source: branches/2817-BinPackingSpeedup/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory.CSharp-5.5.0/Analysis/ControlFlow.cs @ 15303

// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
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using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using ICSharpCode.NRefactory.CSharp.Resolver;
using ICSharpCode.NRefactory.CSharp.TypeSystem;
using ICSharpCode.NRefactory.Semantics;
using ICSharpCode.NRefactory.TypeSystem;
using ICSharpCode.NRefactory.TypeSystem.Implementation;
using ICSharpCode.NRefactory.Utils;

namespace ICSharpCode.NRefactory.CSharp.Analysis
{
  /// <summary>
  /// Represents a node in the control flow graph of a C# method.
  /// </summary>
  public class ControlFlowNode
  {
    public readonly Statement PreviousStatement;
    public readonly Statement NextStatement;
    
    public readonly ControlFlowNodeType Type;
    
    public readonly List<ControlFlowEdge> Outgoing = new List<ControlFlowEdge>();
    public readonly List<ControlFlowEdge> Incoming = new List<ControlFlowEdge>();
    
    public ControlFlowNode(Statement previousStatement, Statement nextStatement, ControlFlowNodeType type)
    {
      if (previousStatement == null && nextStatement == null)
        throw new ArgumentException("previousStatement and nextStatement must not be both null");
      this.PreviousStatement = previousStatement;
      this.NextStatement = nextStatement;
      this.Type = type;
    }
  }
  
  public enum ControlFlowNodeType
  {
    /// <summary>
    /// Unknown node type
    /// </summary>
    None,
    /// <summary>
    /// Node in front of a statement
    /// </summary>
    StartNode,
    /// <summary>
    /// Node between two statements
    /// </summary>
    BetweenStatements,
    /// <summary>
    /// Node at the end of a statement list
    /// </summary>
    EndNode,
    /// <summary>
    /// Node representing the position before evaluating the condition of a loop.
    /// </summary>
    LoopCondition
  }
  
  public class ControlFlowEdge
  {
    public readonly ControlFlowNode From;
    public readonly ControlFlowNode To;
    public readonly ControlFlowEdgeType Type;
    
    List<TryCatchStatement> jumpOutOfTryFinally;
    
    public ControlFlowEdge(ControlFlowNode from, ControlFlowNode to, ControlFlowEdgeType type)
    {
      if (from == null)
        throw new ArgumentNullException("from");
      if (to == null)
        throw new ArgumentNullException("to");
      this.From = from;
      this.To = to;
      this.Type = type;
    }
    
    internal void AddJumpOutOfTryFinally(TryCatchStatement tryFinally)
    {
      if (jumpOutOfTryFinally == null)
        jumpOutOfTryFinally = new List<TryCatchStatement>();
      jumpOutOfTryFinally.Add(tryFinally);
    }
    
    /// <summary>
    /// Gets whether this control flow edge is leaving any try-finally statements.
    /// </summary>
    public bool IsLeavingTryFinally {
      get { return jumpOutOfTryFinally != null; }
    }
    
    /// <summary>
    /// Gets the try-finally statements that this control flow edge is leaving.
    /// </summary>
    public IEnumerable<TryCatchStatement> TryFinallyStatements {
      get { return jumpOutOfTryFinally ?? Enumerable.Empty<TryCatchStatement>(); }
    }
  }
  
  public enum ControlFlowEdgeType
  {
    /// <summary>
    /// Regular control flow.
    /// </summary>
    Normal,
    /// <summary>
    /// Conditional control flow (edge taken if condition is true)
    /// </summary>
    ConditionTrue,
    /// <summary>
    /// Conditional control flow (edge taken if condition is false)
    /// </summary>
    ConditionFalse,
    /// <summary>
    /// A jump statement (goto, goto case, break or continue)
    /// </summary>
    Jump
  }
  
  /// <summary>
  /// Constructs the control flow graph for C# statements.
  /// </summary>
  public class ControlFlowGraphBuilder
  {
    // Written according to the reachability rules in the C# spec (§8.1 End points and reachability)
    
    protected virtual ControlFlowNode CreateNode(Statement previousStatement, Statement nextStatement, ControlFlowNodeType type)
    {
      cancellationToken.ThrowIfCancellationRequested();
      return new ControlFlowNode(previousStatement, nextStatement, type);
    }
    
    protected virtual ControlFlowEdge CreateEdge(ControlFlowNode from, ControlFlowNode to, ControlFlowEdgeType type)
    {
      cancellationToken.ThrowIfCancellationRequested();
      return new ControlFlowEdge(from, to, type);
    }
    
