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/*
* ProGuard -- shrinking, optimization, obfuscation, and preverification
* of Java bytecode.
*
* Copyright (c) 2002-2014 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.peephole;
import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import proguard.classfile.editor.VariableEditor;
import proguard.classfile.util.*;
import proguard.classfile.visitor.MemberVisitor;
import proguard.optimize.*;
import proguard.optimize.info.*;
/**
* This MemberVisitor removes unused local variables from the code of the methods
* that it visits.
*
* @see ParameterUsageMarker
* @see MethodStaticizer
* @see MethodDescriptorShrinker
* @author Eric Lafortune
*/
public class VariableShrinker
extends SimplifiedVisitor
implements AttributeVisitor
{
private static final boolean DEBUG = false;
private final MemberVisitor extraVariableMemberVisitor;
private final VariableUsageMarker variableUsageMarker = new VariableUsageMarker();
private final VariableEditor variableEditor = new VariableEditor();
/**
* Creates a new VariableShrinker.
*/
public VariableShrinker()
{
this(null);
}
/**
* Creates a new VariableShrinker with an extra visitor.
* @param extraVariableMemberVisitor an optional extra visitor for all
* removed variables.
*/
public VariableShrinker(MemberVisitor extraVariableMemberVisitor)
{
this.extraVariableMemberVisitor = extraVariableMemberVisitor;
}
// Implementations for AttributeVisitor.
public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
{
if ((method.getAccessFlags() & ClassConstants.ACC_ABSTRACT) == 0)
{
// Compute the parameter size.
int parameterSize =
ClassUtil.internalMethodParameterSize(method.getDescriptor(clazz),
method.getAccessFlags());
// Get the total size of the local variable frame.
int maxLocals = codeAttribute.u2maxLocals;
if (DEBUG)
{
System.out.println("VariableShrinker: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
System.out.println(" Parameter size = " + parameterSize);
System.out.println(" Max locals = " + maxLocals);
}
// Figure out the local variables that are used by the code.
variableUsageMarker.visitCodeAttribute(clazz, method, codeAttribute);
// Delete unused local variables from the local variable frame.
variableEditor.reset(maxLocals);
for (int variableIndex = parameterSize; variableIndex < maxLocals; variableIndex++)
{
// Is the variable not required?
if (!variableUsageMarker.isVariableUsed(variableIndex))
{
if (DEBUG)
{
System.out.println(" Deleting local variable #"+variableIndex);
}
// Delete the unused variable.
variableEditor.deleteVariable(variableIndex);
// Visit the method, if required.
if (extraVariableMemberVisitor != null)
{
method.accept(clazz, extraVariableMemberVisitor);
}
}
}
// Shift all remaining parameters and variables in the byte code.
variableEditor.visitCodeAttribute(clazz, method, codeAttribute);
}
}
}
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