[heap] Add optimized RecordWrites

src/heap/heap-inl.h

Index: src/heap/heap-inl.h
diff --git a/src/heap/heap-inl.h b/src/heap/heap-inl.h
index 7b2f5ead9b9a3ff53617f12212ebdfe253f99eac..87c0814faaaf7b82b2a9ef7f9e40141f9d0ac2dd 100644
--- a/src/heap/heap-inl.h
+++ b/src/heap/heap-inl.h
@@ -399,9 +399,20 @@ void Heap::RecordWrite(Object* object, int offset, Object* o) {
   if (!InNewSpace(o) || !object->IsHeapObject() || InNewSpace(object)) {
     return;
   }
-  Page* page = Page::FromAddress(reinterpret_cast<Address>(object));
-  Address slot = HeapObject::cast(object)->address() + offset;
-  RememberedSet<OLD_TO_NEW>::Insert(page, slot);
+  RememberedSet<OLD_TO_NEW>::Insert(
+      Page::FromAddress(reinterpret_cast<Address>(object)),
+      HeapObject::cast(object)->address() + offset);
+}
+
+void Heap::RecordWrites(FixedArray* array, int offset, int length) {
+  if (InNewSpace(array)) return;
+  for (int i = 0; i < length; i++) {
+    if (!InNewSpace((array->data_start() + offset)[i])) continue;

[ulan, 2016/04/01 11:28:32]

why not simply array->get(offset + i)?

[Camillo Bruni, 2016/04/01 13:45:01]

indeed...

+    RememberedSet<OLD_TO_NEW>::Insert(
+        Page::FromAddress(reinterpret_cast<Address>(array)),

[ulan, 2016/04/01 11:28:32]

Let's save the page in local variable before the loop starts.

[Camillo Bruni, 2016/04/01 13:45:01]

right... I remember that I measure some 10% difference when moving the page out
of the loop (some weird clang optimization side-effect), probably just some
flake, can't reproduce.

+        HeapObject::cast(array)->address() +

[ulan, 2016/04/01 11:28:32]

Let's use array->RawFieldOfElementAt(i)

[Camillo Bruni, 2016/04/01 13:45:01]

done

+            array->OffsetOfElementAt(offset + i));
+  }
 }