Faster implementation of Heap::RecordWrites.

src/spaces-inl.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 134 matching lines @@
   intptr_t offset_inside_normal_page = OffsetFrom(addr) & kPageAlignmentMask;
   return static_cast<int>(offset_inside_normal_page >> kRegionSizeLog2);
 }
 
 
 uint32_t Page::GetRegionMaskForAddress(Address addr) {
   return 1 << GetRegionNumberForAddress(addr);
 }
 
 
+uint32_t Page::GetRegionMaskForSpan(Address start, int length_in_bytes) {
+  uint32_t result = 0;
+  if (length_in_bytes >= kPageSize) {
+    result = kAllRegionsDirtyMarks;
+  } else if (length_in_bytes > 0) {
+    int start_region = GetRegionNumberForAddress(start);
+    int end_region =
+        GetRegionNumberForAddress(start + length_in_bytes - kPointerSize);
+    uint32_t start_mask = (~0) << start_region;
+    uint32_t end_mask = ~((~1) << end_region);
+    result = start_mask & end_mask;
+    // if end_region < start_region, the mask is ored.
+    if (result == 0) result = start_mask | end_mask;
+  }
+#ifdef DEBUG
+  if (FLAG_enable_slow_asserts) {
+    uint32_t expected = 0;
+    for (Address a = start; a < start + length_in_bytes; a += kPointerSize) {
+      expected |= GetRegionMaskForAddress(a);
+    }
+    ASSERT(expected == result);
+  }
+#endif
+  return result;
+}
+
+
 void Page::MarkRegionDirty(Address address) {
   SetRegionMarks(GetRegionMarks() | GetRegionMaskForAddress(address));
 }
 
 
 bool Page::IsRegionDirty(Address address) {
   return GetRegionMarks() & GetRegionMaskForAddress(address);
 }
 
 
@@ skipping 282 matching lines @@
 
 bool FreeListNode::IsFreeListNode(HeapObject* object) {
   return object->map() == Heap::raw_unchecked_byte_array_map()
       || object->map() == Heap::raw_unchecked_one_pointer_filler_map()
       || object->map() == Heap::raw_unchecked_two_pointer_filler_map();
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_INL_H_