[heap] Add optimized RecordWrites

src/heap/heap-inl.h

 // 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.
 
 #ifndef V8_HEAP_HEAP_INL_H_
 #define V8_HEAP_HEAP_INL_H_
 
 #include <cmath>
 
 #include "src/base/platform/platform.h"
@@ skipping 381 matching lines @@
   NewSpacePage* page = NewSpacePage::FromAddress(old_address);
   Address age_mark = new_space_.age_mark();
   return page->IsFlagSet(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK) &&
          (!page->ContainsLimit(age_mark) || old_address < age_mark);
 }
 
 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));
+  }
 }
 
 
 bool Heap::AllowedToBeMigrated(HeapObject* obj, AllocationSpace dst) {
   // Object migration is governed by the following rules:
   //
   // 1) Objects in new-space can be migrated to the old space
   //    that matches their target space or they stay in new-space.
   // 2) Objects in old-space stay in the same space when migrating.
   // 3) Fillers (two or more words) can migrate due to left-trimming of
@@ skipping 302 matching lines @@
 
 void VerifySmisVisitor::VisitPointers(Object** start, Object** end) {
   for (Object** current = start; current < end; current++) {
     CHECK((*current)->IsSmi());
   }
 }
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_INL_H_