--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/micro/org/openjdk/bench/vm/compiler/CopyLoop.java	Fri Nov 16 23:39:51 2018 +0100
@@ -0,0 +1,149 @@
+/*
+ * Copyright (c) 2014 Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code 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 Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.openjdk.bench.vm.compiler;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Benchmark measuring effect of loop optimizations.
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Thread)
+public class CopyLoop {
+
+    private MyString s;
+    private Buf b;
+
+    @Setup
+    public void setup() {
+        s = new MyString("foobarba");
+        b = new Buf();
+    }
+
+    /**
+     * Basic implementation, as a Java programmer would write it.
+     */
+    @Benchmark
+    public void testCharAtLoop() throws Exception {
+        for (int i = 0; i < s.length(); i++) {
+            int c = s.charAt(i);
+            b.byteBuf[i] = (byte) c;
+        }
+    }
+
+    /** Inline charAt and remove the redundant bounds checks. */
+    @Benchmark
+    public void testInlineCharAtLoop() throws Exception {
+        for (int i = 0; i < s.count; i++) {
+            int c = s.value[i + s.offset];
+            b.byteBuf[i] = (byte) c;
+        }
+    }
+
+    /**
+     * Unroll the loop (I cheat here because I know that the String will always be an even length, real implementation
+     * would require a pre-loop).
+     */
+    @Benchmark
+    public void testInlineAndUnrollCharAtLoop() throws Exception {
+        int startI = 0;
+        if ((s.count & 0xFFFE) != s.count) {
+            int c = s.value[s.offset];
+            b.byteBuf[0] = (byte) c;
+            startI = 1;
+        }
+        for (int i = startI; i < s.count - 1; i += 2) {
+            int c = s.value[i + s.offset];
+            int d = s.value[i + s.offset + 1];
+            b.byteBuf[i] = (byte) c;
+            b.byteBuf[i + 1] = (byte) d;
+        }
+    }
+
+    /** Hoist computation of constants outside of the loop. */
+    @Benchmark
+    public void testInlineAndUnrollAndHoistCharAtLoop() throws Exception {
+        byte[] byteBuf = b.byteBuf;
+        if (byteBuf == null) {
+            throw new NullPointerException();
+        }
+        char[] value = s.value;
+        int offset = s.offset;
+
+        int startI = offset;
+
+        if ((s.count & 0xFFFE) != s.count) {
+            int c = value[offset];
+            byteBuf[0] = (byte) c;
+            startI++;
+        }
+
+        int maxI = s.count + offset - 1;
+        for (int i = startI; i < maxI; i += 2) {
+            int c = value[i];
+            int d = value[i + 1];
+            byteBuf[i] = (byte) c;
+            byteBuf[i + 1] = (byte) d;
+        }
+    }
+
+    private static class Buf {
+        private byte[] byteBuf = new byte[100];
+    }
+
+    public static final class MyString {
+        private char value[];
+
+        private int offset;
+
+        private int count;
+
+        public MyString(String original) {
+            value = original.toCharArray();
+            offset = 0;
+            count = value.length;
+        }
+
+        public int length() {
+            return count;
+        }
+
+        public char charAt(int index) {
+            if ((index < 0) || (index >= count)) {
+                throw new StringIndexOutOfBoundsException(index);
+            }
+            return value[index + offset];
+        }
+
+    }
+
+}