Use a bitmap to optimize adding to a PropertyDeclarationBlock.

components/style/properties/declaration_block.rs

@@ -41,7 +41,7 @@ impl Importance {
 }
 
 /// Overridden declarations are skipped.
-#[derive(Debug, PartialEq, Clone)]
+#[derive(Clone)]
 pub struct PropertyDeclarationBlock {
     /// The group of declarations, along with their importance.
     ///
@@ -50,6 +50,14 @@ pub struct PropertyDeclarationBlock {
 
     /// The number of entries in `self.declaration` with `Importance::Important`
     important_count: usize,
+
+    longhands: LonghandIdSet,
+}
+
+impl fmt::Debug for PropertyDeclarationBlock {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.declarations.fmt(f)
+    }
 }
 
 impl PropertyDeclarationBlock {
@@ -58,14 +66,20 @@ impl PropertyDeclarationBlock {
         PropertyDeclarationBlock {
             declarations: Vec::new(),
             important_count: 0,
+            longhands: LonghandIdSet::new(),
         }
     }
 
     /// Create a block with a single declaration
     pub fn with_one(declaration: PropertyDeclaration, importance: Importance) -> Self {
+        let mut longhands = LonghandIdSet::new();
+        if let PropertyDeclarationId::Longhand(id) = declaration.id() {
+            longhands.insert(id);
+        }
         PropertyDeclarationBlock {
             declarations: vec![(declaration, importance)],
             important_count: if importance.important() { 1 } else { 0 },
+            longhands: longhands,
         }
     }
 
@@ -198,28 +212,39 @@ impl PropertyDeclarationBlock {
 
     fn push_common(&mut self, declaration: PropertyDeclaration, importance: Importance,
                    overwrite_more_important: bool) -> bool {
-        for slot in &mut *self.declarations {
-            if slot.0.id() == declaration.id() {
-                match (slot.1, importance) {
-                    (Importance::Normal, Importance::Important) => {
-                        self.important_count += 1;
-                    }
-                    (Importance::Important, Importance::Normal) => {
-                        if overwrite_more_important {
-                            self.important_count -= 1;
-                        } else {
-                            return false
+        let definitely_new = if let PropertyDeclarationId::Longhand(id) = declaration.id() {
+            !self.longhands.contains(id)
+        } else {
+            false  // For custom properties, always scan
+        };
+
+        if !definitely_new {
+            for slot in &mut *self.declarations {
+                if slot.0.id() == declaration.id() {
+                    match (slot.1, importance) {
+                        (Importance::Normal, Importance::Important) => {
+                            self.important_count += 1;
+                        }
+                        (Importance::Important, Importance::Normal) => {
+                            if overwrite_more_important {
+                                self.important_count -= 1;
+                            } else {
+                                return false
+                            }
+                        }
+                        _ => if slot.0 == declaration {
+                            return false;
                         }
                     }
-                    _ => if slot.0 == declaration {
-                        return false;
-                    }
+                    *slot = (declaration, importance);
+                    return true
                 }
-                *slot = (declaration, importance);
-                return true;
             }
         }
 
+        if let PropertyDeclarationId::Longhand(id) = declaration.id() {
+            self.longhands.insert(id);
+        }
         self.declarations.push((declaration, importance));
         if importance.important() {
             self.important_count += 1;
@@ -256,6 +281,11 @@ impl PropertyDeclarationBlock {
     ///
     /// Returns whether any declaration was actually removed.
     pub fn remove_property(&mut self, property: &PropertyId) -> bool {
+        if let PropertyId::Longhand(id) = *property {
+            if !self.longhands.contains(id) {
+                return false
+            }
+        }
         let important_count = &mut self.important_count;
         let mut removed_at_least_one = false;
         self.declarations.retain(|&(ref declaration, importance)| {
@@ -269,6 +299,10 @@ impl PropertyDeclarationBlock {
             !remove
         });
 
+        if let PropertyId::Longhand(id) = *property {
+            debug_assert!(removed_at_least_one);
+            self.longhands.remove(id);
+        }
         removed_at_least_one
     }
 

components/style/properties/properties.mako.rs

@@ -177,6 +177,7 @@ pub mod animated_properties {
 }
 
 /// A set of longhand properties
+#[derive(Clone)]
 pub struct LonghandIdSet {
     storage: [u32; (${len(data.longhands)} - 1 + 32) / 32]
 }
@@ -202,6 +203,13 @@ impl LonghandIdSet {
         self.storage[bit / 32] |= 1 << (bit % 32);
     }
 
+    /// Remove the given property from the set
+    #[inline]
+    pub fn remove(&mut self, id: LonghandId) {
+        let bit = id as usize;
+        self.storage[bit / 32] &= !(1 << (bit % 32));
+    }
+
     /// Set the corresponding bit of TransitionProperty.
     /// This function will panic if TransitionProperty::All is given.
     pub fn set_transition_property_bit(&mut self, property: &TransitionProperty) {

ports/geckolib/glue.rs

@@ -738,7 +738,8 @@ pub extern "C" fn Servo_DeclarationBlock_Clone(declarations: RawServoDeclaration
 pub extern "C" fn Servo_DeclarationBlock_Equals(a: RawServoDeclarationBlockBorrowed,
                                                 b: RawServoDeclarationBlockBorrowed)
                                                 -> bool {
-    *RwLock::<PropertyDeclarationBlock>::as_arc(&a).read() == *RwLock::<PropertyDeclarationBlock>::as_arc(&b).read()
+    *RwLock::<PropertyDeclarationBlock>::as_arc(&a).read().declarations() ==
+    *RwLock::<PropertyDeclarationBlock>::as_arc(&b).read().declarations()
 }
 
 #[no_mangle]