8330247: C2: CTW fail with assert(adr_t->is_known_instance_field()) failed: instance required

Reviewed-by: kvn

src/hotspot/share/opto/macro.cpp

@@ -573,6 +573,9 @@ bool PhaseMacroExpand::can_eliminate_allocation(PhaseIterGVN* igvn, AllocateNode
     if (res_type == nullptr) {
       NOT_PRODUCT(fail_eliminate = "Neither instance or array allocation";)
       can_eliminate = false;
+    } else if (!res_type->klass_is_exact()) {
+      NOT_PRODUCT(fail_eliminate = "Not an exact type.";)
+      can_eliminate = false;
     } else if (res_type->isa_aryptr()) {
       int length = alloc->in(AllocateNode::ALength)->find_int_con(-1);
       if (length < 0) {

test/hotspot/jtreg/compiler/c2/TestReduceAllocationAndNonExactAllocate.java

@@ -0,0 +1,73 @@
+/*
+ * 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
+ * @bug 8330247
+ * @summary Check that Reduce Allocation Merges doesn't try to reduce non-exact allocations.
+ * @library /test/lib /
+ * @modules java.base/jdk.internal.misc
+ * @requires vm.debug & vm.flagless & vm.compiler2.enabled & vm.opt.final.EliminateAllocations
+ * @run main/othervm -XX:CompileCommand=compileonly,*TestReduceAllocationAndNonExactAllocate*::test
+ *                   -XX:CompileCommand=compileonly,*::allocateInstance
+ *                   -XX:CompileCommand=dontinline,*TestReduceAllocationAndNonExactAllocate*::*
+ *                   -XX:+UnlockDiagnosticVMOptions
+ *                   -XX:+TraceReduceAllocationMerges
+ *                   -XX:-TieredCompilation
+ *                   -Xbatch
+ *                   -Xcomp
+ *                   -server
+ *                   compiler.c2.TestReduceAllocationAndNonExactAllocate
+ */
+
+package compiler.c2;
+
+import jdk.internal.misc.Unsafe;
+
+public class TestReduceAllocationAndNonExactAllocate {
+    private static final Unsafe UNSAFE = Unsafe.getUnsafe();
+
+    public static void main(String[] args) {
+        try {
+            if (test(20, Integer.class) != 2032) {
+                throw new RuntimeException("Expected the value to be 2032.");
+            }
+        }
+        catch (InstantiationException e) {
+            e.printStackTrace();
+        }
+    }
+
+    public static int test(int val, Class<?> c) throws InstantiationException {
+        Object p = null;
+
+        if (val == 20) {
+            p = UNSAFE.allocateInstance(c);
+        }
+
+        dummy();
+        return p != null ? 2032 : 3242;
+    }
+
+    static int dummy() { return 42; }
+}