1/* 2 * ProGuard -- shrinking, optimization, obfuscation, and preverification 3 * of Java bytecode. 4 * 5 * Copyright (c) 2002-2009 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 */ 21package proguard.optimize.info; 22 23import proguard.classfile.*; 24import proguard.classfile.attribute.*; 25import proguard.classfile.attribute.visitor.AttributeVisitor; 26import proguard.classfile.instruction.*; 27import proguard.classfile.instruction.visitor.InstructionVisitor; 28import proguard.classfile.util.SimplifiedVisitor; 29 30/** 31 * This AttributeVisitor marks the local variables that are used in the code 32 * attributes that it visits. 33 * 34 * @author Eric Lafortune 35 */ 36public class VariableUsageMarker 37extends SimplifiedVisitor 38implements AttributeVisitor, 39 InstructionVisitor 40{ 41 private boolean[] variableUsed = new boolean[ClassConstants.TYPICAL_VARIABLES_SIZE]; 42 43 44 /** 45 * Returns whether the given variable has been marked as being used. 46 */ 47 public boolean isVariableUsed(int variableIndex) 48 { 49 return variableUsed[variableIndex]; 50 } 51 52 53 // Implementations for AttributeVisitor. 54 55 public void visitAnyAttribute(Clazz clazz, Attribute attribute) {} 56 57 58 public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) 59 { 60 int maxLocals = codeAttribute.u2maxLocals; 61 62 // Try to reuse the previous array. 63 if (variableUsed.length < maxLocals) 64 { 65 variableUsed = new boolean[maxLocals]; 66 } 67 else 68 { 69 for (int index = 0; index < maxLocals; index++) 70 { 71 variableUsed[index] = false; 72 } 73 } 74 75 codeAttribute.instructionsAccept(clazz, method, this); 76 } 77 78 79 // Implementations for InstructionVisitor. 80 81 public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {} 82 83 84 public void visitVariableInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, VariableInstruction variableInstruction) 85 { 86 // Mark the variable. 87 variableUsed[variableInstruction.variableIndex] = true; 88 89 // Account for Category 2 instructions, which take up two entries. 90 if (variableInstruction.isCategory2()) 91 { 92 variableUsed[variableInstruction.variableIndex + 1] = true; 93 } 94 } 95} 96