/**
* Constructs the online graph for the analysis. Additionally an offline graph for HCD is
* constructed to speed up the computation of the dynamic transitive closure with it.
*
* @param bConstr List of all {@link BaseConstraint}s that should be considered.<br>
* A {@link BaseConstraint} leads to an entry in a nodes points-to set.
* @param sConstr List of all {@link SimpleConstraint}s that should be considered.<br>
* A {@link SimpleConstraint} represents an edge in the graph.
* @param cConstr List of all {@link ComplexConstraint}s that should be considered.<br>
* {@link ComplexConstraint}s are stored in nodes, so they can be accessed faster when
* computing the dynamic transitive closure.
* @param g The resulting graph. Should be empty.
*/
private static void buildGraph(
Set<BaseConstraint> bConstr,
Set<SimpleConstraint> sConstr,
Set<ComplexConstraint> cConstr,
DirectedGraph g) {
// HCD offline - build offline graph
List<List<String>> sccs = buildOfflineGraphAndFindSCCs(sConstr, cConstr);
// build online graph
for (BaseConstraint bc : bConstr) {
DirectedGraph.Node n = g.getNode(bc.getSuperVar());
n.addPointerTarget(bc.getSubVar());
}
for (SimpleConstraint sc : sConstr) {
DirectedGraph.Node src = g.getNode(sc.getSubVar());
DirectedGraph.Node dest = g.getNode(sc.getSuperVar());
g.addEdge(src, dest);
}
for (ComplexConstraint cc : cConstr) {
DirectedGraph.Node n;
if (cc.isSubDerefed()) {
n = g.getNode(cc.getSubVar());
n.complexConstrMeSub.add(cc.getSuperVar());
} else {
n = g.getNode(cc.getSuperVar());
n.complexConstrMeSuper.add(cc.getSubVar());
}
}
// for HCD
mergeOrMarkSCCs(g, sccs); // ... in online graph
}
/**
* Merges all non-ref nodes in an SCC. For every ref-node the last remaining non-ref Node is
* stored.
*
* @param g The (online) points-to graph for the analysis.
* @param sccs List of all found SCCs in the offline version of the graph.
*/
private static void mergeOrMarkSCCs(DirectedGraph g, List<List<String>> sccs) {
for (List<String> scc : sccs) {
LinkedList<DirectedGraph.Node> refNodes = new LinkedList<>();
LinkedList<DirectedGraph.Node> normNodes = new LinkedList<>();
for (String n : scc) {
// translate to new node
if (n.charAt(0) == '*') {
refNodes.add(g.getNode(n.substring(1)));
} else {
normNodes.add(g.getNode(n));
}
}
DirectedGraph.Node merged = g.mergeNodes(normNodes.poll(), normNodes);
for (DirectedGraph.Node n : refNodes) {
n.mergePts = merged;
}
}
}
/**
* Recursive part of tarjans algorithm to find strongly connected components. Algorithm is e.g.
* described in <a
* href="http://en.wikipedia.org/wiki/Tarjan's_strongly_connected_components_algorithm">wikipedia</a>
*
* @param maxdfs The current value for maxdfs.
* @param v The current Node to process.
* @param workset Set of all unreached Nodes.
* @param stack Temporary datastructure for algorithm.
* @param nodeStrMap Because the sccs are returned as a list of variables (i.e. Strings), the
* mapping from Node to String must be given.
* @param sccs All found strongly connected components are added to this list.
* @return an updated value for maxdfs.
*/
private static int tarjan(
int maxdfs,
DirectedGraph.Node v,
Set<DirectedGraph.Node> workset,
LinkedList<DirectedGraph.Node> stack,
Map<DirectedGraph.Node, String> nodeStrMap,
List<List<String>> sccs) {
v.dfs = maxdfs;
v.lowlink = maxdfs;
maxdfs++;
stack.push(v);
workset.remove(v);
for (DirectedGraph.Node succ : v.getSuccessors()) {
if (workset.contains(succ)) {
maxdfs = tarjan(maxdfs, succ, workset, stack, nodeStrMap, sccs);
v.lowlink = Math.min(v.lowlink, succ.lowlink);
} else if (succ.dfs > 0) { // <==> stack.contains(succ)
v.lowlink = Math.min(v.lowlink, succ.dfs);
}
}
if (v.lowlink == v.dfs) {
DirectedGraph.Node succ;
LinkedList<String> scc = new LinkedList<>();
do {
succ = stack.pop();
succ.dfs = -succ.dfs;
scc.add(nodeStrMap.get(succ));
} while (!succ.equals(v));
if (scc.size() > 1) {
sccs.add(scc);
}
}
return maxdfs;
}
/**
* Computes the dynamic transitive closure of the given constraint system and writes the resulting
* points-to sets to the {@link Map} <code>ptSets</code>.
*
* @param bConstr {@link Set} of {@link BaseConstraint}s in the constraint system.
* @param sConstr {@link Set} of {@link SimpleConstraint}s in the constraint system.
* @param cConstr {@link Set} of {@link ComplexConstraint}s in the constraint system.
* @param ptSets Writes all found points-to relations to this {@link Map}.<br>
* <i>Note:</i> The map is cleared, before the results are written.
*/
private static void computeDynTransitiveClosure(
Set<BaseConstraint> bConstr,
Set<SimpleConstraint> sConstr,
Set<ComplexConstraint> cConstr,
Map<String, String[]> ptSets) {
// build initial graph
DirectedGraph g = new DirectedGraph();
buildGraph(bConstr, sConstr, cConstr, g);
HashSet<DirectedGraph.Node> workset = new HashSet<>();
// add all nodes in graph to the initial workset
for (Map.Entry<String, DirectedGraph.Node> entry : g.getNameMappings()) {
workset.add(entry.getValue());
}
HashSet<DirectedGraph.Edge> tested = new HashSet<>();
// dynamic transitive closure
while (!workset.isEmpty()) {
DirectedGraph.Node n = workset.iterator().next();
workset.remove(n);
if (!n.isValid()) {
// node is invalid, if it was merged into another one
continue;
}
// two lines for HCD
if (n.mergePts != null) {
g.mergeNodes(n.mergePts, n.getPointsToNodesSet());
}
for (DirectedGraph.Node v : n.getPointsToNodesSet()) {
for (String aStr : n.complexConstrMeSub) {
DirectedGraph.Node a = g.getNode(aStr);
if (!v.isSuccessor(a)) {
g.addEdge(v, a);
workset.add(v);
}
}
for (String bStr : n.complexConstrMeSuper) {
DirectedGraph.Node b = g.getNode(bStr);
if (!b.isSuccessor(v)) {
g.addEdge(b, v);
workset.add(b);
}
}
} // for (String vStr : n.pointsToSet)
for (DirectedGraph.Node z : n.getSuccessors()) {
// LCD code
DirectedGraph.Edge edge = new DirectedGraph.Edge(n, z);
if (z.getPointsToSet().equals(n.getPointsToSet()) && !tested.contains(edge)) {
tested.add(edge);
DirectedGraph.Node merged = g.detectAndCollapseCycleContainingEdge(edge);
if (merged != null) {
workset.add(merged);
break;
}
} else /* END LCD code */ if (n.propagatePointerTargetsTo(z)) {
workset.add(z);
}
}
} // while (!workset.isEmpty())
// clear result map
ptSets.clear();
// write results to map
for (Map.Entry<String, DirectedGraph.Node> e : g.getNameMappings()) {
Collection<String> ptSetNode = e.getValue().getPointsToSet();
ptSets.put(e.getKey(), ptSetNode.toArray(new String[ptSetNode.size()]));
}
}
