Replace HeapNumber as doublebox with an explicit MutableHeapNumber.

src/mips/macro-assembler-mips.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 <limits.h>  // For LONG_MIN, LONG_MAX.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_MIPS
 
@@ skipping 3256 matching lines @@
 }
 
 
 // Allocates a heap number or jumps to the label if the young space is full and
 // a scavenge is needed.
 void MacroAssembler::AllocateHeapNumber(Register result,
                                         Register scratch1,
                                         Register scratch2,
                                         Register heap_number_map,
                                         Label* need_gc,
-                                        TaggingMode tagging_mode) {
+                                        TaggingMode tagging_mode,
+                                        MutableMode mode) {
   // Allocate an object in the heap for the heap number and tag it as a heap
   // object.
   Allocate(HeapNumber::kSize, result, scratch1, scratch2, need_gc,
            tagging_mode == TAG_RESULT ? TAG_OBJECT : NO_ALLOCATION_FLAGS);
 
+  Heap::RootListIndex map_index = mode == MUTABLE
+      ? Heap::kMutableHeapNumberMapRootIndex
+      : Heap::kHeapNumberMapRootIndex;
+  AssertIsRoot(heap_number_map, map_index);
+
   // Store heap number map in the allocated object.
-  AssertIsRoot(heap_number_map, Heap::kHeapNumberMapRootIndex);
   if (tagging_mode == TAG_RESULT) {
     sw(heap_number_map, FieldMemOperand(result, HeapObject::kMapOffset));
   } else {
     sw(heap_number_map, MemOperand(result, HeapObject::kMapOffset));
   }
 }
 
 
 void MacroAssembler::AllocateHeapNumberWithValue(Register result,
                                                  FPURegister value,
@@ skipping 2461 matching lines @@
   }
   if (ms.shift() > 0) sra(result, result, ms.shift());
   srl(at, dividend, 31);
   Addu(result, result, Operand(at));
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS