--- a/src/hotspot/share/opto/memnode.hpp	Thu Sep 20 21:47:13 2018 +0200
+++ b/src/hotspot/share/opto/memnode.hpp	Thu Sep 20 22:01:12 2018 +0200
@@ -190,7 +190,7 @@
 public:
 
   LoadNode(Node *c, Node *mem, Node *adr, const TypePtr* at, const Type *rt, MemOrd mo, ControlDependency control_dependency)
-    : MemNode(c,mem,adr,at), _type(rt), _mo(mo), _control_dependency(control_dependency) {
+    : MemNode(c,mem,adr,at), _control_dependency(control_dependency), _mo(mo), _type(rt) {
     init_class_id(Class_Load);
   }
   inline bool is_unordered() const { return !is_acquire(); }
@@ -607,6 +607,8 @@
 
   // have all possible loads of the value stored been optimized away?
   bool value_never_loaded(PhaseTransform *phase) const;
+
+  MemBarNode* trailing_membar() const;
 };
 
 //------------------------------StoreBNode-------------------------------------
@@ -816,6 +818,7 @@
   virtual const class TypePtr *adr_type() const { return _adr_type; }  // returns bottom_type of address
 
   bool result_not_used() const;
+  MemBarNode* trailing_membar() const;
 };
 
 class LoadStoreConditionalNode : public LoadStoreNode {
@@ -1142,6 +1145,20 @@
   // Memory type this node is serializing.  Usually either rawptr or bottom.
   const TypePtr* _adr_type;
 
+  // How is this membar related to a nearby memory access?
+  enum {
+    Standalone,
+    TrailingLoad,
+    TrailingStore,
+    LeadingStore,
+    TrailingLoadStore,
+    LeadingLoadStore
+  } _kind;
+
+#ifdef ASSERT
+  uint _pair_idx;
+#endif
+
 public:
   enum {
     Precedent = TypeFunc::Parms  // optional edge to force precedence
@@ -1159,6 +1176,24 @@
   static MemBarNode* make(Compile* C, int opcode,
                           int alias_idx = Compile::AliasIdxBot,
                           Node* precedent = NULL);
+
+  MemBarNode* trailing_membar() const;
+  MemBarNode* leading_membar() const;
+
+  void set_trailing_load() { _kind = TrailingLoad; }
+  bool trailing_load() const { return _kind == TrailingLoad; }
+  bool trailing_store() const { return _kind == TrailingStore; }
+  bool leading_store() const { return _kind == LeadingStore; }
+  bool trailing_load_store() const { return _kind == TrailingLoadStore; }
+  bool leading_load_store() const { return _kind == LeadingLoadStore; }
+  bool trailing() const { return _kind == TrailingLoad || _kind == TrailingStore || _kind == TrailingLoadStore; }
+  bool leading() const { return _kind == LeadingStore || _kind == LeadingLoadStore; }
+  bool standalone() const { return _kind == Standalone; }
+
+  static void set_store_pair(MemBarNode* leading, MemBarNode* trailing);
+  static void set_load_store_pair(MemBarNode* leading, MemBarNode* trailing);
+
+  void remove(PhaseIterGVN *igvn);
 };
 
 // "Acquire" - no following ref can move before (but earlier refs can