8310299: C2: 8275201 broke constant folding of array store check in some cases

Reviewed-by: thartmann, kvn

src/hotspot/share/opto/memnode.cpp

@@ -2378,7 +2378,7 @@ const Type* LoadNode::klass_value_common(PhaseGVN* phase) const {
 
       // The array's TypeKlassPtr was declared 'precise' or 'not precise'
       // according to the element type's subclassing.
-      return tkls->is_aryklassptr()->elem();
+      return tkls->is_aryklassptr()->elem()->isa_klassptr()->cast_to_exactness(tkls->klass_is_exact());
     }
     if (tkls->isa_instklassptr() != nullptr && tkls->klass_is_exact() &&
         tkls->offset() == in_bytes(Klass::super_offset())) {

test/hotspot/jtreg/compiler/c2/irTests/TestArrayElementTypeLoad.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2023, Red Hat, Inc. 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 compiler.c2.irTests;
+
+import compiler.lib.ir_framework.*;
+
+/*
+ * @test
+ * @library /test/lib /
+ * @run driver compiler.c2.irTests.TestArrayElementTypeLoad
+ */
+
+public class TestArrayElementTypeLoad {
+    public static void main(String[] args) {
+        TestFramework.run();
+    }
+
+    static final A[] array = new A[1];
+
+    @Test
+    @IR(phase = { CompilePhase.ITER_GVN1 }, failOn = { IRNode.SUBTYPE_CHECK })
+    public static void test1(A a) {
+        array[0] = a;
+    }
+
+    @Run(test = "test1")
+    private void test1Runner() {
+        test1(new A());
+        test1(new B());
+    }
+
+    static class A {
+    }
+
+    static class B extends A {
+    }
+}

test/hotspot/jtreg/compiler/lib/ir_framework/IRNode.java

@@ -1193,6 +1193,11 @@ public class IRNode {
         beforeMatchingNameRegex(SUB_V, "SubV(B|S|I|L|F|D)");
     }
 
+    public static final String SUBTYPE_CHECK = PREFIX + "SUBTYPE_CHECK" + POSTFIX;
+    static {
+        beforeMatchingNameRegex(SUBTYPE_CHECK, "SubTypeCheck");
+    }
+
     public static final String TRAP = PREFIX + "TRAP" + POSTFIX;
     static {
         trapNodes(TRAP,"reason");