soot.jimple.toolkits.scalar.pre.EarliestnessComputation Maven / Gradle / Ivy
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/* Soot - a J*va Optimization Framework
* Copyright (C) 2002 Florian Loitsch
*
* 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.
*/
/*
* Modified by the Sable Research Group and others 1997-2002.
* See the 'credits' file distributed with Soot for the complete list of
* contributors. (Soot is distributed at http://www.sable.mcgill.ca/soot)
*/
package soot.jimple.toolkits.scalar.pre;
import soot.*;
import soot.toolkits.scalar.*;
import soot.toolkits.graph.*;
import soot.jimple.*;
import java.util.*;
/**
* Computes the earliest points for the given expressions.
* This basicly finds the highest point in the flow-graph where we can put each
* computation, without introducing new computations on any path.
* More technically: A computation is earliest, if at the current point the
* computation is down-safe, and if either:
*
* - any of the predecessors is not transparent, or
*
- if any predecessors is not "safe" (ie. the insertion of
* this computation would insert it on a path, where it was not before).
*
* Intuitively: If the one predecessor is not transparent, we can't push the
* computation further up. If one of the predecessor is not safe, we would
* introduce a new computation on its path. Hence we can't push further up.
* Note that this computation is linear in the number of units, as we don't need
* to find any fixed-point.
*
* @see UpSafetyAnalysis
* @see DownSafetyAnalysis
*/
public class EarliestnessComputation {
private Map unitToEarliest;
/**
* given an UpSafetyAnalysis and a DownSafetyAnalysis, performs the
* earliest-computation.
*
* @param unitGraph the Unitgraph we'll work on.
* @param upSafe a UpSafetyAnalysis of unitGraph
* @param downSafe a DownSafetyAnalysis of unitGraph
* @param sideEffect the SideEffectTester that will tell if a node is
* transparent or not.
*/
public EarliestnessComputation(UnitGraph unitGraph, UpSafetyAnalysis upSafe,
DownSafetyAnalysis downSafe, SideEffectTester sideEffect) {
this(unitGraph, upSafe, downSafe, sideEffect, new ArraySparseSet());
}
/**
* given an UpSafetyAnalysis and a DownSafetyAnalysis, performs the
* earliest-computation.
* allows to share sets over multiple analyses (set-operations are usually
* more efficient, if the sets come from the same source).
*
* @param unitGraph the Unitgraph we'll work on.
* @param upSafe a UpSafetyAnalysis of unitGraph
* @param downSafe a DownSafetyAnalysis of unitGraph
* @param sideEffect the SideEffectTester that will tell if a node is
* transparent or not.
* @param set the shared set.
*/
public EarliestnessComputation(UnitGraph unitGraph, UpSafetyAnalysis upSafe,
DownSafetyAnalysis downSafe, SideEffectTester sideEffect, FlowSet set) {
unitToEarliest = new HashMap(unitGraph.size() + 1, 0.7f);
Iterator unitIt = unitGraph.iterator();
while (unitIt.hasNext()) {
/* create a new Earliest-list for each unit */
Unit currentUnit = (Unit)unitIt.next();
FlowSet earliest = (FlowSet)set.emptySet();
unitToEarliest.put(currentUnit, earliest);
/* get a copy of the downSafe-set at the current unit */
FlowSet downSafeSet =
((FlowSet)downSafe.getFlowBefore(currentUnit)).clone();
List predList = unitGraph.getPredsOf(currentUnit);
if (predList.size() == 0) { //no predecessor
/* we are obviously at the earliest position for any downsafe
* computation */
earliest.union(downSafeSet);
} else {
Iterator predIt = predList.iterator();
while(predIt.hasNext()) {
Unit predecessor = (Unit)predIt.next();
{ /* if a predecessor is not transparent for a certain computation,
* that is downsafe here, we can't push the computation further up,
* and the earliest computation is before the current point.*/
/* for each element in the downSafe-set, look if it passes through
* the predecessor */
Iterator downSafeIt = downSafeSet.iterator();
while (downSafeIt.hasNext()) {
EquivalentValue equiVal = (EquivalentValue)downSafeIt.next();
Value avail = equiVal.getValue();
if (avail instanceof FieldRef) {
if (sideEffect.unitCanWriteTo(predecessor, avail)) {
earliest.add(equiVal);
downSafeIt.remove();
}
} else {
Iterator usesIt = avail.getUseBoxes().iterator();
// iterate over uses in each avail.
while (usesIt.hasNext()) {
Value use = ((ValueBox)usesIt.next()).getValue();
if (sideEffect.unitCanWriteTo(predecessor, use)) {
earliest.add(equiVal);
downSafeIt.remove();
break;
}
}
}
}
}
{ /* look if one of the expressions is not upsafe and not downsafe in
* one of the predecessors */
Iterator downSafeIt = downSafeSet.iterator();
while (downSafeIt.hasNext()) {
EquivalentValue equiVal = (EquivalentValue)downSafeIt.next();
FlowSet preDown = (FlowSet)downSafe.getFlowBefore(predecessor);
FlowSet preUp = (FlowSet)upSafe.getFlowBefore(predecessor);
if (!preDown.contains(equiVal) && !preUp.contains(equiVal)) {
earliest.add(equiVal);
downSafeIt.remove();
}
}
}
}
}
}
}
/**
* returns the FlowSet of expressions, that have their earliest computation just
* before node.
*
* @param node a Object of the flow-graph (in our case always a unit).
* @return a FlowSet containing the expressions.
*/
public Object getFlowBefore(Object node) {
return unitToEarliest.get(node);
}
}