1848765 - nsDisplayList::Sort should use nsTArray::StableSort

Status: RESOLVED FIXED

(Core :: Web Painting, enhancement)

Description

[Olli Pettay [:smaug][[e-mail]]]

Currently the method uses std::stable_sort on top of nsTArray
https://searchfox.org/mozilla-central/rev/ce049e593c7d062a039938cabccaab4c14b8ebfd/layout/painting/nsDisplayList.h#3197
That triggers ElementAt calls which do bound checks.
nsTArray::StableSort would avoid that.

https://bugzilla.mozilla.org/show_bug.cgi?id=1668200 has a similar fix for some animation code.

The ElementAt calls do show up in the profiles

Comment 1

[Jens Stutte [:jstutte]]

FWIW, nsTArray<>::StableSort is based on std::stable_sort since bug 1147091.

But: nsTArray<>::StableSort uses Elements() to make it operate on the plain C/C++ array, which should avoid ElementsAt. Note that std::stable_sort may always need an additional (fallible) allocation to reach O(n*log(n)).

Comment 2

[Jens Stutte [:jstutte]]

Attachment: Bug 1848765 - Use nsTArray<>::StableSort for nsDisplayList::Sort. r?smaug

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/cee7118d2c81
Use nsTArray<>::StableSort for nsDisplayList::Sort. r=smaug

Comment 4

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/cee7118d2c81