8336779: [lworld] C2 compilations hits "what's left behind is null" a…

…ssert in do_checkcast

src/hotspot/share/opto/graphKit.cpp

@@ -1299,6 +1299,7 @@ Node* GraphKit::null_check_common(Node* value, BasicType type,
       // vtptr = InlineTypeNode::make_null(_gvn, vtptr->type()->inline_klass());
       // replace_in_map(value, vtptr);
       // return vtptr;
+      replace_in_map(value, null());
       return null();
     }
     bool do_replace_in_map = (null_control == nullptr || (*null_control) == top());

test/hotspot/jtreg/compiler/valhalla/inlinetypes/TestUnloadedCastType.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2024, 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
+ * @summary Test casting of value objects to an unloaded type.
+ * @enablePreview
+ * @library /test/lib
+ * @run main/othervm -Xbatch -XX:CompileCommand=dontinline,TestUnloadedCastType::test*
+ *                   TestUnloadedCastType
+ */
+
+import jdk.test.lib.Asserts;
+
+public class TestUnloadedCastType {
+
+    static value class MyValue {
+        int x = 0;
+    }
+
+    static class Unloaded { }
+
+    public static Object test(MyValue val) {
+        Object obj = val;
+        return (Unloaded)obj;
+    }
+
+    public static void main(String[] args) {
+        for (int i = 0; i < 50_000; ++i) {
+            Asserts.assertEQ(test(null), null);
+        }
+        try {
+            test(new MyValue());
+            throw new RuntimeException("No ClassCastException thrown");
+        } catch (ClassCastException e) {
+            // Expected
+        }
+    }
+}