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LibWeb: Skip quick selector rejection using ancestor filter if possible

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If selector does not have any descendant combinators then we know for
sure it won't be filtered out by ancestor filter, which means there is
no need to check for it.

This change makes hover style invalidation go faster on Discord where
with this change we spend 4-5% in `should_reject_with_ancestor_filter()`
instead of 20%.
This commit is contained in:
Aliaksandr Kalenik 2025-02-20 16:25:29 +01:00 • committed by Alexander Kalenik
commit 1843a54df7
Notes: github-actions[bot] 2025-02-20 18:49:27 +00:00
4 changed files with 6 additions and 2 deletions
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1
Libraries/LibWeb/CSS/Selector.cpp
View file

@ -154,6 +154,7 @@ void Selector::collect_ancestor_hashes()
for (ssize_t compound_selector_index = static_cast<ssize_t>(m_compound_selectors.size()) - 2; compound_selector_index >= 0; --compound_selector_index) {
auto const& compound_selector = m_compound_selectors[compound_selector_index];
if (last_combinator == Combinator::Descendant || last_combinator == Combinator::ImmediateChild) {
m_can_use_ancestor_filter = true;
for (auto const& simple_selector : compound_selector.simple_selectors) {
switch (simple_selector.type) {
case SimpleSelector::Type::Id:

2
Libraries/LibWeb/CSS/Selector.h
View file

@ -269,6 +269,7 @@ public:
auto const& ancestor_hashes() const { return m_ancestor_hashes; }
bool can_use_fast_matches() const { return m_can_use_fast_matches; }
bool can_use_ancestor_filter() const { return m_can_use_ancestor_filter; }
private:
explicit Selector(Vector<CompoundSelector>&&);
@ -277,6 +278,7 @@ private:
mutable Optional<u32> m_specificity;
Optional<Selector::PseudoElement> m_pseudo_element;
bool m_can_use_fast_matches { false };
bool m_can_use_ancestor_filter { false };
bool m_contains_the_nesting_selector { false };
bool m_contains_hover_pseudo_class { false };

3
Libraries/LibWeb/CSS/StyleComputer.cpp
View file

@ -503,7 +503,8 @@ Vector<MatchingRule const*> StyleComputer::collect_matching_rules(DOM::Element c
if (!rule_is_relevant_for_current_scope)
return;
if (should_reject_with_ancestor_filter(rule_to_run.selector))
auto const& selector = rule_to_run.selector;
if (selector.can_use_ancestor_filter() && should_reject_with_ancestor_filter(selector))
return;
rules_to_run.unchecked_append(rule_to_run);

2
Libraries/LibWeb/DOM/Document.cpp
View file

@ -1741,7 +1741,7 @@ void Document::invalidate_style_for_elements_affected_by_hover_change(Node& old_
return false;
auto const& selector = rule.selector;
if (style_computer.should_reject_with_ancestor_filter(selector))
if (selector.can_use_ancestor_filter() && style_computer.should_reject_with_ancestor_filter(selector))
return false;
SelectorEngine::MatchContext context;