Replace HeapNumber as doublebox with an explicit MutableHeapNumber.

src/heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2838 matching lines @@
     }
 
 #define ALLOCATE_VARSIZE_MAP(instance_type, field_name)                        \
     ALLOCATE_MAP(instance_type, kVariableSizeSentinel, field_name)
 
     ALLOCATE_VARSIZE_MAP(FIXED_ARRAY_TYPE, fixed_cow_array)
     ASSERT(fixed_array_map() != fixed_cow_array_map());
 
     ALLOCATE_VARSIZE_MAP(FIXED_ARRAY_TYPE, scope_info)
     ALLOCATE_MAP(HEAP_NUMBER_TYPE, HeapNumber::kSize, heap_number)
+    ALLOCATE_MAP(
+        MUTABLE_HEAP_NUMBER_TYPE, HeapNumber::kSize, mutable_heap_number)
     ALLOCATE_MAP(SYMBOL_TYPE, Symbol::kSize, symbol)
     ALLOCATE_MAP(FOREIGN_TYPE, Foreign::kSize, foreign)
 
     for (unsigned i = 0; i < ARRAY_SIZE(string_type_table); i++) {
       const StringTypeTable& entry = string_type_table[i];
       { MaybeObject* maybe_obj = AllocateMap(entry.type, entry.size);
         if (!maybe_obj->ToObject(&obj)) return false;
       }
       roots_[entry.index] = Map::cast(obj);
     }
@@ skipping 90 matching lines @@
     }
 
     TYPED_ARRAYS(ALLOCATE_EMPTY_FIXED_TYPED_ARRAY)
 #undef ALLOCATE_EMPTY_FIXED_TYPED_ARRAY
   }
   ASSERT(!InNewSpace(empty_fixed_array()));
   return true;
 }
 
 
-MaybeObject* Heap::AllocateHeapNumber(double value, PretenureFlag pretenure) {
+MaybeObject* Heap::AllocateHeapNumber(double value,
+                                      MutableMode mode,
+                                      PretenureFlag pretenure) {
   // Statically ensure that it is safe to allocate heap numbers in paged
   // spaces.
   int size = HeapNumber::kSize;
   STATIC_ASSERT(HeapNumber::kSize <= Page::kMaxRegularHeapObjectSize);
 
   AllocationSpace space = SelectSpace(size, OLD_DATA_SPACE, pretenure);
 
   Object* result;
   { MaybeObject* maybe_result = AllocateRaw(size, space, OLD_DATA_SPACE);
     if (!maybe_result->ToObject(&result)) return maybe_result;
   }
 
-  HeapObject::cast(result)->set_map_no_write_barrier(heap_number_map());
+  Map* map = mode == MUTABLE ? mutable_heap_number_map() : heap_number_map();
+  HeapObject::cast(result)->set_map_no_write_barrier(map);
   HeapNumber::cast(result)->set_value(value);
   return result;
 }
 
 
 MaybeObject* Heap::AllocateCell(Object* value) {
   int size = Cell::kSize;
   STATIC_ASSERT(Cell::kSize <= Page::kMaxRegularHeapObjectSize);
 
   Object* result;
@@ skipping 128 matching lines @@
   // To workaround the problem, make separate functions without inlining.
   Heap::CreateJSEntryStub();
   Heap::CreateJSConstructEntryStub();
 }
 
 
 bool Heap::CreateInitialObjects() {
   Object* obj;
 
   // The -0 value must be set before NumberFromDouble works.
-  { MaybeObject* maybe_obj = AllocateHeapNumber(-0.0, TENURED);
+  { MaybeObject* maybe_obj = AllocateHeapNumber(-0.0, IMMUTABLE, TENURED);
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   set_minus_zero_value(HeapNumber::cast(obj));
   ASSERT(std::signbit(minus_zero_value()->Number()) != 0);
 
-  { MaybeObject* maybe_obj = AllocateHeapNumber(OS::nan_value(), TENURED);
+  { MaybeObject* maybe_obj = AllocateHeapNumber(
+        OS::nan_value(), IMMUTABLE, TENURED);
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   set_nan_value(HeapNumber::cast(obj));
 
-  { MaybeObject* maybe_obj = AllocateHeapNumber(V8_INFINITY, TENURED);
+  { MaybeObject* maybe_obj = AllocateHeapNumber(
+        V8_INFINITY, IMMUTABLE, TENURED);
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   set_infinity_value(HeapNumber::cast(obj));
 
   // The hole has not been created yet, but we want to put something
   // predictable in the gaps in the string table, so lets make that Smi zero.
   set_the_hole_value(reinterpret_cast<Oddball*>(Smi::FromInt(0)));
 
   // Allocate initial string table.
   { MaybeObject* maybe_obj =
@@ skipping 661 matching lines @@
   return FixedTypedArrayBase::cast(
       roots_[RootIndexForEmptyFixedTypedArray(map->elements_kind())]);
 }
 
 
 MaybeObject* Heap::NumberFromDouble(double value, PretenureFlag pretenure) {
   // We need to distinguish the minus zero value and this cannot be
   // done after conversion to int. Doing this by comparing bit
   // patterns is faster than using fpclassify() et al.
   if (IsMinusZero(value)) {
-    return AllocateHeapNumber(-0.0, pretenure);
+    return AllocateHeapNumber(-0.0, IMMUTABLE, pretenure);
   }
 
   int int_value = FastD2I(value);
   if (value == int_value && Smi::IsValid(int_value)) {
     return Smi::FromInt(int_value);
   }
 
   // Materialize the value in the heap.
-  return AllocateHeapNumber(value, pretenure);
+  return AllocateHeapNumber(value, IMMUTABLE, pretenure);
 }
 
 
 MaybeObject* Heap::AllocateForeign(Address address, PretenureFlag pretenure) {
   // Statically ensure that it is safe to allocate foreigns in paged spaces.
   STATIC_ASSERT(Foreign::kSize <= Page::kMaxRegularHeapObjectSize);
   AllocationSpace space = (pretenure == TENURED) ? OLD_DATA_SPACE : NEW_SPACE;
   Foreign* result;
   MaybeObject* maybe_result = Allocate(foreign_map(), space);
   if (!maybe_result->To(&result)) return maybe_result;
@@ skipping 4023 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   OS::MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   OS::MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 
 } }  // namespace v8::internal