--- old/src/share/vm/opto/memnode.cpp	Tue Nov 17 16:51:07 2009
+++ new/src/share/vm/opto/memnode.cpp	Tue Nov 17 16:51:06 2009
@@ -123,6 +123,19 @@
       } else {
         assert(false, "unexpected projection");
       }
+    } else if (result->Opcode() == Op_ClearArray) {
+      intptr_t offset;
+      AllocateNode* alloc = AllocateNode::Ideal_allocation(result->in(3), phase, offset);
+      // We can not bypass initialization of the instance we are looking for
+      // or when something is wrong.
+      if (alloc == NULL || alloc->_idx == (uint)tinst->instance_id())
+        break;
+      // Otherwise skip it.
+      InitializeNode* init = alloc->initialization();
+      if (init != NULL)
+        result = init->in(TypeFunc::Memory);
+      else
+        result = alloc->in(TypeFunc::Memory);
     } else if (result->is_MergeMem()) {
       result = step_through_mergemem(phase, result->as_MergeMem(), t_adr, NULL, tty);
     }
@@ -537,6 +550,20 @@
       } else if (mem->is_Proj() && mem->in(0)->is_MemBar()) {
         mem = mem->in(0)->in(TypeFunc::Memory);
         continue;           // (a) advance through independent MemBar memory
+      } else if (mem->Opcode() == Op_ClearArray) {
+        intptr_t offset;
+        AllocateNode* alloc = AllocateNode::Ideal_allocation(mem->in(3), phase, offset);
+        // We can not bypass initialization of the instance we are looking for
+        // or when something is wrong.
+        if (alloc == NULL || alloc->_idx == (uint)addr_t->instance_id())
+          return mem;
+        // Otherwise skip it.
+        InitializeNode* init = alloc->initialization();
+        if (init != NULL)
+          mem = init->in(TypeFunc::Memory);
+        else
+          mem = alloc->in(TypeFunc::Memory);
+        continue;           // (a) advance through independent allocation memory
       } else if (mem->is_MergeMem()) {
         int alias_idx = phase->C->get_alias_index(adr_type());
         mem = mem->as_MergeMem()->memory_at(alias_idx);
@@ -2606,7 +2633,30 @@
 // Return a node which is more "ideal" than the current node.  Strip out
 // control copies
 Node *MemBarNode::Ideal(PhaseGVN *phase, bool can_reshape) {
-  return remove_dead_region(phase, can_reshape) ? this : NULL;
+  if (remove_dead_region(phase, can_reshape)) return this;
+
+  // Eliminate volatile MemBars for scalar replaced objects.
+  if (can_reshape && req() == (Precedent+1) &&
+      (Opcode() == Op_MemBarAcquire || Opcode() == Op_MemBarVolatile)) {
+    // Volatile field loads and stores.
+    Node* my_mem = in(MemBarNode::Precedent);
+    if (my_mem != NULL && my_mem->is_Mem()) {
+      const TypeOopPtr* t_oop = my_mem->in(MemNode::Address)->bottom_type()->isa_oopptr();
+      // Check for scalar replaced object reference.
+      if( t_oop != NULL && t_oop->is_known_instance_field() &&
+          t_oop->offset() != Type::OffsetBot &&
+          t_oop->offset() != Type::OffsetTop) {
+        // Replace MemBar projections by its inputs.
+        PhaseIterGVN* igvn = phase->is_IterGVN();
+        igvn->replace_node(proj_out(TypeFunc::Memory), in(TypeFunc::Memory));
+        igvn->replace_node(proj_out(TypeFunc::Control), in(TypeFunc::Control));
+        // Must return either the original node (now dead) or a new node
+        // (Do not return a top here, since that would break the uniqueness of top.)
+        return new (phase->C, 1) ConINode(TypeInt::ZERO);
+      }
+    }
+  }
+  return NULL;
 }
 
 //------------------------------Value------------------------------------------