1 /*
2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
3  *             of Java bytecode.
4  *
5  * Copyright (c) 2002-2014 Eric Lafortune (eric@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.CodeAttributeEditor;
27 import proguard.classfile.instruction.Instruction;
28 import proguard.classfile.instruction.visitor.InstructionVisitor;
29 import proguard.classfile.util.SimplifiedVisitor;
30 
31 /**
32  * This InstructionVisitor deletes blocks of code that can never be reached by
33  * regular calls or branches.
34  *
35  * @author Eric Lafortune
36  */
37 public class UnreachableCodeRemover
38 extends      SimplifiedVisitor
39 implements   AttributeVisitor,
40              InstructionVisitor
41 {
42     //*
43     private static final boolean DEBUG = false;
44     /*/
45     private static       boolean DEBUG = true;
46     //*/
47 
48     private final InstructionVisitor  extraInstructionVisitor;
49 
50     private final ReachableCodeMarker reachableCodeMarker = new ReachableCodeMarker();
51     private final CodeAttributeEditor codeAttributeEditor = new CodeAttributeEditor();
52 
53 
54     /**
55      * Creates a new UnreachableCodeRemover.
56      */
UnreachableCodeRemover()57     public UnreachableCodeRemover()
58     {
59         this(null);
60     }
61 
62 
63     /**
64      * Creates a new UnreachableCodeRemover.
65      * @param extraInstructionVisitor an optional extra visitor for all
66      *                                deleted instructions.
67      */
UnreachableCodeRemover(InstructionVisitor extraInstructionVisitor)68     public UnreachableCodeRemover(InstructionVisitor  extraInstructionVisitor)
69     {
70         this.extraInstructionVisitor = extraInstructionVisitor;
71     }
72 
73 
74     // Implementations for AttributeVisitor.
75 
visitAnyAttribute(Clazz clazz, Attribute attribute)76     public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
77 
78 
visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)79     public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
80     {
81 //        DEBUG =
82 //            clazz.getName().equals("abc/Def") &&
83 //            method.getName(clazz).equals("abc");
84 
85         // TODO: Remove this when the code has stabilized.
86         // Catch any unexpected exceptions from the actual visiting method.
87         try
88         {
89             // Process the code.
90             visitCodeAttribute0(clazz, method, codeAttribute);
91         }
92         catch (RuntimeException ex)
93         {
94             System.err.println("Unexpected error while removing unreachable code:");
95             System.err.println("  Class       = ["+clazz.getName()+"]");
96             System.err.println("  Method      = ["+method.getName(clazz)+method.getDescriptor(clazz)+"]");
97             System.err.println("  Exception   = ["+ex.getClass().getName()+"] ("+ex.getMessage()+")");
98 
99             throw ex;
100         }
101     }
102 
103 
visitCodeAttribute0(Clazz clazz, Method method, CodeAttribute codeAttribute)104     public void visitCodeAttribute0(Clazz clazz, Method method, CodeAttribute codeAttribute)
105     {
106         if (DEBUG)
107         {
108             System.out.println("UnreachableCodeRemover: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
109         }
110 
111         reachableCodeMarker.visitCodeAttribute(clazz, method, codeAttribute);
112 
113         codeAttributeEditor.reset(codeAttribute.u4codeLength);
114 
115         codeAttribute.instructionsAccept(clazz, method, this);
116 
117         codeAttributeEditor.visitCodeAttribute(clazz, method, codeAttribute);
118     }
119 
120 
121     // Implementations for InstructionVisitor.
122 
visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction)123     public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction)
124     {
125         if (DEBUG)
126         {
127             System.out.println("  "+(reachableCodeMarker.isReachable(offset) ? "+" : "-")+" "+instruction.toString(offset));
128         }
129 
130         // Is this instruction unreachable?
131         if (!reachableCodeMarker.isReachable(offset))
132         {
133             // Then delete it.
134             codeAttributeEditor.deleteInstruction(offset);
135 
136             // Visit the instruction, if required.
137             if (extraInstructionVisitor != null)
138             {
139                 instruction.accept(clazz, method, codeAttribute, offset, extraInstructionVisitor);
140             }
141         }
142     }
143 }
144