Bug 1845095: Bloom filter for fast-rejecting :has(). r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D184525

servo/components/selectors/context.rs

@@ -7,6 +7,7 @@ use crate::bloom::BloomFilter;
 use crate::nth_index_cache::{NthIndexCache, NthIndexCacheInner};
 use crate::parser::{Selector, SelectorImpl};
 use crate::relative_selector::cache::RelativeSelectorCache;
+use crate::relative_selector::filter::RelativeSelectorFilterMap;
 use crate::tree::{Element, OpaqueElement};
 
 /// What kind of selector matching mode we should use.
@@ -142,13 +143,15 @@ impl RelativeSelectorMatchingState {
     }
 }
 
-/// Set of caches that speed up expensive selector matches.
+/// Set of caches (And cache-likes) that speed up expensive selector matches.
 #[derive(Default)]
 pub struct SelectorCaches {
     /// A cache to speed up nth-index-like selectors.
     pub nth_index: NthIndexCache,
     /// A cache to speed up relative selector matches. See module documentation.
     pub relative_selector: RelativeSelectorCache,
+    /// A map of bloom filters to fast-reject relative selector matches.
+    pub relative_selector_filter_map: RelativeSelectorFilterMap,
 }
 
 /// Data associated with the matching process for a element.  This context is

servo/components/selectors/matching.rs

@@ -463,6 +463,25 @@ fn matches_relative_selectors<E: Element>(
             // Did not match, continue on.
             continue;
         }
+        // See if we can fast-reject.
+        if context
+            .selector_caches
+            .relative_selector_filter_map
+            .fast_reject(
+                element,
+                relative_selector,
+                context.quirks_mode(),
+            )
+        {
+            // Alright, add as unmatched to cache.
+            context.selector_caches.relative_selector.add(
+                element.opaque(),
+                relative_selector,
+                RelativeSelectorCachedMatch::NotMatched,
+            );
+            // Then continue on.
+            continue;
+        }
 
         let matched = matches_relative_selector(relative_selector, element, context, rightmost);
         context.selector_caches.relative_selector.add(

servo/components/selectors/parser.rs

@@ -203,9 +203,9 @@ macro_rules! with_all_bounds {
         pub trait SelectorImpl: Clone + Debug + Sized + 'static {
             type ExtraMatchingData<'a>: Sized + Default;
             type AttrValue: $($InSelector)*;
-            type Identifier: $($InSelector)*;
-            type LocalName: $($InSelector)* + Borrow<Self::BorrowedLocalName>;
-            type NamespaceUrl: $($CommonBounds)* + Default + Borrow<Self::BorrowedNamespaceUrl>;
+            type Identifier: $($InSelector)* + PrecomputedHash;
+            type LocalName: $($InSelector)* + Borrow<Self::BorrowedLocalName> + PrecomputedHash;
+            type NamespaceUrl: $($CommonBounds)* + Default + Borrow<Self::BorrowedNamespaceUrl> + PrecomputedHash;
             type NamespacePrefix: $($InSelector)* + Default;
             type BorrowedNamespaceUrl: ?Sized + Eq;
             type BorrowedLocalName: ?Sized + Eq;
@@ -523,18 +523,17 @@ pub struct AncestorHashes {
     pub packed_hashes: [u32; 3],
 }
 
-fn collect_ancestor_hashes<Impl: SelectorImpl>(
-    iter: SelectorIter<Impl>,
+pub(crate) fn collect_selector_hashes<'a, Impl: SelectorImpl, Iter>(
+    iter: Iter,
     quirks_mode: QuirksMode,
     hashes: &mut [u32; 4],
     len: &mut usize,
+    create_inner_iterator: fn(&'a Selector<Impl>) -> Iter,
 ) -> bool
 where
-    Impl::Identifier: PrecomputedHash,
-    Impl::LocalName: PrecomputedHash,
-    Impl::NamespaceUrl: PrecomputedHash,
+    Iter: Iterator<Item = &'a Component<Impl>>,
 {
-    for component in AncestorIter::new(iter) {
+    for component in iter {
         let hash = match *component {
             Component::LocalName(LocalName {
                 ref name,
@@ -590,7 +589,13 @@ where
                 // in the filter if there's more than one selector, as that'd
                 // exclude elements that may match one of the other selectors.
                 if list.len() == 1 &&
-                    !collect_ancestor_hashes(list.slice()[0].iter(), quirks_mode, hashes, len)
+                    !collect_selector_hashes(
+                        create_inner_iterator(&list.slice()[0]),
+                        quirks_mode,
+                        hashes,
+                        len,
+                        create_inner_iterator,
+                    )
                 {
                     return false;
                 }
@@ -608,12 +613,17 @@ where
     true
 }
 
