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      1 /*
      2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
      3  *             of Java bytecode.
      4  *
      5  * Copyright (c) 2002-2009 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.classfile.editor;
     22 
     23 import proguard.classfile.*;
     24 import proguard.classfile.attribute.*;
     25 import proguard.classfile.attribute.visitor.AttributeVisitor;
     26 import proguard.classfile.util.SimplifiedVisitor;
     27 
     28 /**
     29  * This AttributeVisitor accumulates specified changes to local variables, and
     30  * then applies these accumulated changes to the code attributes that it visits.
     31  *
     32  * @author Eric  Lafortune
     33  */
     34 public class VariableEditor
     35 extends      SimplifiedVisitor
     36 implements   AttributeVisitor
     37 {
     38     private boolean   modified;
     39 
     40     private boolean[] deleted     = new boolean[ClassConstants.TYPICAL_VARIABLES_SIZE];
     41     private int[]     variableMap = new int[ClassConstants.TYPICAL_VARIABLES_SIZE];
     42 
     43     private final VariableRemapper variableRemapper = new VariableRemapper();
     44 
     45 
     46     /**
     47      * Resets the accumulated code changes.
     48      * @param maxLocals the length of the local variable frame that will be
     49      *                  edited next.
     50      */
     51     public void reset(int maxLocals)
     52     {
     53         // Try to reuse the previous array.
     54         if (deleted.length < maxLocals)
     55         {
     56             deleted = new boolean[maxLocals];
     57         }
     58         else
     59         {
     60             for (int index = 0; index < maxLocals; index++)
     61             {
     62                 deleted[index] = false;
     63             }
     64         }
     65 
     66         modified = false;
     67     }
     68 
     69 
     70     /**
     71      * Remembers to delete the given variable.
     72      * @param variableIndex the index of the variable to be deleted.
     73      */
     74     public void deleteVariable(int variableIndex)
     75     {
     76         deleted[variableIndex] = true;
     77 
     78         modified = true;
     79     }
     80 
     81 
     82     /**
     83      * Returns whether the given variable at the given offset has deleted.
     84      */
     85     public boolean isDeleted(int instructionOffset)
     86     {
     87         return deleted[instructionOffset];
     88     }
     89 
     90 
     91     // Implementations for AttributeVisitor.
     92 
     93     public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
     94 
     95 
     96     public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
     97     {
     98         // Avoid doing any work if nothing is changing anyway.
     99         if (!modified)
    100         {
    101             return;
    102         }
    103 
    104         int oldMaxLocals = codeAttribute.u2maxLocals;
    105 
    106         // Make sure there is a sufficiently large variable map.
    107         if (variableMap.length < oldMaxLocals)
    108         {
    109             variableMap = new int[oldMaxLocals];
    110         }
    111 
    112         // Fill out the variable map.
    113         int newVariableIndex = 0;
    114         for (int oldVariableIndex = 0; oldVariableIndex < oldMaxLocals; oldVariableIndex++)
    115         {
    116             variableMap[oldVariableIndex] = deleted[oldVariableIndex] ?
    117                 -1 : newVariableIndex++;
    118         }
    119 
    120         // Set the map.
    121         variableRemapper.setVariableMap(variableMap);
    122 
    123         // Remap the variables.
    124         variableRemapper.visitCodeAttribute(clazz, method, codeAttribute);
    125 
    126         // Update the length of local variable frame.
    127         codeAttribute.u2maxLocals = newVariableIndex;
    128     }
    129 }
    130