diff -r 9cbafea410f5 -r f7691a80458c src/share/vm/opto/loopnode.cpp
--- a/src/share/vm/opto/loopnode.cpp	Mon May 25 07:03:06 2020 +0100
+++ b/src/share/vm/opto/loopnode.cpp	Mon May 25 14:24:27 2020 +0800
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2020, 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
@@ -1538,10 +1538,18 @@
   // If I am a shared header (multiple backedges), peel off the many
   // backedges into a private merge point and use the merge point as
   // the one true backedge.
-  if (_head->req() > 3 && !_irreducible) {
+  if (_head->req() > 3) {
     // Merge the many backedges into a single backedge but leave
     // the hottest backedge as separate edge for the following peel.
-    merge_many_backedges( phase );
+    if (!_irreducible) {
+      merge_many_backedges( phase );
+    }
+
+    // When recursively beautify my children, split_fall_in can change
+    // loop tree structure when I am an irreducible loop. Then the head
+    // of my children has a req() not bigger than 3. Here we need to set
+    // result to true to catch that case in order to tell the caller to
+    // rebuild loop tree. See issue JDK-8244407 for details.
     result = true;
   }