--- old/src/hotspot/share/opto/loopopts.cpp	2018-11-26 21:30:19.599962610 +0100
+++ new/src/hotspot/share/opto/loopopts.cpp	2018-11-26 21:30:19.438964030 +0100
@@ -44,11 +44,14 @@
 #if INCLUDE_ZGC
 #include "gc/z/c2/zBarrierSetC2.hpp"
 #endif
+#if INCLUDE_SHENANDOAHGC
+#include "gc/shenandoah/c2/shenandoahBarrierSetC2.hpp"
+#endif
 
 //=============================================================================
 //------------------------------split_thru_phi---------------------------------
 // Split Node 'n' through merge point if there is enough win.
-Node *PhaseIdealLoop::split_thru_phi( Node *n, Node *region, int policy ) {
+Node *PhaseIdealLoop::split_thru_phi(Node *n, Node *region, int policy, Node** out_mem_phi) {
   if (n->Opcode() == Op_ConvI2L && n->bottom_type() != TypeLong::LONG) {
     // ConvI2L may have type information on it which is unsafe to push up
     // so disable this for now
@@ -78,6 +81,12 @@
   } else {
     phi = PhiNode::make_blank(region, n);
   }
+  Node* mem_phi = NULL;
+#if INCLUDE_SHENANDOAHGC
+  if (n->Opcode() == Op_ShenandoahWriteBarrier) {
+    mem_phi = new PhiNode(region, Type::MEMORY, C->alias_type(n->adr_type())->adr_type());
+  }
+#endif
   uint old_unique = C->unique();
   for (uint i = 1; i < region->req(); i++) {
     Node *x;
@@ -149,15 +158,38 @@
     if (x != the_clone && the_clone != NULL)
       _igvn.remove_dead_node(the_clone);
     phi->set_req( i, x );
+#if INCLUDE_SHENANDOAHGC
+    if (mem_phi != NULL) {
+      if (x == the_clone) {
+        mem_phi->init_req(i, _igvn.transform(new ShenandoahWBMemProjNode(x)));
+      } else {
+        Node* mem = n->in(ShenandoahBarrierNode::Memory);
+        if (mem->is_Phi() && mem->in(0) == region) {
+          mem = mem->in(i);
+        }
+        mem_phi->init_req(i, mem);
+      }
+    }
+#endif
   }
   // Too few wins?
   if (wins <= policy) {
     _igvn.remove_dead_node(phi);
+#if INCLUDE_SHENANDOAHGC
+    if (mem_phi != NULL) {
+      _igvn.remove_dead_node(mem_phi);
+    }
+#endif
     return NULL;
   }
 
   // Record Phi
   register_new_node( phi, region );
+#if INCLUDE_SHENANDOAHGC
+  if (mem_phi != NULL) {
+    register_new_node(mem_phi, region);
+  }
+#endif
 
   for (uint i2 = 1; i2 < phi->req(); i2++) {
     Node *x = phi->in(i2);
@@ -209,6 +241,25 @@
     }
   }
 
+#if INCLUDE_SHENANDOAHGC
+  if (mem_phi != NULL) {
+    for (uint i2 = 1; i2 < mem_phi->req(); i2++) {
+      Node *x = mem_phi->in(i2);
+      if (x->_idx >= old_unique) {
+        assert(x->Opcode() == Op_ShenandoahWBMemProj, "only for shenandoah memory");
+        set_ctrl(x, get_ctrl(x->in(ShenandoahWBMemProjNode::WriteBarrier)));
+        IdealLoopTree* loop = get_loop(get_ctrl(x));
+        if (loop->_child == NULL) {
+          loop->_body.push(x);
+        }
+
+      }
+    }
+  }
+  if (mem_phi != NULL) {
+    *out_mem_phi = mem_phi;
+  }
+#endif
   return phi;
 }
 
@@ -918,6 +969,12 @@
     return n;
   }
 
+#if INCLUDE_SHENANDOAHGC
+  if (n->Opcode() == Op_ShenandoahReadBarrier) {
+    ((ShenandoahReadBarrierNode*)n)->try_move(n_ctrl, this);
+  }
+#endif
+
   // Attempt to remix address expressions for loop invariants
   Node *m = remix_address_expressions( n );
   if( m ) return m;
@@ -945,7 +1002,7 @@
 
