Do deferred migration of maps after deoptimizing once.

src/objects-inl.h

 // Copyright 2012 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 4271 matching lines @@
   WRITE_FIELD(this, kBitField3Offset, Smi::FromInt(value >> 1));
 }
 
 
 uint32_t Map::bit_field3() {
   Object* value = READ_FIELD(this, kBitField3Offset);
   return Smi::cast(value)->value();
 }
 
 
+void Map::set_bit_field4(uint32_t bits) {
+  // Ensure the upper 2 bits have the same value by sign extending it. This is
+  // necessary to be able to use the 31st bit.

[Toon Verwaest, 2013/11/04 17:52:46]

This trick isn't really necessary if you aren't using the upper bit. And if you
are allocating a whole new word anyway, you may want to remove it from bitfield3
as well, and move that single bit into this field.

[Hannes Payer (out of office), 2013/11/20 10:36:47]

The bit field 3 got cleaned up in the meantime. No need for bit field 4. Can we
also remove the trick in bit field 3 since we are not using the 31 bit right
now?

+  int value = bits << 1;
+  WRITE_FIELD(this, kBitField4Offset, Smi::FromInt(value >> 1));
+}
+
+
+uint32_t Map::bit_field4() {
+  Object* value = READ_FIELD(this, kBitField4Offset);
+  return Smi::cast(value)->value();
+}
+
+
+void Map::set_has_migrated(bool value) {
+  set_bit_field4(HasMigrated::update(bit_field4(), value));
+}
+
+
+bool Map::has_migrated() {
+  return HasMigrated::decode(bit_field4());
+}
+
+
 void Map::ClearTransitions(Heap* heap, WriteBarrierMode mode) {
   Object* back_pointer = GetBackPointer();
 
   if (Heap::ShouldZapGarbage() && HasTransitionArray()) {
     ZapTransitions();
   }
 
   WRITE_FIELD(this, kTransitionsOrBackPointerOffset, back_pointer);
   CONDITIONAL_WRITE_BARRIER(
       heap, this, kTransitionsOrBackPointerOffset, back_pointer, mode);
@@ skipping 2098 matching lines @@
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_