Object.observe: prevent observed objects from using fast elements.

Object.observe: prevent observed objects from using fast elements.

This is necessary because polymorphic stores generally
do not perform a map check but only an instance type check,
which misses out on changes in the observation status.
Unfortunately, there currently is no efficient way in V8
to maintain that optimisation in the presence of Object.observe.

R=mstarzinger@chromium.org
BUG=v8:2409
Committed: http://code.google.com/p/v8/source/detail?r=13205

[Michael Starzinger, 2012-12-11 15:20:19]

LGTM.

https://codereview.chromium.org/11477006/diff/3001/src/objects-inl.h
File src/objects-inl.h (right):

https://codereview.chromium.org/11477006/diff/3001/src/objects-inl.h#newcode1432
src/objects-inl.h:1432: if (IsJSArray())
JSArray::cast(this)->set_length(Smi::FromInt(0));
OMG, having to set the JSArray length to 0 here is extremely ugly. But I guess
it is the most local hack that achieves this.

https://codereview.chromium.org/11477006/diff/3001/test/mjsunit/harmony/objec...
File test/mjsunit/harmony/object-observe.js (right):

https://codereview.chromium.org/11477006/diff/3001/test/mjsunit/harmony/objec...
test/mjsunit/harmony/object-observe.js:28: // Flags: --harmony-observation
--harmony-proxies --harmony-collections --allow-natives-syntax
You can have multiple "// Flags:" lines and thereby get by with 80 characters
per line.

[rossberg, 2012-12-11 15:29:35]

https://codereview.chromium.org/11477006/diff/3001/src/objects-inl.h
File src/objects-inl.h (right):

https://codereview.chromium.org/11477006/diff/3001/src/objects-inl.h#newcode1432
src/objects-inl.h:1432: if (IsJSArray())
JSArray::cast(this)->set_length(Smi::FromInt(0));
On 2012/12/11 15:20:19, Michael Starzinger wrote:
> OMG, having to set the JSArray length to 0 here is extremely ugly. But I guess
> it is the most local hack that achieves this.

Yeah, the whole "abstraction" we have here is bogus, if you ask me.

https://codereview.chromium.org/11477006/diff/3001/test/mjsunit/harmony/objec...
File test/mjsunit/harmony/object-observe.js (right):

https://codereview.chromium.org/11477006/diff/3001/test/mjsunit/harmony/objec...
test/mjsunit/harmony/object-observe.js:28: // Flags: --harmony-observation
--harmony-proxies --harmony-collections --allow-natives-syntax
On 2012/12/11 15:20:19, Michael Starzinger wrote:
> You can have multiple "// Flags:" lines and thereby get by with 80 characters
> per line.

Done.