+fn collect_ancestor_hashes<Impl: SelectorImpl>(
+    iter: SelectorIter<Impl>,
+    quirks_mode: QuirksMode,
+    hashes: &mut [u32; 4],
+    len: &mut usize,
+) {
+    collect_selector_hashes(AncestorIter::new(iter), quirks_mode, hashes, len, |s| AncestorIter(s.iter()));
+}
+
 impl AncestorHashes {
     pub fn new<Impl: SelectorImpl>(selector: &Selector<Impl>, quirks_mode: QuirksMode) -> Self
-    where
-        Impl::Identifier: PrecomputedHash,
-        Impl::LocalName: PrecomputedHash,
-        Impl::NamespaceUrl: PrecomputedHash,
     {
         // Compute ancestor hashes for the bloom filter.
         let mut hashes = [0u32; 4];
@@ -3455,6 +3465,12 @@ pub mod tests {
         }
     }
 
+    impl PrecomputedHash for DummyAtom {
+        fn precomputed_hash(&self) -> u32 {
+            self.0.as_ptr() as u32
+        }
+    }
+
     impl<'i> Parser<'i> for DummyParser {
         type Impl = DummySelectorImpl;
         type Error = SelectorParseErrorKind<'i>;

servo/components/selectors/relative_selector/filter.rs

@@ -0,0 +1,158 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+/// Bloom filter for relative selectors.
+use fxhash::FxHashMap;
+
+use crate::bloom::BloomFilter;
+use crate::context::QuirksMode;
+use crate::parser::{
+    collect_selector_hashes, RelativeSelector, RelativeSelectorMatchHint,
+};
+use crate::tree::{Element, OpaqueElement};
+use crate::SelectorImpl;
+
+enum Entry {
+    /// Filter lookup happened once. Construction of the filter is expensive,
+    /// so this is set when the element for subtree traversal is encountered.
+    Lookup,
+    /// Filter lookup happened more than once, and the filter for this element's
+    /// subtree traversal is constructed. Could use special handlings for pseudo-classes
+    /// such as `:hover` and `:focus`, see Bug 1845503.
+    HasFilter(Box<BloomFilter>),
+}
+
+#[derive(Clone, Copy, Hash, Eq, PartialEq)]
+enum TraversalKind {
+    Children,
+    Descendants,
+}
+
+fn add_to_filter<E: Element>(element: &E, filter: &mut BloomFilter, kind: TraversalKind) -> bool {
+    let mut child = element.first_element_child();
+    while let Some(e) = child {
+        if !e.add_element_unique_hashes(filter) {
+            return false;
+        }
+        if kind == TraversalKind::Descendants {
+            if !add_to_filter(&e, filter, kind) {
+                return false;
+            }
+        }
+        child = e.next_sibling_element();
+    }
+    true
+}
+
+#[derive(Clone, Copy, Hash, Eq, PartialEq)]
+struct Key(OpaqueElement, TraversalKind);
+
+/// Map of bloom filters for fast-rejecting relative selectors.
+#[derive(Default)]
+pub struct RelativeSelectorFilterMap {
+    map: FxHashMap<Key, Entry>,
+}
+
+fn fast_reject<Impl: SelectorImpl>(
+    selector: &RelativeSelector<Impl>,
+    quirks_mode: QuirksMode,
+    filter: &BloomFilter,
+) -> bool {
+    let mut hashes = [0u32; 4];
+    let mut len = 0;
+    // For inner selectors, we only collect from the single rightmost compound.
+    // This is because inner selectors can cause breakouts: e.g. `.anchor:has(:is(.a .b) .c)`
+    // can match when `.a` is the ancestor of `.anchor`. Including `.a` would possibly fast
+    // reject the subtree for not having `.a`, even if the selector would match.
+    // Technically, if the selector's traversal is non-sibling subtree, we can traverse
+    // inner selectors up to the point where a descendant/child combinator is encountered
+    // (e.g. In `.anchor:has(:is(.a ~ .b) .c)`, `.a` is guaranteed to be the a descendant
+    // of `.anchor`). While that can be separately handled, well, this is simpler.
+    collect_selector_hashes(
