Minor Object.observe optimizations

Minor Object.observe optimizations

This patch includes the follow two minor optimizations:

1) When Object.unobserve-ing, instead of deleting from changeObservers, set the index position to null, and null-check when iterating elsewhere
2) Isolate creation of null-proto objects inside a utility function

These former (deleting) was clearly showing up in d8 --prof traces and the later was preventing optimization of containing functions because of non-standard literal. Combined, on MDV construction/teardown benchmark, saves about 10%.

Note that this patch also cleans up retrieving objectInfo inside a utility function.



R=rossberg@chromium.org, rossberg
BUG=

Committed: https://code.google.com/p/v8/source/detail?r=18501

[adamk, 2014-01-03 01:00:32]

https://codereview.chromium.org/123523002/diff/1/src/object-observe.js
File src/object-observe.js (right):

https://codereview.chromium.org/123523002/diff/1/src/object-observe.js#newcod...
src/object-observe.js:267: if (!observer)
Not sure how much is matters, but this could be IS_NULL()

https://codereview.chromium.org/123523002/diff/1/src/object-observe.js#newcod...
src/object-observe.js:439: if (!observer)
Ditto

[rossberg, 2014-01-07 17:27:00]

LGTM with comment

https://codereview.chromium.org/123523002/diff/1/src/object-observe.js
File src/object-observe.js (right):

https://codereview.chromium.org/123523002/diff/1/src/object-observe.js#newcod...
src/object-observe.js:267: if (!observer)
On 2014/01/03 01:00:32, adamk wrote:
> Not sure how much is matters, but this could be IS_NULL()

Yes, please use IS_NULL.

Also, you can just merge this with the other 'if':

if (!IS_NULL(observer) && ObserverIsActive(...)) return true;

[rafaelw, 2014-01-07 20:16:14]

https://codereview.chromium.org/123523002/diff/1/src/object-observe.js
File src/object-observe.js (right):

https://codereview.chromium.org/123523002/diff/1/src/object-observe.js#newcod...
src/object-observe.js:267: if (!observer)
On 2014/01/07 17:27:00, rossberg wrote:
> On 2014/01/03 01:00:32, adamk wrote:
> > Not sure how much is matters, but this could be IS_NULL()
> 
> Yes, please use IS_NULL.
> 
> Also, you can just merge this with the other 'if':
> 
> if (!IS_NULL(observer) && ObserverIsActive(...)) return true;

Done.

https://codereview.chromium.org/123523002/diff/1/src/object-observe.js#newcod...
src/object-observe.js:439: if (!observer)
On 2014/01/03 01:00:32, adamk wrote:
> Ditto

Done.

[rafaelw, 2014-01-08 20:25:13]

Committed patchset #2 manually as r18501 (presubmit successful).