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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.CodeAttribute;
import proguard.classfile.editor.CodeAttributeEditor;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.util.SimplifiedVisitor;
/**
* This InstructionVisitor simplifies unconditional branches to other
* unconditional branches.
*
* @author Eric Lafortune
*/
public class GotoGotoReplacer
extends SimplifiedVisitor
implements InstructionVisitor
{
private final CodeAttributeEditor codeAttributeEditor;
private final InstructionVisitor extraInstructionVisitor;
/**
* Creates a new GotoGotoReplacer.
* @param codeAttributeEditor a code editor that can be used for
* accumulating changes to the code.
*/
public GotoGotoReplacer(CodeAttributeEditor codeAttributeEditor)
{
this(codeAttributeEditor, null);
}
/**
* Creates a new GotoGotoReplacer.
* @param codeAttributeEditor a code editor that can be used for
* accumulating changes to the code.
* @param extraInstructionVisitor an optional extra visitor for all replaced
* goto instructions.
*/
public GotoGotoReplacer(CodeAttributeEditor codeAttributeEditor,
InstructionVisitor extraInstructionVisitor)
{
this.codeAttributeEditor = codeAttributeEditor;
this.extraInstructionVisitor = extraInstructionVisitor;
}
// Implementations for InstructionVisitor.
public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
public void visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction)
{
// Check if the instruction is an unconditional goto instruction.
byte opcode = branchInstruction.opcode;
if (opcode == InstructionConstants.OP_GOTO ||
opcode == InstructionConstants.OP_GOTO_W)
{
// Check if the goto instruction points to another simple goto
// instruction.
int branchOffset = branchInstruction.branchOffset;
int targetOffset = offset + branchOffset;
if (branchOffset != branchInstruction.length(offset) &&
!codeAttributeEditor.isModified(offset) &&
!codeAttributeEditor.isModified(targetOffset))
{
Instruction targetInstruction =
InstructionFactory.create(codeAttribute.code, targetOffset);
if (targetInstruction.opcode == InstructionConstants.OP_GOTO)
{
// Simplify the goto instruction.
int targetBranchOffset = ((BranchInstruction)targetInstruction).branchOffset;
Instruction newBranchInstruction =
new BranchInstruction(opcode,
(branchOffset + targetBranchOffset));
codeAttributeEditor.replaceInstruction(offset,
newBranchInstruction);
// Visit the instruction, if required.
if (extraInstructionVisitor != null)
{
extraInstructionVisitor.visitBranchInstruction(clazz, method, codeAttribute, offset, branchInstruction);
}
}
}
}
}
}
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