec,
                                                new [] { ec.BuiltinTypes.String, ec.BuiltinTypes.Int }),
                                        loc);
                        } else if (ec.Module.PredefinedTypes.Hashtable.Define ()) {
                                string_dictionary_type = new TypeExpression (ec.Module.PredefinedTypes.Hashtable.TypeSpec, loc);
                        } else {
                                ec.Module.PredefinedTypes.Dictionary.Resolve ();
                                return;
                        }

                        var ctype = ec.CurrentMemberDefinition.Parent.PartialContainer;
                        Field field = new Field (ctype, string_dictionary_type,
                                Modifiers.STATIC | Modifiers.PRIVATE | Modifiers.COMPILER_GENERATED,
                                new MemberName (CompilerGeneratedContainer.MakeName (null, "f", "switch$map", ec.Module.CounterSwitchTypes++), loc), null);
                        if (!field.Define ())
                                return;
                        ctype.AddField (field);

                        var init = new List<Expression> ();
                        int counter = -1;
                        labels = new Dictionary<long, SwitchLabel> (string_labels.Count);
                        string value = null;

                        foreach (SwitchLabel sl in case_labels) {

                                if (sl.SectionStart)
                                        labels.Add (++counter, sl);

                                if (sl == case_default || sl == case_null)
                                        continue;

                                value = (string) sl.Converted.GetValue ();
                                var init_args = new List<Expression> (2);
                                init_args.Add (new StringLiteral (ec.BuiltinTypes, value, sl.Location));

                                sl.Converted = new IntConstant (ec.BuiltinTypes, counter, loc);
                                init_args.Add (sl.Converted);

                                init.Add (new CollectionElementInitializer (init_args, loc));
                        }
        
                        Arguments args = new Arguments (1);
                        args.Add (new Argument (new IntConstant (ec.BuiltinTypes, init.Count, loc)));
                        Expression initializer = new NewInitialize (string_dictionary_type, args,
                                new CollectionOrObjectInitializers (init, loc), loc);

                        switch_cache_field = new FieldExpr (field, loc);
                        string_dictionary = new SimpleAssign (switch_cache_field, initializer.Resolve (ec));
                }

                void DoEmitStringSwitch (EmitContext ec)
                {
                        Label l_initialized = ec.DefineLabel ();

                        //
                        // Skip initialization when value is null
                        //
                        value.EmitBranchable (ec, nullLabel, false);

                        //
                        // Check if string dictionary is initialized and initialize
                        //
                        switch_cache_field.EmitBranchable (ec, l_initialized, true);
                        using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
                                string_dictionary.EmitStatement (ec);
                        }
                        ec.MarkLabel (l_initialized);

                        LocalTemporary string_switch_variable = new LocalTemporary (ec.BuiltinTypes.Int);

                        ResolveContext rc = new ResolveContext (ec.MemberContext);

                        if (switch_cache_field.Type.IsGeneric) {
                                Arguments get_value_args = new Arguments (2);
                                get_value_args.Add (new Argument (value));
                                get_value_args.Add (new Argument (string_switch_variable, Argument.AType.Out));
                                Expression get_item = new Invocation (new MemberAccess (switch_cache_field, "TryGetValue", loc), get_value_args).Resolve (rc);
                                if (get_item == null)
                                        return;

                                //
                                // A value was not found, go to default case
                                //
                                get_item.EmitBranchable (ec, defaultLabel, false);
                        } else {
                                Arguments get_value_args = new Arguments (1);
                                get_value_args.Add (new Argument (value));

                                Expression get_item = new ElementAccess (switch_cache_field, get_value_args, loc).Resolve (rc);
                                if (get_item == null)
                                        return;

                                LocalTemporary get_item_object = new LocalTemporary (ec.BuiltinTypes.Object);
                                get_item_object.EmitAssign (ec, get_item, true, false);
                                ec.Emit (OpCodes.Brfalse, defaultLabel);

                                ExpressionStatement get_item_int = (ExpressionStatement) new SimpleAssign (string_switch_variable,
                                        new Cast (new TypeExpression (ec.BuiltinTypes.Int, loc), get_item_object, loc)).Resolve (rc);

                                get_item_int.EmitStatement (ec);
                                get_item_object.Release (ec);
                        }

                        EmitTableSwitch (ec, string_switch_variable);
                        string_switch_variable.Release (ec);
                }

                //
                // Emits switch using simple if/else comparison for small label count (4 + optional default)
                //
                void EmitShortSwitch (EmitContext ec)
                {
                        MethodSpec equal_method = null;
                        if (SwitchType.BuiltinType == BuiltinTypeSpec.Type.String) {
                                equal_method = ec.Module.PredefinedMembers.StringEqual.Resolve (loc);
                        }

                        if (equal_method != null) {
                                value.EmitBranchable (ec, nullLabel, false);
                        }

                        for (int i = 0; i < case_labels.Count; ++i) {
                                var label = case_labels [i];
                                if (label == case_default || label == case_null)
                                        continue;

                                var constant = label.Converted;

                                if (equal_method != null) {
                                        value.Emit (ec);
                                        constant.Emit (ec);

                                        var call = new CallEmitter ();
                                        call.EmitPredefined (ec, equal_method, new Arguments (0));
                                        ec.Emit (OpCodes.Brtrue, label.GetILLabel (ec));
                                        continue;
                                }

                                if (constant.IsZeroInteger && constant.Type.BuiltinType != BuiltinTypeSpec.Type.Long && constant.Type.BuiltinType != BuiltinTypeSpec.Type.ULong) {
                                        value.EmitBranchable (ec, label.GetILLabel (ec), false);
                                        continue;
                                }

                                value.Emit (ec);
                                constant.Emit (ec);
                                ec.Emit (OpCodes.Beq, label.GetILLabel (ec));
                        }

                        ec.Emit (OpCodes.Br, defaultLabel);
                }

                void EmitDispatch (EmitContext ec)
                {
                        if (value == null) {
                                //
                                // Constant switch, we already done the work
                                //
                                return;
                        }

                        //
                        // Mark sequence point explicitly to switch
                        //
                        ec.Mark (block.StartLocation);
                        block.IsCompilerGenerated = true;

                        if (string_dictionary != null) {
                                DoEmitStringSwitch (ec);
                        } else if (case_labels.Count < 4 || string_labels != null) {
                                EmitShortSwitch (ec);
                        } else {
                                EmitTableSwitch (ec, value);
                        }
                }

                protected override void DoEmit (EmitContext ec)
                {
                        // Workaround broken flow-analysis
                        block.HasUnreachableClosingBrace = true;

                        //
                        // Setup the codegen context
                        //
                        Label old_end = ec.LoopEnd;
                        Switch old_switch = ec.Switch;

                        ec.LoopEnd = ec.DefineLabel ();
                        ec.Switch = this;

                        defaultLabel = case_default == null ? ec.LoopEnd : case_default.GetILLabel (ec);
                        nullLabel = case_null == null ? defaultLabel : case_null.GetILLabel (ec);

                        if (value != null) {
                                ec.Mark (loc);
                                if (IsNullable) {
                                        unwrap.EmitCheck (ec);
                                        ec.Emit (OpCodes.Brfalse, nullLabel);
                                        value.EmitAssign (ec, new_expr, false, false);
                                } else if (new_expr != value) {
                                        value.EmitAssign (ec, new_expr, false, false);
                                }
                        }

                        block.Emit (ec);

                        // Restore context state. 
                        ec.MarkLabel (ec.LoopEnd);

                        //
                        // Restore the previous context
                        //
                        ec.LoopEnd = old_end;
                        ec.Switch = old_switch;
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Switch target = (Switch) t;

