From 34712f6bbc3c2c664ee641c78d4a2f8cfe427880 Mon Sep 17 00:00:00 2001
Date: Fri, 28 Feb 2020 15:17:44 +0000
Subject: [PATCH] prohibition of irreducible loop in mergers

Summary: C2Compiler: irreducible loop should not enter merge_many_backedges
LLT: NA
Bug url: NA
---
 hotspot/src/share/vm/opto/loopnode.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hotspot/src/share/vm/opto/loopnode.cpp b/hotspot/src/share/vm/opto/loopnode.cpp
index e2c0645cf8..bbb2e2bf98 100644
--- a/hotspot/src/share/vm/opto/loopnode.cpp
+++ b/hotspot/src/share/vm/opto/loopnode.cpp
@@ -1542,7 +1542,7 @@ bool IdealLoopTree::beautify_loops( PhaseIdealLoop *phase ) {
   // 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 );
-- 
2.12.3