    Statement rootStatement;
    CSharpTypeResolveContext typeResolveContext;
    Func<AstNode, CancellationToken, ResolveResult> resolver;
    List<ControlFlowNode> nodes;
    Dictionary<string, ControlFlowNode> labels;
    List<ControlFlowNode> gotoStatements;
    CancellationToken cancellationToken;
    
    public IList<ControlFlowNode> BuildControlFlowGraph(Statement statement, CancellationToken cancellationToken = default(CancellationToken))
    {
      if (statement == null)
        throw new ArgumentNullException("statement");
      CSharpResolver r = new CSharpResolver(MinimalCorlib.Instance.CreateCompilation());
      return BuildControlFlowGraph(statement, new CSharpAstResolver(r, statement), cancellationToken);
    }
    
    public IList<ControlFlowNode> BuildControlFlowGraph(Statement statement, CSharpAstResolver resolver, CancellationToken cancellationToken = default(CancellationToken))
    {
      if (statement == null)
        throw new ArgumentNullException("statement");
      if (resolver == null)
        throw new ArgumentNullException("resolver");
      return BuildControlFlowGraph(statement, resolver.Resolve, resolver.TypeResolveContext, cancellationToken);
    }
    
    internal IList<ControlFlowNode> BuildControlFlowGraph(Statement statement, Func<AstNode, CancellationToken, ResolveResult> resolver, CSharpTypeResolveContext typeResolveContext, CancellationToken cancellationToken)
    {
      NodeCreationVisitor nodeCreationVisitor = new NodeCreationVisitor();
      nodeCreationVisitor.builder = this;
      try {
        this.nodes = new List<ControlFlowNode>();
        this.labels = new Dictionary<string, ControlFlowNode>();
        this.gotoStatements = new List<ControlFlowNode>();
        this.rootStatement = statement;
        this.resolver = resolver;
        this.typeResolveContext = typeResolveContext;
        this.cancellationToken = cancellationToken;
        
        ControlFlowNode entryPoint = CreateStartNode(statement);
        statement.AcceptVisitor(nodeCreationVisitor, entryPoint);
        
        // Resolve goto statements:
        foreach (ControlFlowNode gotoStmt in gotoStatements) {
          string label = ((GotoStatement)gotoStmt.NextStatement).Label;
          ControlFlowNode labelNode;
          if (labels.TryGetValue(label, out labelNode))
            nodeCreationVisitor.Connect(gotoStmt, labelNode, ControlFlowEdgeType.Jump);
        }
        
        AnnotateLeaveEdgesWithTryFinallyBlocks();
        
        return nodes;
      } finally {
        this.nodes = null;
        this.labels = null;
        this.gotoStatements = null;
        this.rootStatement = null;
        this.resolver = null;
        this.typeResolveContext = null;
        this.cancellationToken = CancellationToken.None;
      }
    }
    
    void AnnotateLeaveEdgesWithTryFinallyBlocks()
    {
      foreach (ControlFlowEdge edge in nodes.SelectMany(n => n.Outgoing)) {
        if (edge.Type != ControlFlowEdgeType.Jump) {
          // Only jumps are potential candidates for leaving try-finally blocks.
          // Note that the regular edges leaving try or catch blocks are already annotated by the visitor.
          continue;
        }
        Statement gotoStatement = edge.From.NextStatement;
        Debug.Assert(gotoStatement is GotoStatement || gotoStatement is GotoDefaultStatement || gotoStatement is GotoCaseStatement || gotoStatement is BreakStatement || gotoStatement is ContinueStatement);
        Statement targetStatement = edge.To.PreviousStatement ?? edge.To.NextStatement;
        if (gotoStatement.Parent == targetStatement.Parent)
          continue;
        HashSet<TryCatchStatement> targetParentTryCatch = new HashSet<TryCatchStatement>(targetStatement.Ancestors.OfType<TryCatchStatement>());
        for (AstNode node = gotoStatement.Parent; node != null; node = node.Parent) {
          TryCatchStatement leftTryCatch = node as TryCatchStatement;
          if (leftTryCatch != null) {
            if (targetParentTryCatch.Contains(leftTryCatch))
              break;
            if (!leftTryCatch.FinallyBlock.IsNull)
              edge.AddJumpOutOfTryFinally(leftTryCatch);
          }
        }
      }
    }
    
