Bug 1352306 - Part 1: stylo: Only snapshot attributes if there is some rule that depends on that attribute. r=emilio

MozReview-Commit-ID: Emey96ovc2a

--HG--
extra : rebase_source : b60b5114e8faf5bb39bf34fd0d985b071b9ec2dc

layout/base/ServoRestyleManager.cpp

@@ -611,6 +611,17 @@ ServoRestyleManager::AttributeWillChange(Element* aElement,
   }
 
   ServoElementSnapshot& snapshot = SnapshotFor(aElement);
+  if (snapshot.HasAttrs()) {
+    return;
+  }
+
+  if (!((aNameSpaceID == kNameSpaceID_None &&
+        (aAttribute == nsGkAtoms::id ||
+         aAttribute == nsGkAtoms::_class)) ||
+        StyleSet()->MightHaveAttributeDependency(aAttribute))) {
+    return;
+  }
+
   snapshot.AddAttrs(aElement);
 
   if (Element* parent = aElement->GetFlattenedTreeParentElementForStyle()) {
@@ -624,7 +635,6 @@ ServoRestyleManager::AttributeChanged(Element* aElement, int32_t aNameSpaceID,
                                       const nsAttrValue* aOldValue)
 {
   MOZ_ASSERT(!mInStyleRefresh);
-  MOZ_ASSERT_IF(mSnapshots.Get(aElement), mSnapshots.Get(aElement)->HasAttrs());
 
   nsIFrame* primaryFrame = aElement->GetPrimaryFrame();
   if (primaryFrame) {

layout/style/ServoBindingList.h

@@ -82,6 +82,10 @@ SERVO_BINDING_FUNC(Servo_StyleSet_ResolveForDeclarations,
                    RawServoStyleSetBorrowed set,
                    ServoComputedValuesBorrowedOrNull parent_style,
                    RawServoDeclarationBlockBorrowed declarations)
+SERVO_BINDING_FUNC(Servo_StyleSet_MightHaveAttributeDependency, bool,
+                   RawServoStyleSetBorrowed set,
+                   nsIAtom* local_name)
+
 
 // CSSRuleList
 SERVO_BINDING_FUNC(Servo_CssRules_ListTypes, void,

layout/style/ServoStyleSet.cpp

@@ -1155,4 +1155,10 @@ ServoStyleSet::RunPostTraversalTasks()
   }
 }
 
+bool
+ServoStyleSet::MightHaveAttributeDependency(nsIAtom* aAttribute)
+{
+  return Servo_StyleSet_MightHaveAttributeDependency(mRawSet.get(), aAttribute);
+}
+
 ServoStyleSet* ServoStyleSet::sInServoTraversal = nullptr;

layout/style/ServoStyleSet.h

@@ -339,6 +339,16 @@ public:
     mPostTraversalTasks.AppendElement(aTask);
   }
 
+  /**
+   * Returns true if a modification to an an attribute with the specified
+   * local name might require us to restyle the element.
+   *
+   * This function allows us to skip taking a an attribute snapshot when
+   * the modified attribute doesn't appear in an attribute selector in
+   * a style sheet.
+   */
+  bool MightHaveAttributeDependency(nsIAtom* aAttribute);
+
 private:
   // On construction, sets sInServoTraversal to the given ServoStyleSet.
   // On destruction, clears sInServoTraversal and calls RunPostTraversalTasks.