8326638: Crash in PhaseIdealLoop::remix_address_expressions due to unexpected Region instead of Loop

src/hotspot/share/opto/loopopts.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 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
@@ -571,8 +571,8 @@ Node* PhaseIdealLoop::remix_address_expressions(Node* n) {
   }
 
   // Replace ((I1 +p V) +p I2) with ((I1 +p I2) +p V),
-  // but not if I2 is a constant.
-  if (n_op == Op_AddP) {
+  // but not if I2 is a constant. Skip for irreducible loops.
+  if (n_op == Op_AddP && n_loop->_head->is_Loop()) {
     if (n2_loop == n_loop && n3_loop != n_loop) {
       if (n->in(2)->Opcode() == Op_AddP && !n->in(3)->is_Con()) {
         Node* n22_ctrl = get_ctrl(n->in(2)->in(2));

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

@@ -0,0 +1,57 @@
+/*
+ * 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 8326638
+ * @summary Test handling of irreducible loops in PhaseIdealLoop::remix_address_expressions.
+ * @run main/othervm -XX:-TieredCompilation -Xbatch
+ *                   -XX:CompileCommand=compileonly,TestRemixAddressExpressionsWithIrreducibleLoop::test
+ *                   TestRemixAddressExpressionsWithIrreducibleLoop
+ */
+
+public class TestRemixAddressExpressionsWithIrreducibleLoop {
+
+    public static void main(String[] args) {
+        test("4");
+    }
+
+    public static void test(String arg) {
+        for (int i = 0; i < 100_000; ++i) {
+            int j = 0;
+            while (true) {
+                boolean tmp = "1\ufff0".startsWith(arg, 2 - arg.length());
+                if (j++ > 100)
+                    break;
+            }
+        loop:
+            while (i >= 100) {
+                for (int i2 = 0; i2 < 1; i2 = 1)
+                    if (j > 300)
+                        break loop;
+                j++;
+            }
+        }
+    }
+}