Provide a tagged allocation top pointer.

src/arm64/code-stubs-arm64.cc

 // Copyright 2013 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_ARM64
 
 #include "src/code-stubs.h"
 #include "src/api-arguments.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 4574 matching lines @@
 
   // Fall back to runtime if the target differs from the new target's
   // initial map constructor.
   __ Ldr(x0, FieldMemOperand(x2, Map::kConstructorOrBackPointerOffset));
   __ CompareAndBranch(x0, x1, ne, &new_object);
 
   // Allocate the JSObject on the heap.
   Label allocate, done_allocate;
   __ Ldrb(x4, FieldMemOperand(x2, Map::kInstanceSizeOffset));
   __ Allocate(x4, x0, x5, x6, &allocate, SIZE_IN_WORDS);
+  __ Sub(x5, x5, Operand(kHeapObjectTag));  // Untag result end.
   __ Bind(&done_allocate);
 
   // Initialize the JSObject fields.
   STATIC_ASSERT(JSObject::kMapOffset == 0 * kPointerSize);
   __ Str(x2, FieldMemOperand(x0, JSObject::kMapOffset));
   __ LoadRoot(x3, Heap::kEmptyFixedArrayRootIndex);
   STATIC_ASSERT(JSObject::kPropertiesOffset == 1 * kPointerSize);
   STATIC_ASSERT(JSObject::kElementsOffset == 2 * kPointerSize);
   __ Str(x3, FieldMemOperand(x0, JSObject::kPropertiesOffset));
   __ Str(x3, FieldMemOperand(x0, JSObject::kElementsOffset));
@@ skipping 127 matching lines @@
   __ Bind(&no_rest_parameters);
   {
     // ----------- S t a t e -------------
     //  -- cp : context
     //  -- lr : return address
     // -----------------------------------
 
     // Allocate an empty rest parameter array.
     Label allocate, done_allocate;
     __ Allocate(JSArray::kSize, x0, x1, x2, &allocate, NO_ALLOCATION_FLAGS);
+    __ Sub(x1, x1, Operand(kHeapObjectTag));  // Untag result end.
     __ Bind(&done_allocate);
 
     // Setup the rest parameter array in x0.
     __ LoadNativeContextSlot(Context::JS_ARRAY_FAST_ELEMENTS_MAP_INDEX, x1);
     __ Str(x1, FieldMemOperand(x0, JSArray::kMapOffset));
     __ LoadRoot(x1, Heap::kEmptyFixedArrayRootIndex);
     __ Str(x1, FieldMemOperand(x0, JSArray::kPropertiesOffset));
     __ Str(x1, FieldMemOperand(x0, JSArray::kElementsOffset));
     __ Mov(x1, Smi::FromInt(0));
     __ Str(x1, FieldMemOperand(x0, JSArray::kLengthOffset));
@@ skipping 997 matching lines @@
                            kStackUnwindSpace, NULL, spill_offset,
                            return_value_operand, NULL);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM64