[turbofan] Add initial support for global specialization.

src/compiler/js-context-specialization.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/js-context-specialization.h"
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/js-operator.h"
 #include "src/compiler/node-matchers.h"
@@ skipping 77 matching lines @@
   // before the function to which it belongs has initialized the slot.
   // We must be conservative and check if the value in the slot is currently the
   // hole or undefined. If it is neither of these, then it must be initialized.
   if (value->IsUndefined() || value->IsTheHole()) {
     return NoChange();
   }
 
   // Success. The context load can be replaced with the constant.
   // TODO(titzer): record the specialization for sharing code across multiple
   // contexts that have the same value in the corresponding context slot.
+  if (value->IsConsString()) {
+    value = String::Flatten(Handle<String>::cast(value), TENURED);
+  }
   Node* constant = jsgraph_->Constant(value);
   ReplaceWithValue(node, constant);
   return Replace(constant);
 }
 
 
 Reduction JSContextSpecialization::ReduceJSStoreContext(Node* node) {
   DCHECK_EQ(IrOpcode::kJSStoreContext, node->opcode());
 
   // Get the specialization context from the node.
@@ skipping 22 matching lines @@
 }
 
 
 JSOperatorBuilder* JSContextSpecialization::javascript() const {
   return jsgraph()->javascript();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8