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diff --git a/src/proguard/optimize/info/ReadWriteFieldMarker.java b/src/proguard/optimize/info/ReadWriteFieldMarker.java
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+++ b/src/proguard/optimize/info/ReadWriteFieldMarker.java
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+/*
+ * ProGuard -- shrinking, optimization, obfuscation, and preverification
+ *             of Java bytecode.
+ *
+ * Copyright (c) 2002-2009 Eric Lafortune (eric@graphics.cornell.edu)
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+package proguard.optimize.info;
+
+import proguard.classfile.*;
+import proguard.classfile.attribute.CodeAttribute;
+import proguard.classfile.constant.*;
+import proguard.classfile.constant.visitor.ConstantVisitor;
+import proguard.classfile.instruction.*;
+import proguard.classfile.instruction.visitor.InstructionVisitor;
+import proguard.classfile.util.SimplifiedVisitor;
+import proguard.classfile.visitor.MemberVisitor;
+
+/**
+ * This InstructionVisitor marks all fields that are write-only.
+ *
+ * @author Eric Lafortune
+ */
+public class ReadWriteFieldMarker
+extends      SimplifiedVisitor
+implements   InstructionVisitor,
+             ConstantVisitor,
+             MemberVisitor
+{
+    // Parameters for the visitor methods.
+    private boolean reading = true;
+    private boolean writing = true;
+
+
+    // Implementations for InstructionVisitor.
+
+    public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
+
+
+    public void visitConstantInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, ConstantInstruction constantInstruction)
+    {
+        byte opcode = constantInstruction.opcode;
+
+        // Check for instructions that involve fields.
+        switch (opcode)
+        {
+            case InstructionConstants.OP_LDC:
+            case InstructionConstants.OP_LDC_W:
+                // Mark the field, if any, as being read from and written to.
+                reading = true;
+                writing = true;
+                clazz.constantPoolEntryAccept(constantInstruction.constantIndex, this);
+                break;
+
+            case InstructionConstants.OP_GETSTATIC:
+            case InstructionConstants.OP_GETFIELD:
+                // Mark the field as being read from.
+                reading = true;
+                writing = false;
+                clazz.constantPoolEntryAccept(constantInstruction.constantIndex, this);
+                break;
+
+            case InstructionConstants.OP_PUTSTATIC:
+            case InstructionConstants.OP_PUTFIELD:
+                // Mark the field as being written to.
+                reading = false;
+                writing = true;
+                clazz.constantPoolEntryAccept(constantInstruction.constantIndex, this);
+                break;
+        }
+    }
+
+
+    // Implementations for ConstantVisitor.
+
+    public void visitAnyConstant(Clazz clazz, Constant constant) {}
+
+
+    public void visitStringConstant(Clazz clazz, StringConstant stringConstant)
+    {
+        // Mark the referenced field, if any.
+        stringConstant.referencedMemberAccept(this);
+    }
+
+
+    public void visitFieldrefConstant(Clazz clazz, FieldrefConstant fieldrefConstant)
+    {
+        // Mark the referenced field.
+        fieldrefConstant.referencedMemberAccept(this);
+    }
+
+
+    // Implementations for MemberVisitor.
+
+    public void visitAnyMember(Clazz Clazz, Member member) {}
+
+
+    public void visitProgramField(ProgramClass programClass, ProgramField programField)
+    {
+        // Mark the field if it is being read from.
+        if (reading)
+        {
+            markAsRead(programField);
+        }
+
+        // Mark the field if it is being written to.
+        if (writing)
+        {
+            markAsWritten(programField);
+        }
+    }
+
+
+    // Small utility methods.
+
+    private static void markAsRead(Field field)
+    {
+        FieldOptimizationInfo info = FieldOptimizationInfo.getFieldOptimizationInfo(field);
+        if (info != null)
+        {
+            info.setRead();
+        }
+    }
+
+
+    public static boolean isRead(Field field)
+    {
+        FieldOptimizationInfo info = FieldOptimizationInfo.getFieldOptimizationInfo(field);
+        return info == null ||
+               info.isRead();
+    }
+
+
+    private static void markAsWritten(Field field)
+    {
+        FieldOptimizationInfo info = FieldOptimizationInfo.getFieldOptimizationInfo(field);
+        if (info != null)
+        {
+            info.setWritten();
+        }
+    }
+
+
+    public static boolean isWritten(Field field)
+    {
+        FieldOptimizationInfo info = FieldOptimizationInfo.getFieldOptimizationInfo(field);
+        return info == null ||
+               info.isWritten();
+    }
+}