001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.commons.nabla.algorithmic.forward.trimming; 018 019 import org.objectweb.asm.Opcodes; 020 import org.objectweb.asm.tree.AbstractInsnNode; 021 import org.objectweb.asm.tree.InsnList; 022 023 /** Trimmer removing (DLOAD i, POP2). 024 */ 025 public class DLoadPop2Trimmer extends BytecodeTrimmer { 026 027 // CHECKSTYLE: stop HideUtilityClassConstructor 028 /** Holder for the singleton instance.*/ 029 private static class LazyHolder { 030 /** The singleton instance. */ 031 private static final BytecodeTrimmer INSTANCE = new DLoadPop2Trimmer(); 032 } 033 // CHECKSTYLE: resume HideUtilityClassConstructor 034 035 /** Hidden constructor. 036 */ 037 private DLoadPop2Trimmer() { 038 super(2); 039 } 040 041 /** Get the singleton instance. 042 * <p>We use here the Initialization on Demand Holder idiom.</p> 043 * @return the singleton instance 044 */ 045 public static BytecodeTrimmer getInstance() { 046 return LazyHolder.INSTANCE; 047 } 048 049 /** {@inheritDoc} */ 050 @Override 051 protected boolean trimWindow(final InsnList instructions, 052 final AbstractInsnNode[] window) { 053 054 if ((window[0].getOpcode() == Opcodes.DUP2) && 055 (window[1].getOpcode() == Opcodes.POP2)) { 056 057 // remove the no-op instructions pair 058 instructions.remove(window[0]); 059 instructions.remove(window[1]); 060 061 return true; 062 063 } 064 065 // nothing have been done 066 return false; 067 068 } 069 070 }