   // Check for having no control input; not pinned.  Allow
   // dominating control.
-  if (n->in(0)) {
+  if (n->in(0) && !(n->Opcode() == Op_ShenandoahWriteBarrier && n->in(0) == n_blk)) {
     Node *dom = idom(n_blk);
     if (dom_lca(n->in(0), dom) != n->in(0)) {
       return n;
@@ -970,17 +1027,27 @@
   if( C->live_nodes() > 35000 ) return n; // Method too big
 
   // Split 'n' through the merge point if it is profitable
-  Node *phi = split_thru_phi( n, n_blk, policy );
+  Node* mem_phi = NULL;
+  Node *phi = split_thru_phi(n, n_blk, policy, &mem_phi);
   if (!phi) return n;
 
   // Found a Phi to split thru!
   // Replace 'n' with the new phi
-  _igvn.replace_node( n, phi );
+  if (n->Opcode() == Op_ShenandoahWriteBarrier) {
+    Node* proj = n->find_out_with(Op_ShenandoahWBMemProj);
+    _igvn.replace_node(proj, mem_phi);
+  }
+  _igvn.replace_node(n, phi);
   // Moved a load around the loop, 'en-registering' something.
   if (n_blk->is_Loop() && n->is_Load() &&
       !phi->in(LoopNode::LoopBackControl)->is_Load())
     C->set_major_progress();
 
+  // Moved a barrier around the loop, 'en-registering' something.
+  if (n_blk->is_Loop() && n->is_ShenandoahBarrier() &&
+      !phi->in(LoopNode::LoopBackControl)->is_ShenandoahBarrier())
+    C->set_major_progress();
+
   return phi;
 }
 
@@ -1019,6 +1086,11 @@
         Node* m = n->fast_out(j);
         if (m->is_FastLock())
           return false;
+#if INCLUDE_SHENANDOAHGC
+        if (m->is_ShenandoahBarrier() && m->has_out_with(Op_FastLock)) {
+          return false;
+        }
+#endif
 #ifdef _LP64
         if (m->Opcode() == Op_ConvI2L)
           return false;
@@ -1335,7 +1407,7 @@
             // For inner loop uses get the preheader area.
             x_ctrl = place_near_use(x_ctrl);
 
-            if (n->is_Load()) {
+            if (n->is_Load() || n->Opcode() == Op_ShenandoahReadBarrier) {
               // For loads, add a control edge to a CFG node outside of the loop
               // to force them to not combine and return back inside the loop
               // during GVN optimization (4641526).
@@ -1343,7 +1415,9 @@
               // Because we are setting the actual control input, factor in
               // the result from get_late_ctrl() so we respect any
               // anti-dependences. (6233005).
-              x_ctrl = dom_lca(late_load_ctrl, x_ctrl);
+              if (n->is_Load()) {
+                x_ctrl = dom_lca(late_load_ctrl, x_ctrl);
+              }
 
               // Don't allow the control input to be a CFG splitting node.
               // Such nodes should only have ProjNodes as outs, e.g. IfNode
@@ -1365,7 +1439,7 @@
             // to fold a StoreP and an AddP together (as part of an
             // address expression) and the AddP and StoreP have
             // different controls.
-            if (!x->is_Load() && !x->is_DecodeNarrowPtr()) _igvn._worklist.yank(x);
+            if (!x->is_Load() && !x->is_DecodeNarrowPtr() && !x->is_ShenandoahBarrier() && !x->is_MergeMem()) _igvn._worklist.yank(x);
           }
           _igvn.remove_dead_node(n);
         }
@@ -3132,7 +3206,7 @@
 
           // if not pinned and not a load (which maybe anti-dependent on a store)
           // and not a CMove (Matcher expects only bool->cmove).
-          if ( n->in(0) == NULL && !n->is_Load() && !n->is_CMove() ) {
+          if (n->in(0) == NULL && !n->is_Load() && !n->is_CMove() && n->Opcode() != Op_ShenandoahWBMemProj) {
             cloned_for_outside_use += clone_for_use_outside_loop( loop, n, worklist );
             sink_list.push(n);
             peel     >>= n->_idx; // delete n from peel set.