Auto merge of #18191 - emilio:incremental-rebuilds, r=SimonSapin,heycam

style: Implement finer-grained stylist rebuilds.

This is on top of #18170, and aims to resolve https://bugzilla.mozilla.org/show_bug.cgi?id=1386045.

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components/style/stylesheet_set.rs

@@ -9,16 +9,25 @@ use invalidation::stylesheets::StylesheetInvalidationSet;
 use media_queries::Device;
 use shared_lock::SharedRwLockReadGuard;
 use std::slice;
-use stylesheets::{OriginSet, PerOrigin, StylesheetInDocument};
+use stylesheets::{Origin, OriginSet, PerOrigin, StylesheetInDocument};
 
-/// Entry for a StylesheetSet. We don't bother creating a constructor, because
-/// there's no sensible defaults for the member variables.
+/// Entry for a StylesheetSet.
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
-pub struct StylesheetSetEntry<S>
+struct StylesheetSetEntry<S>
 where
     S: StylesheetInDocument + PartialEq + 'static,
 {
     sheet: S,
+    dirty: bool,
+}
+
+impl<S> StylesheetSetEntry<S>
+where
+    S: StylesheetInDocument + PartialEq + 'static,
+{
+    fn new(sheet: S) -> Self {
+        Self { sheet, dirty: true }
+    }
 }
 
 /// A iterator over the stylesheets of a list of entries in the StylesheetSet.
@@ -38,6 +47,136 @@ where
     }
 }
 
+/// The validity of the data in a given cascade origin.
+#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
+#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+pub enum OriginValidity {
+    /// The origin is clean, all the data already there is valid, though we may
+    /// have new sheets at the end.
+    Valid = 0,
+
+    /// The cascade data is invalid, but not the invalidation data (which is
+    /// order-independent), and thus only the cascade data should be inserted.
+    CascadeInvalid = 1,
+
+    /// Everything needs to be rebuilt.
+    FullyInvalid = 2,
+}
+
+impl Default for OriginValidity {
+    fn default() -> Self {
+        OriginValidity::Valid
+    }
+}
+
+/// A struct to iterate over the different stylesheets to be flushed.
+pub struct StylesheetFlusher<'a, 'b, S>
+where
+    'b: 'a,
+    S: StylesheetInDocument + PartialEq + 'static,
+{
+    iter: slice::IterMut<'a, StylesheetSetEntry<S>>,
+    guard: &'a SharedRwLockReadGuard<'b>,
+    origins_dirty: OriginSet,
+    origin_data_validity: PerOrigin<OriginValidity>,
+    author_style_disabled: bool,
+    had_invalidations: bool,
+}
+
+/// The type of rebuild that we need to do for a given stylesheet.
+pub enum SheetRebuildKind {
+    /// A full rebuild, of both cascade data and invalidation data.
+    Full,
+    /// A partial rebuild, of only the cascade data.
+    CascadeOnly,
+}
+
+impl SheetRebuildKind {
+    /// Whether the stylesheet invalidation data should be rebuilt.
+    pub fn should_rebuild_invalidation(&self) -> bool {
+        matches!(*self, SheetRebuildKind::Full)
+    }
+}
+
+impl<'a, 'b, S> StylesheetFlusher<'a, 'b, S>
+where
+    'b: 'a,
+    S: StylesheetInDocument + PartialEq + 'static,
+{
+    /// The data validity for a given origin.
+    pub fn origin_validity(&self, origin: Origin) -> OriginValidity {
+        *self.origin_data_validity.borrow_for_origin(&origin)
+    }
+
+    /// Returns whether running the whole flushing process would be a no-op.
+    pub fn nothing_to_do(&self) -> bool {
+        self.origins_dirty.is_empty()
+    }
+
+    /// Returns whether any DOM invalidations were processed as a result of the
+    /// stylesheet flush.
+    pub fn had_invalidations(&self) -> bool {
+        self.had_invalidations
+    }
+}
+
+#[cfg(debug_assertions)]
+impl<'a, 'b, S> Drop for StylesheetFlusher<'a, 'b, S>
+where
+    'b: 'a,
+    S: StylesheetInDocument + PartialEq + 'static,
+{
+    fn drop(&mut self) {
+        debug_assert!(
+            self.iter.next().is_none(),
+            "You're supposed to fully consume the flusher"
+        );
+    }
+}
+
+impl<'a, 'b, S> Iterator for StylesheetFlusher<'a, 'b, S>
+where
+    'b: 'a,
+    S: StylesheetInDocument + PartialEq + 'static,
+{
+    type Item = (&'a S, SheetRebuildKind);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        use std::mem;
+
+        loop {
+            let potential_sheet = match self.iter.next() {
+                None => return None,
+                Some(s) => s,
+            };
+
+            let dirty = mem::replace(&mut potential_sheet.dirty, false);
+
+            if dirty {
+                // If the sheet was dirty, we need to do a full rebuild anyway.
+                return Some((&potential_sheet.sheet, SheetRebuildKind::Full))
+            }
+
+            let origin = potential_sheet.sheet.contents(self.guard).origin;
+            if !self.origins_dirty.contains(origin.into()) {
+                continue;
+            }
+
+            if self.author_style_disabled && matches!(origin, Origin::Author) {
+                continue;
+            }
+
+            let rebuild_kind = match self.origin_validity(origin) {
+                OriginValidity::Valid => continue,
+                OriginValidity::CascadeInvalid => SheetRebuildKind::CascadeOnly,
+                OriginValidity::FullyInvalid => SheetRebuildKind::Full,
+            };
+
+            return Some((&potential_sheet.sheet, rebuild_kind));
+        }
+    }
+}
+
 /// The set of stylesheets effective for a given document.
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct StylesheetSet<S>
@@ -51,8 +190,19 @@ where
     /// include recursive `@import` rules.
     entries: Vec<StylesheetSetEntry<S>>,
 
