1/*
2 * ProGuard -- shrinking, optimization, obfuscation, and preverification
3 *             of Java bytecode.
4 *
5 * Copyright (c) 2002-2014 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.peephole;
22
23import proguard.classfile.*;
24import proguard.classfile.attribute.*;
25import proguard.classfile.attribute.visitor.AttributeVisitor;
26import proguard.classfile.editor.VariableEditor;
27import proguard.classfile.util.*;
28import proguard.classfile.visitor.MemberVisitor;
29import proguard.optimize.*;
30import proguard.optimize.info.*;
31
32/**
33 * This MemberVisitor removes unused local variables from the code of the methods
34 * that it visits.
35 *
36 * @see ParameterUsageMarker
37 * @see MethodStaticizer
38 * @see MethodDescriptorShrinker
39 * @author Eric Lafortune
40 */
41public class VariableShrinker
42extends      SimplifiedVisitor
43implements   AttributeVisitor
44{
45    private static final boolean DEBUG = false;
46
47
48    private final MemberVisitor extraVariableMemberVisitor;
49
50    private final VariableUsageMarker variableUsageMarker = new VariableUsageMarker();
51    private final VariableEditor      variableEditor      = new VariableEditor();
52
53
54    /**
55     * Creates a new VariableShrinker.
56     */
57    public VariableShrinker()
58    {
59        this(null);
60    }
61
62
63    /**
64     * Creates a new VariableShrinker with an extra visitor.
65     * @param extraVariableMemberVisitor an optional extra visitor for all
66     *                                   removed variables.
67     */
68    public VariableShrinker(MemberVisitor extraVariableMemberVisitor)
69    {
70        this.extraVariableMemberVisitor = extraVariableMemberVisitor;
71    }
72
73
74    // Implementations for AttributeVisitor.
75
76    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
77
78
79    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
80    {
81        if ((method.getAccessFlags() & ClassConstants.ACC_ABSTRACT) == 0)
82        {
83            // Compute the parameter size.
84            int parameterSize =
85                ClassUtil.internalMethodParameterSize(method.getDescriptor(clazz),
86                                                      method.getAccessFlags());
87
88            // Get the total size of the local variable frame.
89            int maxLocals = codeAttribute.u2maxLocals;
90
91            if (DEBUG)
92            {
93                System.out.println("VariableShrinker: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
94                System.out.println("  Parameter size = " + parameterSize);
95                System.out.println("  Max locals     = " + maxLocals);
96            }
97
98            // Figure out the local variables that are used by the code.
99            variableUsageMarker.visitCodeAttribute(clazz, method, codeAttribute);
100
101            // Delete unused local variables from the local variable frame.
102            variableEditor.reset(maxLocals);
103
104            for (int variableIndex = parameterSize; variableIndex < maxLocals; variableIndex++)
105            {
106                // Is the variable not required?
107                if (!variableUsageMarker.isVariableUsed(variableIndex))
108                {
109                    if (DEBUG)
110                    {
111                        System.out.println("  Deleting local variable #"+variableIndex);
112                    }
113
114                    // Delete the unused variable.
115                    variableEditor.deleteVariable(variableIndex);
116
117                    // Visit the method, if required.
118                    if (extraVariableMemberVisitor != null)
119                    {
120                        method.accept(clazz, extraVariableMemberVisitor);
121                    }
122                }
123            }
124
125            // Shift all remaining parameters and variables in the byte code.
126            variableEditor.visitCodeAttribute(clazz, method, codeAttribute);
127        }
128    }
129}
130