/*
* FindBugs - Find Bugs in Java programs
* Copyright (C) 2006-2007 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.npe;
import org.apache.bcel.generic.InstructionHandle;
import edu.umd.cs.findbugs.ba.BasicAbstractDataflowAnalysis;
import edu.umd.cs.findbugs.ba.BasicBlock;
import edu.umd.cs.findbugs.ba.BlockOrder;
import edu.umd.cs.findbugs.ba.CFG;
import edu.umd.cs.findbugs.ba.DataflowAnalysisException;
import edu.umd.cs.findbugs.ba.DepthFirstSearch;
import edu.umd.cs.findbugs.ba.Edge;
import edu.umd.cs.findbugs.ba.ReverseDFSOrder;
import edu.umd.cs.findbugs.ba.ReverseDepthFirstSearch;
/**
* A dataflow analysis to determine, at each location in a method's CFG, whether
* or not it is possible to return normally at that location.
*
* @author David Hovemeyer
*/
public class ReturnPathTypeAnalysis extends BasicAbstractDataflowAnalysis<ReturnPathType> {
private final CFG cfg;
private final DepthFirstSearch dfs;
private final ReverseDepthFirstSearch rdfs;
/**
* Constructor.
*
* @param cfg
* the method's CFG
* @param rdfs
* a ReverseDepthFirstSearch on the method's CFG
* @param dfs
* a DepthFirstSearch on the method's CFG
*/
public ReturnPathTypeAnalysis(CFG cfg, ReverseDepthFirstSearch rdfs, DepthFirstSearch dfs) {
this.cfg = cfg;
this.dfs = dfs;
this.rdfs = rdfs;
}
@Override
public void copy(ReturnPathType source, ReturnPathType dest) {
dest.copyFrom(source);
}
@Override
public ReturnPathType createFact() {
ReturnPathType fact = new ReturnPathType();
fact.setTop();
return fact;
}
@Override
public void edgeTransfer(Edge edge, ReturnPathType fact) {
// The edges leading into the exit block create the "seed" values
// for the analysis. The exception edges create values indicating
// that a normal (non-exception) return is not possible,
// while the non-exception edges create values indicating that
// a normal return is possible.
if (edge.getTarget() == cfg.getExit()) {
fact.setCanReturnNormally(!edge.isExceptionEdge());
}
}
@Override
public void finishIteration() {
// nothing to do
}
@Override
public BlockOrder getBlockOrder(CFG cfg) {
return new ReverseDFSOrder(cfg, rdfs, dfs);
}
@Override
public int getLastUpdateTimestamp(ReturnPathType fact) {
return 0;
}
/*
* Look up a dataflow value in given map, creating a new (top) fact if no
* fact currently exists.
*
* @param map
* the map
* @param block
* BasicBlock used as key in map
* @return the dataflow fact for the block
*
private ReturnPathType getOrCreateFact(HashMap<BasicBlock, ReturnPathType> map, BasicBlock block) {
ReturnPathType returnPathType = map.get(block);
if (returnPathType == null) {
returnPathType = createFact();
map.put(block, returnPathType);
}
return returnPathType;
}
*/
@Override
public void initEntryFact(ReturnPathType result) throws DataflowAnalysisException {
// By default, we assume that paths reaching the exit block
// can return normally. If we traverse exception edges which
// lead to the exit block, then we'll mark those as "can't return
// normally" (see edgeTransfer() method).
result.setCanReturnNormally(true);
}
@Override
public boolean isForwards() {
return false;
}
@Override
public boolean isTop(ReturnPathType fact) {
return fact.isTop();
}
@Override
public void makeFactTop(ReturnPathType fact) {
fact.setTop();
}
@Override
public void meetInto(ReturnPathType fact, Edge edge, ReturnPathType result) throws DataflowAnalysisException {
result.mergeWith(fact);
}
@Override
public boolean same(ReturnPathType fact1, ReturnPathType fact2) {
return fact1.sameAs(fact2);
}
@Override
public void setLastUpdateTimestamp(ReturnPathType fact, int timestamp) {
// ignore
}
@Override
public void startIteration() {
// nothing to do
}
@Override
public void transfer(BasicBlock basicBlock, InstructionHandle end, ReturnPathType start, ReturnPathType result)
throws DataflowAnalysisException {
// just copy the start fact
result.copyFrom(start);
}
}