1066799 - AVM2 duplicates scope lookups

Status: RESOLVED INCOMPLETE

(Firefox Graveyard :: Shumway, defect)

Description

[Till Schneidereit [:till]]

Stumbled upon this while debugging some AVM1 event handling stuff. For the _addEventHandlerProxy function in [1], AVM2 generates the attached code.

For the lines highlighted in [2], it generates four findScopeProperty calls for the same property. I understand that we might call a function closing over the same scope and potentially modifying the property, so it's not safe in the general case to hoist the lookup. Would it at least be possible to hoist it within sequences that don't contain function calls?

[1]: https://github.com/mozilla/shumway/blob/a6cdada99687d7584e0a04ce82aaace789856091/src/avm1lib/AVM1Utils.as#L87
[2]: https://github.com/mozilla/shumway/blob/a6cdada99687d7584e0a04ce82aaace789856091/src/avm1lib/AVM1Utils.as#L105-L108

Comment 1

[Till Schneidereit [:till]]

Attachment: AVM2-compiled code

And now actually with the compiled code. Dunno why that wasn't attached originally.

Comment 2

[Chris Peterson [:cpeterson]]

Low-priority optimization.