1 /* 2 * ProGuard -- shrinking, optimization, obfuscation, and preverification 3 * of Java bytecode. 4 * 5 * Copyright (c) 2002-2013 Eric Lafortune (eric (at) 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.*; 25 import proguard.classfile.attribute.visitor.*; 26 import proguard.classfile.instruction.*; 27 import proguard.classfile.util.SimplifiedVisitor; 28 import proguard.optimize.info.ExceptionInstructionChecker; 29 30 /** 31 * This AttributeVisitor removes exception handlers that are unreachable in the 32 * code attributes that it visits. 33 * 34 * @author Eric Lafortune 35 */ 36 public class UnreachableExceptionRemover 37 extends SimplifiedVisitor 38 implements AttributeVisitor, 39 ExceptionInfoVisitor 40 { 41 private final ExceptionInfoVisitor extraExceptionInfoVisitor; 42 43 44 private final ExceptionInstructionChecker exceptionInstructionChecker = new ExceptionInstructionChecker(); 45 46 47 /** 48 * Creates a new UnreachableExceptionRemover. 49 */ 50 public UnreachableExceptionRemover() 51 { 52 this(null); 53 } 54 55 56 /** 57 * Creates a new UnreachableExceptionRemover. 58 * @param extraExceptionInfoVisitor an optional extra visitor for all 59 * removed exceptions. 60 */ 61 public UnreachableExceptionRemover(ExceptionInfoVisitor extraExceptionInfoVisitor) 62 { 63 this.extraExceptionInfoVisitor = extraExceptionInfoVisitor; 64 } 65 66 67 // Implementations for AttributeVisitor. 68 69 public void visitAnyAttribute(Clazz clazz, Attribute attribute) {} 70 71 72 public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) 73 { 74 // Go over the exception table. 75 codeAttribute.exceptionsAccept(clazz, method, this); 76 77 // Remove exceptions with empty code blocks. 78 codeAttribute.u2exceptionTableLength = 79 removeEmptyExceptions(codeAttribute.exceptionTable, 80 codeAttribute.u2exceptionTableLength); 81 } 82 83 84 // Implementations for ExceptionInfoVisitor. 85 86 public void visitExceptionInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, ExceptionInfo exceptionInfo) 87 { 88 if (!mayThrowExceptions(clazz, 89 method, 90 codeAttribute, 91 exceptionInfo.u2startPC, 92 exceptionInfo.u2endPC)) 93 { 94 // Make the code block empty. 95 exceptionInfo.u2endPC = exceptionInfo.u2startPC; 96 97 if (extraExceptionInfoVisitor != null) 98 { 99 extraExceptionInfoVisitor.visitExceptionInfo(clazz, method, codeAttribute, exceptionInfo); 100 } 101 } 102 } 103 104 105 // Small utility methods. 106 107 /** 108 * Returns whether the specified block of code may throw exceptions. 109 */ 110 private boolean mayThrowExceptions(Clazz clazz, 111 Method method, 112 CodeAttribute codeAttribute, 113 int startOffset, 114 int endOffset) 115 { 116 byte[] code = codeAttribute.code; 117 118 // Go over all instructions. 119 int offset = startOffset; 120 while (offset < endOffset) 121 { 122 // Get the current instruction. 123 Instruction instruction = InstructionFactory.create(code, offset); 124 125 // Check if it may be throwing exceptions. 126 if (exceptionInstructionChecker.mayThrowExceptions(clazz, 127 method, 128 codeAttribute, 129 offset, 130 instruction)) 131 { 132 return true; 133 } 134 135 // Go to the next instruction. 136 offset += instruction.length(offset); 137 } 138 139 return false; 140 } 141 142 143 /** 144 * Returns the given list of exceptions, without the ones that have empty 145 * code blocks. 146 */ 147 private int removeEmptyExceptions(ExceptionInfo[] exceptionInfos, 148 int exceptionInfoCount) 149 { 150 // Overwrite all empty exceptions. 151 int newIndex = 0; 152 for (int index = 0; index < exceptionInfoCount; index++) 153 { 154 ExceptionInfo exceptionInfo = exceptionInfos[index]; 155 if (exceptionInfo.u2startPC < exceptionInfo.u2endPC) 156 { 157 exceptionInfos[newIndex++] = exceptionInfo; 158 } 159 } 160 161 return newIndex; 162 } 163 } 164