1 /* 2 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 package org.openjdk.bench.vm.compiler; 24 25 import org.openjdk.jmh.annotations.Benchmark; 26 import org.openjdk.jmh.annotations.BenchmarkMode; 27 import org.openjdk.jmh.annotations.Mode; 28 import org.openjdk.jmh.annotations.OutputTimeUnit; 29 import org.openjdk.jmh.annotations.Scope; 30 import org.openjdk.jmh.annotations.Setup; 31 import org.openjdk.jmh.annotations.State; 32 33 import java.util.concurrent.TimeUnit; 34 35 /** 36 * Benchmark measuring effect of loop optimizations. 37 */ 38 @BenchmarkMode(Mode.AverageTime) 39 @OutputTimeUnit(TimeUnit.NANOSECONDS) 40 @State(Scope.Thread) 41 public class CopyLoop { 42 43 private MyString s; 44 private Buf b; 45 46 @Setup 47 public void setup() { 48 s = new MyString("foobarba"); 49 b = new Buf(); 50 } 51 52 /** 53 * Basic implementation, as a Java programmer would write it. 54 */ 55 @Benchmark 56 public void testCharAtLoop() throws Exception { 57 for (int i = 0; i < s.length(); i++) { 58 int c = s.charAt(i); 59 b.byteBuf[i] = (byte) c; 60 } 61 } 62 63 /** Inline charAt and remove the redundant bounds checks. */ 64 @Benchmark 65 public void testInlineCharAtLoop() throws Exception { 66 for (int i = 0; i < s.count; i++) { 67 int c = s.value[i + s.offset]; 68 b.byteBuf[i] = (byte) c; 69 } 70 } 71 72 /** 73 * Unroll the loop (I cheat here because I know that the String will always be an even length, real implementation 74 * would require a pre-loop). 75 */ 76 @Benchmark 77 public void testInlineAndUnrollCharAtLoop() throws Exception { 78 int startI = 0; 79 if ((s.count & 0xFFFE) != s.count) { 80 int c = s.value[s.offset]; 81 b.byteBuf[0] = (byte) c; 82 startI = 1; 83 } 84 for (int i = startI; i < s.count - 1; i += 2) { 85 int c = s.value[i + s.offset]; 86 int d = s.value[i + s.offset + 1]; 87 b.byteBuf[i] = (byte) c; 88 b.byteBuf[i + 1] = (byte) d; 89 } 90 } 91 92 /** Hoist computation of constants outside of the loop. */ 93 @Benchmark 94 public void testInlineAndUnrollAndHoistCharAtLoop() throws Exception { 95 byte[] byteBuf = b.byteBuf; 96 if (byteBuf == null) { 97 throw new NullPointerException(); 98 } 99 char[] value = s.value; 100 int offset = s.offset; 101 102 int startI = offset; 103 104 if ((s.count & 0xFFFE) != s.count) { 105 int c = value[offset]; 106 byteBuf[0] = (byte) c; 107 startI++; 108 } 109 110 int maxI = s.count + offset - 1; 111 for (int i = startI; i < maxI; i += 2) { 112 int c = value[i]; 113 int d = value[i + 1]; 114 byteBuf[i] = (byte) c; 115 byteBuf[i + 1] = (byte) d; 116 } 117 } 118 119 private static class Buf { 120 private byte[] byteBuf = new byte[100]; 121 } 122 123 public static final class MyString { 124 private char value[]; 125 126 private int offset; 127 128 private int count; 129 130 public MyString(String original) { 131 value = original.toCharArray(); 132 offset = 0; 133 count = value.length; 134 } 135 136 public int length() { 137 return count; 138 } 139 140 public char charAt(int index) { 141 if ((index < 0) || (index >= count)) { 142 throw new StringIndexOutOfBoundsException(index); 143 } 144 return value[index + offset]; 145 } 146 147 } 148 149 }