/*
* 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 final String fieldVarName;
private final 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());
}
}
}