Improve load elimination handling of transitioning stores.

Improve load elimination handling of transitioning stores.

BUG=
R=verwaest@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=18388

[titzer, 2013-12-06 08:40:04]

https://codereview.chromium.org/106973005/diff/1/src/hydrogen-load-eliminatio...
File src/hydrogen-load-elimination.cc (left):

https://codereview.chromium.org/106973005/diff/1/src/hydrogen-load-eliminatio...
src/hydrogen-load-elimination.cc:46: HLoadNamedField* last_load_;
Note that this field was really only used for debugging, so I am going ahead and
removing it in this CL.

[Toon Verwaest, 2013-12-06 10:14:50]

LGTM.
We should also use transitioning information to distinguish receivers. The
receiver cannot alias any other object that already had at least the target
number of fields.

[titzer, 2013-12-20 09:05:11]

On 2013/12/06 10:14:50, Toon Verwaest wrote:
> LGTM.

I've added a test case and verified this optimization triggers. Landing...

> We should also use transitioning information to distinguish receivers. The
> receiver cannot alias any other object that already had at least the target
> number of fields.


As discussed in person (two weeks ago), this would make a nice addition to the
AliasAnalyzer, which would also improve check elimination.

[titzer, 2013-12-20 12:12:47]

Committed patchset #2 manually as r18388 (presubmit successful).