--- old/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.nodes/src/org/graalvm/compiler/nodes/java/InstanceOfNode.java	2017-11-03 23:57:17.620842123 -0700
+++ new/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.nodes/src/org/graalvm/compiler/nodes/java/InstanceOfNode.java	2017-11-03 23:57:17.293827489 -0700
@@ -49,6 +49,8 @@
 import jdk.vm.ci.meta.JavaTypeProfile;
 import jdk.vm.ci.meta.TriState;
 
+import java.util.Objects;
+
 /**
  * The {@code InstanceOfNode} represents an instanceof test.
  */
@@ -56,7 +58,7 @@
 public class InstanceOfNode extends UnaryOpLogicNode implements Lowerable, Virtualizable {
     public static final NodeClass<InstanceOfNode> TYPE = NodeClass.create(InstanceOfNode.class);
 
-    protected final ObjectStamp checkedStamp;
+    private ObjectStamp checkedStamp;
 
     private JavaTypeProfile profile;
     @OptionalInput(Anchor) protected AnchoringNode anchor;
@@ -126,7 +128,9 @@
                 // The check will always succeed, the union of the two stamps is equal to the
                 // checked stamp.
                 return LogicConstantNode.tautology();
-            } else if (checkedStamp.type().equals(meetStamp.type()) && checkedStamp.isExactType() == meetStamp.isExactType() && checkedStamp.alwaysNull() == meetStamp.alwaysNull()) {
+            } else if (checkedStamp.alwaysNull()) {
+                return IsNullNode.create(object);
+            } else if (Objects.equals(checkedStamp.type(), meetStamp.type()) && checkedStamp.isExactType() == meetStamp.isExactType() && checkedStamp.alwaysNull() == meetStamp.alwaysNull()) {
                 assert checkedStamp.nonNull() != inputStamp.nonNull();
                 // The only difference makes the null-ness of the value => simplify the check.
                 if (checkedStamp.nonNull()) {
@@ -135,8 +139,8 @@
                     return IsNullNode.create(object);
                 }
             }
+            assert checkedStamp.type() != null;
         }
-
         return null;
     }
 
@@ -204,4 +208,13 @@
     public AnchoringNode getAnchor() {
         return anchor;
     }
+
+    public ObjectStamp getCheckedStamp() {
+        return checkedStamp;
+    }
+
+    public void strengthenCheckedStamp(ObjectStamp newCheckedStamp) {
+        assert this.checkedStamp.join(newCheckedStamp).equals(newCheckedStamp) : "stamp can only improve";
+        this.checkedStamp = newCheckedStamp;
+    }
 }