8293978: Duplicate simple loop back-edge will crash the vm

Reviewed-by: roland, chagedorn

Author: casparcwang

src/hotspot/share/opto/loopopts.cpp

@@ -3920,7 +3920,8 @@ bool PhaseIdealLoop::duplicate_loop_backedge(IdealLoopTree *loop, Node_List &old
     }
 
     // With an extra phi for the candidate iv?
-    if (!incr->is_Phi()) {
+    // Or the region node is the loop head
+    if (!incr->is_Phi() || incr->in(0) == head) {
       return false;
     }
 

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

@@ -0,0 +1,65 @@
+/*
+  * Copyright (c) 2022 THL A29 Limited, a Tencent company. 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 8293978
+  * @summary Crash in PhaseIdealLoop::verify_strip_mined_scheduling
+  *
+  * @run main/othervm -Xbatch TestDuplicateSimpleLoopBackedge
+  *
+  */
+
+public class TestDuplicateSimpleLoopBackedge {
+    static void zero(Byte[] a) {
+        for (int e = 0; e < a.length; e++) {
+            a[e] = 0;
+        }
+    }
+
+    int foo(int g) {
+        Byte h[] = new Byte[500];
+        zero(h);
+        short i = 7;
+        while (i != 1) {
+            i = (short)(i - 3);
+        }
+        return 0;
+    }
+
+    void bar(String[] k) {
+        try {
+            int l = 5;
+            if (l < foo(l)) {
+            }
+        } catch (Exception m) {
+        }
+    }
+
+    public static void main(String[] args) {
+        TestDuplicateSimpleLoopBackedge n = new TestDuplicateSimpleLoopBackedge();
+        for (int i = 0; i < 10000; ++i) {
+            n.bar(args);
+        }
+    }
+}