RFR (XS) 8229350: Shenandoah does not need barriers before CreateEx

[Aleksey Shipilev]

Bug:
  https://bugs.openjdk.java.net/browse/JDK-8229350

Fix:

diff -r 2e38a71e6038 src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp
--- a/src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp  Fri Aug 09 03:51:20 2019 +0200
+++ b/src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp  Fri Aug 09 12:18:09 2019 +0200
@@ -3091,10 +3091,12 @@
     case Op_CMoveP:
       return needs_barrier_impl(phase, n->in(2), visited) ||
              needs_barrier_impl(phase, n->in(3), visited);
     case Op_ShenandoahEnqueueBarrier:
       return needs_barrier_impl(phase, n->in(1), visited);
+    case Op_CreateEx:
+      return false;
     default:
       break;
   }
 #ifdef ASSERT
   tty->print("need barrier on?: ");


Testing: {x86_64, x86_32} x {hotspot_gc_shenandoah, vmTestbase_vm_mlvm}

-- 
Thanks,
-Aleksey