Remove unused byte from Map::instance_sizes field.

src/objects.h

 // 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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 5536 matching lines @@
 //  - Size information about the object
 //  - How to iterate over an object (for garbage collection)
 class Map: public HeapObject {
  public:
   // Instance size.
   // Size in bytes or kVariableSizeSentinel if instances do not have
   // a fixed size.
   inline int instance_size();
   inline void set_instance_size(int value);
 
+  // Only to clear an unused byte, remove once byte is used.
+  inline void clear_unused();
+
   // Count of properties allocated in the object.
   inline int inobject_properties();
   inline void set_inobject_properties(int value);
 
-  // Count of property fields pre-allocated in the object when first allocated.
-  inline int pre_allocated_property_fields();
-  inline void set_pre_allocated_property_fields(int value);
-
   // Instance type.
   inline InstanceType instance_type();
   inline void set_instance_type(InstanceType value);
 
   // Tells how many unused property fields are available in the
   // instance (only used for JSObject in fast mode).
   inline int unused_property_fields();
   inline void set_unused_property_fields(int value);
 
   // Bit field.
@@ skipping 421 matching lines @@
   static Handle<Map> Create(Isolate* isolate, int inobject_properties);
 
   // Returns the next free property index (only valid for FAST MODE).
   int NextFreePropertyIndex();
 
   // Returns the number of properties described in instance_descriptors
   // filtering out properties with the specified attributes.
   int NumberOfDescribedProperties(DescriptorFlag which = OWN_DESCRIPTORS,
                                   PropertyAttributes filter = NONE);
 
-  // Returns the number of slots allocated for the initial properties
-  // backing storage for instances of this map.
-  int InitialPropertiesLength() {
-    return pre_allocated_property_fields() + unused_property_fields() -
-        inobject_properties();
-  }
-
   DECLARE_CAST(Map)
 
   // Code cache operations.
 
   // Clears the code cache.
   inline void ClearCodeCache(Heap* heap);
 
   // Update code cache.
   static void UpdateCodeCache(Handle<Map> map,
                               Handle<Name> name,
@@ skipping 115 matching lines @@
   // Layout of pointer fields. Heap iteration code relies on them
   // being continuously allocated.
   static const int kPointerFieldsBeginOffset = Map::kPrototypeOffset;
   static const int kPointerFieldsEndOffset = kSize;
 
   // Byte offsets within kInstanceSizesOffset.
   static const int kInstanceSizeOffset = kInstanceSizesOffset + 0;
   static const int kInObjectPropertiesByte = 1;
   static const int kInObjectPropertiesOffset =
       kInstanceSizesOffset + kInObjectPropertiesByte;
-  static const int kPreAllocatedPropertyFieldsByte = 2;
-  static const int kPreAllocatedPropertyFieldsOffset =
-      kInstanceSizesOffset + kPreAllocatedPropertyFieldsByte;
+  // Note there is one byte available for use here.
+  static const int kUnusedByte = 2;
+  static const int kUnusedOffset = kInstanceSizesOffset + kUnusedByte;
   static const int kVisitorIdByte = 3;
   static const int kVisitorIdOffset = kInstanceSizesOffset + kVisitorIdByte;
 
   // Byte offsets within kInstanceAttributesOffset attributes.
 #if V8_TARGET_LITTLE_ENDIAN
   // Order instance type and bit field together such that they can be loaded
   // together as a 16-bit word with instance type in the lower 8 bits regardless
   // of endianess. Also provide endian-independent offset to that 16-bit word.
   static const int kInstanceTypeOffset = kInstanceAttributesOffset + 0;
   static const int kBitFieldOffset = kInstanceAttributesOffset + 1;
 #else
   static const int kBitFieldOffset = kInstanceAttributesOffset + 0;
   static const int kInstanceTypeOffset = kInstanceAttributesOffset + 1;
 #endif
   static const int kInstanceTypeAndBitFieldOffset =
       kInstanceAttributesOffset + 0;
   static const int kBitField2Offset = kInstanceAttributesOffset + 2;
+  static const int kUnusedPropertyFieldsByte = 3;
   static const int kUnusedPropertyFieldsOffset = kInstanceAttributesOffset + 3;
 
   STATIC_ASSERT(kInstanceTypeAndBitFieldOffset ==
                 Internals::kMapInstanceTypeAndBitFieldOffset);
 
   // Bit positions for bit field.
   static const int kHasNonInstancePrototype = 0;
   static const int kIsHiddenPrototype = 1;
   static const int kHasNamedInterceptor = 2;
   static const int kHasIndexedInterceptor = 3;
@@ skipping 4653 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_