8238190: [JVMCI] Fix single implementor speculation for diamond shapes

Reviewed-by: kvn

src/hotspot/share/oops/instanceKlass.cpp

@@ -1172,7 +1172,7 @@ void InstanceKlass::add_implementor(Klass* k) {
   Klass* ik = implementor();
   if (ik == NULL) {
     set_implementor(k);
-  } else if (ik != this) {
+  } else if (ik != this && ik != k) {
     // There is already an implementor. Use itself as an indicator of
     // more than one implementors.
     set_implementor(this);

test/hotspot/jtreg/compiler/jvmci/jdk.vm.ci.runtime.test/src/jdk/vm/ci/runtime/test/TestSingleImplementor.java

@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2020, 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 8238190
+ * @summary Verify single interface implementor recording supports diamond-shaped class hierarchies
+ * @requires vm.jvmci
+ * @library ../../../../../
+ * @modules java.base/jdk.internal.reflect
+ *          jdk.internal.vm.ci/jdk.vm.ci.meta
+ *          jdk.internal.vm.ci/jdk.vm.ci.runtime
+ *          jdk.internal.vm.ci/jdk.vm.ci.common
+ *          java.base/jdk.internal.misc
+ * @run junit/othervm -XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCI -XX:-UseJVMCICompiler jdk.vm.ci.runtime.test.TestSingleImplementor
+ */
+
+package jdk.vm.ci.runtime.test;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import jdk.vm.ci.meta.ResolvedJavaType;
+
+
+public class TestSingleImplementor extends TypeUniverse {
+
+    static int SideEffect;
+
+    interface I {
+        void foo();
+    }
+
+    interface I1 extends I {
+    }
+
+    interface I2 extends I {
+    }
+
+    static class Impl implements I1, I2 {
+        @Override
+        public void foo() {
+            SideEffect = 42;
+        }
+    }
+
+    public static void snippetDiamond(I i) {
+        i.foo();
+    }
+
+    @Test
+    public void testDiamondShape() throws Throwable {
+        snippetDiamond(new Impl());
+        ResolvedJavaType interfaceType = metaAccess.lookupJavaType(I.class);
+        ResolvedJavaType implementationType = metaAccess.lookupJavaType(Impl.class);
+        Assert.assertEquals(implementationType, interfaceType.getSingleImplementor());
+    }
+
+    interface IF1 {
+        void foo();
+    }
+
+    static class Impl1 implements IF1 {
+        @Override
+        public void foo() {
+            SideEffect = 43;
+        }
+    }
+
+    public static void snippetRegular(IF1 i) {
+        i.foo();
+    }
+
+    @Test
+    public void testRegularShape() throws Throwable {
+        snippetRegular(new Impl1());
+        ResolvedJavaType interfaceType = metaAccess.lookupJavaType(IF1.class);
+        ResolvedJavaType implementationType = metaAccess.lookupJavaType(Impl1.class);
+        Assert.assertEquals(implementationType, interfaceType.getSingleImplementor());
+    }
+
+}