Do deferred migration of maps after deoptimizing once.

Do deferred migration of maps after deoptimizing once.

BUG=
R=verwaest@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=17949

[danno, 2013-11-04 17:37:29]

Getting there, but I think you need to make sure that bit_field4 is set to zero
in heap.cc when you allocate a new map, just like bit_field3.

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

https://codereview.chromium.org/50213003/diff/1/src/objects-inl.h
File src/objects-inl.h (right):

https://codereview.chromium.org/50213003/diff/1/src/objects-inl.h#newcode4294
src/objects-inl.h:4294: // necessary to be able to use the 31st bit.
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]

https://codereview.chromium.org/50213003/diff/1/src/objects-inl.h
File src/objects-inl.h (right):

https://codereview.chromium.org/50213003/diff/1/src/objects-inl.h#newcode4294
src/objects-inl.h:4294: // necessary to be able to use the 31st bit.
On 2013/11/04 17:52:46, Toon Verwaest wrote:
> 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.

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?

[Toon Verwaest, 2013-11-20 10:45:54]

https://codereview.chromium.org/50213003/diff/70001/src/hydrogen-instructions.h
File src/hydrogen-instructions.h (right):

https://codereview.chromium.org/50213003/diff/70001/src/hydrogen-instructions...
src/hydrogen-instructions.h:2828: map->has_migrated()) {
The map cannot both be a migration target and have migrated. Currently this
disables the feature entirely. I think what you want is limit the scope in which
"is_migration_target" is set to true; eg only if the map was ever used in a
migration.

[Toon Verwaest, 2013-11-20 14:30:54]

lgtm

[Hannes Payer (out of office), 2013-11-21 09:16:42]

Committed patchset #4 manually as r17949.