Bug 144456 – TypeOfIsUndefined by-type folding should take advantage of the masquerades-as-undefined watchpoint

• Status: NEW
• Component: JavaScriptCore

[Filip Pizlo]

This would allow us to fold more things.

[Alexey Shvayka]

Created attachment 434939 [details]
Patch

[Alexey Shvayka]

(In reply to Alexey Shvayka from comment #1)
> Created attachment 434939 [details]
> Patch

                                                    r280626                    patch

is-undefined-fold-tricky-spec-object-other      30.6171+-0.7028     ^     21.8494+-0.6913        ^ definitely 1.4013x faster

[Filip Pizlo]

Comment on attachment 434939 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=434939&action=review

> Source/JavaScriptCore/ChangeLog:12
> +        TypeOfIsObject / TypeOfIsFunction by-type folding can't be improved in the same way:
> +        even if SpecObjectOther is a proven non-masquerader, we don't know if it's callable.

Can you replace the FIXME's with comments to this effect?  This is an easy detail to forget.  I would say something like - we could use the masquerade watchpoint to prove it's not undefined, but we don't have a trick for callability.