[heap] Prepare Heap::CopyFixedArrayWithMap for black allocation

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 6b098a3f5bd187e3cec25be32bd55fe5df45e5aa..509fb7dacc299e50e102c99f63e2e7f9696277d7 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -3822,17 +3822,20 @@ AllocationResult Heap::CopyFixedArrayWithMap(FixedArray* src, Map* map) {
     if (!allocation.To(&obj)) return allocation;
   }
   obj->set_map_no_write_barrier(map);
-  if (InNewSpace(obj)) {
+
+  FixedArray* result = FixedArray::cast(obj);
+  DisallowHeapAllocation no_gc;
+  WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
+
+  // Eliminate the write barrier if possible.
+  if (InNewSpace(obj) && (mode == SKIP_WRITE_BARRIER)) {

[Hannes Payer (out of office), 2016/07/28 15:30:53]

You can skip the new space check, since GetWriteBarrierMode checks that already.

[Michael Lippautz, 2016/07/28 15:32:26]

Done.

     CopyBlock(obj->address() + kPointerSize, src->address() + kPointerSize,
               FixedArray::SizeFor(len) - kPointerSize);
     return obj;
   }
-  FixedArray* result = FixedArray::cast(obj);
-  result->set_length(len);
 
-  // Copy the content.
-  DisallowHeapAllocation no_gc;
-  WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
+  // Slow case: Just copy the content one-by-one.
+  result->set_length(len);
   for (int i = 0; i < len; i++) result->set(i, src->get(i), mode);
   return result;
 }