[compiler] Improve let+const decision in AstNumbering.

src/ast/ast-numbering.cc

 // Copyright 2012 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/ast/ast-numbering.h"
 
 #include "src/ast/ast.h"
 #include "src/ast/scopes.h"
 
 namespace v8 {
@@ skipping 143 matching lines @@
     case VariableLocation::LOOKUP:
       DisableFullCodegenAndCrankshaft(
           kReferenceToAVariableWhichRequiresDynamicLookup);
       break;
     case VariableLocation::MODULE:
       DisableFullCodegenAndCrankshaft(kReferenceToModuleVariable);
       break;
     default:
       break;
   }
-  if (IsLexicalVariableMode(node->var()->mode())) {
+  if (node->var()->binding_needs_init()) {
+    // Disable FCG+CS for all variable bindings that need explicit
+    // initialization, i.e. ES2015 stylt const and let, but not

[Yang, 2016/12/06 05:48:14]

Is 'stylt' a typo?

+    // named function expressions.
     DisableFullCodegenAndCrankshaft(kReferenceToLetOrConstVariable);
   }
   node->set_base_id(ReserveIdRange(VariableProxy::num_ids()));
 }
 
 
 void AstNumberingVisitor::VisitVariableProxy(VariableProxy* node) {
   VisitVariableProxyReference(node);
   ReserveFeedbackSlots(node);
 }
@@ skipping 464 matching lines @@
 }
 
 
 bool AstNumbering::Renumber(Isolate* isolate, Zone* zone,
                             FunctionLiteral* function) {
   AstNumberingVisitor visitor(isolate, zone);
   return visitor.Renumber(function);
 }
 }  // namespace internal
 }  // namespace v8