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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.util;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.*;
import proguard.classfile.editor.*;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.visitor.ClassVisitor;
import proguard.evaluation.*;
import proguard.evaluation.value.*;

/**
 * This {@link ClassVisitor} replaces array initialization instructions with optimized primitive
 * array constants.
 *
 * These constants are not supported by any Java specification and therefore only for internal
 * use.
 *
 * @see PrimitiveArrayConstantReplacer
 * @author Thomas Neidhart
 */
public class ArrayInitializationReplacer
    implements ClassVisitor,

        // Implementation interfaces.
        AttributeVisitor,
        InstructionVisitor {
  private final ValueFactory valueFactory =
      new ParticularValueFactory(new BasicValueFactory(), new BasicValueFactory());
  private final PartialEvaluator partialEvaluator =
      new PartialEvaluator(valueFactory, new BasicInvocationUnit(valueFactory), true);
  private final ArrayInitializationMatcher arrayInitializationMatcher =
      new ArrayInitializationMatcher(partialEvaluator);
  private final CodeAttributeEditor codeAttributeEditor = new CodeAttributeEditor();

  private ConstantPoolEditor constantPoolEditor;
  private int lastInstructionOffset;
  private int lastInstructionStackPushCount;
  private int arrayInitializationStart;
  private int arrayInitializationEnd;

  // Implementations for ClassVisitor.

  @Override
  public void visitAnyClass(Clazz clazz) {}

  @Override
  public void visitProgramClass(ProgramClass programClass) {
    constantPoolEditor = new ConstantPoolEditor(programClass);

    // Visit all methods that have "NEWARRAY" instructions.
    programClass.methodsAccept(new AllAttributeVisitor(new ArrayInitializationFilter(this)));
  }

  // Implementations for AttributeVisitor.

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

  public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) {
    codeAttributeEditor.reset(codeAttribute.u4codeLength);

    partialEvaluator.visitCodeAttribute(clazz, method, codeAttribute);

    lastInstructionOffset = -1;
    lastInstructionStackPushCount = -1;
    arrayInitializationStart = -1;
    arrayInitializationEnd = -1;
    codeAttribute.instructionsAccept(clazz, method, this);

    if (codeAttributeEditor.isModified()) {
      codeAttributeEditor.visitCodeAttribute(clazz, method, codeAttribute);
    }
  }

  // Implementations for InstructionVisitor.

  public void visitAnyInstruction(
      Clazz clazz,
      Method method,
      CodeAttribute codeAttribute,
      int offset,
      Instruction instruction) {
    // Verify that the previous instruction pushed the array size on the
    // stack: the java compiler will always do so, but obfuscators may
    // have reordered the instructions.
    if (instruction.opcode == Instruction.OP_NEWARRAY && lastInstructionStackPushCount == 1) {
      if (arrayInitializationMatcher.matchesArrayInitialization(
          clazz, method, codeAttribute, offset, (SimpleInstruction) instruction)) {
        Object values = arrayInitializationMatcher.array();
        int constantIndex = constantPoolEditor.addPrimitiveArrayConstant(values);

        // We need to replace the previous instruction, which pushes
        // the array length onto the stack.
        codeAttributeEditor.replaceInstruction(
            lastInstructionOffset, new ConstantInstruction(Instruction.OP_LDC, constantIndex));

        // Remove the newarray instruction itself.
        codeAttributeEditor.deleteInstruction(offset);

        // Mark the start/end of the array initialization sequence.
        arrayInitializationStart = arrayInitializationMatcher.arrayInitializationStart();
        arrayInitializationEnd = arrayInitializationMatcher.arrayInitializationEnd();
      }
    }

    // Remove any instruction inside the array initialization sequence.
    if (arrayInitializationEnd != -1
        && offset >= arrayInitializationStart
        && offset <= arrayInitializationEnd) {
      codeAttributeEditor.deleteInstruction(offset);
    }

    lastInstructionOffset = offset;
    lastInstructionStackPushCount = instruction.stackPushCount(clazz);
  }

  /** Private utility class to visit only CodeAttributes that contain "NEWARRAY" instructions. */
  private static class ArrayInitializationFilter implements AttributeVisitor {
    private final AttributeVisitor acceptedVisitor;

    public ArrayInitializationFilter(AttributeVisitor acceptedVisitor) {
      this.acceptedVisitor = acceptedVisitor;
    }

    // Implementations for AttributeVisitor.

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

    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) {
      boolean delegateVisit = false;
      // Directly iterate of all instructions and exit early if
      // we encounter a "NEWARRAY" instruction.
      for (int offset = 0; offset < codeAttribute.u4codeLength; ) {
        Instruction instruction = InstructionFactory.create(codeAttribute.code, offset);
        if (instruction.opcode == Instruction.OP_NEWARRAY) {
          delegateVisit = true;
          break;
        }

        offset += instruction.length(offset);
      }

      if (delegateVisit) {
        acceptedVisitor.visitCodeAttribute(clazz, method, codeAttribute);
      }
    }
  }
}