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.*;
26import proguard.classfile.instruction.*;
27import proguard.classfile.instruction.visitor.InstructionVisitor;
28import proguard.classfile.util.SimplifiedVisitor;
29import proguard.optimize.info.VariableUsageMarker;
30
31/**
32 * This AttributeVisitor cleans up unused variables in all attributes that it
33 * visits.
34 *
35 * @author Eric Lafortune
36 */
37public class VariableCleaner
38extends      SimplifiedVisitor
39implements   AttributeVisitor
40{
41    private final VariableUsageMarker variableUsageMarker = new VariableUsageMarker();
42
43
44    // Implementations for AttributeVisitor.
45
46    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
47
48
49    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
50    {
51        // Figure out the local variables that are used by the code.
52        variableUsageMarker.visitCodeAttribute(clazz, method, codeAttribute);
53
54        // Clean up the variables of the attributes.
55        codeAttribute.attributesAccept(clazz, method, this);
56    }
57
58
59    public void visitLocalVariableTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTableAttribute localVariableTableAttribute)
60    {
61        // Clean up local variables that aren't used.
62        localVariableTableAttribute.u2localVariableTableLength =
63            removeEmptyLocalVariables(localVariableTableAttribute.localVariableTable,
64                                      localVariableTableAttribute.u2localVariableTableLength,
65                                      codeAttribute.u2maxLocals);
66    }
67
68
69    public void visitLocalVariableTypeTableAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute, LocalVariableTypeTableAttribute localVariableTypeTableAttribute)
70    {
71        // Clean up local variables that aren't used.
72        localVariableTypeTableAttribute.u2localVariableTypeTableLength =
73            removeEmptyLocalVariableTypes(localVariableTypeTableAttribute.localVariableTypeTable,
74                                          localVariableTypeTableAttribute.u2localVariableTypeTableLength,
75                                          codeAttribute.u2maxLocals);
76    }
77
78
79    // Small utility methods.
80
81    /**
82     * Returns the given list of local variables, without the ones that aren't
83     * used
84     */
85    private int removeEmptyLocalVariables(LocalVariableInfo[] localVariableInfos,
86                                          int                 localVariableInfoCount,
87                                          int                 maxLocals)
88    {
89        // Overwrite all empty local variable entries.
90        int newIndex = 0;
91        for (int index = 0; index < localVariableInfoCount && index < maxLocals; index++)
92        {
93            if (variableUsageMarker.isVariableUsed(index))
94            {
95                localVariableInfos[newIndex++] = localVariableInfos[index];
96            }
97        }
98
99        // Clean up any remaining array elements.
100        for (int index = newIndex; index < localVariableInfoCount; index++)
101        {
102            localVariableInfos[index] = null;
103        }
104
105        return newIndex;
106    }
107
108
109    /**
110     * Returns the given list of local variable types, without the ones that
111     * aren't used
112     */
113    private int removeEmptyLocalVariableTypes(LocalVariableTypeInfo[] localVariableTypeInfos,
114                                              int                     localVariableTypeInfoCount,
115                                              int                     maxLocals)
116    {
117        // Overwrite all empty local variable type entries.
118        int newIndex = 0;
119        for (int index = 0; index < localVariableTypeInfoCount && index < maxLocals; index++)
120        {
121            if (variableUsageMarker.isVariableUsed(index))
122            {
123                localVariableTypeInfos[newIndex++] = localVariableTypeInfos[index];
124            }
125        }
126
127        // Clean up any remaining array elements.
128        for (int index = newIndex; index < localVariableTypeInfoCount; index++)
129        {
130            localVariableTypeInfos[index] = null;
131        }
132
133        return newIndex;
134    }
135}