-    /// Per-origin stylesheet invalidation data.
-    invalidation_data: PerOrigin<InvalidationData>,
+    /// The invalidations for stylesheets added or removed from this document.
+    invalidations: StylesheetInvalidationSet,
+
+    /// The origins whose stylesheets have changed so far.
+    origins_dirty: OriginSet,
+
+    /// The validity of the data that was already there for a given origin.
+    ///
+    /// Note that an origin may appear on `origins_dirty`, but still have
+    /// `OriginValidity::Valid`, if only sheets have been appended into it (in
+    /// which case the existing data is valid, but the origin needs to be
+    /// rebuilt).
+    origin_data_validity: PerOrigin<OriginValidity>,
 
     /// Has author style been disabled?
     author_style_disabled: bool,
@@ -66,7 +216,9 @@ where
     pub fn new() -> Self {
         StylesheetSet {
             entries: vec![],
-            invalidation_data: Default::default(),
+            invalidations: StylesheetInvalidationSet::new(),
+            origins_dirty: OriginSet::empty(),
+            origin_data_validity: Default::default(),
             author_style_disabled: false,
         }
     }
@@ -97,12 +249,28 @@ where
         sheet: &S,
         guard: &SharedRwLockReadGuard,
     ) {
-        let origin = sheet.contents(guard).origin;
-        let data = self.invalidation_data.borrow_mut_for_origin(&origin);
         if let Some(device) = device {
-            data.invalidations.collect_invalidations_for(device, sheet, guard);
+            self.invalidations.collect_invalidations_for(device, sheet, guard);
         }
-        data.dirty = true;
+        self.origins_dirty |= sheet.contents(guard).origin;
+    }
+
+    fn set_data_validity_at_least(
+        &mut self,
+        origin: Origin,
+        validity: OriginValidity,
+    ) {
+        use std::cmp;
+
+        debug_assert!(
+            self.origins_dirty.contains(origin.into()),
+            "data_validity should be a subset of origins_dirty"
+        );
+
+        let existing_validity =
+            self.origin_data_validity.borrow_mut_for_origin(&origin);
+
+        *existing_validity = cmp::max(*existing_validity, validity);
     }
 
