Remove usages of Heap::NewSpaceStart and its external reference

src/arm64/macro-assembler-arm64.cc

Index: src/arm64/macro-assembler-arm64.cc
diff --git a/src/arm64/macro-assembler-arm64.cc b/src/arm64/macro-assembler-arm64.cc
index 6abc639fb38b6eeca798ed1c1fd35012bef67ffc..52ce013b767fb0a3bd53303332a5ad01ec61531c 100644
--- a/src/arm64/macro-assembler-arm64.cc
+++ b/src/arm64/macro-assembler-arm64.cc
@@ -1556,24 +1556,33 @@ void MacroAssembler::TestJSArrayForAllocationMemento(Register receiver,
                                                      Register scratch1,
                                                      Register scratch2,
                                                      Label* no_memento_found) {
-  ExternalReference new_space_start =
-      ExternalReference::new_space_start(isolate());
+  Label map_check;
   ExternalReference new_space_allocation_top =
       ExternalReference::new_space_allocation_top_address(isolate());
-
-  Add(scratch1, receiver,
-      JSArray::kSize + AllocationMemento::kSize - kHeapObjectTag);
-  Cmp(scratch1, new_space_start);
-  B(lt, no_memento_found);
-
-  Mov(scratch2, new_space_allocation_top);
-  Ldr(scratch2, MemOperand(scratch2));
-  Cmp(scratch1, scratch2);
+  const int kMementoMapOffset = JSArray::kSize - kHeapObjectTag;
+  const int kMementoEndOffset = kMementoMapOffset + AllocationMemento::kSize;
+
+  // Bail out if the object sits on the page boundary as no memento can follow
+  // and we cannot touch the memory following it.
+  Add(scratch1, receiver, kMementoEndOffset);
+  Eor(scratch2, scratch1, receiver);
+  Cmp(scratch2, Operand(Page::kPageSize));
   B(gt, no_memento_found);
-
-  Ldr(scratch1, MemOperand(scratch1, -AllocationMemento::kSize));
-  Cmp(scratch1,
-      Operand(isolate()->factory()->allocation_memento_map()));
+  // Bail out if the object is not in new space. Reuse scratch1 from above.
+  JumpIfNotInNewSpace(scratch1, 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(scratch2, receiver, kMementoEndOffset);
+  Eor(scratch2, scratch2, new_space_allocation_top);
+  Tst(scratch2, ~Page::kPageAlignmentMask);
+  B(ne, no_memento_found);
+  // Otherwise, we have to check whether we are still below top, to ensure that
+  // we are not checking against a stale memento.
+  Cmp(scratch1, new_space_allocation_top);
+  B(gt, no_memento_found);
+  bind(&map_check);
+  Ldr(scratch1, MemOperand(receiver, kMementoMapOffset));
+  Cmp(scratch1, Operand(isolate()->factory()->allocation_memento_map()));
 }