/*
 * Bytecode Analysis Framework
 * Copyright (C) 2003-2006, 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.Iterator;

import org.apache.bcel.generic.InstructionHandle;

import edu.umd.cs.findbugs.SystemProperties;
import edu.umd.cs.findbugs.annotations.CheckForNull;
import edu.umd.cs.findbugs.annotations.CheckReturnValue;

/**
 * Abstract base class providing functionality that will be useful for most
 * dataflow analysis implementations that model instructions within basic
 * blocks.
 * 
 * @author David Hovemeyer
 * @see Dataflow
 * @see DataflowAnalysis
 */
public abstract class AbstractDataflowAnalysis<Fact> extends BasicAbstractDataflowAnalysis<Fact> {
    private static final boolean DEBUG = SystemProperties.getBoolean("dataflow.transfer");

    /*
     * ----------------------------------------------------------------------
     * Public methods
     * ----------------------------------------------------------------------
     */

    /**
     * Transfer function for a single instruction.
     * 
     * @param handle
     *            the instruction
     * @param basicBlock
     *            the BasicBlock containing the instruction; needed to
     *            disambiguate instructions in inlined JSR subroutines
     * @param fact
     *            which should be modified based on the instruction
     */
    public abstract void transferInstruction(InstructionHandle handle, BasicBlock basicBlock, Fact fact)
            throws DataflowAnalysisException;

    /**
     * Determine whether the given fact is <em>valid</em> (neither top nor
     * bottom).
     */
    @CheckReturnValue
    public abstract boolean isFactValid(Fact fact);

    /**
     * Get the dataflow fact representing the point just before given Location.
     * Note "before" is meant in the logical sense, so for backward analyses,
     * before means after the location in the control flow sense.
     * 
     * @param location
     *            the location
     * @return the fact at the point just before the location
     */
    @Override
    public Fact getFactAtLocation(Location location) throws DataflowAnalysisException {
        Fact start = getStartFact(location.getBasicBlock());
        Fact result = createFact();
        makeFactTop(result);
        transfer(location.getBasicBlock(), location.getHandle(), start, result);
        return result;
    }

    /**
     * Get the dataflow fact representing the point just after given Location.
     * Note "after" is meant in the logical sense, so for backward analyses,
     * after means before the location in the control flow sense.
     * 
     * @param location
     *            the location
     * @return the fact at the point just after the location
     */
    @Override
    public Fact getFactAfterLocation(Location location) throws DataflowAnalysisException {
        BasicBlock basicBlock = location.getBasicBlock();
        InstructionHandle handle = location.getHandle();

        if (handle == (isForwards() ? basicBlock.getLastInstruction() : basicBlock.getFirstInstruction()))
            return getResultFact(basicBlock);
        else
            return getFactAtLocation(new Location(isForwards() ? handle.getNext() : handle.getPrev(), basicBlock));
    }

    /*
     * ----------------------------------------------------------------------
     * Implementations of interface methods
     * ----------------------------------------------------------------------
     */

    public void transfer(BasicBlock basicBlock, @CheckForNull InstructionHandle end, Fact start, Fact result)
            throws DataflowAnalysisException {
        copy(start, result);

        if (isFactValid(result)) {
            Iterator<InstructionHandle> i = isForwards() ? basicBlock.instructionIterator() : basicBlock
                    .instructionReverseIterator();

            while (i.hasNext()) {
                InstructionHandle handle = i.next();
                if (handle == end)
                    break;

                if (DEBUG && end == null)
                    System.out.print("Transfer " + handle);

                // Transfer the dataflow value
                transferInstruction(handle, basicBlock, result);

                if (DEBUG && end == null)
                    System.out.println(" ==> " + result.toString());
            }
        }
    }

}

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