     /// Appends a new stylesheet to the current set.
@@ -117,7 +285,9 @@ where
         debug!("StylesheetSet::append_stylesheet");
         self.remove_stylesheet_if_present(&sheet);
         self.collect_invalidations_for(device, &sheet, guard);
-        self.entries.push(StylesheetSetEntry { sheet });
+        // Appending sheets doesn't alter the validity of the existing data, so
+        // we don't need to change `origin_data_validity` here.
+        self.entries.push(StylesheetSetEntry::new(sheet));
     }
 
     /// Prepend a new stylesheet to the current set.
@@ -130,7 +300,12 @@ where
         debug!("StylesheetSet::prepend_stylesheet");
         self.remove_stylesheet_if_present(&sheet);
         self.collect_invalidations_for(device, &sheet, guard);
-        self.entries.insert(0, StylesheetSetEntry { sheet });
+
+        // Inserting stylesheets somewhere but at the end changes the validity
+        // of the cascade data, but not the invalidation data.
+        self.set_data_validity_at_least(sheet.contents(guard).origin, OriginValidity::CascadeInvalid);
+
+        self.entries.insert(0, StylesheetSetEntry::new(sheet));
     }
 
     /// Insert a given stylesheet before another stylesheet in the document.
@@ -147,7 +322,11 @@ where
             entry.sheet == before_sheet
         }).expect("`before_sheet` stylesheet not found");
         self.collect_invalidations_for(device, &sheet, guard);
-        self.entries.insert(index, StylesheetSetEntry { sheet });
+
+        // Inserting stylesheets somewhere but at the end changes the validity
+        // of the cascade data, but not the invalidation data.
+        self.set_data_validity_at_least(sheet.contents(guard).origin, OriginValidity::CascadeInvalid);
+        self.entries.insert(index, StylesheetSetEntry::new(sheet));
     }
 
     /// Remove a given stylesheet from the set.
@@ -159,7 +338,12 @@ where
     ) {
         debug!("StylesheetSet::remove_stylesheet");
         self.remove_stylesheet_if_present(&sheet);
+
         self.collect_invalidations_for(device, &sheet, guard);
+
+        // Removing sheets makes us tear down the whole cascade and invalidation
+        // data.
+        self.set_data_validity_at_least(sheet.contents(guard).origin, OriginValidity::FullyInvalid);
     }
 
     /// Notes that the author style has been disabled for this document.
@@ -169,61 +353,53 @@ where
             return;
         }
         self.author_style_disabled = disabled;
-        self.invalidation_data.author.invalidations.invalidate_fully();
-        self.invalidation_data.author.dirty = true;
+        self.invalidations.invalidate_fully();
+        self.origins_dirty |= Origin::Author;
     }
 
     /// Returns whether the given set has changed from the last flush.
     pub fn has_changed(&self) -> bool {
-        self.invalidation_data
-            .iter_origins()
-            .any(|(d, _)| d.dirty)
+        !self.origins_dirty.is_empty()
     }
 
-    /// Flush the current set, unmarking it as dirty, and returns an iterator
-    /// over the new stylesheet list.
-    ///
-    /// Returns true if any elements were invalidated.
-    pub fn flush<E>(
-        &mut self,
+    /// Flush the current set, unmarking it as dirty, and returns a
+    /// `StylesheetFlusher` in order to rebuild the stylist.
+    pub fn flush<'a, 'b, E>(
+        &'a mut self,
         document_element: Option<E>,
-    ) -> (StylesheetIterator<S>, OriginSet, bool)
+        guard: &'a SharedRwLockReadGuard<'b>,
+    ) -> StylesheetFlusher<'a, 'b, S>
     where
         E: TElement,
     {
+        use std::mem;
+
         debug!("StylesheetSet::flush");
 
