--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/com.oracle.graal.jtt/src/com/oracle/graal/jtt/bytecode/BC_instanceof01.java	Thu Apr 30 18:09:36 2015 +0200
@@ -0,0 +1,105 @@
+/*
+ * Copyright (c) 2015, 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.
+ */
+package com.oracle.graal.jtt.bytecode;
+
+import org.junit.*;
+
+import com.oracle.graal.api.code.*;
+import com.oracle.graal.api.meta.*;
+import com.oracle.graal.compiler.common.*;
+import com.oracle.graal.compiler.phases.*;
+import com.oracle.graal.jtt.*;
+import com.oracle.graal.nodes.*;
+import com.oracle.graal.options.*;
+import com.oracle.graal.options.OptionValue.*;
+import com.oracle.graal.phases.tiers.*;
+
+/**
+ * Tests the instanceof works, when casting an array of interface.
+ */
+public class BC_instanceof01 extends JTTTest {
+
+    public interface IObject {
+
+    }
+
+    public interface IDerivedObject extends IObject {
+
+    }
+
+    private static class BaseClass {
+
+    }
+
+    private static class TestClass extends BaseClass implements IObject {
+    }
+
+    private static class DerivedTestClass extends BaseClass implements IDerivedObject {
+
+    }
+
+    static TestClass[] a1 = {new TestClass()};
+    static DerivedTestClass[] a2 = {new DerivedTestClass()};
+
+    public static BaseClass[] getBaseClassArray() {
+        return a1;
+    }
+
+    public static BaseClass[] getDerivedBaseClassArray() {
+        return a2;
+    }
+
+    public static boolean test() {
+        return getBaseClassArray() instanceof IObject[];
+    }
+
+    public static int testConditionalElimination() {
+        BaseClass[] result = getDerivedBaseClassArray();
+        if (result instanceof IDerivedObject[]) {
+            if (result instanceof IObject[]) {
+                return 1;
+            } else {
+                return 2;
+            }
+        } else {
+            return 3;
+        }
+    }
+
+    @Test
+    public void run0() throws Throwable {
+        runTest("test");
+    }
+
+    @Override
+    protected Suites getSuites() {
+        try (OverrideScope scope = OptionValue.override(HighTier.Options.Inline, false)) {
+            return super.getSuites();
+        }
+    }
+
+    @Test
+    public void run1() throws Throwable {
+        runTest("testConditionalElimination");
+    }
+}

--- a/graal/com.oracle.graal.nodes/src/com/oracle/graal/nodes/java/InstanceOfNode.java	Thu Apr 30 13:49:24 2015 +0200
+++ b/graal/com.oracle.graal.nodes/src/com/oracle/graal/nodes/java/InstanceOfNode.java	Thu Apr 30 18:09:36 2015 +0200
@@ -128,7 +128,7 @@
                 return LogicConstantNode.contradiction();
             } else {
                 boolean superType = inputType.isAssignableFrom(type);
-                if (!superType && !inputType.isInterface() && !type.isInterface()) {
+                if (!superType && !isInterfaceOrArrayOfInterface(inputType) && !isInterfaceOrArrayOfInterface(type)) {
                     return LogicConstantNode.contradiction();
                 }
                 // since the subtype comparison was only performed on a declared type we don't
@@ -199,4 +199,8 @@
         }
         return TriState.UNKNOWN;
     }
+
+    private static boolean isInterfaceOrArrayOfInterface(ResolvedJavaType t) {
+        return t.isInterface() || (t.isArray() && t.getElementalType().isInterface());
+    }
 }