1367711 - Fast path(s) for reflowing placeholder frames?

Status: RESOLVED FIXED

(Core :: Layout: Positioned, enhancement)

Description

[Mats Palmgren (inactive)]

nsPlaceholderFrame::Reflow is pretty much a NOP:
http://searchfox.org/mozilla-central/rev/35b37316149108d53a02fb8498e250ea8a22ab5d/layout/generic/nsPlaceholderFrame.cpp#108
I wonder if it would be possible to "fast path" that in some ways, 
e.g. cheating on setting up its reflow state (ReflowInput).

Comment 1

[Mats Palmgren (inactive)]

Bug 1359341 has a testcase (attachment 8869972 [details]) that generates a lot of placeholder reflows.

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: Bail out early when initializing ReflowInput for a placeholder frame, which has a trivial Reflow method

This sounded like a sufficiently worthwhile idea that I thought I'd try an experiment to see how much we could gain for minimal effort. This patch seems to pass all tests on tryserver, and on my local opt build it reduces the average time reported by the testcase from 0.735s to 0.634s.

Comment 3

[Mats Palmgren (inactive)]

Comment on attachment 8872083 [details] [diff] [review]
Bail out early when initializing ReflowInput for a placeholder frame, which has a trivial Reflow method

I suggest adding a comment in nsPlaceholderFrame::Reflow about this.

It would good if dbaron also has time to take a look at this...

Comment 4

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Comment on attachment 8872083 [details] [diff] [review]
Bail out early when initializing ReflowInput for a placeholder frame, which has a trivial Reflow method

sounds fine to me, although it would perhaps be good to investigate making the rest of the work faster...

Comment 5

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/e4ac809a2e76161c335b9a8dbac2a4a243f33952
Bug 1367711 - Bail out early when initializing ReflowInput for a placeholder frame, which has a trivial Reflow method. r=mats

Comment 6

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/e4ac809a2e76