-        let mut origins = OriginSet::empty();
-        let mut have_invalidations = false;
-        for (data, origin) in self.invalidation_data.iter_mut_origins() {
-            if data.dirty {
-                have_invalidations |= data.invalidations.flush(document_element);
-                data.dirty = false;
-                origins |= origin;
-            }
-        }
+        let had_invalidations = self.invalidations.flush(document_element);
+        let origins_dirty = mem::replace(&mut self.origins_dirty, OriginSet::empty());
+        let origin_data_validity =
+            mem::replace(&mut self.origin_data_validity, Default::default());
 
-        (self.iter(), origins, have_invalidations)
+        StylesheetFlusher {
+            iter: self.entries.iter_mut(),
+            author_style_disabled: self.author_style_disabled,
+            had_invalidations,
+            origins_dirty,
+            origin_data_validity,
+            guard,
+        }
     }
 
     /// Flush stylesheets, but without running any of the invalidation passes.
-    ///
-    /// FIXME(emilio): This should eventually disappear. Please keep this
-    /// Servo-only.
     #[cfg(feature = "servo")]
-    pub fn flush_without_invalidation(&mut self) -> (StylesheetIterator<S>, OriginSet) {
+    pub fn flush_without_invalidation(&mut self) -> OriginSet {
+        use std::mem;
+
         debug!("StylesheetSet::flush_without_invalidation");
 
-        let mut origins = OriginSet::empty();
-        for (data, origin) in self.invalidation_data.iter_mut_origins() {
-            if data.dirty {
-                data.invalidations.clear();
-                data.dirty = false;
-                origins |= origin;
-            }
-        }
-
-        (self.iter(), origins)
+        self.invalidations.clear();
+        mem::replace(&mut self.origins_dirty, OriginSet::empty())
     }
 
     /// Returns an iterator over the current list of stylesheets.
@@ -234,30 +410,11 @@ where
     /// Mark the stylesheets for the specified origin as dirty, because
     /// something external may have invalidated it.
     pub fn force_dirty(&mut self, origins: OriginSet) {
+        self.invalidations.invalidate_fully();
+        self.origins_dirty |= origins;
         for origin in origins.iter() {
-            let data = self.invalidation_data.borrow_mut_for_origin(&origin);
-            data.invalidations.invalidate_fully();
-            data.dirty = true;
-        }
-    }
-}
-
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
-struct InvalidationData {
-    /// The stylesheet invalidations for this origin that we still haven't
-    /// processed.
-    invalidations: StylesheetInvalidationSet,
-
-    /// Whether the sheets for this origin in the `StylesheetSet`'s entry list
-    /// has changed since the last restyle.
-    dirty: bool,
-}
-
-impl Default for InvalidationData {
-    fn default() -> Self {
-        InvalidationData {
-            invalidations: StylesheetInvalidationSet::new(),
-            dirty: false,
+            // We don't know what happened, assume the worse.
+            self.set_data_validity_at_least(origin, OriginValidity::FullyInvalid);
         }
     }
 }

components/style/stylesheets/origin.rs

@@ -40,6 +40,7 @@ impl Origin {
 
 bitflags! {
     /// A set of origins. This is equivalent to Gecko's OriginFlags.
+    #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
     pub flags OriginSet: u8 {
         /// https://drafts.csswg.org/css-cascade/#cascade-origin-user-agent
         const ORIGIN_USER_AGENT = Origin::UserAgent as u8,

components/style/stylist.rs

@@ -38,7 +38,7 @@ use smallvec::VecLike;
 use std::fmt::Debug;
 use std::ops;
 use style_traits::viewport::ViewportConstraints;
-use stylesheet_set::{StylesheetSet, StylesheetIterator};
+use stylesheet_set::{OriginValidity, SheetRebuildKind, StylesheetSet, StylesheetIterator, StylesheetFlusher};
 #[cfg(feature = "gecko")]
 use stylesheets::{CounterStyleRule, FontFaceRule};
 use stylesheets::{CssRule, StyleRule};
@@ -83,33 +83,44 @@ impl DocumentCascadeData {
 
