soot.jimple.toolkits.scalar.DeadAssignmentEliminator Maven / Gradle / Ivy
package soot.jimple.toolkits.scalar;
/*-
* #%L
* Soot - a J*va Optimization Framework
* %%
* Copyright (C) 1997 - 1999 Raja Vallee-Rai
* %%
* 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 2.1 of the
* License, 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 Lesser Public License for more details.
*
* You should have received a copy of the GNU General Lesser Public
* License along with this program. If not, see
* .
* #L%
*/
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import soot.Body;
import soot.BodyTransformer;
import soot.G;
import soot.IntType;
import soot.Local;
import soot.LongType;
import soot.NullType;
import soot.PhaseOptions;
import soot.RefType;
import soot.Scene;
import soot.Singletons;
import soot.Timers;
import soot.Trap;
import soot.Type;
import soot.Unit;
import soot.UnknownType;
import soot.Value;
import soot.ValueBox;
import soot.jimple.ArrayRef;
import soot.jimple.AssignStmt;
import soot.jimple.BinopExpr;
import soot.jimple.CastExpr;
import soot.jimple.DivExpr;
import soot.jimple.FieldRef;
import soot.jimple.InstanceFieldRef;
import soot.jimple.IntConstant;
import soot.jimple.InvokeExpr;
import soot.jimple.Jimple;
import soot.jimple.LongConstant;
import soot.jimple.NewArrayExpr;
import soot.jimple.NewExpr;
import soot.jimple.NewMultiArrayExpr;
import soot.jimple.NopStmt;
import soot.jimple.NullConstant;
import soot.jimple.RemExpr;
import soot.jimple.Stmt;
import soot.options.Options;
import soot.toolkits.scalar.LocalDefs;
import soot.toolkits.scalar.LocalUses;
import soot.toolkits.scalar.UnitValueBoxPair;
import soot.util.Chain;
public class DeadAssignmentEliminator extends BodyTransformer {
private static final Logger logger = LoggerFactory.getLogger(DeadAssignmentEliminator.class);
public DeadAssignmentEliminator(Singletons.Global g) {
}
public static DeadAssignmentEliminator v() {
return G.v().soot_jimple_toolkits_scalar_DeadAssignmentEliminator();
}
/**
* Eliminates dead code in a linear fashion. Complexity is linear with respect to the statements.
*
* Does not work on grimp code because of the check on the right hand side for side effects.
*/
@Override
protected void internalTransform(Body b, String phaseName, Map options) {
boolean eliminateOnlyStackLocals = PhaseOptions.getBoolean(options, "only-stack-locals");
final Options soptions = Options.v();
if (soptions.verbose()) {
logger.debug("[" + b.getMethod().getName() + "] Eliminating dead code...");
}
if (soptions.time()) {
Timers.v().deadCodeTimer.start();
}
Chain units = b.getUnits();
Deque q = new ArrayDeque(units.size());
// Make a first pass through the statements, noting
// the statements we must absolutely keep.
boolean isStatic = b.getMethod().isStatic();
boolean allEssential = true;
boolean checkInvoke = false;
Local thisLocal = null;
for (Iterator it = units.iterator(); it.hasNext();) {
Unit s = it.next();
boolean isEssential = true;
if (s instanceof NopStmt) {
// Hack: do not remove nop if is is used for a Trap
// which is at the very end of the code.
