8289954: C2: Assert failed in PhaseCFG::verify() after JDK-8183390

Reviewed-by: kvn, thartmann, roland

Author: Pengfei Li

src/hotspot/share/opto/superword.cpp

@@ -414,7 +414,9 @@ void SuperWord::unrolling_analysis(int &local_loop_unroll_factor) {
       cl->mark_passed_slp();
     }
     cl->mark_was_slp();
-    cl->set_slp_max_unroll(local_loop_unroll_factor);
+    if (cl->is_main_loop() || cl->is_rce_post_loop()) {
+      cl->set_slp_max_unroll(local_loop_unroll_factor);
+    }
   }
 }
 

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

@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2022, Arm Limited. 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 8289954
+ * @summary C2: Assert failed in PhaseCFG::verify() after JDK-8183390
+ *
+ * @run main/othervm -Xcomp -Xbatch
+ *      -XX:CompileOnly=compiler/loopopts/TestUnreachableInnerLoop
+ *      compiler.loopopts.TestUnreachableInnerLoop
+ */
+
+package compiler.loopopts;
+
+public class TestUnreachableInnerLoop {
+
+    public static int field = 0;
+    public static int arr[] = new int[500];
+
+    public static void fun() {
+        for (int elem : arr) {
+            int x = 1, y = 2, z = 3;
+            int i, j;
+
+            // This is a good loop
+            for (i = 2; i < 63; i++) {
+                arr[i] = arr[i] + 3592870;
+            }
+
+            // The inner loop looks quite complex but it's unreachable
+            // code as loop condition "k < 2" never satisfies
+            for (j = 3; j < 63; j++) {
+                for (int k = j; k < 2; k++) {
+                    arr[j] <<= k;
+                    try {
+                        x = k / i;
+                        y = j % 6;
+                        arr[k] = 88 % elem;
+                    } catch (ArithmeticException ex) {}
+                    switch (2) {
+                        case 2: {
+                            try {
+                                y = arr[j] % y;
+                                z = x / 2345;
+                                elem = j % -2;
+                            } catch (ArithmeticException ex) {}
+                            break;
+                        }
+                        case 3: {
+                            y = arr[j] / 2;
+                            z -= k;
+                            break;
+                        }
+                    }
+                    arr[100] -= j;
+                    field += k;
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        fun();
+    }
+}