     /// Rebuild the cascade data for the given document stylesheets, and
     /// optionally with a set of user agent stylesheets.
-    fn rebuild<'a, I, S>(
+    fn rebuild<'a, 'b, S>(
         &mut self,
         device: &Device,
         quirks_mode: QuirksMode,
-        doc_stylesheets: I,
+        flusher: StylesheetFlusher<'a, 'b, S>,
         guards: &StylesheetGuards,
         ua_stylesheets: Option<&UserAgentStylesheets>,
-        author_style_disabled: bool,
         extra_data: &mut PerOrigin<ExtraStyleData>,
-        origins_to_rebuild: OriginSet,
     )
     where
-        I: Iterator<Item = &'a S> + Clone,
-        S: StylesheetInDocument + ToMediaListKey + 'static,
+        'b: 'a,
+        S: StylesheetInDocument + ToMediaListKey + PartialEq + 'static,
     {
-        debug_assert!(!origins_to_rebuild.is_empty());
+        debug_assert!(!flusher.nothing_to_do());
+
+        for (cascade_data, origin) in self.per_origin.iter_mut_origins() {
+            let validity = flusher.origin_validity(origin);
+
+            if validity == OriginValidity::Valid {
+                continue;
+            }
+
+            if origin == Origin::UserAgent {
+                self.precomputed_pseudo_element_decls.clear();
+            }
 
-        for origin in origins_to_rebuild.iter() {
             extra_data.borrow_mut_for_origin(&origin).clear();
-            self.per_origin.borrow_mut_for_origin(&origin).clear();
-        }
-
-        if origins_to_rebuild.contains(Origin::UserAgent.into()) {
-            self.precomputed_pseudo_element_decls.clear();
+            if validity == OriginValidity::CascadeInvalid {
+                cascade_data.clear_cascade_data()
+            } else {
+                debug_assert_eq!(validity, OriginValidity::FullyInvalid);
+                cascade_data.clear();
+            }
         }
 
         if let Some(ua_stylesheets) = ua_stylesheets {
+            debug_assert!(cfg!(feature = "servo"));
+
             for stylesheet in &ua_stylesheets.user_or_user_agent_stylesheets {
                 let sheet_origin =
                     stylesheet.contents(guards.ua_or_user).origin;
@@ -119,15 +130,26 @@ impl DocumentCascadeData {
                     Origin::UserAgent | Origin::User
                 ));
 
-                if origins_to_rebuild.contains(sheet_origin.into()) {
-                    self.add_stylesheet(
-                        device,
-                        quirks_mode,
-                        stylesheet,
-                        guards.ua_or_user,
-                        extra_data,
-                    );
+                let validity = flusher.origin_validity(sheet_origin);
+
+                // Servo doesn't support to incrementally mutate UA sheets.
+                debug_assert!(matches!(
+                    validity,
+                    OriginValidity::Valid | OriginValidity::FullyInvalid
+                ));
+
+                if validity == OriginValidity::Valid {
+                    continue;
                 }
+
+                self.add_stylesheet(
+                    device,
+                    quirks_mode,
+                    stylesheet,
+                    guards.ua_or_user,
+                    extra_data,
+                    SheetRebuildKind::Full,
+                );
             }
 
             if quirks_mode != QuirksMode::NoQuirks {
@@ -140,34 +162,35 @@ impl DocumentCascadeData {
                     Origin::UserAgent | Origin::User
                 ));
 
-                if origins_to_rebuild.contains(sheet_origin.into()) {
+                let validity = flusher.origin_validity(sheet_origin);
+
+                // Servo doesn't support to incrementally mutate UA sheets.
+                debug_assert!(matches!(
+                    validity,
+                    OriginValidity::Valid | OriginValidity::FullyInvalid
+                ));
+
+                if validity != OriginValidity::Valid {
                     self.add_stylesheet(
                         device,
                         quirks_mode,
                         &ua_stylesheets.quirks_mode_stylesheet,
                         guards.ua_or_user,
-                        extra_data
+                        extra_data,
+                        SheetRebuildKind::Full,
                     );
                 }
             }
         }
 
