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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.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.visitor.InstructionVisitor;
     28 import proguard.classfile.util.SimplifiedVisitor;
     29 
     30 /**
     31  * This AttributeVisitor sets up and applies the peephole optimizations of its
     32  * instruction visitor. The instruction visitor should be using the same
     33  * (optional) branch target finder and code attribute editor.
     34  *
     35  * @author Eric Lafortune
     36  */
     37 public class PeepholeOptimizer
     38 extends      SimplifiedVisitor
     39 implements   AttributeVisitor
     40 {
     41     private final BranchTargetFinder  branchTargetFinder;
     42     private final CodeAttributeEditor codeAttributeEditor;
     43     private final InstructionVisitor  instructionVisitor;
     44 
     45 
     46     /**
     47      * Creates a new PeepholeOptimizer.
     48      * @param codeAttributeEditor the code attribute editor that will be reset
     49      *                            and then executed.
     50      * @param instructionVisitor  the instruction visitor that performs
     51      *                            peephole optimizations using the above code
     52      *                            attribute editor.
     53      */
     54     public PeepholeOptimizer(CodeAttributeEditor codeAttributeEditor,
     55                              InstructionVisitor  instructionVisitor)
     56     {
     57         this(null, codeAttributeEditor, instructionVisitor);
     58     }
     59 
     60 
     61     /**
     62      * Creates a new PeepholeOptimizer.
     63      * @param branchTargetFinder  branch target finder that will be initialized
     64      *                            to indicate branch targets in the visited code.
     65      * @param codeAttributeEditor the code attribute editor that will be reset
     66      *                            and then executed.
     67      * @param instructionVisitor  the instruction visitor that performs
     68      *                            peephole optimizations using the above code
     69      *                            attribute editor.
     70      */
     71     public PeepholeOptimizer(BranchTargetFinder  branchTargetFinder,
     72                              CodeAttributeEditor codeAttributeEditor,
     73                              InstructionVisitor  instructionVisitor)
     74     {
     75         this.branchTargetFinder  = branchTargetFinder;
     76         this.codeAttributeEditor = codeAttributeEditor;
     77         this.instructionVisitor  = instructionVisitor;
     78     }
     79 
     80 
     81     // Implementations for AttributeVisitor.
     82 
     83     public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
     84 
     85 
     86     public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
     87     {
     88         if (branchTargetFinder != null)
     89         {
     90             // Set up the branch target finder.
     91             branchTargetFinder.visitCodeAttribute(clazz, method, codeAttribute);
     92         }
     93 
     94         // Set up the code attribute editor.
     95         codeAttributeEditor.reset(codeAttribute.u4codeLength);
     96 
     97         // Find the peephole optimizations.
     98         codeAttribute.instructionsAccept(clazz, method, instructionVisitor);
     99 
    100         // Apply the peephole optimizations.
    101         codeAttributeEditor.visitCodeAttribute(clazz, method, codeAttribute);
    102     }
    103 }
    104