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      1 /*
      2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
      3  *             of Java bytecode.
      4  *
      5  * Copyright (c) 2002-2009 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;
     22 
     23 import proguard.classfile.*;
     24 import proguard.classfile.attribute.*;
     25 import proguard.classfile.attribute.visitor.AttributeVisitor;
     26 import proguard.classfile.editor.*;
     27 import proguard.classfile.util.*;
     28 import proguard.classfile.visitor.MemberVisitor;
     29 import proguard.optimize.info.ParameterUsageMarker;
     30 
     31 /**
     32  * This MemberVisitor removes unused parameters from the code of the methods
     33  * that it visits.
     34  *
     35  * @see ParameterUsageMarker
     36  * @see MethodStaticizer
     37  * @see MethodDescriptorShrinker
     38  * @author Eric Lafortune
     39  */
     40 public class ParameterShrinker
     41 extends      SimplifiedVisitor
     42 implements   AttributeVisitor
     43 {
     44     private static final boolean DEBUG = false;
     45 
     46 
     47     private final MemberVisitor extraVariableMemberVisitor;
     48 
     49     private final VariableRemapper variableRemapper = new VariableRemapper();
     50 
     51 
     52     /**
     53      * Creates a new ParameterShrinker.
     54      */
     55     public ParameterShrinker()
     56     {
     57         this(null);
     58     }
     59 
     60 
     61     /**
     62      * Creates a new ParameterShrinker with an extra visitor.
     63      * @param extraVariableMemberVisitor an optional extra visitor for all
     64      *                                   removed parameters.
     65      */
     66     public ParameterShrinker(MemberVisitor extraVariableMemberVisitor)
     67     {
     68         this.extraVariableMemberVisitor = extraVariableMemberVisitor;
     69     }
     70 
     71 
     72     // Implementations for AttributeVisitor.
     73 
     74     public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
     75 
     76 
     77     public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
     78     {
     79         // Get the original parameter size that was saved.
     80         int oldParameterSize = ParameterUsageMarker.getParameterSize(method);
     81 
     82         // Compute the new parameter size from the shrunk descriptor.
     83         int newParameterSize =
     84             ClassUtil.internalMethodParameterSize(method.getDescriptor(clazz),
     85                                                   method.getAccessFlags());
     86 
     87         if (oldParameterSize > newParameterSize)
     88         {
     89             // Get the total size of the local variable frame.
     90             int maxLocals = codeAttribute.u2maxLocals;
     91 
     92             if (DEBUG)
     93             {
     94                 System.out.println("ParameterShrinker: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
     95                 System.out.println("  Old parameter size = " + oldParameterSize);
     96                 System.out.println("  New parameter size = " + newParameterSize);
     97                 System.out.println("  Max locals         = " + maxLocals);
     98             }
     99 
    100             // Create a variable map.
    101             int[] variableMap = new int[maxLocals];
    102 
    103             // Move unused parameters right after the parameter block.
    104             int usedParameterIndex   = 0;
    105             int unusedParameterIndex = newParameterSize;
    106             for (int parameterIndex = 0; parameterIndex < oldParameterSize; parameterIndex++)
    107             {
    108                 // Is the variable required as a parameter?
    109                 if (ParameterUsageMarker.isParameterUsed(method, parameterIndex))
    110                 {
    111                     // Keep the variable as a parameter.
    112                     variableMap[parameterIndex] = usedParameterIndex++;
    113                 }
    114                 else
    115                 {
    116                     if (DEBUG)
    117                     {
    118                         System.out.println("  Deleting parameter #"+parameterIndex);
    119                     }
    120 
    121                     // Shift the variable to the unused parameter block,
    122                     // in case it is still used as a variable.
    123                     variableMap[parameterIndex] = unusedParameterIndex++;
    124 
    125                     // Visit the method, if required.
    126                     if (extraVariableMemberVisitor != null)
    127                     {
    128                         method.accept(clazz, extraVariableMemberVisitor);
    129                     }
    130                 }
    131             }
    132 
    133             // Fill out the remainder of the map.
    134             for (int variableIndex = oldParameterSize; variableIndex < maxLocals; variableIndex++)
    135             {
    136                 variableMap[variableIndex] = variableIndex;
    137             }
    138 
    139             // Set the map.
    140             variableRemapper.setVariableMap(variableMap);
    141 
    142             // Remap the variables.
    143             variableRemapper.visitCodeAttribute(clazz, method, codeAttribute);
    144         }
    145     }
    146 }
    147