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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.info;
     22 
     23 import proguard.classfile.*;
     24 import proguard.classfile.attribute.CodeAttribute;
     25 import proguard.classfile.instruction.*;
     26 import proguard.classfile.instruction.visitor.InstructionVisitor;
     27 import 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  */
     35 public class BackwardBranchMarker
     36 extends      SimplifiedVisitor
     37 implements   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