servo: Merge #18497 - style: Don't cache styles that got a cache hit on the second pass (from emilio:no-cache-if-cached); r=heycam

This avoids doing wasted work, at least in the recascade case, and pretty likely
in the other as well.

Source-Repo: https://github.com/servo/servo
Source-Revision: 988728e9d5c66e6bf2f9e0e03a50a814d0e1f2ab

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 68555686bb062ce696e70ffcbdbd07fe6960a5da

servo/components/style/sharing/mod.rs

@@ -82,6 +82,7 @@ use smallvec::SmallVec;
 use std::marker::PhantomData;
 use std::mem;
 use std::ops::Deref;
+use style_resolver::PrimaryStyle;
 use stylist::Stylist;
 
 mod checks;
@@ -546,11 +547,18 @@ impl<E: TElement> StyleSharingCache<E> {
     ///
     /// NB: We pass a source for the validation data, rather than the data itself,
     /// to avoid memmoving at each function call. See rust issue #42763.
-    pub fn insert_if_possible(&mut self,
-                              element: &E,
-                              style: &ComputedValues,
-                              validation_data_holder: Option<&mut StyleSharingTarget<E>>,
-                              dom_depth: usize) {
+    pub fn insert_if_possible(
+        &mut self,
+        element: &E,
+        style: &PrimaryStyle,
+        validation_data_holder: Option<&mut StyleSharingTarget<E>>,
+        dom_depth: usize,
+    ) {
+        if style.0.reused_via_rule_node {
+            debug!("Failing to insert into the cached: this was a cached style");
+            return;
+        }
+
         let parent = match element.traversal_parent() {
             Some(element) => element,
             None => {
@@ -583,7 +591,7 @@ impl<E: TElement> StyleSharingCache<E> {
         //
         // These are things we don't check in the candidate match because they
         // are either uncommon or expensive.
-        let box_style = style.get_box();
+        let box_style = style.style().get_box();
         if box_style.specifies_transitions() {
             debug!("Failing to insert to the cache: transitions");
             return;

servo/components/style/traversal.rs

@@ -678,14 +678,12 @@ where
                         resolver.resolve_style_with_default_parents()
                     };
 
-                    context.thread_local
-                        .sharing_cache
-                        .insert_if_possible(
-                            &element,
-                            new_styles.primary.style(),
-                            Some(&mut target),
-                            traversal_data.current_dom_depth,
-                        );
+                    context.thread_local.sharing_cache.insert_if_possible(
+                        &element,
+                        &new_styles.primary,
+                        Some(&mut target),
+                        traversal_data.current_dom_depth,
+                    );
 
                     new_styles
                 }
@@ -724,9 +722,10 @@ where
 
                 resolver.cascade_styles_with_default_parents(cascade_inputs)
             };
+
             context.thread_local.sharing_cache.insert_if_possible(
                 &element,
-                new_styles.primary.style(),
+                &new_styles.primary,
                 None,
                 traversal_data.current_dom_depth,
             );