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Java > Open Source Codes > proguard > optimize > info > ReadWriteFieldMarker


1 /*
2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
3  * of Java bytecode.
4  *
5  * Copyright (c) 2002-2007 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  */
21 package proguard.optimize.info;
22
23 import proguard.classfile.*;
24 import proguard.classfile.attribute.CodeAttribute;
25 import proguard.classfile.constant.*;
26 import proguard.classfile.constant.visitor.ConstantVisitor;
27 import proguard.classfile.instruction.*;
28 import proguard.classfile.instruction.visitor.InstructionVisitor;
29 import proguard.classfile.util.SimplifiedVisitor;
30 import proguard.classfile.visitor.MemberVisitor;
31
32 /**
33  * This InstructionVisitor marks all fields that are write-only.
34  *
35  * @author Eric Lafortune
36  */
37 public class ReadWriteFieldMarker
38 extends SimplifiedVisitor
39 implements InstructionVisitor,
40              ConstantVisitor,
41              MemberVisitor
42 {
43     // Parameters for the visitor methods.
44 private boolean reading;
45     private boolean writing;
46
47
48     // Implementations for InstructionVisitor.
49
50     public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
51
52
53     public void visitConstantInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, ConstantInstruction constantInstruction)
54     {
55         byte opcode = constantInstruction.opcode;
56
57         // Check for instructions that involve fields.
58 switch (opcode)
59         {
60             case InstructionConstants.OP_LDC:
61             case InstructionConstants.OP_LDC_W:
62                 // Mark the field, if any, as being read from and written to.
63 reading = true;
64                 writing = true;
65                 clazz.constantPoolEntryAccept(constantInstruction.constantIndex, this);
66                 break;
67
68             case InstructionConstants.OP_GETSTATIC:
69             case InstructionConstants.OP_GETFIELD:
70                 // Mark the field as being read from.
71 reading = true;
72                 writing = false;
73                 clazz.constantPoolEntryAccept(constantInstruction.constantIndex, this);
74                 break;
75
76             case InstructionConstants.OP_PUTSTATIC:
77             case InstructionConstants.OP_PUTFIELD:
78                 // Mark the field as being written to.
79 reading = false;
80                 writing = true;
81                 clazz.constantPoolEntryAccept(constantInstruction.constantIndex, this);
82                 break;
83         }
84     }
85
86
87     // Implementations for ConstantVisitor.
88
89     public void visitAnyConstant(Clazz clazz, Constant constant) {}
90
91
92     public void visitStringConstant(Clazz clazz, StringConstant stringConstant)
93     {
94         // Mark the referenced field, if any.
95 stringConstant.referencedMemberAccept(this);
96     }
97
98
99     public void visitFieldrefConstant(Clazz clazz, FieldrefConstant fieldrefConstant)
100     {
101         // Mark the referenced field.
102 fieldrefConstant.referencedMemberAccept(this);
103     }
104
105
106     // Implementations for MemberVisitor.
107
108     public void visitAnyMember(Clazz Clazz, Member member) {}
109
110
111     public void visitProgramField(ProgramClass programClass, ProgramField programField)
112     {
113         // Mark the field if it is being read from.
114 if (reading)
115         {
116             markAsRead(programField);
117         }
118
119         // Mark the field if it is being written to.
120 if (writing)
121         {
122             markAsWritten(programField);
123         }
124     }
125
126
127     // Small utility methods.
128
129     private static void markAsRead(Field field)
130     {
131         FieldOptimizationInfo info = FieldOptimizationInfo.getFieldOptimizationInfo(field);
132         if (info != null)
133         {
134             info.setRead();
135         }
136     }
137
138
139     public static boolean isRead(Field field)
140     {
141         FieldOptimizationInfo info = FieldOptimizationInfo.getFieldOptimizationInfo(field);
142         return info == null ||
143                info.isRead();
144     }
145
146
147     private static void markAsWritten(Field field)
148     {
149         FieldOptimizationInfo info = FieldOptimizationInfo.getFieldOptimizationInfo(field);
150         if (info != null)
151         {
152             info.setWritten();
153         }
154     }
155
156
157     public static boolean isWritten(Field field)
158     {
159         FieldOptimizationInfo info = FieldOptimizationInfo.getFieldOptimizationInfo(field);
160         return info == null ||
161                info.isWritten();
162     }
163 }
164
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