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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;
     22 
     23 import proguard.classfile.*;
     24 import proguard.classfile.attribute.*;
     25 import proguard.classfile.attribute.visitor.AttributeVisitor;
     26 import proguard.classfile.editor.VariableRemapper;
     27 import proguard.classfile.util.*;
     28 import proguard.classfile.visitor.MemberVisitor;
     29 import proguard.optimize.info.ParameterUsageMarker;
     30 
     31 /**
     32  * This AttributeVisitor 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     //*
     45     private static final boolean DEBUG = false;
     46     /*/
     47     private static       boolean DEBUG = System.getProperty("ps") != null;
     48     //*/
     49 
     50 
     51     private final MemberVisitor extraVariableMemberVisitor;
     52 
     53     private final VariableRemapper variableRemapper = new VariableRemapper();
     54 
     55 
     56     /**
     57      * Creates a new ParameterShrinker.
     58      */
     59     public ParameterShrinker()
     60     {
     61         this(null);
     62     }
     63 
     64 
     65     /**
     66      * Creates a new ParameterShrinker with an extra visitor.
     67      * @param extraVariableMemberVisitor an optional extra visitor for all
     68      *                                   removed parameters.
     69      */
     70     public ParameterShrinker(MemberVisitor extraVariableMemberVisitor)
     71     {
     72         this.extraVariableMemberVisitor = extraVariableMemberVisitor;
     73     }
     74 
     75 
     76     // Implementations for AttributeVisitor.
     77 
     78     public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
     79 
     80 
     81     public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
     82     {
     83         // Get the original parameter size that was saved.
     84         int oldParameterSize = ParameterUsageMarker.getParameterSize(method);
     85 
     86         // Compute the new parameter size from the shrunk descriptor.
     87         int newParameterSize =
     88             ClassUtil.internalMethodParameterSize(method.getDescriptor(clazz),
     89                                                   method.getAccessFlags());
     90 
     91         if (oldParameterSize > newParameterSize)
     92         {
     93             // Get the total size of the local variable frame.
     94             int maxLocals = codeAttribute.u2maxLocals;
     95 
     96             if (DEBUG)
     97             {
     98                 System.out.println("ParameterShrinker: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
     99                 System.out.println("  Old parameter size = " + oldParameterSize);
    100                 System.out.println("  New parameter size = " + newParameterSize);
    101                 System.out.println("  Max locals         = " + maxLocals);
    102             }
    103 
    104             // Create a variable map.
    105             int[] variableMap = new int[maxLocals];
    106 
    107             // Move unused parameters right after the parameter block.
    108             int usedParameterIndex   = 0;
    109             int unusedParameterIndex = newParameterSize;
    110             for (int parameterIndex = 0; parameterIndex < oldParameterSize; parameterIndex++)
    111             {
    112                 // Is the variable required as a parameter?
    113                 if (ParameterUsageMarker.isParameterUsed(method, parameterIndex))
    114                 {
    115                     // Keep the variable as a parameter.
    116                     variableMap[parameterIndex] = usedParameterIndex++;
    117                 }
    118                 else
    119                 {
    120                     if (DEBUG)
    121                     {
    122                         System.out.println("  Deleting parameter #"+parameterIndex);
    123                     }
    124 
    125                     // Shift the variable to the unused parameter block,
    126                     // in case it is still used as a variable.
    127                     variableMap[parameterIndex] = unusedParameterIndex++;
    128 
    129                     // Visit the method, if required.
    130                     if (extraVariableMemberVisitor != null)
    131                     {
    132                         method.accept(clazz, extraVariableMemberVisitor);
    133                     }
    134                 }
    135             }
    136 
    137             // Fill out the remainder of the map.
    138             for (int variableIndex = oldParameterSize; variableIndex < maxLocals; variableIndex++)
    139             {
    140                 variableMap[variableIndex] = variableIndex;
    141             }
    142 
    143             // Set the map.
    144             variableRemapper.setVariableMap(variableMap);
    145 
    146             // Remap the variables.
    147             variableRemapper.visitCodeAttribute(clazz, method, codeAttribute);
    148         }
    149     }
    150 }
    151