--- /dev/null 2016-08-26 11:23:41.521213300 +0200 +++ new/test/compiler/unsafe/UnsafeSmallOffsetBooleanAccessTest.java 2016-08-26 15:43:19.803278597 +0200 @@ -0,0 +1,85 @@ +/* + * Copyright (c) 2016, 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. + */ + +/* + * @test + * @bug 8161720 + * @modules java.base/jdk.internal.misc + * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -Xbatch -XX:-TieredCompilation UnsafeSmallOffsetBooleanAccessTest + * @run main/othervm -Xbatch UnsafeSmallOffsetBooleanAccessTest + */ + +import java.util.Random; +import jdk.internal.misc.Unsafe; + +public class UnsafeSmallOffsetBooleanAccessTest { + static final Unsafe UNSAFE = Unsafe.getUnsafe(); + static final long F_OFFSET; + static final Random random = new Random(); + + static { + try { + F_OFFSET = UNSAFE.objectFieldOffset(T.class.getDeclaredField("f")); + System.out.println("The offset is: " + F_OFFSET); + } catch (Exception e) { + throw new Error(e); + } + } + + static class T { + boolean f; + } + + // Always return false in a way that is not obvious to the compiler. + public static boolean myRandom() { + if (random.nextInt(101) > 134) { + return true; + } else { + return false; + } + } + + public static boolean test(T t) { + boolean result = false; + for (int i = 0; i < 20000; i++) { + boolean random = myRandom(); + // If myRandom() returns false, access t.f. + // + // If myRandom() returns true, access virtual address + // F_OFFSET. That address is most likely not mapped, + // therefore the access will most likely cause a + // crash. We're not concerned about that, though, because + // myRandom() always returns false. However, the C2 + // compiler avoids normalization of the value returned by + // getBoolean in this case. + result = UNSAFE.getBoolean(myRandom() ? null : t, F_OFFSET); + } + return result; + } + + public static void main(String[] args) { + T t = new T(); + UNSAFE.putBoolean(t, F_OFFSET, true); + System.out.println("The result for t is: " + test(t)); + } +}