769041 - Remove some unneeded __proto__ special-cases

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jeff Walden [:Waldo]]

Old "optimizations" to handle __proto__ outside of fast paths don't pay their way complexity-wise.

Comment 1

[Jeff Walden [:Waldo]]

Attachment: Don't use special opcodes when emitting bytecode for getting obj.__proto__

Comment 2

[Jeff Walden [:Waldo]]

Attachment: Remove more special opcoding for dotted property access involving __proto__

Comment 3

[Jeff Walden [:Waldo]]

Attachment: Don't specially handle __proto__ in array_getProperty

We now pass along the receiver when delegating access to properties the array doesn't have, so things will just work without this code.

I thought for a moment that this code actually indicated the presence of a bug, if called when obj != receiver, but I think it's not actually an issue, because the only way such a case could happen is if array_lookupProperty indicated that __proto__ existed on the array in question.  But I wrote the tests before coming to that conclusion, and they seem reasonable to have, so I've left them in the patch.

Comment 4

[Jeff Walden [:Waldo]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/76ae14b30bb3
https://hg.mozilla.org/integration/mozilla-inbound/rev/3451a9f921e6
https://hg.mozilla.org/integration/mozilla-inbound/rev/d8fa108aee43
https://hg.mozilla.org/integration/mozilla-inbound/rev/dc013da3bb9b

I think there's still more on this front I can do, perhaps with a little more work.  Keeping this open for now to address that.

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/76ae14b30bb3
https://hg.mozilla.org/mozilla-central/rev/3451a9f921e6
https://hg.mozilla.org/mozilla-central/rev/d8fa108aee43
https://hg.mozilla.org/mozilla-central/rev/dc013da3bb9b

Comment 6

[Jeff Walden [:Waldo]]

Nope, in hindsight this looks done.  The remaining special-casing happens because we reuse initprop for both normal properties in literals, and for the __proto__ special case, and that we can't really remove.  (Although we probably should have a different JSOp for the __proto__-as-key case here, but that aside.)