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      1 /*
      2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
      3  *             of Java bytecode.
      4  *
      5  * Copyright (c) 2002-2014 Eric Lafortune (eric (at) 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 = true;
     45     private boolean writing = true;
     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