constantanalysis.java

A static analysis tool to find bugs in Java programs

/*
 * Bytecode Analysis Framework
 * Copyright (C) 2005, 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.constant;

import org.apache.bcel.classfile.Method;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.MethodGen;

import edu.umd.cs.findbugs.ba.BasicBlock;
import edu.umd.cs.findbugs.ba.CFGBuilderException;
import edu.umd.cs.findbugs.ba.ClassContext;
import edu.umd.cs.findbugs.ba.Dataflow;
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.FrameDataflowAnalysis;
import edu.umd.cs.findbugs.ba.Location;

/**
 * Dataflow analysis to find constant values.
 * 
 * @see edu.umd.cs.findbugs.ba.constant.Constant
 * @author David Hovemeyer
 */
public class ConstantAnalysis extends FrameDataflowAnalysis<Constant, ConstantFrame> {
	private MethodGen methodGen;
	private ConstantFrameModelingVisitor visitor;

	public ConstantAnalysis(MethodGen methodGen, DepthFirstSearch dfs) {
		super(dfs);
		this.methodGen = methodGen;
		this.visitor = new ConstantFrameModelingVisitor(methodGen.getConstantPool());
	}

	public ConstantFrame createFact() {
		return new ConstantFrame(methodGen.getMaxLocals());
	}

	public void initEntryFact(ConstantFrame frame) {
		frame.setValid();
		frame.clearStack();
		int numSlots = frame.getNumSlots();
		for (int i = 0; i < numSlots; ++i) {
			frame.setValue(i, new Constant("parameter" + i));
		}
	}

	@Override
		 public void transferInstruction(
			InstructionHandle handle,
			BasicBlock basicBlock,
			ConstantFrame frame) throws DataflowAnalysisException {
		visitor.setFrameAndLocation(frame, new Location(handle, basicBlock));
		visitor.analyzeInstruction(handle.getInstruction());
	}

	public void meetInto(
			ConstantFrame fact,
			Edge edge,
			ConstantFrame result) throws DataflowAnalysisException {

		if (fact.isValid()) {
			ConstantFrame tmpFact = null;

			if (edge.isExceptionEdge()) {
				tmpFact = modifyFrame(fact, tmpFact);
				tmpFact.clearStack();
				tmpFact.pushValue(Constant.NOT_CONSTANT);
			}

			if (tmpFact != null) {
				fact = tmpFact;
			}
		}

		mergeInto(fact, result);
	}

	@Override
		 protected void mergeValues(ConstantFrame otherFrame, ConstantFrame resultFrame, int slot)
			throws DataflowAnalysisException {
		Constant value = Constant.merge(resultFrame.getValue(slot), otherFrame.getValue(slot));
		resultFrame.setValue(slot, value);
	}

	/*
	 * Test driver.
	 */
	public static void main(String[] argv) throws Exception {
		if (argv.length != 1) {
			System.err.println("Usage: " + ConstantAnalysis.class.getName() + " <class file>");
			System.exit(1);
		}

		DataflowTestDriver<ConstantFrame, ConstantAnalysis> driver =
			new DataflowTestDriver<ConstantFrame, ConstantAnalysis>() {
				@Override
								 public Dataflow<ConstantFrame, ConstantAnalysis> createDataflow(
						ClassContext classContext,
						Method method) throws CFGBuilderException, DataflowAnalysisException {
					return classContext.getConstantDataflow(method);
				}
			};

		driver.execute(argv[0]);
	}
}