1797246 - https://codepen.io/aragakey/pen/LYmXqEp takes some time to redraw on mouse click

Status: NEW

(Core :: JavaScript Engine, enhancement, P3)

Description

[Mayank Bansal]

go to https://codepen.io/aragakey/pen/LYmXqEp
Click to redraw/randomize the demo

ER: fast redraw
AR: Somewhat laggy redraw

Profile: https://share.firefox.dev/3ssiJIk

Chrome is also slow in this case so not sure if much time should be spent in investigation here.

The profile seems to suggest a couple of places ( mozilla::detail::VectorImpl::new_ , arena_t::RallocSmallOrLarge , BoyerMooreHorspool ) which spent a lot of time in Baseline. Maybe worthwhile to probe that a bit?

Comment 1

[Mayank Bansal]

Attachment: Profile_annotated.png

Screenshot from profiler which show the functions I have mentioned in the comment above.

Comment 2

[Nicolas B. Pierron [:nbp]]

The memset highlighted in the profile comes from reallocations done from String.unespace, which does a realloc in ExtractWellSized, which suggest that a lot of characters were escaped.

Maybe there is a fast path to be implemented here, for cases where escaped characters are more frequent than unescaped ones, but this sounds like a low priority for the moment.

Comment 3

[Mayank Bansal]

Latest profile: https://share.firefox.dev/4dKsk2U