                        target.Expr = Expr.Clone (clonectx);
                        target.block = (ExplicitBlock) block.Clone (clonectx);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        // A place where execution can restart in an iterator
        public abstract class ResumableStatement : Statement
        {
                bool prepared;
                protected Label resume_point;

                public Label PrepareForEmit (EmitContext ec)
                {
                        if (!prepared) {
                                prepared = true;
                                resume_point = ec.DefineLabel ();
                        }
                        return resume_point;
                }

                public virtual Label PrepareForDispose (EmitContext ec, Label end)
                {
                        return end;
                }

                public virtual void EmitForDispose (EmitContext ec, LocalBuilder pc, Label end, bool have_dispatcher)
                {
                }
        }

        public abstract class TryFinallyBlock : ExceptionStatement
        {
                protected Statement stmt;
                Label dispose_try_block;
                bool prepared_for_dispose, emitted_dispose;
                Method finally_host;

                protected TryFinallyBlock (Statement stmt, Location loc)
                        : base (loc)
                {
                        this.stmt = stmt;
                }

                #region Properties

                public Statement Statement {
                        get {
                                return stmt;
                        }
                }

                #endregion

                protected abstract void EmitTryBody (EmitContext ec);
                public abstract void EmitFinallyBody (EmitContext ec);

                public override Label PrepareForDispose (EmitContext ec, Label end)
                {
                        if (!prepared_for_dispose) {
                                prepared_for_dispose = true;
                                dispose_try_block = ec.DefineLabel ();
                        }
                        return dispose_try_block;
                }

                protected sealed override void DoEmit (EmitContext ec)
                {
                        EmitTryBodyPrepare (ec);
                        EmitTryBody (ec);

                        ec.BeginFinallyBlock ();

                        Label start_finally = ec.DefineLabel ();
                        if (resume_points != null) {
                                var state_machine = (StateMachineInitializer) ec.CurrentAnonymousMethod;

                                ec.Emit (OpCodes.Ldloc, state_machine.SkipFinally);
                                ec.Emit (OpCodes.Brfalse_S, start_finally);
                                ec.Emit (OpCodes.Endfinally);
                        }

                        ec.MarkLabel (start_finally);

                        if (finally_host != null) {
                                finally_host.Define ();
                                finally_host.Emit ();

                                // Now it's safe to add, to close it properly and emit sequence points
                                finally_host.Parent.AddMember (finally_host);

                                var ce = new CallEmitter ();
                                ce.InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, loc);
                                ce.EmitPredefined (ec, finally_host.Spec, new Arguments (0));
                        } else {
                                EmitFinallyBody (ec);
                        }

                        ec.EndExceptionBlock ();
                }

                public override void EmitForDispose (EmitContext ec, LocalBuilder pc, Label end, bool have_dispatcher)
                {
                        if (emitted_dispose)
                                return;

                        emitted_dispose = true;

                        Label end_of_try = ec.DefineLabel ();

                        // Ensure that the only way we can get into this code is through a dispatcher
                        if (have_dispatcher)
                                ec.Emit (OpCodes.Br, end);

                        ec.BeginExceptionBlock ();

                        ec.MarkLabel (dispose_try_block);

                        Label[] labels = null;
                        for (int i = 0; i < resume_points.Count; ++i) {
                                ResumableStatement s = resume_points[i];
                                Label ret = s.PrepareForDispose (ec, end_of_try);
                                if (ret.Equals (end_of_try) && labels == null)
                                        continue;
                                if (labels == null) {
                                        labels = new Label[resume_points.Count];
                                        for (int j = 0; j < i; ++j)
                                                labels[j] = end_of_try;
                                }
                                labels[i] = ret;
                        }

                        if (labels != null) {
                                int j;
                                for (j = 1; j < labels.Length; ++j)
                                        if (!labels[0].Equals (labels[j]))
                                                break;
                                bool emit_dispatcher = j < labels.Length;

                                if (emit_dispatcher) {
                                        ec.Emit (OpCodes.Ldloc, pc);
                                        ec.EmitInt (first_resume_pc);
                                        ec.Emit (OpCodes.Sub);
                                        ec.Emit (OpCodes.Switch, labels);
                                }

                                foreach (ResumableStatement s in resume_points)
                                        s.EmitForDispose (ec, pc, end_of_try, emit_dispatcher);
                        }

                        ec.MarkLabel (end_of_try);

                        ec.BeginFinallyBlock ();

                        if (finally_host != null) {
                                var ce = new CallEmitter ();
                                ce.InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, loc);
                                ce.EmitPredefined (ec, finally_host.Spec, new Arguments (0));
                        } else {
                                EmitFinallyBody (ec);
                        }

                        ec.EndExceptionBlock ();
                }

                public override bool Resolve (BlockContext bc)
                {
                        //
                        // Finally block inside iterator is called from MoveNext and
                        // Dispose methods that means we need to lift the block into
                        // newly created host method to emit the body only once. The
                        // original block then simply calls the newly generated method.
                        //
                        if (bc.CurrentIterator != null && !bc.IsInProbingMode) {
                                var b = stmt as Block;
                                if (b != null && b.Explicit.HasYield) {
                                        finally_host = bc.CurrentIterator.CreateFinallyHost (this);
                                }
                        }

                        return base.Resolve (bc);
                }
        }

        //
        // Base class for blocks using exception handling
        //
        public abstract class ExceptionStatement : ResumableStatement
        {
#if !STATIC
                bool code_follows;
#endif
                protected List<ResumableStatement> resume_points;
                protected int first_resume_pc;

                protected ExceptionStatement (Location loc)
                {
                        this.loc = loc;
                }

                protected virtual void EmitTryBodyPrepare (EmitContext ec)
                {
                        StateMachineInitializer state_machine = null;
                        if (resume_points != null) {
                                state_machine = (StateMachineInitializer) ec.CurrentAnonymousMethod;

                                ec.EmitInt ((int) IteratorStorey.State.Running);
                                ec.Emit (OpCodes.Stloc, state_machine.CurrentPC);
                        }

                        ec.BeginExceptionBlock ();

                        if (resume_points != null) {
                                ec.MarkLabel (resume_point);

                                // For normal control flow, we want to fall-through the Switch
                                // So, we use CurrentPC rather than the $PC field, and initialize it to an outside value above
                                ec.Emit (OpCodes.Ldloc, state_machine.CurrentPC);
                                ec.EmitInt (first_resume_pc);
                                ec.Emit (OpCodes.Sub);

                                Label[] labels = new Label[resume_points.Count];
                                for (int i = 0; i < resume_points.Count; ++i)
                                        labels[i] = resume_points[i].PrepareForEmit (ec);
                                ec.Emit (OpCodes.Switch, labels);
                        }
                }

                public void SomeCodeFollows ()
                {
#if !STATIC
                        code_follows = true;
#endif
                }

                public override bool Resolve (BlockContext ec)
                {
#if !STATIC
                        // System.Reflection.Emit automatically emits a 'leave' at the end of a try clause
                        // So, ensure there's some IL code after this statement.
                        if (!code_follows && resume_points == null && ec.CurrentBranching.CurrentUsageVector.IsUnreachable)
                                ec.NeedReturnLabel ();
#endif
                        return true;
                }

                public void AddResumePoint (ResumableStatement stmt, int pc)
                {
                        if (resume_points == null) {
                                resume_points = new List<ResumableStatement> ();
                                first_resume_pc = pc;
                        }

                        if (pc != first_resume_pc + resume_points.Count)
                                throw new InternalErrorException ("missed an intervening AddResumePoint?");

                        resume_points.Add (stmt);
                }

        }

        public class Lock : TryFinallyBlock
        {
                Expression expr;
                TemporaryVariableReference expr_copy;
                TemporaryVariableReference lock_taken;
                        
                public Lock (Expression expr, Statement stmt, Location loc)
                        : base (stmt, loc)
                {
                        this.expr = expr;
                }

                public Expression Expr {
                        get {
                                return this.expr;
                        }
                }

                public override bool Resolve (BlockContext ec)
                {
                        expr = expr.Resolve (ec);
                        if (expr == null)
                                return false;

                        if (!TypeSpec.IsReferenceType (expr.Type)) {
                                ec.Report.Error (185, loc,
                                        "`{0}' is not a reference type as required by the lock statement",
                                        expr.Type.GetSignatureForError ());
                        }

                        if (expr.Type.IsGenericParameter) {
                                expr = Convert.ImplicitTypeParameterConversion (expr, (TypeParameterSpec)expr.Type, ec.BuiltinTypes.Object);
                        }

