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/*
 * 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.bcp;

import org.apache.bcel.generic.ConstantPoolGen;
import org.apache.bcel.generic.IFNONNULL;
import org.apache.bcel.generic.IFNULL;
import org.apache.bcel.generic.Instruction;
import org.apache.bcel.generic.InstructionHandle;

import edu.umd.cs.findbugs.ba.DataflowAnalysisException;
import edu.umd.cs.findbugs.ba.Edge;
import edu.umd.cs.findbugs.ba.EdgeTypes;
import edu.umd.cs.findbugs.ba.vna.ValueNumberFrame;

public class IfNull extends OneVariableInstruction implements EdgeTypes {

    public IfNull(String varName) {
        super(varName);
    }

    @Override
    public MatchResult match(InstructionHandle handle, ConstantPoolGen cpg, ValueNumberFrame before, ValueNumberFrame after,
            BindingSet bindingSet) throws DataflowAnalysisException {

        // Instruction must be IFNULL or IFNONNULL.
        Instruction ins = handle.getInstruction();
        if (!(ins instanceof IFNULL || ins instanceof IFNONNULL)) {
            return null;
        }

        // Ensure reference used is consistent with previous uses of
        // same variable.
        LocalVariable ref = new LocalVariable(before.getTopValue());
        return addOrCheckDefinition(ref, bindingSet);
    }

    @Override
    public boolean acceptBranch(Edge edge, InstructionHandle source) {
        boolean isIfNull = (source.getInstruction() instanceof IFNULL);
        return edge.getType() == (isIfNull ? IFCMP_EDGE : FALL_THROUGH_EDGE);
    }
}