/*
* ProGuard -- shrinking, optimization, obfuscation, and preverification
* of Java bytecode.
*
* Copyright (c) 2002-2010 Eric Lafortune (eric@graphics.cornell.edu)
*
* 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 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 Public License for
* more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package proguard.optimize.evaluation;
import proguard.classfile.*;
import proguard.classfile.visitor.MemberVisitor;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import proguard.classfile.editor.VariableRemapper;
import proguard.classfile.util.*;
/**
* This AttributeVisitor optimizes variable allocation based on their the liveness,
* in the code attributes that it visits.
*
* @author Eric Lafortune
*/
public class VariableOptimizer
extends SimplifiedVisitor
implements AttributeVisitor
{
//*
private static final boolean DEBUG = false;
/*/
private static boolean DEBUG = true;
//*/
private static final int MAX_VARIABLES_SIZE = 64;
private final boolean reuseThis;
private final MemberVisitor extraVariableMemberVisitor;
private final LivenessAnalyzer livenessAnalyzer = new LivenessAnalyzer();
private final VariableRemapper variableRemapper = new VariableRemapper();
private int[] variableMap = new int[ClassConstants.TYPICAL_VARIABLES_SIZE];
/**
* Creates a new VariableOptimizer.
* @param reuseThis specifies whether the 'this' variable can be reused.
* Many JVMs for JME and IBM's JVMs for JSE can't handle
* such reuse.
*/
public VariableOptimizer(boolean reuseThis)
{
this(reuseThis, null);
}
/**
* Creates a new VariableOptimizer with an extra visitor.
* @param reuseThis specifies whether the 'this' variable
* can be reused. Many JVMs for JME and
* IBM's JVMs for JSE can't handle such
* reuse.
* @param extraVariableMemberVisitor an optional extra visitor for all
* removed variables.
*/
public VariableOptimizer(boolean reuseThis,
MemberVisitor extraVariableMemberVisitor)
{
this.reuseThis = reuseThis;
this.extraVariableMemberVisitor = extraVariableMemberVisitor;
}
// Implementations for AttributeVisitor.
public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
{
// DEBUG =
// clazz.getName().equals("abc/Def") &&
// method.getName(clazz).equals("abc");
// Initialize the global arrays.
initializeArrays(codeAttribute);
// Analyze the liveness of the variables in the code.
livenessAnalyzer.visitCodeAttribute(clazz, method, codeAttribute);
int startIndex =
(method.getAccessFlags() & ClassConstants.INTERNAL_ACC_STATIC) != 0 ||
reuseThis ? 0 : 1;
int parameterSize =
ClassUtil.internalMethodParameterSize(method.getDescriptor(clazz),
method.getAccessFlags());
int variableSize = codeAttribute.u2maxLocals;
int codeLength = codeAttribute.u4codeLength;
boolean remapping = false;
// Loop over all variables.
for (int oldIndex = 0; oldIndex < variableSize; oldIndex++)
{
// By default, the variable will be mapped onto itself.
variableMap[oldIndex] = oldIndex;
// Only try remapping the variable if it's not a parameter.
if (oldIndex >= parameterSize &&
oldIndex < MAX_VARIABLES_SIZE)
{
// Try to remap the variable to a variable with a smaller index.
for (int newIndex = startIndex; newIndex < oldIndex; newIndex++)
{
if (areNonOverlapping(oldIndex, newIndex, codeLength))
{
variableMap[oldIndex] = newIndex;
updateLiveness(oldIndex, newIndex, codeLength);
remapping = true;
// This variable has been remapped. Go to the next one.
break;
}
}
}
}
// Remap the variables.
if (remapping)
{
if (DEBUG)
{
System.out.println("VariableOptimizer: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
for (int index= 0; index < variableSize; index++)
{
System.out.println(" v"+index+" -> "+variableMap[index]);
}
}
variableRemapper.setVariableMap(variableMap);
variableRemapper.visitCodeAttribute(clazz, method, codeAttribute);
// Visit the method, if required.
if (extraVariableMemberVisitor != null)
{
method.accept(clazz, extraVariableMemberVisitor);
}
}
}
// Small utility methods.
/**
* Initializes the global arrays.
*/
private void initializeArrays(CodeAttribute codeAttribute)
{
int codeLength = codeAttribute.u4codeLength;
// Create new arrays for storing information at each instruction offset.
if (variableMap.length < codeLength)
{
variableMap = new int[codeLength];
}
}
/**
* Returns whether the given variables are never alive at the same time.
*/
private boolean areNonOverlapping(int variableIndex1,
int variableIndex2,
int codeLength)
{
// Loop over all instructions.
for (int offset = 0; offset < codeLength; offset++)
{
if ((livenessAnalyzer.isAliveBefore(offset, variableIndex1) &&
livenessAnalyzer.isAliveBefore(offset, variableIndex2)) ||
(livenessAnalyzer.isAliveAfter(offset, variableIndex1) &&
livenessAnalyzer.isAliveAfter(offset, variableIndex2)) ||
// For now, exclude Category 2 variables.
livenessAnalyzer.isCategory2(offset, variableIndex1))
{
return false;
}
}
return true;
}
/**
* Updates the liveness resulting from mapping the given old variable on
* the given new variable.
*/
private void updateLiveness(int oldVariableIndex,
int newVariableIndex,
int codeLength)
{
// Loop over all instructions.
for (int offset = 0; offset < codeLength; offset++)
{
// Update the liveness before the instruction.
if (livenessAnalyzer.isAliveBefore(offset, oldVariableIndex))
{
livenessAnalyzer.setAliveBefore(offset, oldVariableIndex, false);
livenessAnalyzer.setAliveBefore(offset, newVariableIndex, true);
}
// Update the liveness after the instruction.
if (livenessAnalyzer.isAliveAfter(offset, oldVariableIndex))
{
livenessAnalyzer.setAliveAfter(offset, oldVariableIndex, false);
livenessAnalyzer.setAliveAfter(offset, newVariableIndex, true);
}
}
}
}