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 */
21package proguard.classfile.editor;
22
23import proguard.classfile.*;
24import proguard.classfile.attribute.*;
25import proguard.classfile.attribute.visitor.AttributeVisitor;
26import proguard.classfile.util.SimplifiedVisitor;
27
28import java.util.Arrays;
29
30/**
31 * This AttributeVisitor accumulates specified changes to local variables, and
32 * then applies these accumulated changes to the code attributes that it visits.
33 *
34 * @author Eric  Lafortune
35 */
36public class VariableEditor
37extends      SimplifiedVisitor
38implements   AttributeVisitor
39{
40    private boolean   modified;
41
42    private boolean[] deleted     = new boolean[ClassConstants.TYPICAL_VARIABLES_SIZE];
43    private int[]     variableMap = new int[ClassConstants.TYPICAL_VARIABLES_SIZE];
44
45    private final VariableRemapper variableRemapper = new VariableRemapper();
46
47
48    /**
49     * Resets the accumulated code changes.
50     * @param maxLocals the length of the local variable frame that will be
51     *                  edited next.
52     */
53    public void reset(int maxLocals)
54    {
55        // Try to reuse the previous array.
56        if (deleted.length < maxLocals)
57        {
58            // Create a new array.
59            deleted = new boolean[maxLocals];
60        }
61        else
62        {
63            // Reset the array.
64            Arrays.fill(deleted, 0, maxLocals, false);
65        }
66
67        modified = false;
68    }
69
70
71    /**
72     * Remembers to delete the given variable.
73     * @param variableIndex the index of the variable to be deleted.
74     */
75    public void deleteVariable(int variableIndex)
76    {
77        deleted[variableIndex] = true;
78
79        modified = true;
80    }
81
82
83    /**
84     * Returns whether the given variable at the given offset has deleted.
85     */
86    public boolean isDeleted(int instructionOffset)
87    {
88        return deleted[instructionOffset];
89    }
90
91
92    // Implementations for AttributeVisitor.
93
94    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
95
96
97    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
98    {
99        // Avoid doing any work if nothing is changing anyway.
100        if (!modified)
101        {
102            return;
103        }
104
105        int oldMaxLocals = codeAttribute.u2maxLocals;
106
107        // Make sure there is a sufficiently large variable map.
108        if (variableMap.length < oldMaxLocals)
109        {
110            variableMap = new int[oldMaxLocals];
111        }
112
113        // Fill out the variable map.
114        int newVariableIndex = 0;
115        for (int oldVariableIndex = 0; oldVariableIndex < oldMaxLocals; oldVariableIndex++)
116        {
117            variableMap[oldVariableIndex] = deleted[oldVariableIndex] ?
118                -1 : newVariableIndex++;
119        }
120
121        // Set the map.
122        variableRemapper.setVariableMap(variableMap);
123
124        // Remap the variables.
125        variableRemapper.visitCodeAttribute(clazz, method, codeAttribute);
126
127        // Update the length of local variable frame.
128        codeAttribute.u2maxLocals = newVariableIndex;
129    }
130}
131