/* Soot - a J*va Optimization Framework
* Copyright (C) 2005 Navindra Umanee <navindra@cs.mcgill.ca>
* Copyright (C) 2007 Eric Bodden
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
package soot.toolkits.graph;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/**
* Calculate dominators for basic blocks.
* <p> Uses the algorithm contained in Dragon book, pg. 670-1.
* <pre>
* D(n0) := { n0 }
* for n in N - { n0 } do D(n) := N;
* while changes to any D(n) occur do
* for n in N - {n0} do
* D(n) := {n} U (intersect of D(p) over all predecessors p of n)
* </pre>
* 2007/07/03 - updated to use {@link BitSet}s instead of {@link HashSet}s, as the most expensive
* operation in this algorithm used to be cloning of the fullSet, which is very cheap
* for {@link BitSet}s.
*
* @author Navindra Umanee
* @author Eric Bodden
**/
public class MHGDominatorsFinder<N> implements DominatorsFinder<N>
{
protected DirectedGraph<N> graph;
protected BitSet fullSet;
protected List<N> heads;
protected Map<N,BitSet> nodeToFlowSet;
protected Map<N,Integer> nodeToIndex;
protected Map<Integer,N> indexToNode;
protected int lastIndex = 0;
public MHGDominatorsFinder(DirectedGraph<N> graph)
{
this.graph = graph;
doAnalysis();
}
protected void doAnalysis()
{
heads = graph.getHeads();
nodeToFlowSet = new HashMap<N, BitSet>();
nodeToIndex = new HashMap<N, Integer>();
indexToNode = new HashMap<Integer,N>();
//build full set
fullSet = new BitSet(graph.size());
fullSet.flip(0, graph.size());//set all to true
//set up domain for intersection: head nodes are only dominated by themselves,
//other nodes are dominated by everything else
for(Iterator<N> i = graph.iterator(); i.hasNext();){
N o = i.next();
if(heads.contains(o)){
BitSet self = new BitSet();
self.set(indexOf(o));
nodeToFlowSet.put(o, self);
}
else{
nodeToFlowSet.put(o, fullSet);
}
}
boolean changed = true;
do{
changed = false;
for(Iterator<N> i = graph.iterator(); i.hasNext();){
N o = i.next();
if(heads.contains(o)) continue;
//initialize to the "neutral element" for the intersection
//this clone() is fast on BitSets (opposed to on HashSets)
BitSet predsIntersect = (BitSet) fullSet.clone();
//intersect over all predecessors
for(Iterator<N> j = graph.getPredsOf(o).iterator(); j.hasNext();){
BitSet predSet = nodeToFlowSet.get(j.next());
predsIntersect.and(predSet);
}
BitSet oldSet = nodeToFlowSet.get(o);
//each node dominates itself
predsIntersect.set(indexOf(o));
if(!predsIntersect.equals(oldSet)){
nodeToFlowSet.put(o, predsIntersect);
changed = true;
}
}
} while(changed);
}
protected int indexOf(N o) {
Integer index = nodeToIndex.get(o);
if(index==null) {
index = lastIndex;
nodeToIndex.put(o,index);
indexToNode.put(index,o);
lastIndex++;
}
return index;
}
public DirectedGraph<N> getGraph()
{
return graph;
}
public List<N> getDominators(Object node)
{
//reconstruct list of dominators from bitset
List<N> result = new ArrayList<N>();
BitSet bitSet = nodeToFlowSet.get(node);
for(int i=0;i<bitSet.length();i++) {
if(bitSet.get(i)) {
result.add(indexToNode.get(i));
}
}
return result;
}
public N getImmediateDominator(Object node)
{
// root node
if(getGraph().getHeads().contains(node))
return null;
// could be memoised, I guess
List<N> dominatorsList = getDominators(node);
dominatorsList.remove(node);
Iterator<N> dominatorsIt = dominatorsList.iterator();
N immediateDominator = null;
while((immediateDominator == null) && dominatorsIt.hasNext()){
N dominator = dominatorsIt.next();
if(isDominatedByAll(dominator, dominatorsList))
immediateDominator = dominator;
}
assert immediateDominator!=null;
return immediateDominator;
}
public boolean isDominatedBy(N node, N dominator)
{
return getDominators(node).contains(dominator);
}
public boolean isDominatedByAll(N node, Collection<N> dominators)
{
return getDominators(node).containsAll(dominators);
}
}