+/// InitDAGTopologicalSorting - create the initial topological
+/// ordering from the DAG to be scheduled.
+
+/// The idea of the algorithm is taken from
+/// "Online algorithms for managing the topological order of
+/// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
+/// This is the MNR algorithm, which was first introduced by
+/// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
+/// "Maintaining a topological order under edge insertions".
+///
+/// Short description of the algorithm:
+///
+/// Topological ordering, ord, of a DAG maps each node to a topological
+/// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
+///
+/// This means that if there is a path from the node X to the node Z,
+/// then ord(X) < ord(Z).
+///
+/// This property can be used to check for reachability of nodes:
+/// if Z is reachable from X, then an insertion of the edge Z->X would
+/// create a cycle.
+///
+/// The algorithm first computes a topological ordering for the DAG by
+/// initializing the Index2Node and Node2Index arrays and then tries to keep
+/// the ordering up-to-date after edge insertions by reordering the DAG.
+///
+/// On insertion of the edge X->Y, the algorithm first marks by calling DFS
+/// the nodes reachable from Y, and then shifts them using Shift to lie
+/// immediately after X in Index2Node.
+void ScheduleDAGRRList::InitDAGTopologicalSorting() {
+ unsigned DAGSize = SUnits.size();
+ std::vector<SUnit*> WorkList;
+ WorkList.reserve(DAGSize);
+
+ Index2Node.resize(DAGSize);
+ Node2Index.resize(DAGSize);
+
+ // Initialize the data structures.
+ for (unsigned i = 0, e = DAGSize; i != e; ++i) {
+ SUnit *SU = &SUnits[i];
+ int NodeNum = SU->NodeNum;
+ unsigned Degree = SU->Succs.size();
+ // Temporarily use the Node2Index array as scratch space for degree counts.
+ Node2Index[NodeNum] = Degree;
+
+ // Is it a node without dependencies?
+ if (Degree == 0) {
+ assert(SU->Succs.empty() && "SUnit should have no successors");
+ // Collect leaf nodes.
+ WorkList.push_back(SU);
+ }
+ }
+
+ int Id = DAGSize;
+ while (!WorkList.empty()) {
+ SUnit *SU = WorkList.back();
+ WorkList.pop_back();
+ Allocate(SU->NodeNum, --Id);
+ for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+ I != E; ++I) {
+ SUnit *SU = I->Dep;
+ if (!--Node2Index[SU->NodeNum])
+ // If all dependencies of the node are processed already,
+ // then the node can be computed now.
+ WorkList.push_back(SU);
+ }
+ }
+
+ Visited.resize(DAGSize);
+
+#ifndef NDEBUG
+ // Check correctness of the ordering
+ for (unsigned i = 0, e = DAGSize; i != e; ++i) {
+ SUnit *SU = &SUnits[i];
+ for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+ I != E; ++I) {
+ assert(Node2Index[SU->NodeNum] > Node2Index[I->Dep->NodeNum] &&
+ "Wrong topological sorting");
+ }
+ }
+#endif
+}
+
+/// AddPred - adds an edge from SUnit X to SUnit Y.
+/// Updates the topological ordering if required.
+bool ScheduleDAGRRList::AddPred(SUnit *Y, SUnit *X, bool isCtrl, bool isSpecial,
+ unsigned PhyReg, int Cost) {
+ int UpperBound, LowerBound;
+ LowerBound = Node2Index[Y->NodeNum];
+ UpperBound = Node2Index[X->NodeNum];
+ bool HasLoop = false;
+ // Is Ord(X) < Ord(Y) ?
+ if (LowerBound < UpperBound) {
+ // Update the topological order.
+ Visited.reset();
+ DFS(Y, UpperBound, HasLoop);
+ assert(!HasLoop && "Inserted edge creates a loop!");
+ // Recompute topological indexes.
+ Shift(Visited, LowerBound, UpperBound);
+ }
+ // Now really insert the edge.
+ return Y->addPred(X, isCtrl, isSpecial, PhyReg, Cost);