                        VariableReference lv = expr as VariableReference;
                        bool locked;
                        if (lv != null) {
                                locked = lv.IsLockedByStatement;
                                lv.IsLockedByStatement = true;
                        } else {
                                lv = null;
                                locked = false;
                        }

                        //
                        // Have to keep original lock value around to unlock same location
                        // in the case of original value has changed or is null
                        //
                        expr_copy = TemporaryVariableReference.Create (ec.BuiltinTypes.Object, ec.CurrentBlock, loc);
                        expr_copy.Resolve (ec);

                        //
                        // Ensure Monitor methods are available
                        //
                        if (ResolvePredefinedMethods (ec) > 1) {
                                lock_taken = TemporaryVariableReference.Create (ec.BuiltinTypes.Bool, ec.CurrentBlock, loc);
                                lock_taken.Resolve (ec);
                        }

                        using (ec.Set (ResolveContext.Options.LockScope)) {
                                ec.StartFlowBranching (this);
                                Statement.Resolve (ec);
                                ec.EndFlowBranching ();
                        }

                        if (lv != null) {
                                lv.IsLockedByStatement = locked;
                        }

                        base.Resolve (ec);

                        return true;
                }
                
                protected override void EmitTryBodyPrepare (EmitContext ec)
                {
                        expr_copy.EmitAssign (ec, expr);

                        if (lock_taken != null) {
                                //
                                // Initialize ref variable
                                //
                                lock_taken.EmitAssign (ec, new BoolLiteral (ec.BuiltinTypes, false, loc));
                        } else {
                                //
                                // Monitor.Enter (expr_copy)
                                //
                                expr_copy.Emit (ec);
                                ec.Emit (OpCodes.Call, ec.Module.PredefinedMembers.MonitorEnter.Get ());
                        }

                        base.EmitTryBodyPrepare (ec);
                }

                protected override void EmitTryBody (EmitContext ec)
                {
                        //
                        // Monitor.Enter (expr_copy, ref lock_taken)
                        //
                        if (lock_taken != null) {
                                expr_copy.Emit (ec);
                                lock_taken.LocalInfo.CreateBuilder (ec);
                                lock_taken.AddressOf (ec, AddressOp.Load);
                                ec.Emit (OpCodes.Call, ec.Module.PredefinedMembers.MonitorEnter_v4.Get ());
                        }

                        Statement.Emit (ec);
                }

                public override void EmitFinallyBody (EmitContext ec)
                {
                        //
                        // if (lock_taken) Monitor.Exit (expr_copy)
                        //
                        Label skip = ec.DefineLabel ();

                        if (lock_taken != null) {
                                lock_taken.Emit (ec);
                                ec.Emit (OpCodes.Brfalse_S, skip);
                        }

                        expr_copy.Emit (ec);
                        var m = ec.Module.PredefinedMembers.MonitorExit.Resolve (loc);
                        if (m != null)
                                ec.Emit (OpCodes.Call, m);

                        ec.MarkLabel (skip);
                }

                int ResolvePredefinedMethods (ResolveContext rc)
                {
                        // Try 4.0 Monitor.Enter (object, ref bool) overload first
                        var m = rc.Module.PredefinedMembers.MonitorEnter_v4.Get ();
                        if (m != null)
                                return 4;

                        m = rc.Module.PredefinedMembers.MonitorEnter.Get ();
                        if (m != null)
                                return 1;

                        rc.Module.PredefinedMembers.MonitorEnter_v4.Resolve (loc);
                        return 0;
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Lock target = (Lock) t;

                        target.expr = expr.Clone (clonectx);
                        target.stmt = Statement.Clone (clonectx);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }

        }

        public class Unchecked : Statement {
                public Block Block;
                
                public Unchecked (Block b, Location loc)
                {
                        Block = b;
                        b.Unchecked = true;
                        this.loc = loc;
                }

                public override bool Resolve (BlockContext ec)
                {
                        using (ec.With (ResolveContext.Options.AllCheckStateFlags, false))
                                return Block.Resolve (ec);
                }
                
                protected override void DoEmit (EmitContext ec)
                {
                        using (ec.With (EmitContext.Options.CheckedScope, false))
                                Block.Emit (ec);
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Unchecked target = (Unchecked) t;

                        target.Block = clonectx.LookupBlock (Block);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class Checked : Statement {
                public Block Block;
                
                public Checked (Block b, Location loc)
                {
                        Block = b;
                        b.Unchecked = false;
                        this.loc = loc;
                }

                public override bool Resolve (BlockContext ec)
                {
                        using (ec.With (ResolveContext.Options.AllCheckStateFlags, true))
                                return Block.Resolve (ec);
                }

                protected override void DoEmit (EmitContext ec)
                {
                        using (ec.With (EmitContext.Options.CheckedScope, true))
                                Block.Emit (ec);
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Checked target = (Checked) t;

                        target.Block = clonectx.LookupBlock (Block);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class Unsafe : Statement {
                public Block Block;

                public Unsafe (Block b, Location loc)
                {
                        Block = b;
                        Block.Unsafe = true;
                        this.loc = loc;
                }

                public override bool Resolve (BlockContext ec)
                {
                        if (ec.CurrentIterator != null)
                                ec.Report.Error (1629, loc, "Unsafe code may not appear in iterators");

                        using (ec.Set (ResolveContext.Options.UnsafeScope))
                                return Block.Resolve (ec);
                }
                
                protected override void DoEmit (EmitContext ec)
                {
                        Block.Emit (ec);
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Unsafe target = (Unsafe) t;

                        target.Block = clonectx.LookupBlock (Block);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        // 
        // Fixed statement
        //
        public class Fixed : Statement
        {
                abstract class Emitter : ShimExpression
                {
                        protected LocalVariable vi;

                        protected Emitter (Expression expr, LocalVariable li)
                                : base (expr)
                        {
                                vi = li;
                        }

                        public abstract void EmitExit (EmitContext ec);
                }

                class ExpressionEmitter : Emitter {
                        public ExpressionEmitter (Expression converted, LocalVariable li) :
                                base (converted, li)
                        {
                        }

                        protected override Expression DoResolve (ResolveContext rc)
                        {
                                throw new NotImplementedException ();
                        }

                        public override void Emit (EmitContext ec) {
                                //
                                // Store pointer in pinned location
                                //
                                expr.Emit (ec);
                                vi.EmitAssign (ec);
                        }

                        public override void EmitExit (EmitContext ec)
                        {
                                ec.EmitInt (0);
                                ec.Emit (OpCodes.Conv_U);
                                vi.EmitAssign (ec);
                        }
                }

                class StringEmitter : Emitter
                {
                        LocalVariable pinned_string;

                        public StringEmitter (Expression expr, LocalVariable li, Location loc)
                                : base (expr, li)
                        {
                        }

                        protected override Expression DoResolve (ResolveContext rc)
                        {
                                pinned_string = new LocalVariable (vi.Block, "$pinned",
                                        LocalVariable.Flags.FixedVariable | LocalVariable.Flags.CompilerGenerated | LocalVariable.Flags.Used,
                                        vi.Location);
                                pinned_string.Type = rc.BuiltinTypes.String;

                                eclass = ExprClass.Variable;
                                type = rc.BuiltinTypes.Int;
                                return this;
                        }

                        public override void Emit (EmitContext ec)
                        {
                                pinned_string.CreateBuilder (ec);

                                expr.Emit (ec);
                                pinned_string.EmitAssign (ec);

                                // TODO: Should use Binary::Add
                                pinned_string.Emit (ec);
                                ec.Emit (OpCodes.Conv_I);

                                var m = ec.Module.PredefinedMembers.RuntimeHelpersOffsetToStringData.Resolve (loc);
                                if (m == null)
                                        return;

                                PropertyExpr pe = new PropertyExpr (m, pinned_string.Location);
                                //pe.InstanceExpression = pinned_string;
                                pe.Resolve (new ResolveContext (ec.MemberContext)).Emit (ec);

                                ec.Emit (OpCodes.Add);
                                vi.EmitAssign (ec);
                        }