-        // Only add stylesheets for origins we are updating, and only add
-        // Author level sheets if author style is not disabled.
-        let sheets_to_add = doc_stylesheets.filter(|s| {
-            let sheet_origin = s.contents(guards.author).origin;
-
-            origins_to_rebuild.contains(sheet_origin.into()) &&
-                (!matches!(sheet_origin, Origin::Author) || !author_style_disabled)
-        });
-
-        for stylesheet in sheets_to_add {
+        for (stylesheet, rebuild_kind) in flusher {
             self.add_stylesheet(
                 device,
                 quirks_mode,
                 stylesheet,
                 guards.author,
-                extra_data
+                extra_data,
+                rebuild_kind,
             );
         }
     }
@@ -178,7 +201,8 @@ impl DocumentCascadeData {
         quirks_mode: QuirksMode,
         stylesheet: &S,
         guard: &SharedRwLockReadGuard,
-        _extra_data: &mut PerOrigin<ExtraStyleData>
+        _extra_data: &mut PerOrigin<ExtraStyleData>,
+        rebuild_kind: SheetRebuildKind,
     )
     where
         S: StylesheetInDocument + ToMediaListKey + 'static,
@@ -192,9 +216,11 @@ impl DocumentCascadeData {
         let origin_cascade_data =
             self.per_origin.borrow_mut_for_origin(&origin);
 
-        origin_cascade_data
-            .effective_media_query_results
-            .saw_effective(stylesheet);
+        if rebuild_kind.should_rebuild_invalidation() {
+            origin_cascade_data
+                .effective_media_query_results
+                .saw_effective(stylesheet);
+        }
 
         for rule in stylesheet.effective_rules(device, guard) {
             match *rule {
@@ -248,43 +274,49 @@ impl DocumentCascadeData {
 
                         map.insert(rule, quirks_mode);
 
-                        origin_cascade_data
-                            .invalidation_map
-                            .note_selector(selector, quirks_mode);
-                        let mut visitor = StylistSelectorVisitor {
-                            needs_revalidation: false,
-                            passed_rightmost_selector: false,
-                            attribute_dependencies: &mut origin_cascade_data.attribute_dependencies,
-                            style_attribute_dependency: &mut origin_cascade_data.style_attribute_dependency,
-                            state_dependencies: &mut origin_cascade_data.state_dependencies,
-                            mapped_ids: &mut origin_cascade_data.mapped_ids,
-                        };
+                        if rebuild_kind.should_rebuild_invalidation() {
+                            origin_cascade_data
+                                .invalidation_map
+                                .note_selector(selector, quirks_mode);
+                            let mut visitor = StylistSelectorVisitor {
+                                needs_revalidation: false,
+                                passed_rightmost_selector: false,
+                                attribute_dependencies: &mut origin_cascade_data.attribute_dependencies,
+                                style_attribute_dependency: &mut origin_cascade_data.style_attribute_dependency,
+                                state_dependencies: &mut origin_cascade_data.state_dependencies,
+                                mapped_ids: &mut origin_cascade_data.mapped_ids,
+                            };
 
-                        selector.visit(&mut visitor);
+                            selector.visit(&mut visitor);
 
-                        if visitor.needs_revalidation {
-                            origin_cascade_data.selectors_for_cache_revalidation.insert(
-                                RevalidationSelectorAndHashes::new(selector.clone(), hashes),
-                                quirks_mode
-                            );
+                            if visitor.needs_revalidation {
+                                origin_cascade_data.selectors_for_cache_revalidation.insert(
+                                    RevalidationSelectorAndHashes::new(selector.clone(), hashes),
+                                    quirks_mode
+                                );
+                            }
                         }
                     }
                     origin_cascade_data.rules_source_order += 1;
                 }
                 CssRule::Import(ref lock) => {
-                    let import_rule = lock.read_with(guard);
-                    origin_cascade_data
-                        .effective_media_query_results
-                        .saw_effective(import_rule);
+                    if rebuild_kind.should_rebuild_invalidation() {
+                        let import_rule = lock.read_with(guard);
+                        origin_cascade_data
+                            .effective_media_query_results
+                            .saw_effective(import_rule);
+                    }
 