    #region Create*Node
    ControlFlowNode CreateStartNode(Statement statement)
    {
      if (statement.IsNull)
        return null;
      ControlFlowNode node = CreateNode(null, statement, ControlFlowNodeType.StartNode);
      nodes.Add(node);
      return node;
    }
    
    ControlFlowNode CreateSpecialNode(Statement statement, ControlFlowNodeType type, bool addToNodeList = true)
    {
      ControlFlowNode node = CreateNode(null, statement, type);
      if (addToNodeList)
        nodes.Add(node);
      return node;
    }
    
    ControlFlowNode CreateEndNode(Statement statement, bool addToNodeList = true)
    {
      Statement nextStatement;
      if (statement == rootStatement) {
        nextStatement = null;
      } else {
        // Find the next statement in the same role:
        AstNode next = statement;
        do {
          next = next.NextSibling;
        } while (next != null && next.Role != statement.Role);
        nextStatement = next as Statement;
      }
      ControlFlowNodeType type = nextStatement != null ? ControlFlowNodeType.BetweenStatements : ControlFlowNodeType.EndNode;
      ControlFlowNode node = CreateNode(statement, nextStatement, type);
      if (addToNodeList)
        nodes.Add(node);
      return node;
    }
    #endregion
    
    #region Constant evaluation
    /// <summary>
    /// Gets/Sets whether to handle only primitive expressions as constants (no complex expressions like "a + b").
    /// </summary>
    public bool EvaluateOnlyPrimitiveConstants { get; set; }
    
    /// <summary>
    /// Evaluates an expression.
    /// </summary>
    /// <returns>The constant value of the expression; or null if the expression is not a constant.</returns>
    ResolveResult EvaluateConstant(Expression expr)
    {
      if (expr.IsNull)
        return null;
      if (EvaluateOnlyPrimitiveConstants) {
        if (!(expr is PrimitiveExpression || expr is NullReferenceExpression))
          return null;
      }
      return resolver(expr, cancellationToken);
    }
    
    /// <summary>
    /// Evaluates an expression.
    /// </summary>
    /// <returns>The value of the constant boolean expression; or null if the value is not a constant boolean expression.</returns>
    bool? EvaluateCondition(Expression expr)
    {
      ResolveResult rr = EvaluateConstant(expr);
      if (rr != null && rr.IsCompileTimeConstant)
        return rr.ConstantValue as bool?;
      else
        return null;
    }
    
    bool AreEqualConstants(ResolveResult c1, ResolveResult c2)
    {
      if (c1 == null || c2 == null || !c1.IsCompileTimeConstant || !c2.IsCompileTimeConstant)
        return false;
      CSharpResolver r = new CSharpResolver(typeResolveContext);
      ResolveResult c = r.ResolveBinaryOperator(BinaryOperatorType.Equality, c1, c2);
      return c.IsCompileTimeConstant && (c.ConstantValue as bool?) == true;
    }
    #endregion
    
    sealed class NodeCreationVisitor : DepthFirstAstVisitor<ControlFlowNode, ControlFlowNode>
    {
      // 'data' parameter: input control flow node (start of statement being visited)
      // Return value: result control flow node (end of statement being visited)
      
      internal ControlFlowGraphBuilder builder;
      Stack<ControlFlowNode> breakTargets = new Stack<ControlFlowNode>();
      Stack<ControlFlowNode> continueTargets = new Stack<ControlFlowNode>();
      List<ControlFlowNode> gotoCaseOrDefault = new List<ControlFlowNode>();
      
      internal ControlFlowEdge Connect(ControlFlowNode from, ControlFlowNode to, ControlFlowEdgeType type = ControlFlowEdgeType.Normal)
      {
        if (from == null || to == null)
          return null;
        ControlFlowEdge edge = builder.CreateEdge(from, to, type);
        from.Outgoing.Add(edge);
        to.Incoming.Add(edge);
        return edge;
      }
      
