You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
120 lines
4.0 KiB
120 lines
4.0 KiB
/* DeadCodeAnalysis Copyright (C) 1999 Jochen Hoenicke.
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU 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 General Public License
|
|
* along with this program; see the file COPYING. 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;
|
|
|
|
public class DeadCodeAnalysis {
|
|
|
|
private final static Object reachable = new Integer(1);
|
|
private final static Object reachChanged = new Integer(2);
|
|
|
|
private static void propagateReachability(Instruction firstInstr,
|
|
Instruction reachInstr) {
|
|
if (reachInstr.tmpInfo != null)
|
|
return;
|
|
reachInstr.tmpInfo = reachChanged;
|
|
boolean changed;
|
|
do {
|
|
changed = false;
|
|
for (Instruction instr = firstInstr;
|
|
instr != null; instr = instr.nextByAddr) {
|
|
if (instr.tmpInfo == reachChanged) {
|
|
changed = true;
|
|
instr.tmpInfo = reachable;
|
|
if (instr.succs != null)
|
|
for (int i=0; i< instr.succs.length; i++)
|
|
if (instr.succs[i].tmpInfo == null)
|
|
instr.succs[i].tmpInfo = reachChanged;
|
|
if (!instr.alwaysJumps && instr.nextByAddr != null)
|
|
if (instr.nextByAddr.tmpInfo == null)
|
|
instr.nextByAddr.tmpInfo = reachChanged;
|
|
/*XXX code after jsr reachable iff ret is reachable...*/
|
|
if (instr.opcode == Opcodes.opc_jsr)
|
|
if (instr.nextByAddr.tmpInfo == null)
|
|
instr.nextByAddr.tmpInfo = reachChanged;
|
|
}
|
|
}
|
|
} while (changed);
|
|
}
|
|
|
|
public static void removeDeadCode(BytecodeInfo code) {
|
|
propagateReachability(code.getFirstInstr(), code.getFirstInstr());
|
|
Handler[] handlers = code.getExceptionHandlers();
|
|
boolean changed;
|
|
do {
|
|
changed = false;
|
|
for (int i=0; i < handlers.length; i++) {
|
|
if (handlers[i].catcher.tmpInfo == 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.nextByAddr) {
|
|
if (instr.tmpInfo != null) {
|
|
propagateReachability(code.getFirstInstr(),
|
|
handlers[i].catcher);
|
|
changed = true;
|
|
break;
|
|
}
|
|
if (instr == handlers[i].end)
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
} while (changed);
|
|
/* Now remove the dead code */
|
|
Instruction nextInstr;
|
|
for (Instruction instr = code.getFirstInstr();
|
|
instr != null; instr = nextInstr) {
|
|
nextInstr = instr.nextByAddr;
|
|
if (instr.tmpInfo == null) {
|
|
instr.removeInstruction();
|
|
/* adjust length, since someone may rely on this */
|
|
/* first block is always reachable, so prevByAddr != null */
|
|
instr.prevByAddr.length += instr.length;
|
|
}
|
|
}
|
|
for (int i=0; i< handlers.length; i++) {
|
|
/* A handler is not reachable iff the catcher is not reachable */
|
|
if (handlers[i].catcher.tmpInfo == 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.tmpInfo == null)
|
|
handlers[i].start = handlers[i].start.nextByAddr;
|
|
while (handlers[i].end.tmpInfo == null)
|
|
handlers[i].end = handlers[i].end.prevByAddr;
|
|
}
|
|
}
|
|
/* clean up tmpInfo */
|
|
for (Instruction instr = code.getFirstInstr();
|
|
instr != null; instr = instr.nextByAddr)
|
|
instr.tmpInfo = null;
|
|
}
|
|
}
|
|
|