Implement basic array prefetching hints in Hydrogen.

src/code-stubs-hydrogen.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 64 matching lines @@
   }
   HBasicBlock* next_block = graph()->CreateBasicBlock();
   next_block->SetInitialEnvironment(graph()->start_environment());
   HGoto* jump = new(zone()) HGoto(next_block);
   graph()->entry_block()->Finish(jump);
   set_current_block(next_block);
 
   context_ = new(zone()) HContext();
   AddInstruction(context_);
 
+  HConstant* undefined_constant = new(zone()) HConstant(
+      info_.isolate()->factory()->undefined_value(), Representation::Tagged());
+  AddInstruction(undefined_constant);
+  graph()->set_undefined_constant(undefined_constant);
+
   int major_key = stub()->MajorKey();
   CodeStubInterfaceDescriptor* descriptor =
       info_.isolate()->code_stub_interface_descriptor(major_key);
   if (descriptor->register_param_count_ < 0) {
     stub()->InitializeInterfaceDescriptor(info_.isolate(), descriptor);
   }
   parameters_.Reset(new HParameter*[descriptor->register_param_count_]);
 
   HGraph* graph = this->graph();
   Zone* zone = this->zone();
@@ skipping 36 matching lines @@
 }
 
 
 Handle<Code> KeyedLoadFastElementStub::GenerateCode() {
   CodeStubGraphBuilder<KeyedLoadFastElementStub> builder(this);
   return CodeFromGraph(builder.CreateGraph());
 }
 
 
 } }  // namespace v8::internal