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A Java Optimization Framework
There is a newer version: 4.6.0
package soot.dexpler.instructions;

/*-
 * #%L
 * Soot - a J*va Optimization Framework
 * %%
 * Copyright (C) 2012 Michael Markert, Frank Hartmann
 * 
 * (c) 2012 University of Luxembourg - Interdisciplinary Centre for
 * Security Reliability and Trust (SnT) - All rights reserved
 * Alexandre Bartel
 * 
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2.1 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */

import org.jf.dexlib2.iface.instruction.Instruction;
import org.jf.dexlib2.iface.instruction.TwoRegisterInstruction;
import org.jf.dexlib2.iface.instruction.formats.Instruction12x;

import soot.IntType;
import soot.Local;
import soot.dexpler.DexBody;
import soot.dexpler.IDalvikTyper;
import soot.dexpler.typing.DalvikTyper;
import soot.jimple.AssignStmt;
import soot.jimple.Jimple;
import soot.jimple.LengthExpr;

public class ArrayLengthInstruction extends DexlibAbstractInstruction {

  public ArrayLengthInstruction(Instruction instruction, int codeAdress) {
    super(instruction, codeAdress);
  }

  @Override
  public void jimplify(DexBody body) {
    if (!(instruction instanceof Instruction12x)) {
      throw new IllegalArgumentException("Expected Instruction12x but got: " + instruction.getClass());
    }

    Instruction12x lengthOfArrayInstruction = (Instruction12x) instruction;
    int dest = lengthOfArrayInstruction.getRegisterA();

    Local arrayReference = body.getRegisterLocal(lengthOfArrayInstruction.getRegisterB());

    LengthExpr lengthExpr = Jimple.v().newLengthExpr(arrayReference);

    AssignStmt assign = Jimple.v().newAssignStmt(body.getRegisterLocal(dest), lengthExpr);

    setUnit(assign);
    addTags(assign);
    body.add(assign);

    if (IDalvikTyper.ENABLE_DVKTYPER) {
      DalvikTyper.v().setType(assign.getLeftOpBox(), IntType.v(), false);
    }
  }

  @Override
  boolean overridesRegister(int register) {
    TwoRegisterInstruction i = (TwoRegisterInstruction) instruction;
    int dest = i.getRegisterA();
    return register == dest;
  }
}