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Introduce a new flag and use it to be more permissive about cousin sharing.

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MozReview-Commit-ID: BCJg0Ycsy6M
This commit is contained in:
Bobby Holley 2017-08-04 17:33:26 -07:00
parent ac37f81c1f
commit 54c52910e4
4 changed files with 45 additions and 23 deletions
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30
components/style/sharing/checks.rs
View file

@ -13,18 +13,11 @@ use dom::TElement;
use servo_arc::Arc;
use sharing::{StyleSharingCandidate, StyleSharingTarget};
/// Whether, given two elements, they have pointer-equal computed values.
/// Whether styles may be shared across the children of the given parent elements.
/// This is used to share style across cousins.
///
/// Both elements need to be styled already.
///
/// This is used to know whether we can share style across cousins (if the two
/// parents have the same style).
///
/// We can only prove that they have the same class list, state, etc if they've
/// been restyled at the same time, otherwise the invalidation pass could make
/// them keep the same computed values even though now we wouldn't be able to
/// prove we match the same selectors.
pub fn same_computed_values<E>(first: Option<E>, second: Option<E>) -> bool
pub fn can_share_style_across_parents<E>(first: Option<E>, second: Option<E>) -> bool
where E: TElement,
{
let (first, second) = match (first, second) {
@ -37,13 +30,18 @@ pub fn same_computed_values<E>(first: Option<E>, second: Option<E>) -> bool
let first_data = first.borrow_data().unwrap();
let second_data = second.borrow_data().unwrap();
// FIXME(emilio): This check effectively disables cousin style sharing
// on the initial style.
// If a parent element was already styled and we traversed past it without
// restyling it, that may be because our clever invalidation logic was able
// to prove that the styles of that element would remain unchanged despite
// changes to the id or class attributes. However, style sharing relies in
// the strong guarantee that all the classes and ids up the respective parent
// chains are identical. As such, if we skipped styling for one (or both) of
// the parents on this traversal, we can't share styles across cousins.
//
// This is pretty bad, se the discussion in bug 1381821 for mor details.
//
// Bug 1387116 tracks fixing this, and various solutions are listed there.
if !first_data.restyle.is_restyle() || !second_data.restyle.is_restyle() {
// This is a somewhat conservative check. We could tighten it by having the
// invalidation logic explicitly flag elements for which it ellided styling.
if first_data.restyle.traversed_without_styling() ||
second_data.restyle.traversed_without_styling() {
return false;
}

9
components/style/sharing/mod.rs
View file

@ -610,13 +610,14 @@ impl<E: TElement> StyleSharingCandidateCache<E> {
}
}
// Check that we have the same parent, or at least the same pointer
// identity for parent computed style. The latter check allows us to
// share style between cousins if the parents shared style.
// Check that we have the same parent, or at least that the parents
// share styles and permit sharing across their children. The latter
// check allows us to share style between cousins if the parents
// shared style.
let parent = target.traversal_parent();
let candidate_parent = candidate.element.traversal_parent();
if parent != candidate_parent &&
!checks::same_computed_values(parent, candidate_parent) {
!checks::can_share_style_across_parents(parent, candidate_parent) {
miss!(Parent)
}