/*
* FindBugs - Find Bugs in Java programs
* Copyright (C) 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.npe2;
import java.util.BitSet;
import java.util.HashMap;
import java.util.Map;
import org.apache.bcel.Constants;
import org.apache.bcel.generic.InstructionHandle;
import edu.umd.cs.findbugs.ba.BasicBlock;
import edu.umd.cs.findbugs.ba.CompactLocationNumbering;
import edu.umd.cs.findbugs.ba.DataflowAnalysisException;
//import edu.umd.cs.findbugs.ba.DataflowTestDriver;
import edu.umd.cs.findbugs.ba.DepthFirstSearch;
import edu.umd.cs.findbugs.ba.Edge;
import edu.umd.cs.findbugs.ba.ForwardDataflowAnalysis;
import edu.umd.cs.findbugs.ba.Location;
import edu.umd.cs.findbugs.ba.vna.ValueNumber;
import edu.umd.cs.findbugs.ba.vna.ValueNumberDataflow;
import edu.umd.cs.findbugs.ba.vna.ValueNumberFrame;
/**
* A simple null-pointer analysis that keeps track of which
* value numbers are definitely known to be null.
*
* @author David Hovemeyer
*/
public class DefinitelyNullSetAnalysis extends ForwardDataflowAnalysis<DefinitelyNullSet> {
private ValueNumberDataflow vnaDataflow;
private Map<BasicBlock, Condition> conditionMap;
private static final BitSet IFNULL_OPCODE_SET = new BitSet();
private static final BitSet IFACMP_OPCODE_SET = new BitSet();
private static final BitSet REFCMP_OPCODE_SET = new BitSet();
static {
IFNULL_OPCODE_SET.set(Constants.IFNULL);
IFNULL_OPCODE_SET.set(Constants.IFNONNULL);
IFACMP_OPCODE_SET.set(Constants.IF_ACMPEQ);
IFACMP_OPCODE_SET.set(Constants.IF_ACMPNE);
REFCMP_OPCODE_SET.or(IFNULL_OPCODE_SET);
REFCMP_OPCODE_SET.or(IFACMP_OPCODE_SET);
}
/**
* Constructor.
*
* @param dfs DepthFirstSearch for the method
* @param vnaDataflow value number dataflow for the method
* @param compactLocationNumbering CompactLocationNumbering for the method
*/
//TODO: compactLocationNumbering is ignored. Why?
public DefinitelyNullSetAnalysis(
DepthFirstSearch dfs,
ValueNumberDataflow vnaDataflow,
CompactLocationNumbering compactLocationNumbering) {
super(dfs);
this.vnaDataflow = vnaDataflow;
this.conditionMap = new HashMap<BasicBlock, Condition>();
}
/* (non-Javadoc)
* @see edu.umd.cs.findbugs.ba.AbstractDataflowAnalysis#isFactValid(java.lang.Object)
*/
@Override
public boolean isFactValid(DefinitelyNullSet fact) {
return fact.isValid();
}
/* (non-Javadoc)
* @see edu.umd.cs.findbugs.ba.AbstractDataflowAnalysis#transferInstruction(org.apache.bcel.generic.InstructionHandle, edu.umd.cs.findbugs.ba.BasicBlock, java.lang.Object)
*/
@Override
public void transferInstruction(InstructionHandle handle, BasicBlock basicBlock, DefinitelyNullSet fact) throws DataflowAnalysisException {
Location location = new Location(handle, basicBlock);
ValueNumberFrame vnaFrame = vnaDataflow.getFactAfterLocation(location);
if (!vnaFrame.isValid()) {
fact.setTop();
return;
}
// ACONST_NULL obviously produces a value that is DEFINITELY NULL.
// LDC produces values that are NOT NULL.
// NEW produces values that are NOT NULL.
short opcode = handle.getInstruction().getOpcode();
if (opcode == Constants.ACONST_NULL) {
setTOS(vnaFrame, location, fact, NullnessValue.definitelyNullValue());
} else if (opcode == Constants.LDC || opcode == Constants.NEW) {
setTOS(vnaFrame, location, fact, NullnessValue.definitelyNotNullValue());
}
// TODO: for method invocations, check return annotation
// Refresh condition/decision information
if (handle == basicBlock.getLastInstruction() && REFCMP_OPCODE_SET.get(opcode)) {
Condition condition = getCondition(basicBlock);
if (condition != null) {
//System.out.println("handle: " + handle);
condition.refresh(vnaDataflow.getFactAtLocation(location), fact);
}
}
}
/**
* Get the ConditionDecision providing information about the
* branch at the end of the given basic block.
*
* @param basicBlock
* @return the ConditionDecision, or null if the basic block
* does not end in a reference comparison
*/
private Condition getCondition(BasicBlock basicBlock)
throws DataflowAnalysisException {
Condition condition = conditionMap.get(basicBlock);
if (condition == null) {
Location location = new Location(basicBlock.getLastInstruction(), basicBlock);
short opcode = basicBlock.getLastInstruction().getInstruction().getOpcode();
if (IFNULL_OPCODE_SET.get(opcode)) {
condition = new IfNullCondition(location);
} else if (IFACMP_OPCODE_SET.get(opcode)) {
//condition = new AcmpCondition(location);
return null;
} else {
return null;
}
conditionMap.put(basicBlock, condition);
}
return condition;
}
/* (non-Javadoc)
* @see edu.umd.cs.findbugs.ba.BasicAbstractDataflowAnalysis#edgeTransfer(edu.umd.cs.findbugs.ba.Edge, java.lang.Object)
*/
@Override
public void edgeTransfer(Edge edge, DefinitelyNullSet fact) throws DataflowAnalysisException {
if (!fact.isValid()) {
return;
}
if (edge.getSource().isEmpty()) {
return;
}
Condition condition = getCondition(edge.getSource());
if (condition == null) {
return;
}
Decision decision = condition.getDecision(edge);
if (!decision.isFeasible()) {
// This edge is not feasible.