                        public override void EmitExit (EmitContext ec)
                        {
                                ec.EmitNull ();
                                pinned_string.EmitAssign (ec);
                        }
                }

                public class VariableDeclaration : BlockVariableDeclaration
                {
                        public VariableDeclaration (FullNamedExpression type, LocalVariable li)
                                : base (type, li)
                        {
                        }

                        protected override Expression ResolveInitializer (BlockContext bc, LocalVariable li, Expression initializer)
                        {
                                if (!Variable.Type.IsPointer && li == Variable) {
                                        bc.Report.Error (209, TypeExpression.Location,
                                                "The type of locals declared in a fixed statement must be a pointer type");
                                        return null;
                                }

                                //
                                // The rules for the possible declarators are pretty wise,
                                // but the production on the grammar is more concise.
                                //
                                // So we have to enforce these rules here.
                                //
                                // We do not resolve before doing the case 1 test,
                                // because the grammar is explicit in that the token &
                                // is present, so we need to test for this particular case.
                                //

                                if (initializer is Cast) {
                                        bc.Report.Error (254, initializer.Location, "The right hand side of a fixed statement assignment may not be a cast expression");
                                        return null;
                                }

                                initializer = initializer.Resolve (bc);

                                if (initializer == null)
                                        return null;

                                //
                                // Case 1: Array
                                //
                                if (initializer.Type.IsArray) {
                                        TypeSpec array_type = TypeManager.GetElementType (initializer.Type);

                                        //
                                        // Provided that array_type is unmanaged,
                                        //
                                        if (!TypeManager.VerifyUnmanaged (bc.Module, array_type, loc))
                                                return null;

                                        //
                                        // and T* is implicitly convertible to the
                                        // pointer type given in the fixed statement.
                                        //
                                        ArrayPtr array_ptr = new ArrayPtr (initializer, array_type, loc);

                                        Expression converted = Convert.ImplicitConversionRequired (bc, array_ptr.Resolve (bc), li.Type, loc);
                                        if (converted == null)
                                                return null;

                                        //
                                        // fixed (T* e_ptr = (e == null || e.Length == 0) ? null : converted [0])
                                        //
                                        converted = new Conditional (new BooleanExpression (new Binary (Binary.Operator.LogicalOr,
                                                new Binary (Binary.Operator.Equality, initializer, new NullLiteral (loc)),
                                                new Binary (Binary.Operator.Equality, new MemberAccess (initializer, "Length"), new IntConstant (bc.BuiltinTypes, 0, loc)))),
                                                        new NullLiteral (loc),
                                                        converted, loc);

                                        converted = converted.Resolve (bc);

                                        return new ExpressionEmitter (converted, li);
                                }

                                //
                                // Case 2: string
                                //
                                if (initializer.Type.BuiltinType == BuiltinTypeSpec.Type.String) {
                                        return new StringEmitter (initializer, li, loc).Resolve (bc);
                                }

                                // Case 3: fixed buffer
                                if (initializer is FixedBufferPtr) {
                                        return new ExpressionEmitter (initializer, li);
                                }

                                //
                                // Case 4: & object.
                                //
                                bool already_fixed = true;
                                Unary u = initializer as Unary;
                                if (u != null && u.Oper == Unary.Operator.AddressOf) {
                                        IVariableReference vr = u.Expr as IVariableReference;
                                        if (vr == null || !vr.IsFixed) {
                                                already_fixed = false;
                                        }
                                }

                                if (already_fixed) {
                                        bc.Report.Error (213, loc, "You cannot use the fixed statement to take the address of an already fixed expression");
                                }

                                initializer = Convert.ImplicitConversionRequired (bc, initializer, li.Type, loc);
                                return new ExpressionEmitter (initializer, li);
                        }
                }


                VariableDeclaration decl;
                Statement statement;
                bool has_ret;

                public Fixed (VariableDeclaration decl, Statement stmt, Location l)
                {
                        this.decl = decl;
                        statement = stmt;
                        loc = l;
                }

                #region Properties

                public Statement Statement {
                        get {
                                return statement;
                        }
                }

                public BlockVariableDeclaration Variables {
                        get {
                                return decl;
                        }
                }

                #endregion

                public override bool Resolve (BlockContext ec)
                {
                        using (ec.Set (ResolveContext.Options.FixedInitializerScope)) {
                                if (!decl.Resolve (ec))
                                        return false;
                        }

                        ec.StartFlowBranching (FlowBranching.BranchingType.Conditional, loc);
                        bool ok = statement.Resolve (ec);
                        bool flow_unreachable = ec.EndFlowBranching ();
                        has_ret = flow_unreachable;

                        return ok;
                }
                
                protected override void DoEmit (EmitContext ec)
                {
                        decl.Variable.CreateBuilder (ec);
                        decl.Initializer.Emit (ec);
                        if (decl.Declarators != null) {
                                foreach (var d in decl.Declarators) {
                                        d.Variable.CreateBuilder (ec);
                                        d.Initializer.Emit (ec);
                                }
                        }

                        statement.Emit (ec);

                        if (has_ret)
                                return;

                        //
                        // Clear the pinned variable
                        //
                        ((Emitter) decl.Initializer).EmitExit (ec);
                        if (decl.Declarators != null) {
                                foreach (var d in decl.Declarators) {
                                        ((Emitter)d.Initializer).EmitExit (ec);
                                }
                        }
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Fixed target = (Fixed) t;

                        target.decl = (VariableDeclaration) decl.Clone (clonectx);
                        target.statement = statement.Clone (clonectx);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class Catch : Statement
        {
                Block block;
                LocalVariable li;
                FullNamedExpression type_expr;
                CompilerAssign assign;
                TypeSpec type;
                
                public Catch (Block block, Location loc)
                {
                        this.block = block;
                        this.loc = loc;
                }

                #region Properties

                public Block Block {
                        get {
                                return block;
                        }
                }

                public TypeSpec CatchType {
                        get {
                                return type;
                        }
                }

                public bool IsGeneral {
                        get {
                                return type_expr == null;
                        }
                }

                public FullNamedExpression TypeExpression {
                        get {
                                return type_expr;
                        }
                        set {
                                type_expr = value;
                        }
                }

                public LocalVariable Variable {
                        get {
                                return li;
                        }
                        set {
                                li = value;
                        }
                }

                #endregion

                protected override void DoEmit (EmitContext ec)
                {
                        if (IsGeneral)
                                ec.BeginCatchBlock (ec.BuiltinTypes.Object);
                        else
                                ec.BeginCatchBlock (CatchType);

                        if (li != null) {
                                li.CreateBuilder (ec);

                                //
                                // Special case hoisted catch variable, we have to use a temporary variable
                                // to pass via anonymous storey initialization with the value still on top
                                // of the stack
                                //
                                if (li.HoistedVariant != null) {
                                        LocalTemporary lt = new LocalTemporary (li.Type);
                                        lt.Store (ec);

                                        // switch to assigning from the temporary variable and not from top of the stack
                                        assign.UpdateSource (lt);
                                }
                        } else {
                                ec.Emit (OpCodes.Pop);
                        }

                        Block.Emit (ec);
                }

                public override bool Resolve (BlockContext ec)
                {
                        using (ec.With (ResolveContext.Options.CatchScope, true)) {
                                if (type_expr != null) {
                                        type = type_expr.ResolveAsType (ec);
                                        if (type == null)
                                                return false;

                                        if (type.BuiltinType != BuiltinTypeSpec.Type.Exception && !TypeSpec.IsBaseClass (type, ec.BuiltinTypes.Exception, false)) {
                                                ec.Report.Error (155, loc, "The type caught or thrown must be derived from System.Exception");
                                        } else if (li != null) {
                                                li.Type = type;
                                                li.PrepareForFlowAnalysis (ec);

                                                // source variable is at the top of the stack
                                                Expression source = new EmptyExpression (li.Type);
                                                if (li.Type.IsGenericParameter)
                                                        source = new UnboxCast (source, li.Type);

                                                //
                                                // Uses Location.Null to hide from symbol file
                                                //
                                                assign = new CompilerAssign (new LocalVariableReference (li, Location.Null), source, Location.Null);
                                                Block.AddScopeStatement (new StatementExpression (assign, Location.Null));
                                        }
                                }

                                return Block.Resolve (ec);
                        }
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Catch target = (Catch) t;