      /// <summary>
      /// Creates an end node for <c>stmt</c> and connects <c>from</c> with the new node.
      /// </summary>
      ControlFlowNode CreateConnectedEndNode(Statement stmt, ControlFlowNode from)
      {
        ControlFlowNode newNode = builder.CreateEndNode(stmt);
        Connect(from, newNode);
        return newNode;
      }
      
      protected override ControlFlowNode VisitChildren(AstNode node, ControlFlowNode data)
      {
        // We have overrides for all possible statements and should visit statements only.
        throw new NotSupportedException();
      }
      
      public override ControlFlowNode VisitBlockStatement(BlockStatement blockStatement, ControlFlowNode data)
      {
        // C# 4.0 spec: §8.2 Blocks
        ControlFlowNode childNode = HandleStatementList(blockStatement.Statements, data);
        return CreateConnectedEndNode(blockStatement, childNode);
      }
      
      ControlFlowNode HandleStatementList(AstNodeCollection<Statement> statements, ControlFlowNode source)
      {
        ControlFlowNode childNode = null;
        foreach (Statement stmt in statements) {
          if (childNode == null) {
            childNode = builder.CreateStartNode(stmt);
            if (source != null)
              Connect(source, childNode);
          }
          Debug.Assert(childNode.NextStatement == stmt);
          childNode = stmt.AcceptVisitor(this, childNode);
          Debug.Assert(childNode.PreviousStatement == stmt);
        }
        return childNode ?? source;
      }
      
      public override ControlFlowNode VisitEmptyStatement(EmptyStatement emptyStatement, ControlFlowNode data)
      {
        return CreateConnectedEndNode(emptyStatement, data);
      }
      
      public override ControlFlowNode VisitLabelStatement(LabelStatement labelStatement, ControlFlowNode data)
      {
        ControlFlowNode end = CreateConnectedEndNode(labelStatement, data);
        builder.labels[labelStatement.Label] = end;
        return end;
      }
      
      public override ControlFlowNode VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement, ControlFlowNode data)
      {
        return CreateConnectedEndNode(variableDeclarationStatement, data);
      }
      
      public override ControlFlowNode VisitExpressionStatement(ExpressionStatement expressionStatement, ControlFlowNode data)
      {
        return CreateConnectedEndNode(expressionStatement, data);
      }
      
      public override ControlFlowNode VisitIfElseStatement(IfElseStatement ifElseStatement, ControlFlowNode data)
      {
        bool? cond = builder.EvaluateCondition(ifElseStatement.Condition);
        
        ControlFlowNode trueBegin = builder.CreateStartNode(ifElseStatement.TrueStatement);
        if (cond != false)
          Connect(data, trueBegin, ControlFlowEdgeType.ConditionTrue);
        ControlFlowNode trueEnd = ifElseStatement.TrueStatement.AcceptVisitor(this, trueBegin);
        
        ControlFlowNode falseBegin = builder.CreateStartNode(ifElseStatement.FalseStatement);
        if (cond != true)
          Connect(data, falseBegin, ControlFlowEdgeType.ConditionFalse);
        ControlFlowNode falseEnd = ifElseStatement.FalseStatement.AcceptVisitor(this, falseBegin);
        // (if no else statement exists, both falseBegin and falseEnd will be null)
        
        ControlFlowNode end = builder.CreateEndNode(ifElseStatement);
        Connect(trueEnd, end);
        if (falseEnd != null) {
          Connect(falseEnd, end);
        } else if (cond != true) {
          Connect(data, end, ControlFlowEdgeType.ConditionFalse);
        }
        return end;
      }
      
