74598 - Avoid resolving style on text nodes

Status: RESOLVED FIXED

(Core :: Layout, defect)

Description

[Marc Attinasi]

Text nodes cannot have any style directly applied to them (see bug 56117) so
they should be able to get their style data from their parent rather than have a
style context of their own. We could avoid resolving style on the text nodes
altogether, which could be a performance benefit.

Comment 1

[Marc Attinasi]

An optimization that is already in the style system is to share the style
context across siblings with the same rules. This mechanism allows most text
nodes to share the same style context rather than having their own, however the
cost of evaluating the sharing is still incurred (note: this is not the style
context data sharing that I put in, but rather a more efficient style context
sharing that Peter Linss put in. It simply checks if there are sibling elements
with exactly the same rules using a hash).

Comment 2

[Hixie (not reading bugmail)]

Text nodes can't share the same style context as their parent; they have to use
initial values for things like 'background' and 'border' (i.e., they should only
inherit the inheritable properties).

Otherwise, imagine the result of:

   div { border: solid; }

   <div> hello <-- --> world </div>

Comment 3

[David Hyatt]

Marc, FWIW, I profiled the Reply case that was discussed in the meeting, and the
style system is only responsible for 1.8% or so, a preposterously low number.

I think we should look at this bug more as a footprint win than necessarily a
speed win, given the already-existing optimization you just mentioned.  I still
think it's worth doing though.

Comment 4

[Marc Attinasi]

Ian, you are, of course, absolutely correct. Maybe the current scheme of using
normal style resolution for the first sibling, and the the brute-force sharing
for all subsequent sharing is the best we can do to minimize the _work_ involved
in getting valid style contexts for the text nodes.

David, thanks for the data. Keep in mind that Pierre's new style sharing scheme
may help out on the footprint front.

Comment 5

[Marc Attinasi]

Thsi was fixed by dbaron's fix to bug 56117 - marking FIXED