+        selector.selector.iter(),
+        quirks_mode,
+        &mut hashes,
+        &mut len,
+        |s| s.iter(),
+    );
+    for i in 0..len {
+        if !filter.might_contain_hash(hashes[i]) {
+            // Definitely rejected.
+            return true;
+        }
+    }
+    false
+}
+
+impl RelativeSelectorFilterMap {
+    fn get_filter<E: Element>(&mut self, element: &E, kind: TraversalKind) -> Option<&BloomFilter> {
+        // Insert flag to indicate that we looked up the filter once, and
+        // create the filter if and only if that flag is there.
+        let key = Key(element.opaque(), kind);
+        let entry = self
+            .map
+            .entry(key)
+            .and_modify(|entry| {
+                if !matches!(entry, Entry::Lookup) {
+                    return;
+                }
+                let mut filter = BloomFilter::new();
+                // Go through all children/descendants of this element and add their hashes.
+                if add_to_filter(element, &mut filter, kind) {
+                    *entry = Entry::HasFilter(Box::new(filter));
+                }
+            })
+            .or_insert(Entry::Lookup);
+        match entry {
+            Entry::Lookup => None,
+            Entry::HasFilter(ref filter) => Some(filter.as_ref()),
+        }
+    }
+
+    /// Potentially reject the given selector for this element.
+    /// This may seem redundant in presence of the cache, but the cache keys into the
+    /// selector-element pair specifically, while this filter keys to the element
+    /// and the traversal kind, so it is useful for handling multiple selectors
+    /// that effectively end up looking at the same(-ish, for siblings) subtree.
+    pub fn fast_reject<Impl: SelectorImpl, E: Element>(
+        &mut self,
+        element: &E,
+        selector: &RelativeSelector<Impl>,
+        quirks_mode: QuirksMode,
+    ) -> bool {
+        if matches!(selector.match_hint, RelativeSelectorMatchHint::InNextSibling) {
+            // Don't bother.
+            return false;
+        }
+        let is_sibling = matches!(
+            selector.match_hint,
+            RelativeSelectorMatchHint::InSibling |
+                RelativeSelectorMatchHint::InNextSiblingSubtree |
+                RelativeSelectorMatchHint::InSiblingSubtree
+        );
+        let is_subtree = matches!(
+            selector.match_hint,
+            RelativeSelectorMatchHint::InSubtree |
+                RelativeSelectorMatchHint::InNextSiblingSubtree |
+                RelativeSelectorMatchHint::InSiblingSubtree
+        );
+        let kind = if is_subtree {
+            TraversalKind::Descendants
+        } else {
+            TraversalKind::Children
+        };
+        if is_sibling {
+            // Contain the entirety of the parent's children/subtree in the filter, and use that.
+            // This is less likely to reject, especially for sibling subtree matches; however, it's less
+            // expensive memory-wise, compared to storing filters for each sibling.
+            element.parent_element().map_or(false, |parent| {
+                self.get_filter(&parent, kind)
+                    .map_or(false, |filter| fast_reject(selector, quirks_mode, filter))
+            })
+        } else {
+            self.get_filter(element, kind)
+                .map_or(false, |filter| fast_reject(selector, quirks_mode, filter))
+        }
+    }
+}

servo/components/selectors/relative_selector/mod.rs

@@ -3,3 +3,4 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 pub mod cache;
+pub mod filter;

servo/components/selectors/tree.rs

@@ -6,6 +6,7 @@
 //! between layout and style.
 