      public override ControlFlowNode VisitSwitchStatement(SwitchStatement switchStatement, ControlFlowNode data)
      {
        // First, figure out which switch section will get called (if the expression is constant):
        ResolveResult constant = builder.EvaluateConstant(switchStatement.Expression);
        SwitchSection defaultSection = null;
        SwitchSection sectionMatchedByConstant = null;
        foreach (SwitchSection section in switchStatement.SwitchSections) {
          foreach (CaseLabel label in section.CaseLabels) {
            if (label.Expression.IsNull) {
              defaultSection = section;
            } else if (constant != null && constant.IsCompileTimeConstant) {
              ResolveResult labelConstant = builder.EvaluateConstant(label.Expression);
              if (builder.AreEqualConstants(constant, labelConstant))
                sectionMatchedByConstant = section;
            }
          }
        }
        if (constant != null && constant.IsCompileTimeConstant && sectionMatchedByConstant == null)
          sectionMatchedByConstant = defaultSection;
        
        int gotoCaseOrDefaultInOuterScope = gotoCaseOrDefault.Count;
        List<ControlFlowNode> sectionStartNodes = new List<ControlFlowNode>();
        
        ControlFlowNode end = builder.CreateEndNode(switchStatement, addToNodeList: false);
        breakTargets.Push(end);
        foreach (SwitchSection section in switchStatement.SwitchSections) {
          int sectionStartNodeID = builder.nodes.Count;
          if (constant == null || !constant.IsCompileTimeConstant || section == sectionMatchedByConstant) {
            HandleStatementList(section.Statements, data);
          } else {
            // This section is unreachable: pass null to HandleStatementList.
            HandleStatementList(section.Statements, null);
          }
          // Don't bother connecting the ends of the sections: the 'break' statement takes care of that.
          
          // Store the section start node for 'goto case' statements.
          sectionStartNodes.Add(sectionStartNodeID < builder.nodes.Count ? builder.nodes[sectionStartNodeID] : null);
        }
        breakTargets.Pop();
        if (defaultSection == null && sectionMatchedByConstant == null) {
          Connect(data, end);
        }
        
        if (gotoCaseOrDefault.Count > gotoCaseOrDefaultInOuterScope) {
          // Resolve 'goto case' statements:
          for (int i = gotoCaseOrDefaultInOuterScope; i < gotoCaseOrDefault.Count; i++) {
            ControlFlowNode gotoCaseNode = gotoCaseOrDefault[i];
            GotoCaseStatement gotoCaseStatement = gotoCaseNode.NextStatement as GotoCaseStatement;
            ResolveResult gotoCaseConstant = null;
            if (gotoCaseStatement != null) {
              gotoCaseConstant = builder.EvaluateConstant(gotoCaseStatement.LabelExpression);
            }
            int targetSectionIndex = -1;
            int currentSectionIndex = 0;
            foreach (SwitchSection section in switchStatement.SwitchSections) {
              foreach (CaseLabel label in section.CaseLabels) {
                if (gotoCaseStatement != null) {
                  // goto case
                  if (!label.Expression.IsNull) {
                    ResolveResult labelConstant = builder.EvaluateConstant(label.Expression);
                    if (builder.AreEqualConstants(gotoCaseConstant, labelConstant))
                      targetSectionIndex = currentSectionIndex;
                  }
                } else {
                  // goto default
                  if (label.Expression.IsNull)
                    targetSectionIndex = currentSectionIndex;
                }
              }
              currentSectionIndex++;
            }
            if (targetSectionIndex >= 0 && sectionStartNodes[targetSectionIndex] != null)
              Connect(gotoCaseNode, sectionStartNodes[targetSectionIndex], ControlFlowEdgeType.Jump);
            else
              Connect(gotoCaseNode, end, ControlFlowEdgeType.Jump);
          }
          gotoCaseOrDefault.RemoveRange(gotoCaseOrDefaultInOuterScope, gotoCaseOrDefault.Count - gotoCaseOrDefaultInOuterScope);
        }
        
        builder.nodes.Add(end);
        return end;
      }
      
      public override ControlFlowNode VisitGotoCaseStatement(GotoCaseStatement gotoCaseStatement, ControlFlowNode data)
      {
        gotoCaseOrDefault.Add(data);
        return builder.CreateEndNode(gotoCaseStatement);
      }
      
      public override ControlFlowNode VisitGotoDefaultStatement(GotoDefaultStatement gotoDefaultStatement, ControlFlowNode data)
      {
        gotoCaseOrDefault.Add(data);
        return builder.CreateEndNode(gotoDefaultStatement);
      }
      
      public override ControlFlowNode VisitWhileStatement(WhileStatement whileStatement, ControlFlowNode data)
      {
        // <data> <condition> while (cond) { <bodyStart> embeddedStmt; <bodyEnd> } <end>
        ControlFlowNode end = builder.CreateEndNode(whileStatement, addToNodeList: false);
        ControlFlowNode conditionNode = builder.CreateSpecialNode(whileStatement, ControlFlowNodeType.LoopCondition);
        breakTargets.Push(end);
        continueTargets.Push(conditionNode);
        
