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ProGuardCORE is a free library to read, analyze, modify, and write Java class files.
There is a newer version: 9.1.6
/*
 * ProGuardCORE -- library to process Java bytecode.
 *
 * Copyright (c) 2002-2020 Guardsquare NV
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package proguard.classfile.editor;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.util.*;

/**
 * This {@link AttributeVisitor} lets a given instruction visitor edit the code attributes that it
 * visits. The instruction visitor can use a given (optional) branch target finder and code
 * attribute editor, which this class sets up and applies, for convenience.
 *
 * @author Eric Lafortune
 */
public class PeepholeEditor implements AttributeVisitor {
  private final BranchTargetFinder branchTargetFinder;
  private final CodeAttributeEditor codeAttributeEditor;
  private final InstructionVisitor instructionVisitor;

  /**
   * Creates a new PeepholeEditor.
   *
   * @param codeAttributeEditor the code attribute editor that will be reset and then executed.
   * @param instructionVisitor the instruction visitor that performs peephole optimizations using
   *     the above code attribute editor.
   */
  public PeepholeEditor(
      CodeAttributeEditor codeAttributeEditor, InstructionVisitor instructionVisitor) {
    this(null, codeAttributeEditor, instructionVisitor);
  }

  /**
   * Creates a new PeepholeEditor.
   *
   * @param branchTargetFinder branch target finder that will be initialized to indicate branch
   *     targets in the visited code.
   * @param codeAttributeEditor the code attribute editor that will be reset and then executed.
   * @param instructionVisitor the instruction visitor that performs peephole optimizations using
   *     the above code attribute editor.
   */
  public PeepholeEditor(
      BranchTargetFinder branchTargetFinder,
      CodeAttributeEditor codeAttributeEditor,
      InstructionVisitor instructionVisitor) {
    this.branchTargetFinder = branchTargetFinder;
    this.codeAttributeEditor = codeAttributeEditor;
    this.instructionVisitor = instructionVisitor;
  }

  // Implementations for AttributeVisitor.

  public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}

  public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) {
    if (branchTargetFinder != null) {
      // Set up the branch target finder.
      branchTargetFinder.visitCodeAttribute(clazz, method, codeAttribute);
    }

    // Set up the code attribute editor.
    codeAttributeEditor.reset(codeAttribute.u4codeLength);

    // Find the peephole optimizations.
    codeAttribute.instructionsAccept(clazz, method, instructionVisitor);

    // Apply the peephole optimizations.
    codeAttributeEditor.visitCodeAttribute(clazz, method, codeAttribute);
  }
}