/*
 * 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;

import org.apache.bcel.Constants;
import org.apache.bcel.generic.ConstantPoolGen;
import org.apache.bcel.generic.Instruction;
import org.apache.bcel.generic.InstructionHandle;

/**
 * A really simple forward dataflow analysis to find the depth of
 * the Java operand stack.  This is more of a proof of concept for
 * the dataflow analysis framework than anything useful.
 *
 * @see Dataflow
 * @see DataflowAnalysis
 */
public class StackDepthAnalysis extends ForwardDataflowAnalysis<StackDepth> {
	public static final int TOP = -1;
	public static final int BOTTOM = -2;

	private ConstantPoolGen cpg;

	/**
	 * Constructor.
	 *
	 * @param cpg the ConstantPoolGen of the method whose CFG we're performing the analysis on
	 * @param dfs DepthFirstSearch of the method's CFG
	 */
	public StackDepthAnalysis(ConstantPoolGen cpg, DepthFirstSearch dfs) {
		super(dfs);
		this.cpg = cpg;
	}

	public StackDepth createFact() {
		return new StackDepth(TOP);
	}

	public void makeFactTop(StackDepth fact) {
		fact.setDepth(TOP);
	}
	public boolean isTop(StackDepth fact) {
		return fact.getDepth() == TOP;
	}

	@Override
		 public boolean isFactValid(StackDepth fact) {
		int depth = fact.getDepth();
		return depth != TOP && depth != BOTTOM;
	}

	public void copy(StackDepth source, StackDepth dest) {
		dest.setDepth(source.getDepth());
	}

	public void initEntryFact(StackDepth entryFact) {
		entryFact.setDepth(0); // stack depth == 0 at entry to CFG
	}

	public boolean same(StackDepth fact1, StackDepth fact2) {
		return fact1.getDepth() == fact2.getDepth();
	}

	@Override
		 public void transferInstruction(InstructionHandle handle, BasicBlock basicBlock, StackDepth fact) throws DataflowAnalysisException {
		Instruction ins = handle.getInstruction();
		int produced = ins.produceStack(cpg);
		int consumed = ins.consumeStack(cpg);
		if (produced == Constants.UNPREDICTABLE || consumed == Constants.UNPREDICTABLE)
			throw new IllegalStateException("Unpredictable stack delta for instruction: " + handle);
		int depth = fact.getDepth();
		depth += (produced - consumed);
		if (depth < 0)
			fact.setDepth(BOTTOM);
		else
			fact.setDepth(depth);
	}

	public void meetInto(StackDepth fact, Edge edge, StackDepth result) {
		int a = fact.getDepth();
		int b = result.getDepth();
		int combined;

		if (a == TOP)
			combined = b;
		else if (b == TOP)
			combined = a;
		else if (a == BOTTOM || b == BOTTOM || a != b)
			combined = BOTTOM;
		else
			combined = a;

		result.setDepth(combined);
	}

//	/**
//	 * Command line driver, for testing.
//	 */
//	public static void main(String[] argv) throws Exception {
//		if (argv.length != 1) {
//			System.out.println("Usage: " + StackDepthAnalysis.class.getName() + " <class file>");
//			System.exit(1);
//		}
//
//		DataflowTestDriver<StackDepth, StackDepthAnalysis> driver = new DataflowTestDriver<StackDepth, StackDepthAnalysis>() {
//			@Override
//						 public Dataflow<StackDepth, StackDepthAnalysis> createDataflow(ClassContext classContext, Method method)
//					throws CFGBuilderException, DataflowAnalysisException {
//
//				DepthFirstSearch dfs = classContext.getDepthFirstSearch(method);
//				CFG cfg = classContext.getCFG(method);
//
//				StackDepthAnalysis analysis = new StackDepthAnalysis(classContext.getConstantPoolGen(), dfs);
//				Dataflow<StackDepth, StackDepthAnalysis> dataflow = new Dataflow<StackDepth, StackDepthAnalysis>(cfg, analysis);
//				dataflow.execute();
//
//				return dataflow;
//			}
//		};
//
//		driver.execute(argv[0]);
//	}
}

// vim:ts=4