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ProGuardCORE is a free library to read, analyze, modify, and write Java class files.
/*
* ProGuardCORE -- library to process Java bytecode.
*
* Copyright (c) 2002-2020 Guardsquare NV
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package proguard.classfile.editor;
import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import java.util.Arrays;
/**
* This {@link 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
implements AttributeVisitor
{
private LocalVariableTableAttribute localVariableTableAttribute;
private LocalVariableTypeTableAttribute localVariableTypeTableAttribute;
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)
{
localVariableTableAttribute = null;
localVariableTypeTableAttribute = null;
deleteLocalVariableTableAttribute = false;
deleteLocalVariableTypeTableAttribute = false;
// Trim the local variable table and the local variable type table.
codeAttribute.attributesAccept(clazz, method, this);
// Finally, still trim the code blocks of the local variable types,
// based on the code blocks of the local variables, if we have found
// both. The local variable type table may contain fewer entries,
// but the JVM preverifier complains if variables and corresponding
// variable types are inconsistent.
if (localVariableTableAttribute != null &&
localVariableTypeTableAttribute != null)
{
trimLocalVariableTypes(localVariableTableAttribute.localVariableTable,
localVariableTableAttribute.u2localVariableTableLength,
localVariableTypeTableAttribute.localVariableTypeTable,
localVariableTypeTableAttribute.u2localVariableTypeTableLength);
}
// Delete the local variable table if it ended up empty.
if (deleteLocalVariableTableAttribute)
{
AttributesEditor editor =
new AttributesEditor((ProgramClass)clazz,
(ProgramMember)method,
codeAttribute,
true);
editor.deleteAttribute(Attribute.LOCAL_VARIABLE_TABLE);
}
// 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(Attribute.LOCAL_VARIABLE_TYPE_TABLE);
}
}
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;
}
// We still need to remember the attribute.
this.localVariableTableAttribute = localVariableTableAttribute;
}
public void visitLocalVariableTypeTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTypeTableAttribute localVariableTypeTableAttribute)
{
// Clean up local variable types that aren't used.
localVariableTypeTableAttribute.u2localVariableTypeTableLength =
removeUnusedLocalVariableTypes(localVariableTypeTableAttribute.localVariableTypeTable,
localVariableTypeTableAttribute.u2localVariableTypeTableLength,
codeAttribute.u2maxLocals);
// Trim the code blocks of the local variable types.
trimLocalVariableTypes(localVariableTypeTableAttribute.localVariableTypeTable,
localVariableTypeTableAttribute.u2localVariableTypeTableLength,
codeAttribute.u2maxLocals);
// Delete the attribute in a moment, if it is empty.
if (localVariableTypeTableAttribute.u2localVariableTypeTableLength == 0)
{
deleteLocalVariableTypeTableAttribute = true;
}
// We still need to remember the attribute.
this.localVariableTypeTableAttribute = localVariableTypeTableAttribute;
}
// 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.
// Do keep parameter entries.
int newIndex = 0;
for (int index = 0; index < localVariableInfoCount; index++)
{
LocalVariableInfo localVariableInfo = localVariableInfos[index];
if (localVariableInfo.u2index >= 0 &&
localVariableInfo.u2index < maxLocals &&
(localVariableInfo.u2startPC == 0 ||
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.
// Do keep parameter entries.
int newIndex = 0;
for (int index = 0; index < localVariableTypeInfoCount; index++)
{
LocalVariableTypeInfo localVariableTypeInfo = localVariableTypeInfos[index];
if (localVariableTypeInfo.u2index >= 0 &&
localVariableTypeInfo.u2index < maxLocals &&
(localVariableTypeInfo.u2startPC == 0 ||
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 type entries, starting at the last one.
for (int index = localVariableTypeInfoCount-1; index >= 0; index--)
{
LocalVariableTypeInfo localVariableTypeInfo = localVariableTypeInfos[index];
// Make sure the variable type'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;
}
}
/**
* Trims the code blocks of the given list of local variable types, based
* on the given list of local variables.
*/
private void trimLocalVariableTypes(LocalVariableInfo[] localVariableInfos,
int localVariableInfoCount,
LocalVariableTypeInfo[] localVariableTypeInfos,
int localVariableTypeInfoCount)
{
int typeIndex = 0;
// Go over the sorted list of local variables.
for (int index = 0;
index < localVariableInfoCount &&
typeIndex < localVariableTypeInfoCount;
index++)
{
LocalVariableInfo localVariableInfo = localVariableInfos[index];
LocalVariableTypeInfo localVariableTypeInfo = localVariableTypeInfos[typeIndex];
// Do we have a corresponding variable type?
if (localVariableTypeInfo.u2index == localVariableInfo.u2index &&
localVariableTypeInfo.u2startPC == localVariableInfo.u2startPC)
{
// Just copy the length.
localVariableTypeInfo.u2length = localVariableInfo.u2length;
// Continue with the next local variable type.
typeIndex++;
}
}
}
/**
* 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;
}
}
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