VariableEditor.java revision b72c5c2e5482cf10117b2b25f642f7616b2326c3 
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.classfile.editor;
22
23import proguard.classfile.*;
24import proguard.classfile.attribute.*;
25import proguard.classfile.attribute.visitor.AttributeVisitor;
26import 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 */
34public class VariableEditor
35extends      SimplifiedVisitor
36implements   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