1 /* 2 * ProGuard -- shrinking, optimization, obfuscation, and preverification 3 * of Java bytecode. 4 * 5 * Copyright (c) 2002-2013 Eric Lafortune (eric@graphics.cornell.edu) 6 * 7 * This program is free software; you can redistribute it and/or modify it 8 * under the terms of the GNU General Public License as published by the Free 9 * Software Foundation; either version 2 of the License, or (at your option) 10 * any later version. 11 * 12 * This program is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for 15 * more details. 16 * 17 * You should have received a copy of the GNU General Public License along 18 * with this program; if not, write to the Free Software Foundation, Inc., 19 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 20 */ 21 package proguard.optimize.peephole; 22 23 import proguard.classfile.*; 24 import proguard.classfile.attribute.CodeAttribute; 25 import proguard.classfile.editor.CodeAttributeEditor; 26 import proguard.classfile.instruction.*; 27 import proguard.classfile.instruction.visitor.InstructionVisitor; 28 import proguard.classfile.util.SimplifiedVisitor; 29 30 /** 31 * This InstructionVisitor simplifies unconditional branches to other 32 * unconditional branches. 33 * 34 * @author Eric Lafortune 35 */ 36 public class GotoGotoReplacer 37 extends SimplifiedVisitor 38 implements InstructionVisitor 39 { 40 private final CodeAttributeEditor codeAttributeEditor; 41 private final InstructionVisitor extraInstructionVisitor; 42 43 44 /** 45 * Creates a new GotoGotoReplacer. 46 * @param codeAttributeEditor a code editor that can be used for 47 * accumulating changes to the code. 48 */ GotoGotoReplacer(CodeAttributeEditor codeAttributeEditor)49 public GotoGotoReplacer(CodeAttributeEditor codeAttributeEditor) 50 { 51 this(codeAttributeEditor, null); 52 } 53 54 55 /** 56 * Creates a new GotoGotoReplacer. 57 * @param codeAttributeEditor a code editor that can be used for 58 * accumulating changes to the code. 59 * @param extraInstructionVisitor an optional extra visitor for all replaced 60 * goto instructions. 61 */ GotoGotoReplacer(CodeAttributeEditor codeAttributeEditor, InstructionVisitor extraInstructionVisitor)62 public GotoGotoReplacer(CodeAttributeEditor codeAttributeEditor, 63 InstructionVisitor extraInstructionVisitor) 64 { 65 this.codeAttributeEditor = codeAttributeEditor; 66 this.extraInstructionVisitor = extraInstructionVisitor; 67 } 68 69 70 // Implementations for InstructionVisitor. 71 visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction)72 public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {} 73 74 visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction)75 public void visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction) 76 { 77 // Check if the instruction is an unconditional goto instruction. 78 byte opcode = branchInstruction.opcode; 79 if (opcode == InstructionConstants.OP_GOTO || 80 opcode == InstructionConstants.OP_GOTO_W) 81 { 82 // Check if the goto instruction points to another simple goto 83 // instruction. 84 int branchOffset = branchInstruction.branchOffset; 85 int targetOffset = offset + branchOffset; 86 87 if (branchOffset != 0 && 88 branchOffset != branchInstruction.length(offset) && 89 !codeAttributeEditor.isModified(offset) && 90 !codeAttributeEditor.isModified(targetOffset)) 91 { 92 Instruction targetInstruction = 93 InstructionFactory.create(codeAttribute.code, targetOffset); 94 95 if (targetInstruction.opcode == InstructionConstants.OP_GOTO) 96 { 97 // Simplify the goto instruction. 98 int targetBranchOffset = ((BranchInstruction)targetInstruction).branchOffset; 99 100 Instruction newBranchInstruction = 101 new BranchInstruction(opcode, 102 (branchOffset + targetBranchOffset)); 103 codeAttributeEditor.replaceInstruction(offset, 104 newBranchInstruction); 105 106 // Visit the instruction, if required. 107 if (extraInstructionVisitor != null) 108 { 109 extraInstructionVisitor.visitBranchInstruction(clazz, method, codeAttribute, offset, branchInstruction); 110 } 111 } 112 } 113 } 114 } 115 } 116