NopRemover.java revision cfead78069f3dc32998dc118ee08cab3867acea2 
1/*
2 * ProGuard -- shrinking, optimization, obfuscation, and preverification
3 *             of Java bytecode.
4 *
5 * Copyright (c) 2002-2011 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 */
21package proguard.optimize.peephole;
22
23import proguard.classfile.*;
24import proguard.classfile.attribute.CodeAttribute;
25import proguard.classfile.editor.CodeAttributeEditor;
26import proguard.classfile.instruction.*;
27import proguard.classfile.instruction.visitor.InstructionVisitor;
28import proguard.classfile.util.SimplifiedVisitor;
29
30/**
31 * This InstructionVisitor removes all nop instructions that it encounters.
32 *
33 * @author Eric Lafortune
34 */
35public class NopRemover
36extends      SimplifiedVisitor
37implements   InstructionVisitor
38{
39    private final CodeAttributeEditor codeAttributeEditor;
40    private final InstructionVisitor  extraInstructionVisitor;
41
42
43    /**
44     * Creates a new NopRemover.
45     * @param codeAttributeEditor a code editor that can be used for
46     *                            accumulating changes to the code.
47     */
48    public NopRemover(CodeAttributeEditor codeAttributeEditor)
49    {
50        this(codeAttributeEditor, null);
51    }
52
53
54    /**
55     * Creates a new NopRemover.
56     * @param codeAttributeEditor     a code editor that can be used for
57     *                                accumulating changes to the code.
58     * @param extraInstructionVisitor an optional extra visitor for all removed
59     *                                nop instructions.
60     */
61    public NopRemover(CodeAttributeEditor codeAttributeEditor,
62                      InstructionVisitor  extraInstructionVisitor)
63    {
64        this.codeAttributeEditor     = codeAttributeEditor;
65        this.extraInstructionVisitor = extraInstructionVisitor;
66    }
67
68
69    // Implementations for InstructionVisitor.
70
71    public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
72
73
74    public void visitSimpleInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, SimpleInstruction simpleInstruction)
75    {
76        // Check if the instruction is a nop instruction.
77        if (simpleInstruction.opcode == InstructionConstants.OP_NOP &&
78            !codeAttributeEditor.isModified(offset))
79        {
80            codeAttributeEditor.deleteInstruction(offset);
81
82            // Visit the instruction, if required.
83            if (extraInstructionVisitor != null)
84            {
85                extraInstructionVisitor.visitSimpleInstruction(clazz, method, codeAttribute, offset, simpleInstruction);
86            }
87        }
88    }
89}
90