        Connect(data, conditionNode);
        
        bool? cond = builder.EvaluateCondition(whileStatement.Condition);
        ControlFlowNode bodyStart = builder.CreateStartNode(whileStatement.EmbeddedStatement);
        if (cond != false)
          Connect(conditionNode, bodyStart, ControlFlowEdgeType.ConditionTrue);
        ControlFlowNode bodyEnd = whileStatement.EmbeddedStatement.AcceptVisitor(this, bodyStart);
        Connect(bodyEnd, conditionNode);
        if (cond != true)
          Connect(conditionNode, end, ControlFlowEdgeType.ConditionFalse);
        
        breakTargets.Pop();
        continueTargets.Pop();
        builder.nodes.Add(end);
        return end;
      }
      
      public override ControlFlowNode VisitDoWhileStatement(DoWhileStatement doWhileStatement, ControlFlowNode data)
      {
        // <data> do { <bodyStart> embeddedStmt; <bodyEnd>} <condition> while(cond); <end>
        ControlFlowNode end = builder.CreateEndNode(doWhileStatement, addToNodeList: false);
        ControlFlowNode conditionNode = builder.CreateSpecialNode(doWhileStatement, ControlFlowNodeType.LoopCondition, addToNodeList: false);
        breakTargets.Push(end);
        continueTargets.Push(conditionNode);
        
        ControlFlowNode bodyStart = builder.CreateStartNode(doWhileStatement.EmbeddedStatement);
        Connect(data, bodyStart);
        ControlFlowNode bodyEnd = doWhileStatement.EmbeddedStatement.AcceptVisitor(this, bodyStart);
        Connect(bodyEnd, conditionNode);
        
        bool? cond = builder.EvaluateCondition(doWhileStatement.Condition);
        if (cond != false)
          Connect(conditionNode, bodyStart, ControlFlowEdgeType.ConditionTrue);
        if (cond != true)
          Connect(conditionNode, end, ControlFlowEdgeType.ConditionFalse);
        
        breakTargets.Pop();
        continueTargets.Pop();
        builder.nodes.Add(conditionNode);
        builder.nodes.Add(end);
        return end;
      }
      
      public override ControlFlowNode VisitForStatement(ForStatement forStatement, ControlFlowNode data)
      {
        data = HandleStatementList(forStatement.Initializers, data);
        // for (initializers <data>; <condition>cond; <iteratorStart>iterators<iteratorEnd>) { <bodyStart> embeddedStmt; <bodyEnd> } <end>
        ControlFlowNode end = builder.CreateEndNode(forStatement, addToNodeList: false);
        ControlFlowNode conditionNode = builder.CreateSpecialNode(forStatement, ControlFlowNodeType.LoopCondition);
        Connect(data, conditionNode);
        
        int iteratorStartNodeID = builder.nodes.Count;
        ControlFlowNode iteratorEnd = HandleStatementList(forStatement.Iterators, null);
        ControlFlowNode iteratorStart;
        if (iteratorEnd != null) {
          iteratorStart = builder.nodes[iteratorStartNodeID];
          Connect(iteratorEnd, conditionNode);
        } else {
          iteratorStart = conditionNode;
        }
        
        breakTargets.Push(end);
        continueTargets.Push(iteratorStart);
        
