edu.umd.cs.findbugs.ba.AbstractDominatorsAnalysis Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of spotbugs Show documentation
SpotBugs: Because it's easy!
The newest version!
/*
 * Bytecode Analysis Framework
 * Copyright (C) 2003,2004 University of Maryland
 *
 * 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 edu.umd.cs.findbugs.ba;

import java.util.BitSet;
import java.util.Iterator;

import javax.annotation.CheckForNull;

import org.apache.bcel.generic.InstructionHandle;


/**
 * A dataflow analysis to compute dominator relationships between basic blocks.
 * Use the {@link #getResultFact} method to get the dominator set for a given
 * basic block. The dominator sets are represented using the
 * {@link java.util.BitSet} class, with the individual bits corresponding to the
 * IDs of basic blocks.
 * 
 * Subclasses extend this class to compute either dominators or postdominators.
 * 
 * 
 * An EdgeChooser may be specified to select which edges to take into account.
 * For example, exception edges could be ignored.
 * 
 *
 * @author David Hovemeyer
 * @see DataflowAnalysis
 * @see CFG
 * @see BasicBlock
 */
public abstract class AbstractDominatorsAnalysis extends BasicAbstractDataflowAnalysis {
    private final CFG cfg;

    private final EdgeChooser edgeChooser;

    /**
     * Constructor.
     *
     * @param cfg
     *            the CFG to compute dominator relationships for
     * @param ignoreExceptionEdges
     *            true if exception edges should be ignored
     */
    public AbstractDominatorsAnalysis(CFG cfg, final boolean ignoreExceptionEdges) {
        this(cfg, edge -> {
            return !(ignoreExceptionEdges && edge.isExceptionEdge());
        });
    }

    /**
     * Constructor.
     *
     * @param cfg
     *            the CFG to compute dominator relationships for
     * @param edgeChooser
     *            EdgeChooser to choose which Edges to consider significant
     */
    public AbstractDominatorsAnalysis(CFG cfg, EdgeChooser edgeChooser) {
        this.cfg = cfg;
        this.edgeChooser = edgeChooser;
    }

    @Override
    public BitSet createFact() {
        return new BitSet();
    }

    @Override
    public void copy(BitSet source, BitSet dest) {
        dest.clear();
        dest.or(source);
    }

    @Override
    public void initEntryFact(BitSet result) {
        // No blocks dominate the entry block
        result.clear();
    }

    @Override
    public boolean isTop(BitSet fact) {
        // We represent TOP as a bitset with an illegal bit set
        return fact.get(cfg.getNumBasicBlocks());
    }

    @Override
    public void makeFactTop(BitSet fact) {
        // We represent TOP as a bitset with an illegal bit set
        fact.set(cfg.getNumBasicBlocks());
    }

    @Override
    public boolean same(BitSet fact1, BitSet fact2) {
        return fact1.equals(fact2);
    }

    @Override
    public void transfer(BasicBlock basicBlock, @CheckForNull InstructionHandle end, BitSet start, BitSet result)
            throws DataflowAnalysisException {
        // Start with intersection of dominators of predecessors
        copy(start, result);

        if (!isTop(result)) {
            // Every block dominates itself
            result.set(basicBlock.getLabel());
        }
    }

    @Override
    public void meetInto(BitSet fact, Edge edge, BitSet result) throws DataflowAnalysisException {
        if (!edgeChooser.choose(edge)) {
            return;
        }

        if (isTop(fact)) {
            return;
        } else if (isTop(result)) {
            copy(fact, result);
        } else {
            // Meet is intersection
            result.and(fact);
        }
    }

    /**
     * Get a bitset containing the unique IDs of all blocks which dominate (or
     * postdominate) the given block.
     *
     * @param block
     *            a BasicBlock
     * @return BitSet of the unique IDs of all blocks that dominate (or
     *         postdominate) the BasicBlock
     */
    public BitSet getAllDominatorsOf(BasicBlock block) {
        return getResultFact(block);
    }

    /**
     * Get a bitset containing the unique IDs of all blocks in CFG dominated (or
     * postdominated, depending on how the analysis was done) by given block.
     *
     * @param dominator
     *            we want to get all blocks dominated (or postdominated) by this
     *            block
     * @return BitSet of the ids of all blocks dominated by the given block
     */
    public BitSet getAllDominatedBy(BasicBlock dominator) {
        BitSet allDominated = new BitSet();
        for (Iterator i = cfg.blockIterator(); i.hasNext();) {
            BasicBlock block = i.next();
            BitSet dominators = getResultFact(block);
            if (dominators.get(dominator.getLabel())) {
                allDominated.set(block.getLabel());
            }
        }
        return allDominated;
    }

}