8386482: C2 CountedLoopConverter::filtered_type_from_dominators: assert(_base == Int) failed: Not an Int

Reviewed-by: kvn, qamai

src/hotspot/share/opto/loopnode.cpp

@@ -3892,7 +3892,16 @@ const TypeInt* CountedLoopConverter::filtered_type_from_dominators(Node* val, No
           if (rtn_t == nullptr) {
             rtn_t = if_t;
           } else {
-            rtn_t = rtn_t->join(if_t)->is_int();
+            const Type* join_t = rtn_t->join(if_t);
+            if (!join_t->isa_int()) {
+              // We may have encountered multiple if conditions, that have no
+              // overlap, and produce an empty/top type. Returning nullptr
+              // is conservative, it means we do not constrain the type, which
+              // will just prevent further optimiziations.
+              assert(join_t->empty(), "top");
+              return nullptr;
+            }
+            rtn_t = join_t->is_int();
           }
         }
       }

test/hotspot/jtreg/compiler/loopopts/TestTruncationWrapEmptyType.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2026, 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.
+ */
+
+package compiler.loopopts;
+
+/*
+ * @test
+ * @bug 8386482
+ * @summary Test case for CountedLoopConverter::filtered_type_from_dominators/
+ *          CountedLoopConverter::has_truncation_wrap where the type becomes
+ *          empty / top. This used to trigger the assert:
+ *          assert(_base == Int) failed: Not an Int
+ * @library /test/lib /
+ * @run main/othervm -Xcomp
+ *                   -XX:CompileCommand=compileonly,${test.main.class}::test
+ *                   ${test.main.class}
+ * @run main ${test.main.class}
+ */
+
+public class TestTruncationWrapEmptyType {
+    public static void main(String[] args) {
+        for (int i = 0; i < 10_000; i++) {
+            test(1);
+        }
+    }
+
+    static int test(int init) {
+        if (init < 1) {
+            return -1;
+        }
+        // if implies: init in [1..max_int]
+
+        int i = init;
+        while (i < 0) {
+            // while implies: init in [min_int .. 0]
+            // That contradicts the "if" above: empty intersection
+            //
+            // See CountedLoopConverter::filtered_type_from_dominators:
+            //   rtn_t = rtn_t->join(if_t)->is_int()
+            // -> top type in join, fails "is_int".
+            i = (short)(i + 1);
+        }
+        return 0;
+    }
+}