[turbofan] Introduce a dedicated ConvertTaggedHoleToUndefined operator.

src/objects-debug.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/objects.h"
 
 #include "src/bootstrapper.h"
 #include "src/disasm.h"
 #include "src/disassembler.h"
 #include "src/field-type.h"
@@ skipping 583 matching lines @@
   JSObjectVerify();
 }
 
 
 void Oddball::OddballVerify() {
   CHECK(IsOddball());
   Heap* heap = GetHeap();
   VerifyHeapPointer(to_string());
   Object* number = to_number();
   if (number->IsHeapObject()) {
-    CHECK(number == heap->nan_value());
+    CHECK(number == heap->nan_value() ||
+          number == heap->hole_nan_value());
   } else {
     CHECK(number->IsSmi());
     int value = Smi::cast(number)->value();
     // Hidden oddballs have negative smis.
     const int kLeastHiddenOddballNumber = -7;
     CHECK_LE(value, 1);
     CHECK(value >= kLeastHiddenOddballNumber);
   }
   if (map() == heap->undefined_map()) {
     CHECK(this == heap->undefined_value());
@@ skipping 718 matching lines @@
 
   // Both are done at the same time.
   CHECK_EQ(new_it.done(), old_it.done());
 }
 
 
 #endif  // DEBUG
 
 }  // namespace internal
 }  // namespace v8