1373056 - stylo: Store the prescontext on the rule tree and stop storing it on ServoStyleContext

Status: RESOLVED WONTFIX

(Core :: CSS Parsing and Computation, enhancement)

Description

[Bobby Holley (:bholley)]

Once we do the dependent bugs, we can save a word on the combined ServoStyleContext/ServoComputedValues by adding a PresContext pointer on the root rule node and pointer-chasing to it in the PresContext() accessor (like Gecko does).

Comment 1

[Bobby Holley (:bholley)]

(On dep fixed - when we do fused objects we can do this).

Comment 2

[Bobby Holley (:bholley)]

So I just wrote a patch for this, because I wanted to use the non-existence of a prescontext to indicate rule tree teardown, and figured out would knock this bug out while I was at it.

However, we just discussed it and realized there are a couple of downsides:
* We can't have Option<RuleNode> on the ComputedValues, and would have to use the root (which is extra refcount traffic, and complexity to pass to all the right places).
* The extra indirection may actually cost us in terms of performance, since nsIFrame::PresContext() (which is used all over layout) pointer-chases via the StyleContext.

So I'm going to torpedo this patch and just use a bit to indicate teardown. I'll post the patch here for posterity.

Comment 3

[Bobby Holley (:bholley)]

Attachment: Store the PresContext on the rule tree. v1