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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.peephole;
     22 
     23 import proguard.classfile.*;
     24 import proguard.classfile.attribute.*;
     25 import proguard.classfile.attribute.visitor.AttributeVisitor;
     26 import proguard.classfile.editor.VariableEditor;
     27 import proguard.classfile.util.*;
     28 import proguard.classfile.visitor.MemberVisitor;
     29 import proguard.optimize.*;
     30 import proguard.optimize.info.*;
     31 
     32 /**
     33  * This MemberVisitor removes unused local variables from the code of the methods
     34  * that it visits.
     35  *
     36  * @see ParameterUsageMarker
     37  * @see MethodStaticizer
     38  * @see MethodDescriptorShrinker
     39  * @author Eric Lafortune
     40  */
     41 public class VariableShrinker
     42 extends      SimplifiedVisitor
     43 implements   AttributeVisitor
     44 {
     45     private static final boolean DEBUG = false;
     46 
     47 
     48     private final MemberVisitor extraVariableMemberVisitor;
     49 
     50     private final VariableUsageMarker variableUsageMarker = new VariableUsageMarker();
     51     private final VariableEditor      variableEditor      = new VariableEditor();
     52 
     53 
     54     /**
     55      * Creates a new VariableShrinker.
     56      */
     57     public VariableShrinker()
     58     {
     59         this(null);
     60     }
     61 
     62 
     63     /**
     64      * Creates a new VariableShrinker with an extra visitor.
     65      * @param extraVariableMemberVisitor an optional extra visitor for all
     66      *                                   removed variables.
     67      */
     68     public VariableShrinker(MemberVisitor extraVariableMemberVisitor)
     69     {
     70         this.extraVariableMemberVisitor = extraVariableMemberVisitor;
     71     }
     72 
     73 
     74     // Implementations for AttributeVisitor.
     75 
     76     public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
     77 
     78 
     79     public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
     80     {
     81         if ((method.getAccessFlags() & ClassConstants.ACC_ABSTRACT) == 0)
     82         {
     83             // Compute the parameter size.
     84             int parameterSize =
     85                 ClassUtil.internalMethodParameterSize(method.getDescriptor(clazz),
     86                                                       method.getAccessFlags());
     87 
     88             // Get the total size of the local variable frame.
     89             int maxLocals = codeAttribute.u2maxLocals;
     90 
     91             if (DEBUG)
     92             {
     93                 System.out.println("VariableShrinker: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
     94                 System.out.println("  Parameter size = " + parameterSize);
     95                 System.out.println("  Max locals     = " + maxLocals);
     96             }
     97 
     98             // Figure out the local variables that are used by the code.
     99             variableUsageMarker.visitCodeAttribute(clazz, method, codeAttribute);
    100 
    101             // Delete unused local variables from the local variable frame.
    102             variableEditor.reset(maxLocals);
    103 
    104             for (int variableIndex = parameterSize; variableIndex < maxLocals; variableIndex++)
    105             {
    106                 // Is the variable not required?
    107                 if (!variableUsageMarker.isVariableUsed(variableIndex))
    108                 {
    109                     if (DEBUG)
    110                     {
    111                         System.out.println("  Deleting local variable #"+variableIndex);
    112                     }
    113 
    114                     // Delete the unused variable.
    115                     variableEditor.deleteVariable(variableIndex);
    116 
    117                     // Visit the method, if required.
    118                     if (extraVariableMemberVisitor != null)
    119                     {
    120                         method.accept(clazz, extraVariableMemberVisitor);
    121                     }
    122                 }
    123             }
    124 
    125             // Shift all remaining parameters and variables in the byte code.
    126             variableEditor.visitCodeAttribute(clazz, method, codeAttribute);
    127         }
    128     }
    129 }
    130