[turbofan] We cannot unconditionally flatten cons strings in the JSGraph.

src/compiler/js-graph.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/code-stubs.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/typer.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 Node* JSGraph::ImmovableHeapConstant(Handle<HeapObject> value) {
-  if (value->IsConsString()) {
-    value = String::Flatten(Handle<String>::cast(value), TENURED);
-  }
+  // TODO(bmeurer): Flatten cons strings here before we canonicalize them?
   return graph()->NewNode(common()->HeapConstant(value));
 }
 
 
 #define CACHED(name, expr) \
   cached_nodes_[name] ? cached_nodes_[name] : (cached_nodes_[name] = (expr))
 
 
 Node* JSGraph::CEntryStubConstant(int result_size) {
   if (result_size == 1) {
@@ skipping 176 matching lines @@
   for (size_t i = 0; i < arraysize(cached_nodes_); i++) {
     if (Node* node = cached_nodes_[i]) {
       if (!node->IsDead()) nodes->push_back(node);
     }
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8