                        if (type_expr != null)
                                target.type_expr = (FullNamedExpression) type_expr.Clone (clonectx);

                        target.block = clonectx.LookupBlock (block);
                }
        }

        public class TryFinally : TryFinallyBlock
        {
                Block fini;

                public TryFinally (Statement stmt, Block fini, Location loc)
                         : base (stmt, loc)
                {
                        this.fini = fini;
                }

                public Block Finallyblock {
                        get {
                                return fini;
                        }
                }

                public override bool Resolve (BlockContext ec)
                {
                        bool ok = true;

                        ec.StartFlowBranching (this);

                        if (!stmt.Resolve (ec))
                                ok = false;

                        if (ok)
                                ec.CurrentBranching.CreateSibling (fini, FlowBranching.SiblingType.Finally);

                        using (ec.With (ResolveContext.Options.FinallyScope, true)) {
                                if (!fini.Resolve (ec))
                                        ok = false;
                        }

                        ec.EndFlowBranching ();

                        ok &= base.Resolve (ec);

                        return ok;
                }

                protected override void EmitTryBody (EmitContext ec)
                {
                        stmt.Emit (ec);
                }

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

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        TryFinally target = (TryFinally) t;

                        target.stmt = (Statement) stmt.Clone (clonectx);
                        if (fini != null)
                                target.fini = clonectx.LookupBlock (fini);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class TryCatch : ExceptionStatement
        {
                public Block Block;
                List<Catch> clauses;
                readonly bool inside_try_finally;

                public TryCatch (Block block, List<Catch> catch_clauses, Location l, bool inside_try_finally)
                        : base (l)
                {
                        this.Block = block;
                        this.clauses = catch_clauses;
                        this.inside_try_finally = inside_try_finally;
                }

                public List<Catch> Clauses {
                        get {
                                return clauses;
                        }
                }

                public bool IsTryCatchFinally {
                        get {
                                return inside_try_finally;
                        }
                }

                public override bool Resolve (BlockContext ec)
                {
                        bool ok = true;

                        ec.StartFlowBranching (this);

                        if (!Block.Resolve (ec))
                                ok = false;

                        for (int i = 0; i < clauses.Count; ++i) {
                                var c = clauses[i];
                                ec.CurrentBranching.CreateSibling (c.Block, FlowBranching.SiblingType.Catch);

                                if (!c.Resolve (ec)) {
                                        ok = false;
                                        continue;
                                }

                                TypeSpec resolved_type = c.CatchType;
                                for (int ii = 0; ii < clauses.Count; ++ii) {
                                        if (ii == i)
                                                continue;

                                        if (clauses[ii].IsGeneral) {
                                                if (resolved_type.BuiltinType != BuiltinTypeSpec.Type.Exception)
                                                        continue;

                                                if (!ec.Module.DeclaringAssembly.WrapNonExceptionThrows)
                                                        continue;

                                                if (!ec.Module.PredefinedAttributes.RuntimeCompatibility.IsDefined)
                                                        continue;

                                                ec.Report.Warning (1058, 1, c.loc,
                                                        "A previous catch clause already catches all exceptions. All non-exceptions thrown will be wrapped in a `System.Runtime.CompilerServices.RuntimeWrappedException'");

                                                continue;
                                        }

                                        if (ii >= i)
                                                continue;

                                        var ct = clauses[ii].CatchType;
                                        if (ct == null)
                                                continue;

                                        if (resolved_type == ct || TypeSpec.IsBaseClass (resolved_type, ct, true)) {
                                                ec.Report.Error (160, c.loc,
                                                        "A previous catch clause already catches all exceptions of this or a super type `{0}'",
                                                        ct.GetSignatureForError ());
                                                ok = false;
                                        }
                                }
                        }

                        ec.EndFlowBranching ();

                        return base.Resolve (ec) && ok;
                }

                protected sealed override void DoEmit (EmitContext ec)
                {
                        if (!inside_try_finally)
                                EmitTryBodyPrepare (ec);

                        Block.Emit (ec);

                        foreach (Catch c in clauses)
                                c.Emit (ec);

                        if (!inside_try_finally)
                                ec.EndExceptionBlock ();
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        TryCatch target = (TryCatch) t;

                        target.Block = clonectx.LookupBlock (Block);
                        if (clauses != null){
                                target.clauses = new List<Catch> ();
                                foreach (Catch c in clauses)
                                        target.clauses.Add ((Catch) c.Clone (clonectx));
                        }
                }

                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        public class Using : TryFinallyBlock
        {
                public class VariableDeclaration : BlockVariableDeclaration
                {
                        Statement dispose_call;

                        public VariableDeclaration (FullNamedExpression type, LocalVariable li)
                                : base (type, li)
                        {
                        }

                        public VariableDeclaration (LocalVariable li, Location loc)
                                : base (li)
                        {
                                this.loc = loc;
                        }

                        public VariableDeclaration (Expression expr)
                                : base (null)
                        {
                                loc = expr.Location;
                                Initializer = expr;
                        }

                        #region Properties

                        public bool IsNested { get; private set; }

                        #endregion

                        public void EmitDispose (EmitContext ec)
                        {
                                dispose_call.Emit (ec);
                        }

                        public override bool Resolve (BlockContext bc)
                        {
                                if (IsNested)
                                        return true;

                                return base.Resolve (bc, false);
                        }

                        public Expression ResolveExpression (BlockContext bc)
                        {
                                var e = Initializer.Resolve (bc);
                                if (e == null)
                                        return null;

                                li = LocalVariable.CreateCompilerGenerated (e.Type, bc.CurrentBlock, loc);
                                Initializer = ResolveInitializer (bc, Variable, e);
                                return e;
                        }

                        protected override Expression ResolveInitializer (BlockContext bc, LocalVariable li, Expression initializer)
                        {
                                if (li.Type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
                                        initializer = initializer.Resolve (bc);
                                        if (initializer == null)
                                                return null;

                                        // Once there is dynamic used defer conversion to runtime even if we know it will never succeed
                                        Arguments args = new Arguments (1);
                                        args.Add (new Argument (initializer));
                                        initializer = new DynamicConversion (bc.BuiltinTypes.IDisposable, 0, args, initializer.Location).Resolve (bc);
                                        if (initializer == null)
                                                return null;

                                        var var = LocalVariable.CreateCompilerGenerated (initializer.Type, bc.CurrentBlock, loc);
                                        dispose_call = CreateDisposeCall (bc, var);
                                        dispose_call.Resolve (bc);

                                        return base.ResolveInitializer (bc, li, new SimpleAssign (var.CreateReferenceExpression (bc, loc), initializer, loc));
                                }

                                if (li == Variable) {
                                        CheckIDiposableConversion (bc, li, initializer);
                                        dispose_call = CreateDisposeCall (bc, li);
                                        dispose_call.Resolve (bc);
                                }

                                return base.ResolveInitializer (bc, li, initializer);
                        }

                        protected virtual void CheckIDiposableConversion (BlockContext bc, LocalVariable li, Expression initializer)
                        {
                                var type = li.Type;

                                if (type.BuiltinType != BuiltinTypeSpec.Type.IDisposable && !type.ImplementsInterface (bc.BuiltinTypes.IDisposable, false)) {
                                        if (type.IsNullableType) {
                                                // it's handled in CreateDisposeCall
                                                return;
                                        }

                                        bc.Report.SymbolRelatedToPreviousError (type);
                                        var loc = type_expr == null ? initializer.Location : type_expr.Location;
                                        bc.Report.Error (1674, loc, "`{0}': type used in a using statement must be implicitly convertible to `System.IDisposable'",
                                                type.GetSignatureForError ());

                                        return;
                                }
                        }

                        protected virtual Statement CreateDisposeCall (BlockContext bc, LocalVariable lv)
                        {
                                var lvr = lv.CreateReferenceExpression (bc, lv.Location);
                                var type = lv.Type;
                                var loc = lv.Location;

                                var idt = bc.BuiltinTypes.IDisposable;
                                var m = bc.Module.PredefinedMembers.IDisposableDispose.Resolve (loc);

