1338834 - Optimize compartment check in JSContext::currentScript

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jan de Mooij [:jandem]]

Attachment: Patch

I looked at an Instruments profile for the Google Docs test in bug 1338802 comment 0.

One curious thing I noticed is a CCW call to obj_construct where we then do a slow script/pc lookup by calling currentScript. That's silly because currentScript will discard the script/pc if the compartment doesn't match (currentScript's allowCrossCompartment argument defaults to false), but we can easily do the compartment check *before* we do the relatively slow script/pc lookup.

According to Instruments we spend a few % here so this simple patch should be a decent speedup.

Comment 1

[Jan de Mooij [:jandem]]

(In reply to Jan de Mooij [:jandem] from comment #0)
> a CCW call to obj_construct

Bad wording on my part, there are ton of these calls actually. Some logging confirms this patch speeds up at least 300,000 currentScript calls where we returned nullptr but did the slow GetPcScript call for no good reason.

Comment 2

[Brian Hackett [Laid off!]]

Comment on attachment 8836413 [details] [diff] [review]
Patch

Review of attachment 8836413 [details] [diff] [review]:
-----------------------------------------------------------------

Sorry for the delay.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/62d0c9083f4b
Speed up JSContext::currentScript by doing the compartment check first. r=bhackett

Comment 4

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/62d0c9083f4b