Provide a tagged allocation top pointer.

src/ia32/code-stubs-ia32.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.
 
 #if V8_TARGET_ARCH_IA32
 
 #include "src/code-stubs.h"
 #include "src/api-arguments.h"
 #include "src/base/bits.h"
 #include "src/bootstrapper.h"
@@ skipping 4448 matching lines @@
   // Fall back to runtime if the target differs from the new target's
   // initial map constructor.
   __ cmp(edi, FieldOperand(ecx, Map::kConstructorOrBackPointerOffset));
   __ j(not_equal, &new_object);
 
   // Allocate the JSObject on the heap.
   Label allocate, done_allocate;
   __ movzx_b(ebx, FieldOperand(ecx, Map::kInstanceSizeOffset));
   __ lea(ebx, Operand(ebx, times_pointer_size, 0));
   __ Allocate(ebx, eax, edi, no_reg, &allocate, NO_ALLOCATION_FLAGS);
+  __ dec(edi);  // Untag result end.
   __ bind(&done_allocate);
 
   // Initialize the JSObject fields.
   __ mov(FieldOperand(eax, JSObject::kMapOffset), ecx);
   __ mov(FieldOperand(eax, JSObject::kPropertiesOffset),
          masm->isolate()->factory()->empty_fixed_array());
   __ mov(FieldOperand(eax, JSObject::kElementsOffset),
          masm->isolate()->factory()->empty_fixed_array());
   STATIC_ASSERT(JSObject::kHeaderSize == 3 * kPointerSize);
   __ lea(ebx, FieldOperand(eax, JSObject::kHeaderSize));
@@ skipping 130 matching lines @@
   __ bind(&no_rest_parameters);
   {
     // ----------- S t a t e -------------
     //  -- esi    : context
     //  -- esp[0] : return address
     // -----------------------------------
 
     // Allocate an empty rest parameter array.
     Label allocate, done_allocate;
     __ Allocate(JSArray::kSize, eax, edx, ecx, &allocate, NO_ALLOCATION_FLAGS);
+    __ dec(edx);  // Untag result end.
     __ bind(&done_allocate);
 
     // Setup the rest parameter array in rax.
     __ LoadGlobalFunction(Context::JS_ARRAY_FAST_ELEMENTS_MAP_INDEX, ecx);
     __ mov(FieldOperand(eax, JSArray::kMapOffset), ecx);
     __ mov(ecx, isolate()->factory()->empty_fixed_array());
     __ mov(FieldOperand(eax, JSArray::kPropertiesOffset), ecx);
     __ mov(FieldOperand(eax, JSArray::kElementsOffset), ecx);
     __ mov(FieldOperand(eax, JSArray::kLengthOffset),
            Immediate(Smi::FromInt(0)));
@@ skipping 1020 matching lines @@
                            kStackUnwindSpace, nullptr, return_value_operand,
                            NULL);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_IA32