                                var dispose_mg = MethodGroupExpr.CreatePredefined (m, idt, loc);
                                dispose_mg.InstanceExpression = type.IsNullableType ?
                                        new Cast (new TypeExpression (idt, loc), lvr, loc).Resolve (bc) :
                                        lvr;

                                //
                                // Hide it from symbol file via null location
                                //
                                Statement dispose = new StatementExpression (new Invocation (dispose_mg, null), Location.Null);

                                // Add conditional call when disposing possible null variable
                                if (!type.IsStruct || type.IsNullableType)
                                        dispose = new If (new Binary (Binary.Operator.Inequality, lvr, new NullLiteral (loc)), dispose, dispose.loc);

                                return dispose;
                        }

                        public void ResolveDeclaratorInitializer (BlockContext bc)
                        {
                                Initializer = base.ResolveInitializer (bc, Variable, Initializer);
                        }

                        public Statement RewriteUsingDeclarators (BlockContext bc, Statement stmt)
                        {
                                for (int i = declarators.Count - 1; i >= 0; --i) {
                                        var d = declarators [i];
                                        var vd = new VariableDeclaration (d.Variable, d.Variable.Location);
                                        vd.Initializer = d.Initializer;
                                        vd.IsNested = true;
                                        vd.dispose_call = CreateDisposeCall (bc, d.Variable);
                                        vd.dispose_call.Resolve (bc);

                                        stmt = new Using (vd, stmt, d.Variable.Location);
                                }

                                declarators = null;
                                return stmt;
                        }       

                        public override object Accept (StructuralVisitor visitor)
                        {
                                return visitor.Visit (this);
                        }       
                }

                VariableDeclaration decl;

                public Using (VariableDeclaration decl, Statement stmt, Location loc)
                        : base (stmt, loc)
                {
                        this.decl = decl;
                }

                public Using (Expression expr, Statement stmt, Location loc)
                        : base (stmt, loc)
                {
                        this.decl = new VariableDeclaration (expr);
                }

                #region Properties

                public Expression Expr {
                        get {
                                return decl.Variable == null ? decl.Initializer : null;
                        }
                }

                public BlockVariableDeclaration Variables {
                        get {
                                return decl;
                        }
                }

                #endregion

                public override void Emit (EmitContext ec)
                {
                        //
                        // Don't emit sequence point it will be set on variable declaration
                        //
                        DoEmit (ec);
                }

                protected override void EmitTryBodyPrepare (EmitContext ec)
                {
                        decl.Emit (ec);
                        base.EmitTryBodyPrepare (ec);
                }

                protected override void EmitTryBody (EmitContext ec)
                {
                        stmt.Emit (ec);
                }

                public override void EmitFinallyBody (EmitContext ec)
                {
                        decl.EmitDispose (ec);
                }

                public override bool Resolve (BlockContext ec)
                {
                        VariableReference vr;
                        bool vr_locked = false;

                        using (ec.Set (ResolveContext.Options.UsingInitializerScope)) {
                                if (decl.Variable == null) {
                                        vr = decl.ResolveExpression (ec) as VariableReference;
                                        if (vr != null) {
                                                vr_locked = vr.IsLockedByStatement;
                                                vr.IsLockedByStatement = true;
                                        }
                                } else {
                                        if (decl.IsNested) {
                                                decl.ResolveDeclaratorInitializer (ec);
                                        } else {
                                                if (!decl.Resolve (ec))
                                                        return false;

                                                if (decl.Declarators != null) {
                                                        stmt = decl.RewriteUsingDeclarators (ec, stmt);
                                                }
                                        }

                                        vr = null;
                                }
                        }

                        ec.StartFlowBranching (this);

                        stmt.Resolve (ec);

                        ec.EndFlowBranching ();

                        if (vr != null)
                                vr.IsLockedByStatement = vr_locked;

                        base.Resolve (ec);

                        return true;
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Using target = (Using) t;

                        target.decl = (VariableDeclaration) decl.Clone (clonectx);
                        target.stmt = stmt.Clone (clonectx);
                }

                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }

        /// <summary>
        ///   Implementation of the foreach C# statement
        /// </summary>
        public class Foreach : Statement
        {
                abstract class IteratorStatement : Statement
                {
                        protected readonly Foreach for_each;

                        protected IteratorStatement (Foreach @foreach)
                        {
                                this.for_each = @foreach;
                                this.loc = @foreach.expr.Location;
                        }

                        protected override void CloneTo (CloneContext clonectx, Statement target)
                        {
                                throw new NotImplementedException ();
                        }

                        public override void Emit (EmitContext ec)
                        {
                                if (ec.EmitAccurateDebugInfo) {
                                        ec.Emit (OpCodes.Nop);
                                }

                                base.Emit (ec);
                        }
                }

                sealed class ArrayForeach : IteratorStatement
                {
                        TemporaryVariableReference[] lengths;
                        Expression [] length_exprs;
                        StatementExpression[] counter;
                        TemporaryVariableReference[] variables;

                        TemporaryVariableReference copy;

                        public ArrayForeach (Foreach @foreach, int rank)
                                : base (@foreach)
                        {
                                counter = new StatementExpression[rank];
                                variables = new TemporaryVariableReference[rank];
                                length_exprs = new Expression [rank];

                                //
                                // Only use temporary length variables when dealing with
                                // multi-dimensional arrays
                                //
                                if (rank > 1)
                                        lengths = new TemporaryVariableReference [rank];
                        }

                        public override bool Resolve (BlockContext ec)
                        {
                                Block variables_block = for_each.variable.Block;
                                copy = TemporaryVariableReference.Create (for_each.expr.Type, variables_block, loc);
                                copy.Resolve (ec);

                                int rank = length_exprs.Length;
                                Arguments list = new Arguments (rank);
                                for (int i = 0; i < rank; i++) {
                                        var v = TemporaryVariableReference.Create (ec.BuiltinTypes.Int, variables_block, loc);
                                        variables[i] = v;
                                        counter[i] = new StatementExpression (new UnaryMutator (UnaryMutator.Mode.PostIncrement, v, Location.Null));
                                        counter[i].Resolve (ec);

                                        if (rank == 1) {
                                                length_exprs [i] = new MemberAccess (copy, "Length").Resolve (ec);
                                        } else {
                                                lengths[i] = TemporaryVariableReference.Create (ec.BuiltinTypes.Int, variables_block, loc);
                                                lengths[i].Resolve (ec);

                                                Arguments args = new Arguments (1);
                                                args.Add (new Argument (new IntConstant (ec.BuiltinTypes, i, loc)));
                                                length_exprs [i] = new Invocation (new MemberAccess (copy, "GetLength"), args).Resolve (ec);
                                        }

                                        list.Add (new Argument (v));
                                }

                                var access = new ElementAccess (copy, list, loc).Resolve (ec);
                                if (access == null)
                                        return false;

                                TypeSpec var_type;
                                if (for_each.type is VarExpr) {
                                        // Infer implicitly typed local variable from foreach array type
                                        var_type = access.Type;
                                } else {
                                        var_type = for_each.type.ResolveAsType (ec);

                                        if (var_type == null)
                                                return false;

                                        access = Convert.ExplicitConversion (ec, access, var_type, loc);
                                        if (access == null)
                                                return false;
                                }

                                for_each.variable.Type = var_type;

                                var variable_ref = new LocalVariableReference (for_each.variable, loc).Resolve (ec);
                                if (variable_ref == null)
                                        return false;

                                for_each.body.AddScopeStatement (new StatementExpression (new CompilerAssign (variable_ref, access, Location.Null), for_each.type.Location));

                                bool ok = true;

                                ec.StartFlowBranching (FlowBranching.BranchingType.Loop, loc);
                                ec.CurrentBranching.CreateSibling ();

                                ec.StartFlowBranching (FlowBranching.BranchingType.Embedded, loc);
                                if (!for_each.body.Resolve (ec))
                                        ok = false;
                                ec.EndFlowBranching ();

                                // There's no direct control flow from the end of the embedded statement to the end of the loop
                                ec.CurrentBranching.CurrentUsageVector.Goto ();

                                ec.EndFlowBranching ();

                                return ok;
                        }

                        protected override void DoEmit (EmitContext ec)
                        {
                                copy.EmitAssign (ec, for_each.expr);

                                int rank = length_exprs.Length;
                                Label[] test = new Label [rank];
                                Label[] loop = new Label [rank];

                                for (int i = 0; i < rank; i++) {
                                        test [i] = ec.DefineLabel ();
                                        loop [i] = ec.DefineLabel ();

                                        if (lengths != null)
                                                lengths [i].EmitAssign (ec, length_exprs [i]);
                                }

                                IntConstant zero = new IntConstant (ec.BuiltinTypes, 0, loc);
                                for (int i = 0; i < rank; i++) {
                                        variables [i].EmitAssign (ec, zero);

                                        ec.Emit (OpCodes.Br, test [i]);
                                        ec.MarkLabel (loop [i]);
                                }

                                for_each.body.Emit (ec);

                                ec.MarkLabel (ec.LoopBegin);
                                ec.Mark (for_each.expr.Location);

                                for (int i = rank - 1; i >= 0; i--){
                                        counter [i].Emit (ec);

                                        ec.MarkLabel (test [i]);
                                        variables [i].Emit (ec);

                                        if (lengths != null)
                                                lengths [i].Emit (ec);
                                        else
                                                length_exprs [i].Emit (ec);

                                        ec.Emit (OpCodes.Blt, loop [i]);
                                }

                                ec.MarkLabel (ec.LoopEnd);
                        }
                }

                sealed class CollectionForeach : IteratorStatement, OverloadResolver.IErrorHandler
                {
                        class RuntimeDispose : Using.VariableDeclaration
                        {
                                public RuntimeDispose (LocalVariable lv, Location loc)
                                        : base (lv, loc)
                                {
                                }

                                protected override void CheckIDiposableConversion (BlockContext bc, LocalVariable li, Expression initializer)
                                {
                                        // Defered to runtime check
                                }

                                protected override Statement CreateDisposeCall (BlockContext bc, LocalVariable lv)
                                {
                                        var idt = bc.BuiltinTypes.IDisposable;

                                        //
                                        // Fabricates code like
                                        //
                                        // if ((temp = vr as IDisposable) != null) temp.Dispose ();
                                        //

                                        var dispose_variable = LocalVariable.CreateCompilerGenerated (idt, bc.CurrentBlock, loc);

                                        var idisaposable_test = new Binary (Binary.Operator.Inequality, new CompilerAssign (
                                                dispose_variable.CreateReferenceExpression (bc, loc),
                                                new As (lv.CreateReferenceExpression (bc, loc), new TypeExpression (dispose_variable.Type, loc), loc),
                                                loc), new NullLiteral (loc));

                                        var m = bc.Module.PredefinedMembers.IDisposableDispose.Resolve (loc);

                                        var dispose_mg = MethodGroupExpr.CreatePredefined (m, idt, loc);
                                        dispose_mg.InstanceExpression = dispose_variable.CreateReferenceExpression (bc, loc);

                                        Statement dispose = new StatementExpression (new Invocation (dispose_mg, null));
                                        return new If (idisaposable_test, dispose, loc);
                                }
                        }

                        LocalVariable variable;
                        Expression expr;
                        Statement statement;
                        ExpressionStatement init;
                        TemporaryVariableReference enumerator_variable;
                        bool ambiguous_getenumerator_name;

                        public CollectionForeach (Foreach @foreach, LocalVariable var, Expression expr)
                                : base (@foreach)
                        {
                                this.variable = var;
                                this.expr = expr;
                        }

                        void Error_WrongEnumerator (ResolveContext rc, MethodSpec enumerator)
                        {
                                rc.Report.SymbolRelatedToPreviousError (enumerator);
                                rc.Report.Error (202, loc,
                                        "foreach statement requires that the return type `{0}' of `{1}' must have a suitable public MoveNext method and public Current property",
                                                enumerator.ReturnType.GetSignatureForError (), enumerator.GetSignatureForError ());
                        }

                        MethodGroupExpr ResolveGetEnumerator (ResolveContext rc)
                        {
                                //
                                // Option 1: Try to match by name GetEnumerator first
                                //
                                var mexpr = Expression.MemberLookup (rc, false, expr.Type,
                                        "GetEnumerator", 0, Expression.MemberLookupRestrictions.ExactArity, loc);               // TODO: What if CS0229 ?

                                var mg = mexpr as MethodGroupExpr;
                                if (mg != null) {
                                        mg.InstanceExpression = expr;
                                        Arguments args = new Arguments (0);
                                        mg = mg.OverloadResolve (rc, ref args, this, OverloadResolver.Restrictions.ProbingOnly);

                                        // For ambiguous GetEnumerator name warning CS0278 was reported, but Option 2 could still apply
                                        if (ambiguous_getenumerator_name)
                                                mg = null;

                                        if (mg != null && args.Count == 0 && !mg.BestCandidate.IsStatic && mg.BestCandidate.IsPublic) {
                                                return mg;
                                        }
                                }

                                //
                                // Option 2: Try to match using IEnumerable interfaces with preference of generic version
                                //
                                var t = expr.Type;
                                PredefinedMember<MethodSpec> iface_candidate = null;
                                var ptypes = rc.Module.PredefinedTypes;
                                var gen_ienumerable = ptypes.IEnumerableGeneric;
                                if (!gen_ienumerable.Define ())
                                        gen_ienumerable = null;

                                var ifaces = t.Interfaces;
                                if (ifaces != null) {
                                        foreach (var iface in ifaces) {
                                                if (gen_ienumerable != null && iface.MemberDefinition == gen_ienumerable.TypeSpec.MemberDefinition) {
                                                        if (iface_candidate != null && iface_candidate != rc.Module.PredefinedMembers.IEnumerableGetEnumerator) {
                                                                rc.Report.SymbolRelatedToPreviousError (expr.Type);
                                                                rc.Report.Error (1640, loc,
                                                                        "foreach statement cannot operate on variables of type `{0}' because it contains multiple implementation of `{1}'. Try casting to a specific implementation",
                                                                        expr.Type.GetSignatureForError (), gen_ienumerable.TypeSpec.GetSignatureForError ());

                                                                return null;
                                                        }

                                                        // TODO: Cache this somehow
                                                        iface_candidate = new PredefinedMember<MethodSpec> (rc.Module, iface,
                                                                MemberFilter.Method ("GetEnumerator", 0, ParametersCompiled.EmptyReadOnlyParameters, null));

                                                        continue;
                                                }

                                                if (iface.BuiltinType == BuiltinTypeSpec.Type.IEnumerable && iface_candidate == null) {
                                                        iface_candidate = rc.Module.PredefinedMembers.IEnumerableGetEnumerator;
                                                }
                                        }
                                }

                                if (iface_candidate == null) {
                                        if (expr.Type != InternalType.ErrorType) {
                                                rc.Report.Error (1579, loc,
                                                        "foreach statement cannot operate on variables of type `{0}' because it does not contain a definition for `{1}' or is inaccessible",
                                                        expr.Type.GetSignatureForError (), "GetEnumerator");
                                        }

                                        return null;
                                }

                                var method = iface_candidate.Resolve (loc);
                                if (method == null)
                                        return null;

                                mg = MethodGroupExpr.CreatePredefined (method, expr.Type, loc);
                                mg.InstanceExpression = expr;
                                return mg;
                        }

                        MethodGroupExpr ResolveMoveNext (ResolveContext rc, MethodSpec enumerator)
                        {
                                var ms = MemberCache.FindMember (enumerator.ReturnType,
                                        MemberFilter.Method ("MoveNext", 0, ParametersCompiled.EmptyReadOnlyParameters, rc.BuiltinTypes.Bool),
                                        BindingRestriction.InstanceOnly) as MethodSpec;

                                if (ms == null || !ms.IsPublic) {
                                        Error_WrongEnumerator (rc, enumerator);
                                        return null;
                                }

                                return MethodGroupExpr.CreatePredefined (ms, enumerator.ReturnType, expr.Location);
                        }

                        PropertySpec ResolveCurrent (ResolveContext rc, MethodSpec enumerator)
                        {
                                var ps = MemberCache.FindMember (enumerator.ReturnType,
                                        MemberFilter.Property ("Current", null),
                                        BindingRestriction.InstanceOnly) as PropertySpec;

                                if (ps == null || !ps.IsPublic) {
                                        Error_WrongEnumerator (rc, enumerator);
                                        return null;
                                }

                                return ps;
                        }

                        public override bool Resolve (BlockContext ec)
                        {
                                bool is_dynamic = expr.Type.BuiltinType == BuiltinTypeSpec.Type.Dynamic;

                                if (is_dynamic) {
                                        expr = Convert.ImplicitConversionRequired (ec, expr, ec.BuiltinTypes.IEnumerable, loc);
                                } else if (expr.Type.IsNullableType) {
                                        expr = new Nullable.UnwrapCall (expr).Resolve (ec);
                                }

                                var get_enumerator_mg = ResolveGetEnumerator (ec);
                                if (get_enumerator_mg == null) {
                                        return false;
                                }

                                var get_enumerator = get_enumerator_mg.BestCandidate;
                                enumerator_variable = TemporaryVariableReference.Create (get_enumerator.ReturnType, variable.Block, loc);
                                enumerator_variable.Resolve (ec);

                                // Prepare bool MoveNext ()
                                var move_next_mg = ResolveMoveNext (ec, get_enumerator);
                                if (move_next_mg == null) {
                                        return false;
                                }

                                move_next_mg.InstanceExpression = enumerator_variable;

                                // Prepare ~T~ Current { get; }
                                var current_prop = ResolveCurrent (ec, get_enumerator);
                                if (current_prop == null) {
                                        return false;
                                }

                                var current_pe = new PropertyExpr (current_prop, loc) { InstanceExpression = enumerator_variable }.Resolve (ec);
                                if (current_pe == null)
                                        return false;

                                VarExpr ve = for_each.type as VarExpr;

                                if (ve != null) {
                                        if (is_dynamic) {
                                                // Source type is dynamic, set element type to dynamic too
                                                variable.Type = ec.BuiltinTypes.Dynamic;
                                        } else {
                                                // Infer implicitly typed local variable from foreach enumerable type
                                                variable.Type = current_pe.Type;
                                        }
                                } else {
                                        if (is_dynamic) {
                                                // Explicit cast of dynamic collection elements has to be done at runtime
                                                current_pe = EmptyCast.Create (current_pe, ec.BuiltinTypes.Dynamic);
                                        }

                                        variable.Type = for_each.type.ResolveAsType (ec);

                                        if (variable.Type == null)
                                                return false;

                                        current_pe = Convert.ExplicitConversion (ec, current_pe, variable.Type, loc);
                                        if (current_pe == null)
                                                return false;
                                }

                                var variable_ref = new LocalVariableReference (variable, loc).Resolve (ec);
                                if (variable_ref == null)
                                        return false;

                                for_each.body.AddScopeStatement (new StatementExpression (new CompilerAssign (variable_ref, current_pe, Location.Null), for_each.type.Location));

                                var init = new Invocation (get_enumerator_mg, null);

                                statement = new While (new BooleanExpression (new Invocation (move_next_mg, null)),
                                         for_each.body, Location.Null);

                                var enum_type = enumerator_variable.Type;

                                //
                                // Add Dispose method call when enumerator can be IDisposable
                                //
                                if (!enum_type.ImplementsInterface (ec.BuiltinTypes.IDisposable, false)) {
                                        if (!enum_type.IsSealed && !TypeSpec.IsValueType (enum_type)) {
                                                //
                                                // Runtime Dispose check
                                                //
                                                var vd = new RuntimeDispose (enumerator_variable.LocalInfo, Location.Null);
                                                vd.Initializer = init;
                                                statement = new Using (vd, statement, Location.Null);
                                        } else {
                                                //
                                                // No Dispose call needed
                                                //
                                                this.init = new SimpleAssign (enumerator_variable, init, Location.Null);
                                                this.init.Resolve (ec);
                                        }
                                } else {
                                        //
                                        // Static Dispose check
                                        //
                                        var vd = new Using.VariableDeclaration (enumerator_variable.LocalInfo, Location.Null);
                                        vd.Initializer = init;
                                        statement = new Using (vd, statement, Location.Null);
                                }

                                return statement.Resolve (ec);
                        }

                        protected override void DoEmit (EmitContext ec)
                        {
                                enumerator_variable.LocalInfo.CreateBuilder (ec);

                                if (init != null)
                                        init.EmitStatement (ec);

                                statement.Emit (ec);
                        }

                        #region IErrorHandler Members

                        bool OverloadResolver.IErrorHandler.AmbiguousCandidates (ResolveContext ec, MemberSpec best, MemberSpec ambiguous)
                        {
                                ec.Report.SymbolRelatedToPreviousError (best);
                                ec.Report.Warning (278, 2, expr.Location,
                                        "`{0}' contains ambiguous implementation of `{1}' pattern. Method `{2}' is ambiguous with method `{3}'",
                                        expr.Type.GetSignatureForError (), "enumerable",
                                        best.GetSignatureForError (), ambiguous.GetSignatureForError ());

                                ambiguous_getenumerator_name = true;
                                return true;
                        }

                        bool OverloadResolver.IErrorHandler.ArgumentMismatch (ResolveContext rc, MemberSpec best, Argument arg, int index)
                        {
                                return false;
                        }

                        bool OverloadResolver.IErrorHandler.NoArgumentMatch (ResolveContext rc, MemberSpec best)
                        {
                                return false;
                        }

                        bool OverloadResolver.IErrorHandler.TypeInferenceFailed (ResolveContext rc, MemberSpec best)
                        {
                                return false;
                        }

                        #endregion
                }

                Expression type;
                LocalVariable variable;
                Expression expr;
                Statement statement;
                Block body;

                public Foreach (Expression type, LocalVariable var, Expression expr, Statement stmt, Block body, Location l)
                {
                        this.type = type;
                        this.variable = var;
                        this.expr = expr;
                        this.statement = stmt;
                        this.body = body;
                        loc = l;
                }

                public Expression Expr {
                        get { return expr; }
                }

                public Statement Statement {
                        get { return statement; }
                }

                public Expression TypeExpression {
                        get { return type; }
                }

                public LocalVariable Variable {
                        get { return variable; }
                }

                public override bool Resolve (BlockContext ec)
                {
                        expr = expr.Resolve (ec);
                        if (expr == null)
                                return false;

                        if (expr.IsNull) {
                                ec.Report.Error (186, loc, "Use of null is not valid in this context");
                                return false;
                        }

                        body.AddStatement (statement);

                        if (expr.Type.BuiltinType == BuiltinTypeSpec.Type.String) {
                                statement = new ArrayForeach (this, 1);
                        } else if (expr.Type is ArrayContainer) {
                                statement = new ArrayForeach (this, ((ArrayContainer) expr.Type).Rank);
                        } else {
                                if (expr.eclass == ExprClass.MethodGroup || expr is AnonymousMethodExpression) {
                                        ec.Report.Error (446, expr.Location, "Foreach statement cannot operate on a `{0}'",
                                                expr.ExprClassName);
                                        return false;
                                }

                                statement = new CollectionForeach (this, variable, expr);
                        }

                        return statement.Resolve (ec);
                }

                protected override void DoEmit (EmitContext ec)
                {
                        variable.CreateBuilder (ec);

                        Label old_begin = ec.LoopBegin, old_end = ec.LoopEnd;
                        ec.LoopBegin = ec.DefineLabel ();
                        ec.LoopEnd = ec.DefineLabel ();

                        statement.Emit (ec);

                        ec.LoopBegin = old_begin;
                        ec.LoopEnd = old_end;
                }

                protected override void CloneTo (CloneContext clonectx, Statement t)
                {
                        Foreach target = (Foreach) t;

                        target.type = type.Clone (clonectx);
                        target.expr = expr.Clone (clonectx);
                        target.body = (Block) body.Clone (clonectx);
                        target.statement = statement.Clone (clonectx);
                }
                
                public override object Accept (StructuralVisitor visitor)
                {
                        return visitor.Visit (this);
                }
        }
}