/* This file is part of the db4o object database http://www.db4o.com
Copyright (C) 2004 - 2011 Versant Corporation http://www.versant.com
db4o is free software; you can redistribute it and/or modify it under
the terms of version 3 of the GNU General Public License as published
by the Free Software Foundation.
db4o is distributed in the hope that it will be useful, but WITHOUT ANY
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License along
with this program. If not, see http://www.gnu.org/licenses/. */
package EDU.purdue.cs.bloat.cfg;
import java.util.*;
/**
* <tt>DominanceFrontier</tt> is used to calculate the <i>dominance frontier</i>
* of each node in a control flow graph.
* <p>
* The <i>dominance frontier</i> of a node x is the set of all nodes w such
* that x dominates a predacessor of w, but does not strictly dominate w.
* Basically, nodes in the dominance frontier have one parent that <b>is</b>
* dominated by x and at least one parent that <b>is not</b> dominated by x.
* <p>
* <tt>DominanceFrontier</tt> can be used to calculate both the dominance
* (forward) and the postdominance (reverse) frontiers for a control flow graph.
*
* @see FlowGraph
*/
public class DominanceFrontier {
/**
* Calculates the dominance frontier for a cfg and notifies the blocks in it
* appropriately.
*
* @param graph
* The cfg to operate on
* @param reverse
* Do we calculate the postdominance frontier?
*/
public static void buildFrontier(final FlowGraph graph, boolean reverse) {
if (!reverse) {
DominanceFrontier.calcFrontier(graph.source(), graph, reverse);
} else {
DominanceFrontier.calcFrontier(graph.sink(), graph, reverse);
}
}
/**
* Recursively traverses the cfg and builds up the dominance frontier.
* <p>
* A block n's dominance frontier is the union of two sets of nodes. The
* first set is the nodes in the dominance frontier of the nodes that n
* dominates that are not dominated by n's immediate dominator. The second
* set consists of the successors of n that are not strictly dominated by n.
*
* @param block
* The block to start from (either source or sink)
* @param graph
* The cfg from which to get blocks
* @param reverse
* Do we calculate the dominance or postdominance frontier?
*
* @return The blocks in the (post)dominance frontier of block
*/
private static LinkedList calcFrontier(final Block block,
final FlowGraph graph, boolean reverse) {
// local is an array of Blocks that are in block's dominance
// frontier. It is indexed by the block's pre-order index. I
// suppose an array is used so that no block is added to the
// dominance frontier twice.
final Block[] local = new Block[graph.size()];
Iterator children; // The blocks that are dominated by block
if (!reverse) {
children = block.domChildren().iterator();
} else {
children = block.pdomChildren().iterator();
}
// Recursively calculate the nodes in the dominance frontier of
// block that are not dominated by block's immediate dominator
while (children.hasNext()) {
final Block child = (Block) children.next();
final LinkedList df = DominanceFrontier.calcFrontier(child, graph,
reverse);
final Iterator e = df.iterator();
while (e.hasNext()) {
final Block dfChild = (Block) e.next();
if (!reverse) {
if (block != dfChild.domParent()) {
local[graph.preOrderIndex(dfChild)] = dfChild;
}
} else {
if (block != dfChild.pdomParent()) {
local[graph.preOrderIndex(dfChild)] = dfChild;
}
}
}
}
final Iterator succs = reverse ? graph.preds(block).iterator() : graph
.succs(block).iterator();
// Caculate the successors of block that are not strictly
// dominated by block.
while (succs.hasNext()) {
final Block succ = (Block) succs.next();
// If block is not the immediate (post)dominator of its
// successor, add it to block's dominance frontier.
if (!reverse) {
if (block != succ.domParent()) {
local[graph.preOrderIndex(succ)] = succ;
}
} else {
if (block != succ.pdomParent()) {
local[graph.preOrderIndex(succ)] = succ;
}
}
}
final LinkedList v = new LinkedList(); // The dominance frontier
for (int i = 0; i < local.length; i++) {
if (local[i] != null) {
v.add(local[i]);
}
}
// Set block's (post)dominance frontier
if (!reverse) {
block.domFrontier().clear();
block.domFrontier().addAll(v);
} else {
block.pdomFrontier().clear();
block.pdomFrontier().addAll(v);
}
return v;
}
}