                     // NOTE: effective_rules visits the inner stylesheet if
                     // appropriate.
                 }
                 CssRule::Media(ref lock) => {
-                    let media_rule = lock.read_with(guard);
-                    origin_cascade_data
-                        .effective_media_query_results
-                        .saw_effective(media_rule);
+                    if rebuild_kind.should_rebuild_invalidation() {
+                        let media_rule = lock.read_with(guard);
+                        origin_cascade_data
+                            .effective_media_query_results
+                            .saw_effective(media_rule);
+                    }
                 }
                 CssRule::Keyframes(ref keyframes_rule) => {
                     let keyframes_rule = keyframes_rule.read_with(guard);
@@ -489,14 +521,6 @@ impl Stylist {
             return false;
         }
 
-        let author_style_disabled = self.stylesheets.author_style_disabled();
-        let (doc_stylesheets, origins_to_rebuild, have_invalidations) =
-            self.stylesheets.flush(document_element);
-
-        if origins_to_rebuild.is_empty() {
-            return have_invalidations;
-        }
-
         self.num_rebuilds += 1;
 
         // Update viewport_constraints regardless of which origins'
@@ -515,32 +539,38 @@ impl Stylist {
             // queries defined?)
             let cascaded_rule = ViewportRule {
                 declarations: viewport_rule::Cascade::from_stylesheets(
-                    doc_stylesheets.clone(), guards.author, &self.device
+                    self.stylesheets.iter(),
+                    guards.author,
+                    &self.device,
                 ).finish()
             };
 
             self.viewport_constraints =
-                ViewportConstraints::maybe_new(&self.device,
-                                               &cascaded_rule,
-                                               self.quirks_mode);
+                ViewportConstraints::maybe_new(
+                    &self.device,
+                    &cascaded_rule,
+                    self.quirks_mode,
+                );
 
             if let Some(ref constraints) = self.viewport_constraints {
                 self.device.account_for_viewport_rule(constraints);
             }
         }
 
+        let flusher = self.stylesheets.flush(document_element, &guards.author);
+
+        let had_invalidations = flusher.had_invalidations();
+
         self.cascade_data.rebuild(
             &self.device,
             self.quirks_mode,
-            doc_stylesheets,
+            flusher,
             guards,
             ua_sheets,
-            author_style_disabled,
             extra_data,
-            origins_to_rebuild,
         );
 
-        have_invalidations
+        had_invalidations
     }
 
     /// Insert a given stylesheet before another stylesheet in the document.
@@ -1689,6 +1719,9 @@ impl<'a> SelectorVisitor for StylistSelectorVisitor<'a> {
 
 /// Data resulting from performing the CSS cascade that is specific to a given
 /// origin.
+///
+/// FIXME(emilio): Consider renaming and splitting in `CascadeData` and
+/// `InvalidationData`? That'd make `clear_cascade_data()` clearer.
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 #[derive(Debug)]
 struct CascadeData {
@@ -1784,20 +1817,25 @@ impl CascadeData {
         self.pseudos_map.get(pseudo).is_some()
     }
 
-    fn clear(&mut self) {
+    /// Clears the cascade data, but not the invalidation data.
+    fn clear_cascade_data(&mut self) {
         self.element_map.clear();
         self.pseudos_map.clear();
         self.animations.clear();
+        self.rules_source_order = 0;
+        self.num_selectors = 0;
+        self.num_declarations = 0;
+    }
+
+    fn clear(&mut self) {
+        self.clear_cascade_data();
+        self.effective_media_query_results.clear();
         self.invalidation_map.clear();
         self.attribute_dependencies.clear();
         self.style_attribute_dependency = false;
         self.state_dependencies = ElementState::empty();
         self.mapped_ids.clear();
         self.selectors_for_cache_revalidation.clear();
-        self.effective_media_query_results.clear();
-        self.rules_source_order = 0;
-        self.num_selectors = 0;
-        self.num_declarations = 0;
     }
 }