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Java > Open Source Codes > proguard > optimize > peephole > GotoReturnReplacer


1 /*
2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
3  * of Java bytecode.
4  *
5  * Copyright (c) 2002-2007 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.CodeAttribute;
25 import proguard.classfile.editor.CodeAttributeEditor;
26 import proguard.classfile.instruction.*;
27 import proguard.classfile.instruction.visitor.InstructionVisitor;
28 import proguard.classfile.util.SimplifiedVisitor;
29
30 /**
31  * This InstructionVisitor replaces unconditional branches to return instructions
32  * by these same return instructions.
33  *
34  * @author Eric Lafortune
35  */
36 public class GotoReturnReplacer
37 extends SimplifiedVisitor
38 implements InstructionVisitor
39 {
40     private CodeAttributeEditor codeAttributeEditor;
41     private InstructionVisitor extraInstructionVisitor;
42
43
44     /**
45      * Creates a new GotoReturnReplacer.
46      * @param codeAttributeEditor a code editor that can be used for
47      * accumulating changes to the code.
48      */
49     public GotoReturnReplacer(CodeAttributeEditor codeAttributeEditor)
50     {
51         this(codeAttributeEditor, null);
52     }
53
54
55     /**
56      * Creates a new GotoReturnReplacer.
57      * @param codeAttributeEditor a code editor that can be used for
58      * accumulating changes to the code.
59      * @param extraInstructionVisitor an optional extra visitor for all replaced
60      * goto instructions.
61      */
62     public GotoReturnReplacer(CodeAttributeEditor codeAttributeEditor,
63                               InstructionVisitor extraInstructionVisitor)
64     {
65         this.codeAttributeEditor = codeAttributeEditor;
66         this.extraInstructionVisitor = extraInstructionVisitor;
67     }
68
69
70     // Implementations for InstructionVisitor.
71
72     public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
73
74
75     public void visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction)
76     {
77         // Check if the instruction is an unconditional goto instruction.
78 byte opcode = branchInstruction.opcode;
79         if (opcode == InstructionConstants.OP_GOTO ||
80             opcode == InstructionConstants.OP_GOTO_W)
81         {
82             // Check if the goto instruction points to a return instruction.
83 int targetOffset = offset + branchInstruction.branchOffset;
84
85             if (!codeAttributeEditor.isModified(offset) &&
86                 !codeAttributeEditor.isModified(targetOffset))
87             {
88                 Instruction targetInstruction = InstructionFactory.create(codeAttribute.code,
89                                                                           targetOffset);
90                 switch (targetInstruction.opcode)
91                 {
92                     case InstructionConstants.OP_IRETURN:
93                     case InstructionConstants.OP_LRETURN:
94                     case InstructionConstants.OP_FRETURN:
95                     case InstructionConstants.OP_DRETURN:
96                     case InstructionConstants.OP_ARETURN:
97                     case InstructionConstants.OP_RETURN:
98                         // Replace the goto instruction by the return instruction.
99 Instruction returnInstruction =
100                              new SimpleInstruction(targetInstruction.opcode);
101                         codeAttributeEditor.replaceInstruction(offset,
102                                                                returnInstruction);
103
104                         // Visit the instruction, if required.
105 if (extraInstructionVisitor != null)
106                         {
107                             extraInstructionVisitor.visitBranchInstruction(clazz, method, codeAttribute, offset, branchInstruction);
108                         }
109
110                         break;
111                 }
112             }
113         }
114     }
115 }
116
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