Do deferred migration of maps after deoptimizing once.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index deb33653f7844c70ae9d848f5a59e62cbbe43989..408375f2a87a64d6d57016dcd3478b43b39f3205 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -4289,6 +4289,30 @@ uint32_t Map::bit_field3() {
 }
 
 
+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();