public void SingleNode()
{
var graph = TestGraphs.CreateSingularGraph();
var startNode = graph.GetNodeById(1);
// Record a depth first traversal.
var traversal = new DepthFirstTraversal();
var recorder = new TraversalOrderRecorder(traversal);
traversal.Run(startNode);
Assert.Single(recorder.GetTraversal());
Assert.Equal(0, recorder.GetIndex(startNode));
}
public void PathReversed()
{
// Artificially construct a path of four nodes in sequential order.
var graph = TestGraphs.CreatePath();
// Record a depth first traversal.
var traversal = new DepthFirstTraversal(true);
var recorder = new TraversalOrderRecorder(traversal);
traversal.Run(graph.GetNodeById(4));
// Traversal should exactly be the path.
Assert.Equal(new INode[]
{
graph.GetNodeById(4),
graph.GetNodeById(3),
graph.GetNodeById(2),
graph.GetNodeById(1),
}, recorder.GetTraversal());
}
/// <summary>
/// Computes the dominator tree of a control flow graph, defined by its entrypoint.
/// </summary>
/// <param name="entrypoint">The entrypoint of the control flow graph.</param>
/// <returns>A dictionary mapping all the nodes to their immediate dominator.</returns>
/// <remarks>
/// The algorithm used is based on the one engineered by Lengauer and Tarjan.
/// https://www.cs.princeton.edu/courses/archive/fall03/cs528/handouts/a%20fast%20algorithm%20for%20finding.pdf
/// https://www.cl.cam.ac.uk/~mr10/lengtarj.pdf
/// </remarks>
private static IDictionary <IIdentifiedNode, IIdentifiedNode> GetImmediateDominators(IIdentifiedNode entrypoint)
{
var idom = new Dictionary <IIdentifiedNode, IIdentifiedNode>();
var semi = new Dictionary <IIdentifiedNode, IIdentifiedNode>();
var ancestor = new Dictionary <IIdentifiedNode, IIdentifiedNode>();
var bucket = new Dictionary <IIdentifiedNode, ISet <IIdentifiedNode> >();
var traversal = new DepthFirstTraversal();
var order = new TraversalOrderRecorder(traversal);
var parents = new ParentRecorder(traversal);
traversal.Run(entrypoint);
var orderedNodes = order.GetTraversal();
foreach (var node in orderedNodes.Cast <IIdentifiedNode>())
{
idom[node] = null;
semi[node] = node;
ancestor[node] = null;
bucket[node] = new HashSet <IIdentifiedNode>();
}
for (int i = orderedNodes.Count - 1; i >= 1; i--)
{
var current = (IIdentifiedNode)orderedNodes[i];
var parent = (IIdentifiedNode)parents.GetParent(current);
// step 2
foreach (var predecessor in current.GetPredecessors().Cast <IIdentifiedNode>())
{
var u = Eval(predecessor, ancestor, semi, order);
if (order.GetIndex(semi[current]) > order.GetIndex(semi[u]))
{
semi[current] = semi[u];
}
}
bucket[semi[current]].Add(current);
Link(parent, current, ancestor);
// step 3
foreach (var bucketNode in bucket[parent])
{
var u = Eval(bucketNode, ancestor, semi, order);
if (order.GetIndex(semi[u]) < order.GetIndex(semi[bucketNode]))
{
idom[bucketNode] = u;
}
else
{
idom[bucketNode] = parent;
}
}
bucket[parent].Clear();
}
// step 4
for (int i = 1; i < orderedNodes.Count; i++)
{
var w = (IIdentifiedNode)orderedNodes[i];
if (idom[w] != semi[w])
{
idom[w] = idom[idom[w]];
}
}
idom[entrypoint] = entrypoint;
return(idom);
}