Optimize write barrier of map-only elements transitions

src/assembler.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 1115 matching lines @@
 
 
 ExternalReference ExternalReference::math_log_double_function(
     Isolate* isolate) {
   return ExternalReference(Redirect(isolate,
                                     FUNCTION_ADDR(math_log_double),
                                     BUILTIN_FP_CALL));
 }
 
 
+ExternalReference ExternalReference::page_flags(Page* page) {
+  return ExternalReference(reinterpret_cast<Address>(page) +
+                           MemoryChunk::kFlagsOffset);
+}
+
+
 // Helper function to compute x^y, where y is known to be an
 // integer. Uses binary decomposition to limit the number of
 // multiplications; see the discussion in "Hacker's Delight" by Henry
 // S. Warren, Jr., figure 11-6, page 213.
 double power_double_int(double x, int y) {
   double m = (y < 0) ? 1 / x : x;
   unsigned n = (y < 0) ? -y : y;
   double p = 1;
   while (n != 0) {
     if ((n & 1) != 0) p *= m;
@@ skipping 161 matching lines @@
     assembler_->RecordRelocInfo(RelocInfo::POSITION, state_.current_position);
     state_.written_position = state_.current_position;
     written = true;
   }
 
   // Return whether something was written.
   return written;
 }
 
 } }  // namespace v8::internal