[turbofan] Introduce a dedicated ConvertTaggedHoleToUndefined operator.

src/heap/heap.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/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/context-slot-cache.h"
 #include "src/base/bits.h"
@@ skipping 2611 matching lines @@
   Oddball::Initialize(isolate(), factory->undefined_value(), "undefined",
                       factory->nan_value(), "undefined", Oddball::kUndefined);
 
   // Initialize the null_value.
   Oddball::Initialize(isolate(), factory->null_value(), "null",
                       handle(Smi::FromInt(0), isolate()), "object",
                       Oddball::kNull);
 
   // Initialize the_hole_value.
   Oddball::Initialize(isolate(), factory->the_hole_value(), "hole",
-                      handle(Smi::FromInt(-1), isolate()), "undefined",
-                      Oddball::kTheHole);
+                      factory->NewHeapNumber(bit_cast<double>(kHoleNanInt64)),

[Michael Starzinger, 2016/08/10 13:59:37]

nit: Please pretenure this heap-number to avoid old-to-new reference.

[Benedikt Meurer, 2016/08/10 14:01:00]

Done.

+                      "undefined", Oddball::kTheHole);
 
   // Initialize the true_value.
   Oddball::Initialize(isolate(), factory->true_value(), "true",
                       handle(Smi::FromInt(1), isolate()), "boolean",
                       Oddball::kTrue);
 
   // Initialize the false_value.
   Oddball::Initialize(isolate(), factory->false_value(), "false",
                       handle(Smi::FromInt(0), isolate()), "boolean",
                       Oddball::kFalse);
@@ skipping 3839 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8