/*

  * 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.MethodInsnNode;

 import org.objectweb.asm.tree.TypeInsnNode;

 import org.objectweb.asm.tree.VarInsnNode;

 /** Differentiation transformer for DRETURN instructions.

  * <p>DRETURN instructions are replaced by instructions

  * that build a {@link org.apache.commons.nabla.core.DifferentialPair

  * DifferentialPair} instance from the expanded differential pair

  * on operand stack head and an ARETURN instruction returning this

  * instance.</p>

  */

 public class DReturnTransformer implements InstructionsTransformer {

     /** Holder for the singleton instance.*/

     private static class LazyHolder  {

         /** The singleton instance. */

         private static final InstructionsTransformer INSTANCE = new DReturnTransformer();

     }

     /** Hidden constructor.

      */

     private DReturnTransformer() {

     }

     /** 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 {

         // reuse local variables slots 1, 2, 3 and 4 for temporary storage

         // (this may reduce the number of needed local variables)

         methodDifferentiator.useLocal(1, 4);

         final InsnList list = new InsnList();

         // operand stack initial state: a0, a1

         list.add(new VarInsnNode(Opcodes.DSTORE, 3));             // => a0

         list.add(new VarInsnNode(Opcodes.DSTORE, 1));             // =>

         list.add(new TypeInsnNode(Opcodes.NEW,

                                   MethodDifferentiator.DP_NAME)); // => o,

         list.add(new InsnNode(Opcodes.DUP));                      // => o, o

         list.add(new VarInsnNode(Opcodes.DLOAD, 1));              // => o, o, a0

         list.add(new VarInsnNode(Opcodes.DLOAD, 3));              // => o, o, a0, a1

         list.add(new MethodInsnNode(Opcodes.INVOKESPECIAL,

                                     MethodDifferentiator.DP_NAME,

                                     "<init>", "(DD)V"));          // => dp

         list.add(new InsnNode(Opcodes.ARETURN));                  // =>

         return list;

     }

 }