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118 lines
3.8 KiB
118 lines
3.8 KiB
/* DeadCodeAnalysis Copyright (C) 1999 Jochen Hoenicke.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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* $Id$
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*/
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package jode.decompiler;
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import jode.bytecode.BytecodeInfo;
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import jode.bytecode.Instruction;
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import jode.bytecode.Handler;
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///#def COLLECTIONS java.util
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import java.util.Iterator;
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///#enddef
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public class DeadCodeAnalysis {
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private final static String REACHABLE = "R";
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private final static String REACHCHANGED = "C";
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private static void propagateReachability(BytecodeInfo code) {
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boolean changed;
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do {
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changed = false;
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for (Iterator iter = code.getInstructions().iterator();
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iter.hasNext(); ) {
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Instruction instr = (Instruction) iter.next();
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if (instr.getTmpInfo() == REACHCHANGED) {
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changed = true;
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instr.setTmpInfo(REACHABLE);
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Instruction[] succs = instr.getSuccs();
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if (succs != null)
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for (int i=0; i< succs.length; i++)
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if (succs[i].getTmpInfo() == null)
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succs[i].setTmpInfo(REACHCHANGED);
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if (!instr.doesAlwaysJump()
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&& instr.getNextByAddr() != null)
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if (instr.getNextByAddr().getTmpInfo() == null)
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instr.getNextByAddr().setTmpInfo(REACHCHANGED);
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/*XXX code after jsr reachable iff ret is reachable...*/
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if (instr.getOpcode() == Opcodes.opc_jsr)
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if (instr.getNextByAddr().getTmpInfo() == null)
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instr.getNextByAddr().setTmpInfo(REACHCHANGED);
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}
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}
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} while (changed);
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}
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public static void removeDeadCode(BytecodeInfo code) {
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((Instruction) code.getInstructions().get(0)).setTmpInfo(REACHCHANGED);
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propagateReachability(code);
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Handler[] handlers = code.getExceptionHandlers();
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boolean changed;
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do {
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changed = false;
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for (int i=0; i < handlers.length; i++) {
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if (handlers[i].catcher.getTmpInfo() == null) {
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/* check if the try block is somewhere reachable
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* and mark the catcher as reachable then.
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*/
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for (Instruction instr = handlers[i].start;
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instr != null; instr = instr.getNextByAddr()) {
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if (instr.getTmpInfo() != null) {
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handlers[i].catcher.setTmpInfo(REACHCHANGED);
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propagateReachability(code);
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changed = true;
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break;
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}
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if (instr == handlers[i].end)
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break;
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}
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}
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}
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} while (changed);
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for (int i=0; i< handlers.length; i++) {
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/* A handler is not reachable iff the catcher is not reachable */
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if (handlers[i].catcher.getTmpInfo() == null) {
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/* This is very seldom, so we can make it slow */
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Handler[] newHandlers = new Handler[handlers.length - 1];
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System.arraycopy(handlers, 0, newHandlers, 0, i);
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System.arraycopy(handlers, i+1, newHandlers, i,
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handlers.length - (i+1));
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handlers = newHandlers;
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code.setExceptionHandlers(newHandlers);
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i--;
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} else {
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/* This works! */
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while (handlers[i].start.getTmpInfo() == null)
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handlers[i].start = handlers[i].start.getNextByAddr();
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while (handlers[i].end.getTmpInfo() == null)
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handlers[i].end = handlers[i].end.getPrevByAddr();
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}
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}
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/* Now remove the dead code and clean up tmpInfo */
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for (Iterator i = code.getInstructions().iterator(); i.hasNext(); ) {
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Instruction instr = (Instruction) i.next();
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if (instr.getTmpInfo() != null)
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instr.setTmpInfo(null);
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else
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i.remove();
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}
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}
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}
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