bb-tools/proguard4.7/src/proguard/classfile/editor/VariableCleaner.java
/*
* ProGuard -- shrinking, optimization, obfuscation, and preverification
* of Java bytecode.
*
* Copyright (c) 2002-2011 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.classfile.editor;
import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import proguard.classfile.util.SimplifiedVisitor;
import java.util.Arrays;
/**
* This AttributeVisitor cleans up variable tables in all code attributes that
* it visits. It trims overlapping local variables. It removes empty local
* variables and empty local variable tables.
*
* @author Eric Lafortune
*/
public class VariableCleaner
extends SimplifiedVisitor
implements AttributeVisitor
{
private boolean deleteLocalVariableTableAttribute;
private boolean deleteLocalVariableTypeTableAttribute;
// Implementations for AttributeVisitor.
public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
{
deleteLocalVariableTableAttribute = false;
deleteLocalVariableTypeTableAttribute = false;
// Trim the local variable table and the local variable type table.
codeAttribute.attributesAccept(clazz, method, this);
// Delete the local variable table if it ended up empty.
if (deleteLocalVariableTableAttribute)
{
AttributesEditor editor =
new AttributesEditor((ProgramClass)clazz,
(ProgramMember)method,
codeAttribute,
true);
editor.deleteAttribute(ClassConstants.ATTR_LocalVariableTable);
}
// Delete the local variable type table if it ended up empty.
if (deleteLocalVariableTypeTableAttribute)
{
AttributesEditor editor =
new AttributesEditor((ProgramClass)clazz,
(ProgramMember)method,
codeAttribute,
true);
editor.deleteAttribute(ClassConstants.ATTR_LocalVariableTypeTable);
}
}
public void visitLocalVariableTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTableAttribute localVariableTableAttribute)
{
// Clean up local variables that aren't used.
localVariableTableAttribute.u2localVariableTableLength =
removeUnusedLocalVariables(localVariableTableAttribute.localVariableTable,
localVariableTableAttribute.u2localVariableTableLength,
codeAttribute.u2maxLocals);
// Trim the code blocks of the local variables.
trimLocalVariables(localVariableTableAttribute.localVariableTable,
localVariableTableAttribute.u2localVariableTableLength,
codeAttribute.u2maxLocals);
// Delete the attribute in a moment, if it is empty.
if (localVariableTableAttribute.u2localVariableTableLength == 0)
{
deleteLocalVariableTableAttribute = true;
}
}
public void visitLocalVariableTypeTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTypeTableAttribute localVariableTypeTableAttribute)
{
// Clean up local variables that aren't used.
localVariableTypeTableAttribute.u2localVariableTypeTableLength =
removeUnusedLocalVariableTypes(localVariableTypeTableAttribute.localVariableTypeTable,
localVariableTypeTableAttribute.u2localVariableTypeTableLength,
codeAttribute.u2maxLocals);
// Trim the code blocks of the local variables.
trimLocalVariableTypes(localVariableTypeTableAttribute.localVariableTypeTable,
localVariableTypeTableAttribute.u2localVariableTypeTableLength,
codeAttribute.u2maxLocals);
// Delete the attribute in a moment, if it is empty.
if (localVariableTypeTableAttribute.u2localVariableTypeTableLength == 0)
{
deleteLocalVariableTypeTableAttribute = true;
}
}
// Small utility methods.
/**
* Returns the given list of local variables, without the ones that aren't
* used.
*/
private int removeUnusedLocalVariables(LocalVariableInfo[] localVariableInfos,
int localVariableInfoCount,
int maxLocals)
{
// Overwrite all empty local variable entries.
int newIndex = 0;
for (int index = 0; index < localVariableInfoCount; index++)
{
LocalVariableInfo localVariableInfo = localVariableInfos[index];
if (localVariableInfo.u2index >= 0 &&
localVariableInfo.u2index < maxLocals &&
localVariableInfo.u2length > 0)
{
localVariableInfos[newIndex++] = localVariableInfos[index];
}
}
// Clean up any remaining array elements.
Arrays.fill(localVariableInfos, newIndex, localVariableInfoCount, null);
return newIndex;
}
/**
* Returns the given list of local variable types, without the ones that
* aren't used.
*/
private int removeUnusedLocalVariableTypes(LocalVariableTypeInfo[] localVariableTypeInfos,
int localVariableTypeInfoCount,
int maxLocals)
{
// Overwrite all empty local variable type entries.
int newIndex = 0;
for (int index = 0; index < localVariableTypeInfoCount; index++)
{
LocalVariableTypeInfo localVariableTypeInfo = localVariableTypeInfos[index];
if (localVariableTypeInfo.u2index >= 0 &&
localVariableTypeInfo.u2index < maxLocals &&
localVariableTypeInfo.u2length > 0)
{
localVariableTypeInfos[newIndex++] = localVariableTypeInfos[index];
}
}
// Clean up any remaining array elements.
Arrays.fill(localVariableTypeInfos, newIndex, localVariableTypeInfoCount, null);
return newIndex;
}
/**
* Sorts the given list of local variables and trims their code blocks
* when necessary. The block is trimmed at the end, which is a bit
* arbitrary.
*/
private void trimLocalVariables(LocalVariableInfo[] localVariableInfos,
int localVariableInfoCount,
int maxLocals)
{
// Sort the local variable entries.
Arrays.sort(localVariableInfos, 0, localVariableInfoCount);
int[] startPCs = createMaxArray(maxLocals);
// Trim the local variable entries, starting at the last one.
for (int index = localVariableInfoCount-1; index >= 0; index--)
{
LocalVariableInfo localVariableInfo = localVariableInfos[index];
// Make sure the variable's code block doesn't overlap with the
// next one for the same variable.
int maxLength = startPCs[localVariableInfo.u2index] -
localVariableInfo.u2startPC;
if (localVariableInfo.u2length > maxLength)
{
localVariableInfo.u2length = maxLength;
}
startPCs[localVariableInfo.u2index] = localVariableInfo.u2startPC;
}
}
/**
* Sorts the given list of local variable types and trims their code blocks
* when necessary. The block is trimmed at the end, which is a bit
* arbitrary.
*/
private void trimLocalVariableTypes(LocalVariableTypeInfo[] localVariableTypeInfos,
int localVariableTypeInfoCount,
int maxLocals)
{
// Sort the local variable entries.
Arrays.sort(localVariableTypeInfos, 0, localVariableTypeInfoCount);
int[] startPCs = createMaxArray(maxLocals);
// Trim the local variable entries, starting at the last one.
for (int index = localVariableTypeInfoCount-1; index >= 0; index--)
{
LocalVariableTypeInfo localVariableTypeInfo = localVariableTypeInfos[index];
// Make sure the variable's code block doesn't overlap with the
// next one for the same variable.
int maxLength = startPCs[localVariableTypeInfo.u2index] -
localVariableTypeInfo.u2startPC;
if (localVariableTypeInfo.u2length > maxLength)
{
localVariableTypeInfo.u2length = maxLength;
}
startPCs[localVariableTypeInfo.u2index] = localVariableTypeInfo.u2startPC;
}
}
/**
* Creates an integer array of the given length, initialized with
* Integer.MAX_VALUE.
*/
private int[] createMaxArray(int length)
{
int[] startPCs = new int[length];
for (int index = 0; index < length; index++)
{
startPCs[index] = Integer.MAX_VALUE;
}
return startPCs;
}
}