 use crate::attr::{AttrSelectorOperation, CaseSensitivity, NamespaceConstraint};
+use crate::bloom::BloomFilter;
 use crate::matching::{ElementSelectorFlags, MatchingContext};
 use crate::parser::SelectorImpl;
 use std::fmt::Debug;
@@ -160,4 +161,8 @@ pub trait Element: Sized + Clone + Debug {
     fn ignores_nth_child_selectors(&self) -> bool {
         false
     }
+
+    /// Add hashes unique to this element to the given filter, returning true
+    /// if any got added.
+    fn add_element_unique_hashes(&self, filter: &mut BloomFilter) -> bool;
 }

servo/components/style/bloom.rs

@@ -111,7 +111,8 @@ pub fn is_attr_name_excluded_from_filter(atom: &crate::Atom) -> bool {
     *atom == atom!("class") || *atom == atom!("id") || *atom == atom!("style")
 }
 
-fn each_relevant_element_hash<E, F>(element: E, mut f: F)
+/// Gather all relevant hash for fast-reject filters from an element.
+pub fn each_relevant_element_hash<E, F>(element: E, mut f: F)
 where
     E: TElement,
     F: FnMut(u32),

servo/components/style/context.rs

@@ -651,7 +651,7 @@ pub struct ThreadLocalStyleContext<E: TElement> {
     /// A checker used to ensure that parallel.rs does not recurse indefinitely
     /// even on arbitrarily deep trees.  See Gecko bug 1376883.
     pub stack_limit_checker: StackLimitChecker,
-    /// Collection of caches for speeding up expensive selector matches.
+    /// Collection of caches (And cache-likes) for speeding up expensive selector matches.
     pub selector_caches: SelectorCaches,
 }
 

servo/components/style/data.rs

@@ -312,8 +312,12 @@ impl ElementData {
             return InvalidationResult::empty();
         }
 
-        let mut processor =
-            StateAndAttrInvalidationProcessor::new(shared_context, element, self, selector_caches);
+        let mut processor = StateAndAttrInvalidationProcessor::new(
+            shared_context,
+            element,
+            self,
+            selector_caches,
+        );
 
         let invalidator = TreeStyleInvalidator::new(element, stack_limit_checker, &mut processor);
 

servo/components/style/gecko/wrapper.rs

@@ -15,6 +15,7 @@
 //! the separation between the style system implementation and everything else.
 
 use crate::applicable_declarations::ApplicableDeclarationBlock;
+use crate::bloom::each_relevant_element_hash;
 use crate::context::{PostAnimationTasks, QuirksMode, SharedStyleContext, UpdateAnimationsTasks};
 use crate::data::ElementData;
 use crate::dom::{LayoutIterator, NodeInfo, OpaqueNode, TDocument, TElement, TNode, TShadowRoot};
@@ -69,6 +70,7 @@ use dom::{DocumentState, ElementState};
 use euclid::default::Size2D;
 use fxhash::FxHashMap;
 use selectors::attr::{AttrSelectorOperation, CaseSensitivity, NamespaceConstraint};
+use selectors::bloom::{BloomFilter, BLOOM_HASH_MASK};
 use selectors::matching::VisitedHandlingMode;
 use selectors::matching::{ElementSelectorFlags, MatchingContext};
 use selectors::sink::Push;
@@ -2090,4 +2092,9 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
     fn ignores_nth_child_selectors(&self) -> bool {
         self.is_root_of_native_anonymous_subtree()
     }
+
+    fn add_element_unique_hashes(&self, filter: &mut BloomFilter) -> bool {
+        each_relevant_element_hash(*self, |hash| filter.insert_hash(hash & BLOOM_HASH_MASK));
+        true
+    }
 }

servo/components/style/invalidation/element/element_wrapper.rs

@@ -12,6 +12,7 @@ use crate::values::AtomIdent;
 use crate::{CaseSensitivityExt, LocalName, Namespace, WeakAtom};
 use dom::ElementState;
 use selectors::attr::{AttrSelectorOperation, CaseSensitivity, NamespaceConstraint};
+use selectors::bloom::BloomFilter;
 use selectors::matching::{ElementSelectorFlags, MatchingContext};
 use selectors::{Element, OpaqueElement};
 use std::cell::Cell;
@@ -388,4 +389,9 @@ where
             .assigned_slot()
             .map(|e| ElementWrapper::new(e, self.snapshot_map))
     }
+
+    fn add_element_unique_hashes(&self, _filter: &mut BloomFilter) -> bool {
+        // Should not be relevant in the context of checking past elements in invalidation.
+        false
+    }
 }