519787 - Implement nsLayoutUtils node-position-compare functions on top of nsContentUtils::ComparePosition

Status: NEW

(Core :: Layout, defect)

Description

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

nsLayoutUtils::CompareTreePosition and nsLayoutUtils::DoCompareTreePosition can and should be implemented on top of nsContentUtils::ComparePosition, in order to reduce code duplication. The only overhead would be an extra couple of conditional branches.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Note that the layout version has a common ancestor hint that's actually an important optimization for its callers....

Comment 2

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

Yeah, just noticed that. Looking at how it's used...

Comment 3

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

The only two callsites that take advantage of that optimization are 

Displaylists: IsContentLEQ [1]
Forms: CompareFormControlPosition [2]

I suspect that displaylists are more perf critical here. Maybe even critical enough that we need to keep this function?

[1] http://mxr.mozilla.org/mozilla-central/source/layout/base/nsDisplayList.cpp#503
[2] http://mxr.mozilla.org/mozilla-central/source/content/html/content/src/nsHTMLFormElement.cpp#1303

Comment 4

[Boris Zbarsky [:bzbarsky]]

Display lists are pretty critical.  But I think we should generally be using this more, fwiw....

Comment 5

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

One solution would be to move the function to nsContentUtils and then factor things such that code could be shared once the parent-chains had been built.