style: Add attribute names to the bloom filter

Safari does this. This reduces the runtime in the example linked from
comment 0 quite a lot (40ms on a local opt build, from ~130ms on a
release nightly build).

I added a pref because there's a slight chance of performance
regressions on pages that do not use attribute selectors, as we're now
doing more unconditional work per element (adding the attributes to the
bloom filter). But the trade-off should be worth it, I think.

Differential Revision: https://phabricator.services.mozilla.com/D111689

components/style/bloom.rs

@@ -102,6 +102,15 @@ impl<E: TElement> PushedElement<E> {
     }
 }
 
+/// Returns whether the attribute name is excluded from the bloom filter.
+///
+/// We do this for attributes that are very common but not commonly used in
+/// selectors.
+#[inline]
+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)
 where
     E: TElement,
@@ -115,6 +124,14 @@ where
     }
 
     element.each_class(|class| f(class.get_hash()));
+
+    if static_prefs::pref!("layout.css.bloom-filter-attribute-names.enabled") {
+        element.each_attr_name(|name| {
+            if !is_attr_name_excluded_from_filter(name) {
+                f(name.get_hash())
+            }
+        });
+    }
 }
 
 impl<E: TElement> Drop for StyleBloom<E> {

components/style/dom.rs

@@ -519,6 +519,11 @@ pub trait TElement:
     {
     }
 
+    /// Internal iterator for the attribute names of this element.
+    fn each_attr_name<F>(&self, callback: F)
+    where
+        F: FnMut(&AtomIdent);
+
     /// Internal iterator for the part names that this element exports for a
     /// given part name.
     fn each_exported_part<F>(&self, _name: &AtomIdent, _callback: F)

components/style/gecko/selector_parser.rs

@@ -247,6 +247,11 @@ impl ::selectors::SelectorImpl for SelectorImpl {
 
     type PseudoElement = PseudoElement;
     type NonTSPseudoClass = NonTSPseudoClass;
+
+    fn should_collect_attr_hash(name: &AtomIdent) -> bool {
+        static_prefs::pref!("layout.css.bloom-filter-attribute-names.enabled") &&
+            !crate::bloom::is_attr_name_excluded_from_filter(name)
+    }
 }
 
 impl<'a> SelectorParser<'a> {

components/style/gecko/wrapper.rs

@@ -570,7 +570,7 @@ impl<'le> GeckoElement<'le> {
     }
 
     #[inline(always)]
-    fn attrs(&self) -> &[structs::AttrArray_InternalAttr] {
+    fn non_mapped_attrs(&self) -> &[structs::AttrArray_InternalAttr] {
         unsafe {
             let attrs = match self.0.mAttrs.mImpl.mPtr.as_ref() {
                 Some(attrs) => attrs,
@@ -581,12 +581,29 @@ impl<'le> GeckoElement<'le> {
         }
     }
 
+    #[inline(always)]
+    fn mapped_attrs(&self) -> &[structs::AttrArray_InternalAttr] {
+        unsafe {
+            let attrs = match self.0.mAttrs.mImpl.mPtr.as_ref() {
+                Some(attrs) => attrs,
+                None => return &[],
+            };
+
+            let attrs = match attrs.mMappedAttrs.as_ref() {
+                Some(attrs) => attrs,
+                None => return &[],
+            };
+
+            attrs.mBuffer.as_slice(attrs.mAttrCount as usize)
+        }
+    }
+
     #[inline(always)]
     fn get_part_attr(&self) -> Option<&structs::nsAttrValue> {
         if !self.has_part_attr() {
             return None;
         }
-        snapshot_helpers::find_attr(self.attrs(), &atom!("part"))
+        snapshot_helpers::find_attr(self.non_mapped_attrs(), &atom!("part"))
     }
 
     #[inline(always)]
@@ -602,7 +619,7 @@ impl<'le> GeckoElement<'le> {
             }
         }
 
-        snapshot_helpers::find_attr(self.attrs(), &atom!("class"))
+        snapshot_helpers::find_attr(self.non_mapped_attrs(), &atom!("class"))
     }
 
     #[inline]
@@ -1167,7 +1184,7 @@ impl<'le> TElement for GeckoElement<'le> {
 
     #[inline]
     fn exports_any_part(&self) -> bool {
-        snapshot_helpers::find_attr(self.attrs(), &atom!("exportparts")).is_some()
+        snapshot_helpers::find_attr(self.non_mapped_attrs(), &atom!("exportparts")).is_some()
     }
 
     // FIXME(emilio): we should probably just return a reference to the Atom.
@@ -1177,7 +1194,25 @@ impl<'le> TElement for GeckoElement<'le> {
             return None;
         }
 
-        snapshot_helpers::get_id(self.attrs())
+        snapshot_helpers::get_id(self.non_mapped_attrs())
+    }
+
+    fn each_attr_name<F>(&self, mut callback: F)
+    where
+        F: FnMut(&AtomIdent),
+    {
+        for attr in self.non_mapped_attrs().iter().chain(self.mapped_attrs().iter()) {
+            let is_nodeinfo = attr.mName.mBits & 1 != 0;
+            unsafe {
+                let atom = if is_nodeinfo {
+                    let node_info = &*((attr.mName.mBits & !1) as *const structs::NodeInfo);
+                    node_info.mInner.mName
+                } else {
+                    attr.mName.mBits as *const nsAtom
+                };
+                AtomIdent::with(atom, |a| callback(a))
+            }
+        }
     }
 
     fn each_class<F>(&self, callback: F)
@@ -1197,7 +1232,7 @@ impl<'le> TElement for GeckoElement<'le> {
     where
         F: FnMut(&AtomIdent),
     {
-        snapshot_helpers::each_exported_part(self.attrs(), name, callback)
+        snapshot_helpers::each_exported_part(self.non_mapped_attrs(), name, callback)
     }
 
     fn each_part<F>(&self, callback: F)
@@ -2058,7 +2093,7 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
             return false;
         }
 
-        let element_id = match snapshot_helpers::get_id(self.attrs()) {
+        let element_id = match snapshot_helpers::get_id(self.non_mapped_attrs()) {
             Some(id) => id,
             None => return false,
         };
@@ -2078,7 +2113,7 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
 
     #[inline]
     fn imported_part(&self, name: &AtomIdent) -> Option<AtomIdent> {
-        snapshot_helpers::imported_part(self.attrs(), name)
+        snapshot_helpers::imported_part(self.non_mapped_attrs(), name)
     }
 
     #[inline(always)]