boolean removeNop = it.hasNext();
if (!removeNop) {
removeNop = true;
for (Trap t : b.getTraps()) {
if (t.getEndUnit() == s) {
removeNop = false;
break;
}
}
}
if (removeNop) {
it.remove();
continue;
}
} else if (s instanceof AssignStmt) {
AssignStmt as = (AssignStmt) s;
Value lhs = as.getLeftOp();
Value rhs = as.getRightOp();
// Stmt is of the form a = a which is useless
if (lhs == rhs && lhs instanceof Local) {
it.remove();
continue;
}
if (lhs instanceof Local
&& (!eliminateOnlyStackLocals || ((Local) lhs).getName().startsWith("$") || lhs.getType() instanceof NullType)) {
isEssential = false;
if (!checkInvoke) {
checkInvoke = as.containsInvokeExpr();
}
if (rhs instanceof CastExpr) {
// CastExpr : can trigger ClassCastException, but null-casts never fail
CastExpr ce = (CastExpr) rhs;
Type t = ce.getCastType();
Value v = ce.getOp();
isEssential = !(v instanceof NullConstant && t instanceof RefType);
} else if (rhs instanceof InvokeExpr || rhs instanceof ArrayRef || rhs instanceof NewExpr
|| rhs instanceof NewArrayExpr || rhs instanceof NewMultiArrayExpr) {
// ArrayRef : can have side effects (like throwing a null pointer exception)
// InvokeExpr : can have side effects (like throwing a null pointer exception)
// NewArrayExpr : can throw exception
// NewMultiArrayExpr : can throw exception
// NewExpr : can trigger class initialization
isEssential = true;
} else if (rhs instanceof FieldRef) {
// Can trigger class initialization
isEssential = true;
if (rhs instanceof InstanceFieldRef) {
InstanceFieldRef ifr = (InstanceFieldRef) rhs;
if (!isStatic && thisLocal == null) {
thisLocal = b.getThisLocal();
}
// Any InstanceFieldRef may have side effects,
// unless the base is reading from 'this'
// in a non-static method
isEssential = (isStatic || thisLocal != ifr.getBase());
}
} else if (rhs instanceof DivExpr || rhs instanceof RemExpr) {
BinopExpr expr = (BinopExpr) rhs;
Type t1 = expr.getOp1().getType();
Type t2 = expr.getOp2().getType();
// Can trigger a division by zero
boolean t2Int = t2 instanceof IntType;
isEssential = t2Int || t1 instanceof IntType || t1 instanceof LongType || t2 instanceof LongType
|| t1 instanceof UnknownType || t2 instanceof UnknownType;
if (isEssential && t2Int) {
Value v = expr.getOp2();
if (v instanceof IntConstant) {
IntConstant i = (IntConstant) v;
isEssential = (i.value == 0);
} else {
isEssential = true; // could be 0, we don't know
}
}
if (isEssential && t2 instanceof LongType) {
Value v = expr.getOp2();
if (v instanceof LongConstant) {
LongConstant l = (LongConstant) v;
isEssential = (l.value == 0);
} else {
isEssential = true; // could be 0, we don't know
}
}
}
}
}
if (isEssential) {
q.addFirst(s);
}
allEssential &= isEssential;
}
if (checkInvoke || !allEssential) {
// Add all the statements which are used to compute values
// for the essential statements, recursively
final LocalDefs localDefs = LocalDefs.Factory.newLocalDefs(b);
if (!allEssential) {
Set essential = new HashSet(b.getUnits().size());
while (!q.isEmpty()) {
Unit s = q.removeFirst();
if (essential.add(s)) {
for (ValueBox box : s.getUseBoxes()) {
Value v = box.getValue();
if (v instanceof Local) {
Local l = (Local) v;
List defs = localDefs.getDefsOfAt(l, s);
if (defs != null) {
q.addAll(defs);
}
}
}
}
}
// Remove the dead statements
units.retainAll(essential);
}
if (checkInvoke) {
final LocalUses localUses = LocalUses.Factory.newLocalUses(b, localDefs);
// Eliminate dead assignments from invokes such as x = f(), where
// x is no longer used
List postProcess = new ArrayList();
for (Unit u : units) {
if (u instanceof AssignStmt) {
AssignStmt s = (AssignStmt) u;
if (s.containsInvokeExpr()) {
// Just find one use of l which is essential
boolean deadAssignment = true;
for (UnitValueBoxPair pair : localUses.getUsesOf(s)) {
if (units.contains(pair.unit)) {
deadAssignment = false;
break;
}
}
if (deadAssignment) {
postProcess.add(s);
}
}
}
}
final Jimple jimple = Jimple.v();
for (AssignStmt s : postProcess) {
// Transform it into a simple invoke.
Stmt newInvoke = jimple.newInvokeStmt(s.getInvokeExpr());
newInvoke.addAllTagsOf(s);
units.swapWith(s, newInvoke);
// If we have a callgraph, we need to fix it
if (Scene.v().hasCallGraph()) {
Scene.v().getCallGraph().swapEdgesOutOf(s, newInvoke);
}
}
}
}
if (soptions.time()) {
Timers.v().deadCodeTimer.end();
}
}
}