--- old/src/hotspot/share/opto/memnode.cpp	2018-06-08 19:45:33.128678566 +0200
+++ new/src/hotspot/share/opto/memnode.cpp	2018-06-08 19:45:32.857666808 +0200
@@ -44,7 +44,11 @@
 #include "opto/regmask.hpp"
 #include "utilities/align.hpp"
 #include "utilities/copy.hpp"
+#include "utilities/macros.hpp"
 #include "utilities/vmError.hpp"
+#if INCLUDE_ZGC
+#include "gc/z/c2/zBarrierSetC2.hpp"
+#endif
 
 // Portions of code courtesy of Clifford Click
 
@@ -891,6 +895,14 @@
 // a load node that reads from the source array so we may be able to
 // optimize out the ArrayCopy node later.
 Node* LoadNode::can_see_arraycopy_value(Node* st, PhaseGVN* phase) const {
+#if INCLUDE_ZGC
+  if (UseZGC) {
+    if (bottom_type()->make_oopptr() != NULL) {
+      return NULL;
+    }
+  }
+#endif
+
   Node* ld_adr = in(MemNode::Address);
   intptr_t ld_off = 0;
   AllocateNode* ld_alloc = AllocateNode::Ideal_allocation(ld_adr, phase, ld_off);
@@ -1574,7 +1586,7 @@
   // Is there a dominating load that loads the same value?  Leave
   // anything that is not a load of a field/array element (like
   // barriers etc.) alone
-  if (in(0) != NULL && adr_type() != TypeRawPtr::BOTTOM && can_reshape) {
+  if (in(0) != NULL && !adr_type()->isa_rawptr() && can_reshape) {
     for (DUIterator_Fast imax, i = mem->fast_outs(imax); i < imax; i++) {
       Node *use = mem->fast_out(i);
       if (use != this &&
@@ -2968,6 +2980,16 @@
     return NULL;
   }
 
+#if INCLUDE_ZGC
+  if (UseZGC) {
+    if (req() == (Precedent+1) && in(MemBarNode::Precedent)->in(0) != NULL && in(MemBarNode::Precedent)->in(0)->is_LoadBarrier()) {
+      Node* load_node = in(MemBarNode::Precedent)->in(0)->in(LoadBarrierNode::Oop);
+      set_req(MemBarNode::Precedent, load_node);
+      return this;
+    }
+  }
+#endif
+
   bool progress = false;
   // Eliminate volatile MemBars for scalar replaced objects.
   if (can_reshape && req() == (Precedent+1)) {