FieldAccess.java

/*
 * 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.FieldInstruction;
import org.apache.bcel.generic.Type;

import edu.umd.cs.findbugs.ba.DataflowAnalysisException;
import edu.umd.cs.findbugs.ba.vna.ValueNumber;
import edu.umd.cs.findbugs.ba.vna.ValueNumberFrame;

/**
 * Base class for Load and Store PatternElements. Handles some of the grunt work
 * of representing fields and extracting field values from the stack frame.
 * 
 * @author David Hovemeyer
 * @see Load
 * @see Store
 */
public abstract class FieldAccess extends SingleInstruction implements org.apache.bcel.Constants {
    private String fieldVarName;

    private String valueVarName;

    /**
     * Constructor.
     * 
     * @param fieldVarName
     *            name of the variable to bind to the field
     * @param valueVarName
     *            name of the variable to bind to the value store in or loaded
     *            from the field
     */
    public FieldAccess(String fieldVarName, String valueVarName) {
        this.fieldVarName = fieldVarName;
        this.valueVarName = valueVarName;
    }

    /**
     * Check that the Variables determined for the field and the value
     * loaded/stored are consistent with previous variable definitions.
     * 
     * @param field
     *            Variable representing the field
     * @param value
     *            Variable representing the value loaded/stored
     * @param bindingSet
     *            previous definitions
     * @return a MatchResult containing an updated BindingSet if successful, or
     *         null if unsucessful
     */
    protected MatchResult checkConsistent(Variable field, Variable value, BindingSet bindingSet) {
        // Ensure that the field and value variables are consistent with
        // previous definitions (if any)
        bindingSet = addOrCheckDefinition(fieldVarName, field, bindingSet);
        if (bindingSet == null)
            return null;
        bindingSet = addOrCheckDefinition(valueVarName, value, bindingSet);
        if (bindingSet == null)
            return null;
        return new MatchResult(this, bindingSet);
    }

    /**
     * Return whether the given FieldInstruction accesses a long or double
     * field.
     * 
     * @param fieldIns
     *            the FieldInstruction
     * @param cpg
     *            the ConstantPoolGen for the method
     */
    protected static boolean isLongOrDouble(FieldInstruction fieldIns, ConstantPoolGen cpg) {
        Type type = fieldIns.getFieldType(cpg);
        int code = type.getType();
        return code == T_LONG || code == T_DOUBLE;
    }

    /**
     * Get a Variable representing the stack value which will either be stored
     * into or loaded from a field.
     * 
     * @param fieldIns
     *            the FieldInstruction accessing the field
     * @param cpg
     *            the ConstantPoolGen for the method
     * @param frame
     *            the ValueNumberFrame containing the value to be stored or the
     *            value loaded
     */
    protected static Variable snarfFieldValue(FieldInstruction fieldIns, ConstantPoolGen cpg, ValueNumberFrame frame)
            throws DataflowAnalysisException {

        if (isLongOrDouble(fieldIns, cpg)) {
            int numSlots = frame.getNumSlots();
            ValueNumber topValue = frame.getValue(numSlots - 1);
            ValueNumber nextValue = frame.getValue(numSlots - 2);
            return new LongOrDoubleLocalVariable(topValue, nextValue);
        } else {
            return new LocalVariable(frame.getTopValue());
        }

    }
}

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