900292 - Enable lazy parsing for self-hosting JS

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, defect)

Description

[Till Schneidereit [:till]]

On my machine, JSRuntime::initSelfHosting takes about 9ms. When I remove all the PJS-related code, that goes down to 6ms. Additionally removing the Intl-related code makes that 1.9ms. So enabling Intl adds 4.1ms.

Given that Talos runs on hardware that is quite a bit slower, I guess the 4.1ms translate to maybe 8ms or 10ms in Ts. Enabling lazy parsing for self-hosted JS should enable us to claim back a good part of that.

Comment 1

[Till Schneidereit [:till]]

Attachment: Enable lazy parsing for self-hosting JS. WIP

This almost works. It causes some weird test failures still, which I have to track down.

However, it doesn't really do anything for the time spent under JSRuntime::initSelfHosting. Without Intl, the duration is basically flat. With Intl, it goes down by ~1ms: from ~6ms to ~5ms.

I'm not sure I understand why that is: with PJS (which uses destructuring a lot, so will cause full parsing for most functions) removed, all but five fairly small functions get compiled lazily (measured by printf-ing at the ends of the two `finishFunctionDefinition` functions).

All in all, lazily parsing the self-hosting code might not be worth it. Or I'm just doing something wrong with my measurements.

Comment 2

[Brian Hackett [Laid off!]]

Is the syntax parser getting disabled at some point?  I.e. is FullParseHandler::disableSyntaxParser ever called?

Comment 3

[Till Schneidereit [:till]]

(In reply to Brian Hackett (:bhackett) from comment #2)
> Is the syntax parser getting disabled at some point?  I.e. is
> FullParseHandler::disableSyntaxParser ever called?

It was, before I changed the `let` in Utilities.js:90 to a `var`. But it's not called for the runs I measured.

Comment 4

[Jeff Walden [:Waldo]]

Attachment: Unbitrotted, plus a couple missing null-checks

Comment 5

[Chris Peterson [:cpeterson]]

Till: do we still want lazy parsing of self-hosted JS? Now that we fork B2G content processes using Nuwa, does JSRuntime::initSelfHosting() time matter much?

Comment 6

[Till Schneidereit [:till]]

Yeah, not only don't we want it anymore: it's outright impossible. The self-hosting compartment is shared per-process and must be read-only after startup, so all parsing has to have happened at that point.