/* DeadCodeAnalysis Copyright (C) 1999-2002 Jochen Hoenicke.
 *
 * This program 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, or (at your option)
 * any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; see the file COPYING.LESSER.  If not, write to
 * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * $Id$
 */

package jode.decompiler;
import jode.bytecode.BytecodeInfo;
import jode.bytecode.Instruction;
import jode.bytecode.Handler;

import @COLLECTIONS@.Iterator;

public class DeadCodeAnalysis {

    private final static String REACHABLE = "R";
    private final static String REACHCHANGED = "C";

    private static void propagateReachability(BytecodeInfo code) {
	boolean changed;
	do {
	    changed = false;
	    for (Iterator iter = code.getInstructions().iterator(); 
		 iter.hasNext(); ) {
		Instruction instr = (Instruction) iter.next();
		if (instr.getTmpInfo() == REACHCHANGED) {
		    changed = true;
		    instr.setTmpInfo(REACHABLE);
		    Instruction[] succs = instr.getSuccs();
		    if (succs != null)
			for (int i=0; i< succs.length; i++)
			    if (succs[i].getTmpInfo() == null)
				succs[i].setTmpInfo(REACHCHANGED);
		    if (!instr.doesAlwaysJump()
			&& instr.getNextByAddr() != null)
			if (instr.getNextByAddr().getTmpInfo() == null)
			    instr.getNextByAddr().setTmpInfo(REACHCHANGED);
		    /*XXX code after jsr reachable iff ret is reachable...*/
		    if (instr.getOpcode() == Opcodes.opc_jsr)
			if (instr.getNextByAddr().getTmpInfo() == null)
			    instr.getNextByAddr().setTmpInfo(REACHCHANGED);
		}
	    }
	} while (changed);
    }

    public static void removeDeadCode(BytecodeInfo code) {
	((Instruction) code.getInstructions().get(0)).setTmpInfo(REACHCHANGED);
	propagateReachability(code);
	Handler[] handlers = code.getExceptionHandlers();
	boolean changed;
	do {
	    changed = false;
	    for (int i=0; i < handlers.length; i++) {
		if (handlers[i].catcher.getTmpInfo() == null) {
		    /* check if the try block is somewhere reachable 
		     * and mark the catcher as reachable then.
		     */
		    for (Instruction instr = handlers[i].start; 
			 instr != null; instr = instr.getNextByAddr()) {
			if (instr.getTmpInfo() != null) {
			    handlers[i].catcher.setTmpInfo(REACHCHANGED);
			    propagateReachability(code);
			    changed = true;
			    break;
			}
			if (instr == handlers[i].end)
			    break;
		    }
		}
	    }
	} while (changed);

	for (int i=0; i< handlers.length; i++) {
	    /* A handler is not reachable iff the catcher is not reachable */
	    if (handlers[i].catcher.getTmpInfo() == null) {
		/* This is very seldom, so we can make it slow */
		Handler[] newHandlers = new Handler[handlers.length - 1];
		System.arraycopy(handlers, 0, newHandlers, 0, i);
		System.arraycopy(handlers, i+1, newHandlers, i, 
				 handlers.length - (i+1));
		handlers = newHandlers;
		code.setExceptionHandlers(newHandlers);
		i--;
	    } else {
		/* This works! */
		while (handlers[i].start.getTmpInfo() == null) 
		    handlers[i].start = handlers[i].start.getNextByAddr();
		while (handlers[i].end.getTmpInfo() == null) 
		    handlers[i].end = handlers[i].end.getPrevByAddr();
	    }
	}

	/* Now remove the dead code and clean up tmpInfo */
	for (Iterator i = code.getInstructions().iterator(); i.hasNext(); ) {
	    Instruction instr = (Instruction) i.next();
	    if (instr.getTmpInfo() != null)
		instr.setTmpInfo(null);
	    else
		i.remove();
	}
    }
}