Remove elements transitions from the transition array.

Remove elements transitions from the transition array.

This is preparatory work for reordering the transition tree. Since elements transitions will be at the root of the transition tree, runtime access to them is slow since we have to walk the transition tree backwards first. Hence remove the optimization that promoted them to a special field, requiring a pointer (mostly NULL) in every non-simple transition array.

R=titzer@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=15993

[Toon Verwaest, 2013-07-30 09:37:27]

PTAL

[titzer, 2013-07-31 13:55:46]

I don't have much background on how the maps laid out and supposed to be
accessed, so don't feel comfortable yet; can discuss in person later.

https://codereview.chromium.org/21228002/diff/1/src/transitions-inl.h
File src/transitions-inl.h (right):

https://codereview.chromium.org/21228002/diff/1/src/transitions-inl.h#newcode61
src/transitions-inl.h:61: return kNotFound !=
Search(GetHeap()->elements_transition_symbol());
Yoda condition

https://codereview.chromium.org/21228002/diff/1/src/transitions.h
File src/transitions.h (right):

https://codereview.chromium.org/21228002/diff/1/src/transitions.h#newcode131
src/transitions.h:131:
(*HeapObject::RawField(HeapObject::cast(get(kSimpleTransitionTarget)),
Any reason to use a RawField as opposed to the map() accessor through the
HeapObject?

[Toon Verwaest, 2013-07-31 15:05:23]

Addressed comments.
I used the weird access form since I got it from the IntrusivePrototypeIterator.
Apparently that's not strictly necessary, so I changed it to the simpler map()
as suggested.

https://chromiumcodereview.appspot.com/21228002/diff/1/src/transitions-inl.h
File src/transitions-inl.h (right):

https://chromiumcodereview.appspot.com/21228002/diff/1/src/transitions-inl.h#...
src/transitions-inl.h:61: return kNotFound !=
Search(GetHeap()->elements_transition_symbol());
On 2013/07/31 13:55:46, titzer wrote:
> Yoda condition

Done.

https://chromiumcodereview.appspot.com/21228002/diff/1/src/transitions.h
File src/transitions.h (right):

https://chromiumcodereview.appspot.com/21228002/diff/1/src/transitions.h#newc...
src/transitions.h:131:
(*HeapObject::RawField(HeapObject::cast(get(kSimpleTransitionTarget)),
On 2013/07/31 13:55:46, titzer wrote:
> Any reason to use a RawField as opposed to the map() accessor through the
> HeapObject?

Done.

[titzer, 2013-07-31 16:38:05]

lgtm

[Toon Verwaest, 2013-07-31 17:08:58]

Committed patchset #3 manually as r15993 (presubmit successful).