1/*
2 * ProGuard -- shrinking, optimization, obfuscation, and preverification
3 *             of Java bytecode.
4 *
5 * Copyright (c) 2002-2009 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.info;
22
23import proguard.classfile.*;
24import proguard.classfile.attribute.CodeAttribute;
25import proguard.classfile.instruction.*;
26import proguard.classfile.instruction.visitor.InstructionVisitor;
27import proguard.classfile.util.SimplifiedVisitor;
28
29/**
30 * This InstructionVisitor marks all methods that branch backward in any of the
31 * instructions that it visits.
32 *
33 * @author Eric Lafortune
34 */
35public class BackwardBranchMarker
36extends      SimplifiedVisitor
37implements   InstructionVisitor
38{
39    // Implementations for InstructionVisitor.
40
41    public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
42
43
44    public void visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction)
45    {
46        markBackwardBranch(method, branchInstruction.branchOffset);
47    }
48
49
50    public void visitAnySwitchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, SwitchInstruction switchInstruction)
51    {
52        markBackwardBranch(method, switchInstruction.defaultOffset);
53
54        for (int index = 0; index < switchInstruction.jumpOffsets.length; index++)
55        {
56            markBackwardBranch(method, switchInstruction.jumpOffsets[index]);
57        }
58    }
59
60
61    // Small utility methods.
62
63    /**
64     * Marks the given method if the given branch offset is negative.
65     */
66    private void markBackwardBranch(Method method, int branchOffset)
67    {
68        if (branchOffset < 0)
69        {
70            setBranchesBackward(method);
71        }
72    }
73
74
75    private static void setBranchesBackward(Method method)
76    {
77        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
78        if (info != null)
79        {
80            info.setBranchesBackward();
81        }
82    }
83
84
85    public static boolean branchesBackward(Method method)
86    {
87        MethodOptimizationInfo info = MethodOptimizationInfo.getMethodOptimizationInfo(method);
88        return info == null || info.branchesBackward();
89    }
90}
91