Replace HeapNumber as doublebox with an explicit MutableHeapNumber.

src/ia32/macro-assembler-ia32.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 1814 matching lines @@
   // Allocate heap number in new space.
   Allocate(HeapNumber::kSize, result, scratch1, scratch2, gc_required,
            TAG_OBJECT);
 
   // Set the map.
   mov(FieldOperand(result, HeapObject::kMapOffset),
       Immediate(isolate()->factory()->heap_number_map()));
 }
 
 
+void MacroAssembler::AllocateMutableHeapNumber(Register result,
+                                               Register scratch1,
+                                               Register scratch2,
+                                               Label* gc_required) {
+  // Allocate heap number in new space.
+  Allocate(HeapNumber::kSize, result, scratch1, scratch2, gc_required,
+           TAG_OBJECT);
+
+  // Set the map.
+  mov(FieldOperand(result, HeapObject::kMapOffset),
+      Immediate(isolate()->factory()->mutable_heap_number_map()));
+}
+
+
 void MacroAssembler::AllocateTwoByteString(Register result,
                                            Register length,
                                            Register scratch1,
                                            Register scratch2,
                                            Register scratch3,
                                            Label* gc_required) {
   // Calculate the number of bytes needed for the characters in the string while
   // observing object alignment.
   ASSERT((SeqTwoByteString::kHeaderSize & kObjectAlignmentMask) == 0);
   ASSERT(kShortSize == 2);
@@ skipping 1801 matching lines @@
   if (ms.shift() > 0) sar(edx, ms.shift());
   mov(eax, dividend);
   shr(eax, 31);
   add(edx, eax);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32