        ControlFlowNode bodyStart = builder.CreateStartNode(forStatement.EmbeddedStatement);
        ControlFlowNode bodyEnd = forStatement.EmbeddedStatement.AcceptVisitor(this, bodyStart);
        Connect(bodyEnd, iteratorStart);
        
        breakTargets.Pop();
        continueTargets.Pop();
        
        bool? cond = forStatement.Condition.IsNull ? true : builder.EvaluateCondition(forStatement.Condition);
        if (cond != false)
          Connect(conditionNode, bodyStart, ControlFlowEdgeType.ConditionTrue);
        if (cond != true)
          Connect(conditionNode, end, ControlFlowEdgeType.ConditionFalse);
        
        builder.nodes.Add(end);
        return end;
      }
      
      ControlFlowNode HandleEmbeddedStatement(Statement embeddedStatement, ControlFlowNode source)
      {
        if (embeddedStatement == null || embeddedStatement.IsNull)
          return source;
        ControlFlowNode bodyStart = builder.CreateStartNode(embeddedStatement);
        if (source != null)
          Connect(source, bodyStart);
        return embeddedStatement.AcceptVisitor(this, bodyStart);
      }
      
      public override ControlFlowNode VisitForeachStatement(ForeachStatement foreachStatement, ControlFlowNode data)
      {
        // <data> foreach (<condition>...) { <bodyStart>embeddedStmt<bodyEnd> } <end>
        ControlFlowNode end = builder.CreateEndNode(foreachStatement, addToNodeList: false);
        ControlFlowNode conditionNode = builder.CreateSpecialNode(foreachStatement, ControlFlowNodeType.LoopCondition);
        Connect(data, conditionNode);
        
        breakTargets.Push(end);
        continueTargets.Push(conditionNode);
        
        ControlFlowNode bodyEnd = HandleEmbeddedStatement(foreachStatement.EmbeddedStatement, conditionNode);
        Connect(bodyEnd, conditionNode);
        
        breakTargets.Pop();
        continueTargets.Pop();
        
        Connect(conditionNode, end);
        builder.nodes.Add(end);
        return end;
      }
      
      public override ControlFlowNode VisitBreakStatement(BreakStatement breakStatement, ControlFlowNode data)
      {
        if (breakTargets.Count > 0)
          Connect(data, breakTargets.Peek(), ControlFlowEdgeType.Jump);
        return builder.CreateEndNode(breakStatement);
      }
      
      public override ControlFlowNode VisitContinueStatement(ContinueStatement continueStatement, ControlFlowNode data)
      {
        if (continueTargets.Count > 0)
          Connect(data, continueTargets.Peek(), ControlFlowEdgeType.Jump);
        return builder.CreateEndNode(continueStatement);
      }
      
      public override ControlFlowNode VisitGotoStatement(GotoStatement gotoStatement, ControlFlowNode data)
      {
        builder.gotoStatements.Add(data);
        return builder.CreateEndNode(gotoStatement);
      }
      
      public override ControlFlowNode VisitReturnStatement(ReturnStatement returnStatement, ControlFlowNode data)
      {
        return builder.CreateEndNode(returnStatement); // end not connected with data
      }
      
      public override ControlFlowNode VisitThrowStatement(ThrowStatement throwStatement, ControlFlowNode data)
      {
        return builder.CreateEndNode(throwStatement); // end not connected with data
      }
      
      public override ControlFlowNode VisitTryCatchStatement(TryCatchStatement tryCatchStatement, ControlFlowNode data)
      {
        ControlFlowNode end = builder.CreateEndNode(tryCatchStatement, addToNodeList: false);
        var edge = Connect(HandleEmbeddedStatement(tryCatchStatement.TryBlock, data), end);
        if (!tryCatchStatement.FinallyBlock.IsNull)
          edge.AddJumpOutOfTryFinally(tryCatchStatement);
        foreach (CatchClause cc in tryCatchStatement.CatchClauses) {
          edge = Connect(HandleEmbeddedStatement(cc.Body, data), end);
          if (!tryCatchStatement.FinallyBlock.IsNull)
            edge.AddJumpOutOfTryFinally(tryCatchStatement);
        }
        if (!tryCatchStatement.FinallyBlock.IsNull) {
          // Don't connect the end of the try-finally block to anything.
          // Consumers of the CFG will have to special-case try-finally.
          HandleEmbeddedStatement(tryCatchStatement.FinallyBlock, data);
        }
        builder.nodes.Add(end);
        return end;
      }
      
      public override ControlFlowNode VisitCheckedStatement(CheckedStatement checkedStatement, ControlFlowNode data)
      {
        ControlFlowNode bodyEnd = HandleEmbeddedStatement(checkedStatement.Body, data);
        return CreateConnectedEndNode(checkedStatement, bodyEnd);
      }
      
      public override ControlFlowNode VisitUncheckedStatement(UncheckedStatement uncheckedStatement, ControlFlowNode data)
      {
        ControlFlowNode bodyEnd = HandleEmbeddedStatement(uncheckedStatement.Body, data);
        return CreateConnectedEndNode(uncheckedStatement, bodyEnd);
      }
      
      public override ControlFlowNode VisitLockStatement(LockStatement lockStatement, ControlFlowNode data)
      {
        ControlFlowNode bodyEnd = HandleEmbeddedStatement(lockStatement.EmbeddedStatement, data);
        return CreateConnectedEndNode(lockStatement, bodyEnd);
      }
      
      public override ControlFlowNode VisitUsingStatement(UsingStatement usingStatement, ControlFlowNode data)
      {
        data = HandleEmbeddedStatement(usingStatement.ResourceAcquisition as Statement, data);
        ControlFlowNode bodyEnd = HandleEmbeddedStatement(usingStatement.EmbeddedStatement, data);
        return CreateConnectedEndNode(usingStatement, bodyEnd);
      }
      
      public override ControlFlowNode VisitYieldReturnStatement(YieldReturnStatement yieldStatement, ControlFlowNode data)
      {
        return CreateConnectedEndNode(yieldStatement, data);
      }
      
      public override ControlFlowNode VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement, ControlFlowNode data)
      {
        return builder.CreateEndNode(yieldBreakStatement); // end not connected with data
      }
      
      public override ControlFlowNode VisitUnsafeStatement(UnsafeStatement unsafeStatement, ControlFlowNode data)
      {
        ControlFlowNode bodyEnd = HandleEmbeddedStatement(unsafeStatement.Body, data);
        return CreateConnectedEndNode(unsafeStatement, bodyEnd);
      }
      
      public override ControlFlowNode VisitFixedStatement(FixedStatement fixedStatement, ControlFlowNode data)
      {
        ControlFlowNode bodyEnd = HandleEmbeddedStatement(fixedStatement.EmbeddedStatement, data);
        return CreateConnectedEndNode(fixedStatement, bodyEnd);
      }
    }
    
    /// <summary>
    /// Debugging helper that exports a control flow graph.
    /// </summary>
    public static GraphVizGraph ExportGraph(IList<ControlFlowNode> nodes)
    {
      GraphVizGraph g = new GraphVizGraph();
      GraphVizNode[] n = new GraphVizNode[nodes.Count];
      Dictionary<ControlFlowNode, int> dict = new Dictionary<ControlFlowNode, int>();
      for (int i = 0; i < n.Length; i++) {
        dict.Add(nodes[i], i);
        n[i] = new GraphVizNode(i);
        string name = "#" + i + " = ";
        switch (nodes[i].Type) {
          case ControlFlowNodeType.StartNode:
          case ControlFlowNodeType.BetweenStatements:
            name += nodes[i].NextStatement.DebugToString();
            break;
          case ControlFlowNodeType.EndNode:
            name += "End of " + nodes[i].PreviousStatement.DebugToString();
            break;
          case ControlFlowNodeType.LoopCondition:
            name += "Condition in " + nodes[i].NextStatement.DebugToString();
            break;
          default:
            name += "?";
            break;
        }
        n[i].label = name;
        g.AddNode(n[i]);
      }
      for (int i = 0; i < n.Length; i++) {
        foreach (ControlFlowEdge edge in nodes[i].Outgoing) {
          GraphVizEdge ge = new GraphVizEdge(i, dict[edge.To]);
          if (edge.IsLeavingTryFinally)
            ge.style = "dashed";
          switch (edge.Type) {
            case ControlFlowEdgeType.ConditionTrue:
              ge.color = "green";
              break;
            case ControlFlowEdgeType.ConditionFalse:
              ge.color = "red";
              break;
            case ControlFlowEdgeType.Jump:
              ge.color = "blue";
              break;
          }
          g.AddEdge(ge);
        }
      }
      return g;
    }
  }
}