soot.jimple.toolkits.scalar.IdentityOperationEliminator Maven / Gradle / Ivy
package soot.jimple.toolkits.scalar;
/*-
* #%L
* Soot - a J*va Optimization Framework
* %%
* Copyright (C) 1997 - 2018 Raja Vallée-Rai and others
* %%
* 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.Iterator;
import java.util.Map;
import soot.Body;
import soot.BodyTransformer;
import soot.DoubleType;
import soot.FloatType;
import soot.G;
import soot.IntType;
import soot.LongType;
import soot.Singletons;
import soot.Type;
import soot.Unit;
import soot.Value;
import soot.jimple.AddExpr;
import soot.jimple.AssignStmt;
import soot.jimple.BinopExpr;
import soot.jimple.DoubleConstant;
import soot.jimple.FloatConstant;
import soot.jimple.IntConstant;
import soot.jimple.LongConstant;
import soot.jimple.MulExpr;
import soot.jimple.OrExpr;
import soot.jimple.SubExpr;
/**
* Transformer that eliminates unnecessary logic operations such as
*
* $z0 = a | 0
*
* which can more easily be repesented as
*
* $z0 = a
*
* @author Steven Arzt
*
*/
public class IdentityOperationEliminator extends BodyTransformer {
public IdentityOperationEliminator(Singletons.Global g) {
}
public static IdentityOperationEliminator v() {
return G.v().soot_jimple_toolkits_scalar_IdentityOperationEliminator();
}
@Override
protected void internalTransform(Body b, String phaseName, Map options) {
for (Iterator unitIt = b.getUnits().iterator(); unitIt.hasNext();) {
Unit u = unitIt.next();
if (u instanceof AssignStmt) {
AssignStmt assignStmt = (AssignStmt) u;
// a = b + 0 --> a = b
// a = 0 + b --> a = b
if (assignStmt.getRightOp() instanceof AddExpr) {
BinopExpr aer = (BinopExpr) assignStmt.getRightOp();
if (isConstZero(aer.getOp1())) {
assignStmt.setRightOp(aer.getOp2());
} else if (isConstZero(aer.getOp2())) {
assignStmt.setRightOp(aer.getOp1());
}
}
// a = b - 0 --> a = b
if (assignStmt.getRightOp() instanceof SubExpr) {
BinopExpr aer = (BinopExpr) assignStmt.getRightOp();
if (isConstZero(aer.getOp2())) {
assignStmt.setRightOp(aer.getOp1());
}
}
// a = b * 0 --> a = 0
// a = 0 * b --> a = 0
if (assignStmt.getRightOp() instanceof MulExpr) {
BinopExpr aer = (BinopExpr) assignStmt.getRightOp();
if (isConstZero(aer.getOp1())) {
assignStmt.setRightOp(getZeroConst(assignStmt.getLeftOp().getType()));
} else if (isConstZero(aer.getOp2())) {
assignStmt.setRightOp(getZeroConst(assignStmt.getLeftOp().getType()));
}
}
// a = b | 0 --> a = b
// a = 0 | b --> a = b
if (assignStmt.getRightOp() instanceof OrExpr) {
OrExpr orExpr = (OrExpr) assignStmt.getRightOp();
if (isConstZero(orExpr.getOp1())) {
assignStmt.setRightOp(orExpr.getOp2());
} else if (isConstZero(orExpr.getOp2())) {
assignStmt.setRightOp(orExpr.getOp1());
}
}
}
}
// In a second step, we remove assingments such as
for (Iterator unitIt = b.getUnits().iterator(); unitIt.hasNext();) {
Unit u = unitIt.next();
if (u instanceof AssignStmt) {
AssignStmt assignStmt = (AssignStmt) u;
if (assignStmt.getLeftOp() == assignStmt.getRightOp()) {
unitIt.remove();
}
}
}
}
/**
* Gets the constant value 0 with the given type (integer, float, etc.)
*
* @param type
* The type for which to get the constant zero value
* @return The constant zero value of the given type
*/
private Value getZeroConst(Type type) {
if (type instanceof IntType) {
return IntConstant.v(0);
} else if (type instanceof LongType) {
return LongConstant.v(0);
} else if (type instanceof FloatType) {
return FloatConstant.v(0);
} else if (type instanceof DoubleType) {
return DoubleConstant.v(0);
}
throw new RuntimeException("Unsupported numeric type");
}
/**
* Checks whether the given value is the constant integer 0
*
* @param op
* The value to check
* @return True if the given value is the constant integer 0, otherwise false
*/
private boolean isConstZero(Value op) {
if (op instanceof IntConstant) {
IntConstant ic = (IntConstant) op;
return ic.value == 0;
}
return false;
}
}