There is an ordinary nested loop in the test case.
When entrybci = -1. It has 5 reducible loop.
Normal control flow looks like:

        +------+
        |0:Root |
        +------+
            |  
            |  
            v  
       +---------+
 <-----|1:Region1|<-----------------+
       |if(i<100)|<---------+       |
       +---------+          |       |
          |  ^              |       |
          |  |              |       |
          v  |              |       |
      +-----------+         |       |
      |2:if(mF!=0)|         |       |
      +-----------+         |       |
           |                |       |
           |                |       |
           v                |       |
       +---------+          |       | try-catch
       |3:Region2|          |       |
       |if(j<101)|----------+       |
       +---------+                  |
          |  ^                      |
          |  |                      |
          v  |                      |
       +---------+                  |
       |4:Region3|                  |
       |if(k<102)|                  |
       +---------+                  |
          |  ^                      |
          |  |                      |
          v  |                      |
+-----------------------------+     |
|5:int mI=new Interger(0x1234)|-----+
+-----------------------------+

Current CompileTask:
C2:  13694  832 % !b        Test::testMethod @ 37 (83 bytes)

Problem triggered during the OSR compilation.
It has 3 reducible loop and 1 irreducible loop.
OSR control flow looks like:

                                          +------+
                                          |0:Root|
                                          +---+--+
                                              |
                                              |
                                              v
+-----------------------------+          +----+----+
|5:int mI=new Interger(0x1234)|<---------|4:Region3|
|                             |--------->|if(k<102)|
+------------+----------------+          +--+--+---+
             |                              |  ^
             |                              |  |
             |                              v  |
             |                           +---------+
             |                           |3:Region2|<-----------+
             |  tyr-catch                |if(j<101)|            |
             |                           +---------+            |
             |                                |                 |
             |                                |                 |
             |                                v                 |
             |                           +---------+            |
             +-------------------------->|1:Region1|------>     |
                                         |if(i<100)|            |
                                         +---------+            |
                                            |  ^                |
                                            |  |                |
                                            v  |                |
                                        +-----------+           |
                                        |2:if(mF!=0)|-----------+
                                        +-----------+

In the first beautify_loops, something went wrong when c2 does merge_many_backedges.

2090   // If I am a shared header (multiple backedges), peel off the many
2091   // backedges into a private merge point and use the merge point as
2092   // the one true backedge.
2093   if( _head->req() > 3) {
2094     // Merge the many backedges into a single backedge but leave
2095     // the hottest backedge as separate edge for the following peel.
2096     merge_many_backedges( phase );
2097     result = true;
2098   }

Subgraph before merge_many_backedges:

|                              |
|                              |
|                              v
|                           +---------+
|  try-catch                |3:Region2|<-----------+
|                           |if(j<101)|            |
|                           +---------+            |
|                                |                 |
|                                |                 |
|                                v                 |
|                           +---------+            |
+-------------------------->|1:Region1|----->      |
                            |if(i<100)|            |
                            +---------+            |
                               |  ^                |
                               |  |                |
                               v  |                |
                           +-----------+           |
                           |2:if(mF!=0)|-----------+
                           +-----------+

   
Before line 2096, IdealLoopTree looks like:

IdealLoopTree:
N1/N3 irreducible
  N1/N2 reducible 


Subgraph after merge_many_backedges:

|                              |
|                              |
|                              v
|                           +--+------+
|  try+catch                |3:Region2|<-----------+
|                           |if(j<101)|            |
|                           +---------+            |
|                                |                 |
|                                |                 |
|                                v                 |
|                           +----+----+            |
+-------------------------->|1:Region1|----->      |
                            |if(i<100)|            |
                            ++-------++            |
                             |       ^             |
                             |       |             |
                             |       |             |
                             |     +---------+     |
                             |     |6:Region3|     |
                             |     +---------+     |
                             |       ^             |
                             |       |             |
                             v       |             |
                           +-----------+           |
                           |2:if(mF!=0)|-----------+
                           +-----------+

After line 2096, IdealLoopTree looks like: 

IdealLoopTree:
N1/N6 irreducible
   N1/N3 reducible 

The overall structure of the loop remains the same, but its irreducible attributes
has been modified incorrectly, which further leads to the vm crash.
Proposed fix prevents doing merge_many_backedges when IdealLoopTree is irreducible.

diff -r 67cc6f3948e3 src/hotspot/share/opto/loopnode.cpp
--- a/src/hotspot/share/opto/loopnode.cpp       Wed Mar 04 15:34:53 2020 -0800
+++ b/src/hotspot/share/opto/loopnode.cpp       Thu Mar 05 09:32:57 2020 +0800
@@ -2091,7 +2091,7 @@
   // 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 ) {
+  if (_head->req() > 3 && !_irreducible) {
     // Merge the many backedges into a single backedge but leave
     // the hottest backedge as separate edge for the following peel.
     merge_many_backedges( phase );