src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.nodes/src/org/graalvm/compiler/nodes/java/InstanceOfNode.java

@@ -47,18 +47,20 @@
 import org.graalvm.compiler.nodes.type.StampTool;
 
 import jdk.vm.ci.meta.JavaTypeProfile;
 import jdk.vm.ci.meta.TriState;
 
+import java.util.Objects;
+
 /**
  * The {@code InstanceOfNode} represents an instanceof test.
  */
 @NodeInfo(cycles = CYCLES_8, size = SIZE_8)
 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;
 
     private InstanceOfNode(ObjectStamp checkedStamp, ValueNode object, JavaTypeProfile profile, AnchoringNode anchor) {

@@ -124,21 +126,23 @@
             ObjectStamp meetStamp = (ObjectStamp) checkedStamp.meet(inputStamp);
             if (checkedStamp.equals(meetStamp)) {
                 // 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()) {
                     return LogicNegationNode.create(IsNullNode.create(object));
                 } else {
                     return IsNullNode.create(object);
                 }
             }
+            assert checkedStamp.type() != null;
         }
-
         return null;
     }
 
     /**
      * Gets the type being tested.

@@ -202,6 +206,15 @@
     }
 
     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;
+    }
 }