soot.toolkits.exceptions.TrapTightener Maven / Gradle / Ivy
/* Soot - a J*va Optimization Framework
* Copyright (C) 2003 John Jorgensen
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 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
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library 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 soot.toolkits.exceptions;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import soot.Body;
import soot.BodyTransformer;
import soot.G;
import soot.Singletons;
import soot.Trap;
import soot.Unit;
import soot.options.Options;
import soot.util.Chain;
import soot.toolkits.graph.ExceptionalUnitGraph;
/**
* A {@link BodyTransformer} that shrinks the protected area covered
* by each {@link Trap} in the {@link Body} so that it begins at the first of
* the {@link Body}'s {@link Unit}s which might throw an exception caught by
* the {@link Trap} and ends just after the last {@link Unit} which might
* throw an exception caught by the {@link Trap}. In the case where none
* of the {@link Unit}s protected by a {@link Trap} can throw the exception
* it catches, the {@link Trap}'s protected area is left completely empty,
* which will likely cause the {@link UnreachableCodeEliminator} to remove the
* {@link Trap} completely.
*
* The {@link TrapTightener} is used to reduce the risk of
* unverifiable code which can result from the use of {@link
* ExceptionalUnitGraph}s from which unrealizable exceptional
* control flow edges have been removed.
*/
public final class TrapTightener extends BodyTransformer {
public TrapTightener( Singletons.Global g ) {}
public static TrapTightener v() { return soot.G.v().soot_toolkits_exceptions_TrapTightener(); }
protected void internalTransform(Body body, String phaseName, Map options) {
if(Options.v().verbose())
G.v().out.println("[" + body.getMethod().getName() + "] Tightening trap boundaries...");
Chain trapChain = body.getTraps();
Chain unitChain = body.getUnits();
if (trapChain.size() > 0) {
ExceptionalUnitGraph graph = new ExceptionalUnitGraph(body);
for (Iterator trapIt = trapChain.iterator(); trapIt.hasNext(); ) {
Trap trap = (Trap) trapIt.next();
Unit firstTrappedUnit = trap.getBeginUnit();
Unit firstTrappedThrower = null;
Unit firstUntrappedUnit = trap.getEndUnit();
Unit lastTrappedUnit =
(Unit) unitChain.getPredOf(firstUntrappedUnit);
Unit lastTrappedThrower = null;
for (Unit u = firstTrappedUnit;
u != null && u != firstUntrappedUnit;
u = (Unit) unitChain.getSuccOf(u)) {
if (mightThrowTo(graph, u, trap)) {
firstTrappedThrower = u;
break;
}
}
if (firstTrappedThrower != null) {
for (Unit u = lastTrappedUnit;
u != null; u = (Unit) unitChain.getPredOf(u)) {
if (mightThrowTo(graph, u, trap)) {
lastTrappedThrower = u;
break;
}
}
}
if (firstTrappedThrower != null &&
firstTrappedUnit != firstTrappedThrower) {
trap.setBeginUnit(firstTrappedThrower);
}
if (lastTrappedThrower == null) {
lastTrappedThrower = firstTrappedUnit;
}
if (lastTrappedUnit != lastTrappedThrower) {
trap.setEndUnit((Unit) unitChain.getSuccOf(lastTrappedThrower));
}
}
}
}
/**
* A utility routine which determines if a particular {@link Unit}
* might throw an exception to a particular {@link Trap}, according to
* the information supplied by a particular control flow graph.
*
* @param g The control flow graph providing information about exceptions.
* @param u The unit being inquired about.
* @param t The trap being inquired about.
* @return true if u might throw an exception caught
* by t, according to g