[compiler] Consistently use Ignition+TurboFan for lexical variables.

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 140 matching lines @@
     case VariableLocation::LOOKUP:
       DisableFullCodegenAndCrankshaft(
           kReferenceToAVariableWhichRequiresDynamicLookup);
       break;
     case VariableLocation::MODULE:
       DisableFullCodegenAndCrankshaft(kReferenceToModuleVariable);
       break;
     default:
       break;
   }
+  if (IsLexicalVariableMode(node->var()->mode())) {

[adamk, 2016/12/05 20:47:31]

As noted on the other CL (fixing a perf regression in array.js), it seems like
this check could be narrowed to

  IsLexicalVariableMode() && node->var()->binding_needs_init()

(or maybe you don't even need IsLexicalVariableMode()). That would avoid
disabling crankshaft for the case of named function expressions (which never
need a hole check for the function name var). Thoughts?

[Benedikt Meurer, 2016/12/06 05:10:48]

Ah perfect, thanks a lot Adam for the investigation and the explanation. I was a
bit puzzled that this affected named function expressions. I'll change it to
node->var()->binding_needs_init() only.

+    DisableFullCodegenAndCrankshaft(kReferenceToLetOrConstVariable);
+  }
   node->set_base_id(ReserveIdRange(VariableProxy::num_ids()));
 }
 
 
 void AstNumberingVisitor::VisitVariableProxy(VariableProxy* node) {
   VisitVariableProxyReference(node);
   ReserveFeedbackSlots(node);
 }
 
 
@@ skipping 445 matching lines @@
 }
 
 
 bool AstNumbering::Renumber(Isolate* isolate, Zone* zone,
                             FunctionLiteral* function) {
   AstNumberingVisitor visitor(isolate, zone);
   return visitor.Renumber(function);
 }
 }  // namespace internal
 }  // namespace v8