Revert "Replace HeapNumber as doublebox with an explicit MutableHeapNumber."

src/x64/macro-assembler-x64.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 "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 4575 matching lines @@
 #ifdef DEBUG
   cmpp(object, top_operand);
   Check(below, kUndoAllocationOfNonAllocatedMemory);
 #endif
   movp(top_operand, object);
 }
 
 
 void MacroAssembler::AllocateHeapNumber(Register result,
                                         Register scratch,
-                                        Label* gc_required,
-                                        MutableMode mode) {
+                                        Label* gc_required) {
   // Allocate heap number in new space.
   Allocate(HeapNumber::kSize, result, scratch, no_reg, gc_required, TAG_OBJECT);
 
-  Heap::RootListIndex map_index = mode == MUTABLE
-      ? Heap::kMutableHeapNumberMapRootIndex
-      : Heap::kHeapNumberMapRootIndex;
-
   // Set the map.
-  LoadRoot(kScratchRegister, map_index);
+  LoadRoot(kScratchRegister, Heap::kHeapNumberMapRootIndex);
   movp(FieldOperand(result, HeapObject::kMapOffset), kScratchRegister);
 }
 
 
 void MacroAssembler::AllocateTwoByteString(Register result,
                                            Register length,
                                            Register scratch1,
                                            Register scratch2,
                                            Register scratch3,
                                            Label* gc_required) {
@@ skipping 738 matching lines @@
   if (ms.shift() > 0) sarl(rdx, Immediate(ms.shift()));
   movl(rax, dividend);
   shrl(rax, Immediate(31));
   addl(rdx, rax);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64