public void AddEdgeTo(ControlFlowNode target)
{
this.Successors.Add(target);
target.Predecessors.Add(this);
}
/// <summary>
/// Computes the dominator tree.
/// </summary>
/// <remarks>
/// Precondition: the dominance tree is not already computed for some nodes reachable from entryPoint
/// (i.e. ImmediateDominator and DominatorTreeChildren are both null),
/// and the visited flag is false for any nodes reachable from entryPoint.
///
/// Postcondition: a dominator tree is constructed for all nodes reachable from entryPoint,
/// and the visited flag remains false.
/// </remarks>
public static void ComputeDominance(ControlFlowNode entryPoint, CancellationToken cancellationToken = default(CancellationToken))
{
// A Simple, Fast Dominance Algorithm
// Keith D. Cooper, Timothy J. Harvey and Ken Kennedy
var nodes = new List <ControlFlowNode>();
entryPoint.TraversePostOrder(n => n.Successors, nodes.Add);
Debug.Assert(nodes.Last() == entryPoint);
for (int i = 0; i < nodes.Count; i++)
{
nodes[i].PostOrderNumber = i;
}
// For the purpose of this algorithm, make the entry point its own dominator.
// We'll reset it back to null at the end of this function.
entryPoint.ImmediateDominator = entryPoint;
bool changed;
do
{
changed = false;
cancellationToken.ThrowIfCancellationRequested();
// For all nodes b except the entry point (in reverse post-order)
for (int i = nodes.Count - 2; i >= 0; i--)
{
ControlFlowNode b = nodes[i];
// Compute new immediate dominator:
ControlFlowNode newIdom = null;
foreach (var p in b.Predecessors)
{
// Ignore predecessors that were not processed yet
if (p.ImmediateDominator != null)
{
if (newIdom == null)
{
newIdom = p;
}
else
{
newIdom = FindCommonDominator(p, newIdom);
}
}
}
// The reverse post-order ensures at least one of our predecessors was processed.
Debug.Assert(newIdom != null);
if (newIdom != b.ImmediateDominator)
{
b.ImmediateDominator = newIdom;
changed = true;
}
}
} while(changed);
// Create dominator tree for all reachable nodes:
foreach (ControlFlowNode node in nodes)
{
if (node.ImmediateDominator != null)
{
node.DominatorTreeChildren = new List <ControlFlowNode>();
}
}
entryPoint.ImmediateDominator = null;
foreach (ControlFlowNode node in nodes)
{
// Create list of children in dominator tree
if (node.ImmediateDominator != null)
{
node.ImmediateDominator.DominatorTreeChildren.Add(node);
}
// Also reset the visited flag
node.Visited = false;
}
}
