[stubs] Fix allocation memento detection.

src/arm/macro-assembler-arm.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 <limits.h>  // For LONG_MIN, LONG_MAX.
 
 #if V8_TARGET_ARCH_ARM
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
@@ skipping 3786 matching lines @@
 
 void MacroAssembler::TestJSArrayForAllocationMemento(
     Register receiver_reg,
     Register scratch_reg,
     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_reg, scratch_reg, no_memento_found);
   // If the object is in new space, we need to check whether it is on the same
   // page as the current top.
-  add(scratch_reg, receiver_reg, Operand(kMementoEndOffset));
+  add(scratch_reg, receiver_reg, Operand(kMementoLastWordOffset));
   mov(ip, Operand(new_space_allocation_top_adr));
   ldr(ip, MemOperand(ip));
   eor(scratch_reg, scratch_reg, Operand(ip));
   tst(scratch_reg, Operand(~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.
-  add(scratch_reg, receiver_reg, Operand(kMementoEndOffset));
+  add(scratch_reg, receiver_reg, Operand(kMementoLastWordOffset));
   eor(scratch_reg, scratch_reg, Operand(receiver_reg));
   tst(scratch_reg, Operand(~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);
-  add(scratch_reg, receiver_reg, Operand(kMementoEndOffset));
+  add(scratch_reg, receiver_reg, Operand(kMementoLastWordOffset));
   mov(ip, Operand(new_space_allocation_top_adr));
   ldr(ip, MemOperand(ip));
   cmp(scratch_reg, ip);
-  b(gt, no_memento_found);
+  b(ge, no_memento_found);
   // Memento map check.
   bind(&map_check);
   ldr(scratch_reg, MemOperand(receiver_reg, kMementoMapOffset));
   cmp(scratch_reg, Operand(isolate()->factory()->allocation_memento_map()));
 }
 
 Register GetRegisterThatIsNotOneOf(Register reg1,
                                    Register reg2,
                                    Register reg3,
                                    Register reg4,
@@ skipping 151 matching lines @@
     }
   }
   if (mag.shift > 0) mov(result, Operand(result, ASR, mag.shift));
   add(result, result, Operand(dividend, LSR, 31));
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM