Introduce "optimized_out" oddball marker for compilers.

src/objects.h

 // Copyright 2015 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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/assert-scope.h"
@@ skipping 986 matching lines @@
   V(OrderedHashTable)
 
 #define ODDBALL_LIST(V) \
   V(Undefined)          \
   V(Null)               \
   V(TheHole)            \
   V(Exception)          \
   V(Uninitialized)      \
   V(True)               \
   V(False)              \
-  V(ArgumentsMarker)
+  V(ArgumentsMarker)    \
+  V(OptimizedOut)
 
 // The element types selection for CreateListFromArrayLike.
 enum class ElementTypes { kAll, kStringAndSymbol };
 
 // Object is the abstract superclass for all classes in the
 // object hierarchy.
 // Object does not use any virtual functions to avoid the
 // allocation of the C++ vtable.
 // Since both Smi and HeapObject are subclasses of Object no
 // data members can be present in Object.
@@ skipping 8573 matching lines @@
   static const byte kFalse = 0;
   static const byte kTrue = 1;
   static const byte kNotBooleanMask = ~1;
   static const byte kTheHole = 2;
   static const byte kNull = 3;
   static const byte kArgumentsMarker = 4;
   static const byte kUndefined = 5;
   static const byte kUninitialized = 6;
   static const byte kOther = 7;
   static const byte kException = 8;
+  static const byte kOptimizedOut = 9;
 
   typedef FixedBodyDescriptor<kToStringOffset, kTypeOfOffset + kPointerSize,
                               kSize> BodyDescriptor;
 
   STATIC_ASSERT(kKindOffset == Internals::kOddballKindOffset);
   STATIC_ASSERT(kNull == Internals::kNullOddballKind);
   STATIC_ASSERT(kUndefined == Internals::kUndefinedOddballKind);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(Oddball);
@@ skipping 1277 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_