8232873: Add missing test for 8220416

Adds a missing test which verifies the bug fix of 8220416.

Reviewed-by: roland, thartmann

Author: chhagedorn

test/hotspot/jtreg/compiler/c2/CmpPNodeSubTest.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2019, 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 8220416
+ * @summary This test uses a class pointer comparison optimization which was not applied anymore since JDK-6964458 resulting in a better IR.
+ *
+ * @run main/othervm -Xbatch -XX:-TieredCompilation -XX:+IgnoreUnrecognizedVMOptions -XX:+AlwaysIncrementalInline
+ *                   -XX:CompileOnly=compiler.c2.CompareKlassPointersTest::test compiler.c2.CompareKlassPointersTest
+ */
+
+package compiler.c2;
+
+
+
+public class CompareKlassPointersTest {
+
+    static A a;
+
+    public static void main(String[] args) {
+        a = new C();
+        for (int i = 0; i < 10_000; i++) {
+            test();
+        }
+    }
+
+    public static int test() {
+        Object a = getA();
+
+        /*
+         * This check is now optimized away which was not the case before anymore since JDK-6964458:
+         * The klass pointer comparison optimization sees that the check is always false since a and B are always unrelated klasses
+         */
+        if (a instanceof B) {
+            return 1;
+        }
+        return 0;
+    }
+
+    private static Object getA() {
+        return a;
+    }
+}
+
+class A { }
+
+class B { }
+
+class C extends A { }