--- /dev/null 2017-03-07 11:47:08.059171116 +0100 +++ new/test/compiler/unsafe/TestMaybeNullUnsafeAccess.java 2017-03-13 09:59:08.396632736 +0100 @@ -0,0 +1,96 @@ +/* + * Copyright (c) 2017, Red Hat, Inc. 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 + * @summary cast before unsafe access moved in dominating null check null path causes crash + * @modules java.base/jdk.internal.misc:+open + * + * @run main/othervm TestMaybeNullUnsafeAccess + * + */ + +import jdk.internal.misc.Unsafe; +import java.lang.reflect.Field; + +public class TestMaybeNullUnsafeAccess { + + static final jdk.internal.misc.Unsafe UNSAFE = Unsafe.getUnsafe(); + static final long F_OFFSET; + + static class A { + int f; + A(int f) { + this.f = f; + } + } + + static { + try { + Field fField = A.class.getDeclaredField("f"); + F_OFFSET = UNSAFE.objectFieldOffset(fField); + } catch (Exception e) { + throw new RuntimeException(e); + } + } + + static A test_helper(Object o) { + // this includes a check for null with both branches taken + return (A)o; + } + + + // Loop is unswitched because of the test null for null from the + // checkcast above, unsafe access is copied in each branch, the + // compiler sees a memory access to a null object + static int test1(Object o, long offset) { + int f = 0; + for (int i = 0; i < 100; i++) { + A a = test_helper(o); + f = UNSAFE.getInt(a, offset); + } + return f; + } + + // Same as above except because we know the offset of the access + // is small, we can deduce object a cannot be null + static int test2(Object o) { + int f = 0; + for (int i = 0; i < 100; i++) { + A a = test_helper(o); + f = UNSAFE.getInt(a, F_OFFSET); + } + return f; + } + + static public void main(String[] args) { + A a = new A(0x42); + for (int i = 0; i < 20000; i++) { + test_helper(null); + test_helper(a); + test1(a, F_OFFSET); + test2(a); + } + } + +}