8186670: Implement _onSpinWait() intrinsic for AArch64

Reviewed-by: phh, aph

test/micro/org/openjdk/bench/java/lang/ThreadOnSpinWait.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2021, Amazon.com Inc. 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.java.lang;
+
+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.Threads;
+
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+public class ThreadOnSpinWait {
+    @Benchmark
+    @Threads(1)
+    public void testOnSpinWait() {
+        Thread.onSpinWait();
+    }
+
+    @Benchmark
+    @Threads(1)
+    public void testSleep0() throws InterruptedException {
+        Thread.sleep(0);
+    }
+
+    @Benchmark
+    @Threads(1)
+    public void testEmpty() {
+    }
+}