[stubs] Fix allocation memento detection.

src/arm64/macro-assembler-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/base/bits.h"
 #include "src/base/division-by-constant.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 1514 matching lines @@
 
 void MacroAssembler::TestJSArrayForAllocationMemento(Register receiver,
                                                      Register scratch1,
                                                      Register scratch2,
                                                      Label* no_memento_found) {
   Label map_check;
   Label top_check;
   ExternalReference new_space_allocation_top_adr =
       ExternalReference::new_space_allocation_top_address(isolate());
   const int kMementoMapOffset = JSArray::kSize - kHeapObjectTag;
-  const int kMementoEndOffset = kMementoMapOffset + AllocationMemento::kSize;
+  const int kMementoLastWordOffset =
+      kMementoMapOffset + AllocationMemento::kSize - kPointerSize;
 
   // Bail out if the object is not in new space.
   JumpIfNotInNewSpace(receiver, no_memento_found);
-  Add(scratch1, receiver, kMementoEndOffset);
+  Add(scratch1, receiver, kMementoLastWordOffset);
   // If the object is in new space, we need to check whether it is on the same
   // page as the current top.
   Mov(scratch2, new_space_allocation_top_adr);
   Ldr(scratch2, MemOperand(scratch2));
   Eor(scratch2, scratch1, scratch2);
   Tst(scratch2, ~Page::kPageAlignmentMask);
   B(eq, &top_check);
   // The object is on a different page than allocation top. Bail out if the
   // object sits on the page boundary as no memento can follow and we cannot
   // touch the memory following it.
   Eor(scratch2, scratch1, receiver);
   Tst(scratch2, ~Page::kPageAlignmentMask);
   B(ne, no_memento_found);
   // Continue with the actual map check.
   jmp(&map_check);
   // If top is on the same page as the current object, we need to check whether
   // we are below top.
   bind(&top_check);
   Mov(scratch2, new_space_allocation_top_adr);
   Ldr(scratch2, MemOperand(scratch2));
   Cmp(scratch1, scratch2);
-  B(gt, no_memento_found);
+  B(ge, no_memento_found);
   // Memento map check.
   bind(&map_check);
   Ldr(scratch1, MemOperand(receiver, kMementoMapOffset));
   Cmp(scratch1, Operand(isolate()->factory()->allocation_memento_map()));
 }
 
 
 void MacroAssembler::InNewSpace(Register object,
                                 Condition cond,
                                 Label* branch) {
@@ skipping 3361 matching lines @@
 }
 
 
 #undef __
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM64