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/*
* ProGuard -- shrinking, optimization, obfuscation, and preverification
* of Java bytecode.
*
* Copyright (c) 2002-2009 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.*;
import proguard.classfile.instruction.*;
import proguard.classfile.util.SimplifiedVisitor;
import proguard.optimize.info.ExceptionInstructionChecker;
/**
* This AttributeVisitor removes exception handlers that are unreachable in the
* code attributes that it visits.
*
* @author Eric Lafortune
*/
public class UnreachableExceptionRemover
extends SimplifiedVisitor
implements AttributeVisitor,
ExceptionInfoVisitor
{
private final ExceptionInfoVisitor extraExceptionInfoVisitor;
private final ExceptionInstructionChecker exceptionInstructionChecker = new ExceptionInstructionChecker();
/**
* Creates a new UnreachableExceptionRemover.
*/
public UnreachableExceptionRemover()
{
this(null);
}
/**
* Creates a new UnreachableExceptionRemover.
* @param extraExceptionInfoVisitor an optional extra visitor for all
* removed exceptions.
*/
public UnreachableExceptionRemover(ExceptionInfoVisitor extraExceptionInfoVisitor)
{
this.extraExceptionInfoVisitor = extraExceptionInfoVisitor;
}
// Implementations for AttributeVisitor.
public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
{
// Go over the exception table.
codeAttribute.exceptionsAccept(clazz, method, this);
// Remove exceptions with empty code blocks.
codeAttribute.u2exceptionTableLength =
removeEmptyExceptions(codeAttribute.exceptionTable,
codeAttribute.u2exceptionTableLength);
}
// Implementations for ExceptionInfoVisitor.
public void visitExceptionInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, ExceptionInfo exceptionInfo)
{
if (!mayThrowExceptions(clazz,
method,
codeAttribute,
exceptionInfo.u2startPC,
exceptionInfo.u2endPC))
{
// Make the code block empty.
exceptionInfo.u2endPC = exceptionInfo.u2startPC;
if (extraExceptionInfoVisitor != null)
{
extraExceptionInfoVisitor.visitExceptionInfo(clazz, method, codeAttribute, exceptionInfo);
}
}
}
// Small utility methods.
/**
* Returns whether the specified block of code may throw exceptions.
*/
private boolean mayThrowExceptions(Clazz clazz,
Method method,
CodeAttribute codeAttribute,
int startOffset,
int endOffset)
{
byte[] code = codeAttribute.code;
// Go over all instructions.
int offset = startOffset;
while (offset < endOffset)
{
// Get the current instruction.
Instruction instruction = InstructionFactory.create(code, offset);
// Check if it may be throwing exceptions.
if (exceptionInstructionChecker.mayThrowExceptions(clazz,
method,
codeAttribute,
offset,
instruction))
{
return true;
}
// Go to the next instruction.
offset += instruction.length(offset);
}
return false;
}
/**
* Returns the given list of exceptions, without the ones that have empty
* code blocks.
*/
private int removeEmptyExceptions(ExceptionInfo[] exceptionInfos,
int exceptionInfoCount)
{
// Overwrite all empty exceptions.
int newIndex = 0;
for (int index = 0; index < exceptionInfoCount; index++)
{
ExceptionInfo exceptionInfo = exceptionInfos[index];
if (exceptionInfo.u2startPC < exceptionInfo.u2endPC)
{
exceptionInfos[newIndex++] = exceptionInfo;
}
}
return newIndex;
}
}
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