// Set fact to TOP to avoid polluting dataflow information
// at a future control merge.
fact.setTop();
return;
}
// System.out.println("Setting " + condition.getValueNumber() + " to " + decision.getNullnessValue() + " on edge " + edge);
changeNullnessOfValue(
condition.getValueNumber(),
condition.getLocation(),
fact,
decision.getNullnessValue());
}
/**
* Set the value on top of the stack as either null or unknown.
*
* @param vnaFrame ValueNumberFrame at Location
* @param location the Location
* @param fact DefinitelyNullSet to modify
* @param nullnessValue the nullness of the value number
* @throws DataflowAnalysisException
*/
private void setTOS(ValueNumberFrame vnaFrame, Location location, DefinitelyNullSet fact, NullnessValue nullnessValue)
throws DataflowAnalysisException {
ValueNumber valueNumber = vnaFrame.getTopValue();
changeNullnessOfValue(valueNumber, location, fact, nullnessValue);
}
/**
* Change the nullness of a value number.
*
* @param valueNumber the ValueNumber
* @param location Location where information is gained
* @param fact the DefinitelyNullSet to modify
* @param nullnessValue the nullness of the value number
* @throws DataflowAnalysisException
*/
private void changeNullnessOfValue(ValueNumber valueNumber, Location location, DefinitelyNullSet fact, NullnessValue nullnessValue) throws DataflowAnalysisException {
// fact.setValue(valueNumber, isNull);
// if (isNull) {
// fact.addAssignedNullLocation(valueNumber.getNumber(), compactLocationNumbering.getNumber(location));
// } else {
// fact.clearAssignNullLocations(valueNumber.getNumber());
// }
fact.setNullnessValue(valueNumber, nullnessValue);
if (fact.getNulllessValue(valueNumber) != nullnessValue) {
throw new IllegalStateException();
}
// TODO: set location where value becomes null or non-null
}
/* (non-Javadoc)
* @see edu.umd.cs.findbugs.ba.DataflowAnalysis#copy(java.lang.Object, java.lang.Object)
*/
public void copy(DefinitelyNullSet source, DefinitelyNullSet dest) {
dest.makeSameAs(source);
}
/* (non-Javadoc)
* @see edu.umd.cs.findbugs.ba.DataflowAnalysis#createFact()
*/
public DefinitelyNullSet createFact() {
// TODO: optionally create one with null locations
return new DefinitelyNullSet(vnaDataflow.getAnalysis().getNumValuesAllocated());
}
/* (non-Javadoc)
* @see edu.umd.cs.findbugs.ba.DataflowAnalysis#initEntryFact(java.lang.Object)
*/
public void initEntryFact(DefinitelyNullSet result) throws DataflowAnalysisException {
// TODO: parameter annotations?
result.clear();
}
/* (non-Javadoc)
* @see edu.umd.cs.findbugs.ba.DataflowAnalysis#makeFactTop(java.lang.Object)
*/
public void makeFactTop(DefinitelyNullSet fact) {
fact.setTop();
}
public boolean isTop(DefinitelyNullSet fact) {
return fact.isTop();
}
/* (non-Javadoc)
* @see edu.umd.cs.findbugs.ba.DataflowAnalysis#meetInto(java.lang.Object, edu.umd.cs.findbugs.ba.Edge, java.lang.Object)
*/
public void meetInto(DefinitelyNullSet fact, Edge edge, DefinitelyNullSet result) throws DataflowAnalysisException {
// TODO: use edge information (ifnull, ifnonnull, etc.)
result.mergeWith(fact);
}
/* (non-Javadoc)
* @see edu.umd.cs.findbugs.ba.DataflowAnalysis#same(java.lang.Object, java.lang.Object)
*/
public boolean same(DefinitelyNullSet fact1, DefinitelyNullSet fact2) {
return fact1.equals(fact2);
}
// public static void main(String[] args) throws Exception {
// if (args.length != 1) {
// System.err.println("Usage: " + DefinitelyNullSetAnalysis.class.getName() + " <classfile>");
// System.exit(1);
// }
//
// DataflowTestDriver<DefinitelyNullSet, DefinitelyNullSetAnalysis> driver =
// new DataflowTestDriver<DefinitelyNullSet, DefinitelyNullSetAnalysis>() {
// /* (non-Javadoc)
// * @see edu.umd.cs.findbugs.ba.DataflowTestDriver#createDataflow(edu.umd.cs.findbugs.ba.ClassContext, org.apache.bcel.classfile.Method)
// */
// @Override
// public Dataflow<DefinitelyNullSet, DefinitelyNullSetAnalysis> createDataflow(ClassContext classContext, Method method) throws CFGBuilderException, DataflowAnalysisException {
// return classContext.getDefinitelyNullSetDataflow(method);
// }
// };
//
// driver.execute(args[0]);
// }
}