/*

  * Licensed to the Apache Software Foundation (ASF) under one or more

  * contributor license agreements.  See the NOTICE file distributed with

  * this work for additional information regarding copyright ownership.

  * The ASF licenses this file to You 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 org.apache.commons.nabla.automatic.instructions;

 import org.apache.commons.nabla.automatic.analysis.InstructionsTransformer;

 import org.apache.commons.nabla.automatic.analysis.MethodDifferentiator;

 import org.apache.commons.nabla.core.DifferentiationException;

 import org.objectweb.asm.Opcodes;

 import org.objectweb.asm.tree.AbstractInsnNode;

 import org.objectweb.asm.tree.InsnList;

 import org.objectweb.asm.tree.InsnNode;

 import org.objectweb.asm.tree.VarInsnNode;

 /** Differentiation transformer for DUP2_X2 instructions.

  * <p>DUP2_X2 instructions are replaced by instructions

  * that duplicate the two parts of a differential pair on stack.</p>

  */

 public class Dup2X2Transformer1 implements InstructionsTransformer {

     /** Holder for the singleton instance.*/

     private static class LazyHolder  {

         /** The singleton instance. */

         private static final InstructionsTransformer INSTANCE = new Dup2X2Transformer1();

     }

     /** Hidden constructor.

      */

     private Dup2X2Transformer1() {

     }

     /** Get the singleton instance.

      * <p>We use here the Initialization on Demand Holder idiom.</p>

      * @return the singleton instance

      */

     public static InstructionsTransformer getInstance() {

         return LazyHolder.INSTANCE;

     }

     /** {@inheritDoc} */

     public InsnList getReplacement(final AbstractInsnNode insn,

                                    final MethodDifferentiator methodDifferentiator)

         throws DifferentiationException {

         final int tmp1 = methodDifferentiator.getTmp(1);

         final InsnList list = new InsnList();

         // operand stack initial state: a0, a1, w

         list.add(new InsnNode(Opcodes.DUP2_X2));         // => a0, w, a1, w

         list.add(new InsnNode(Opcodes.POP2));            // => a0, w, a1

         list.add(new VarInsnNode(Opcodes.DSTORE, tmp1)); // => a0, w

         list.add(new InsnNode(Opcodes.DUP2_X2));         // => w, a0, w

         list.add(new VarInsnNode(Opcodes.DLOAD,  tmp1)); // => w, a0, w, a1

         list.add(new InsnNode(Opcodes.DUP2_X2));         // => w, a0, a1, w, a1

         list.add(new InsnNode(Opcodes.POP2));            // => w, a0, a1, w

         return list;

     }

 }