Auto merge of #19696 - upsuper:rule-cache-opt, r=emilio

Skip rule node which contains only inherited properties for rule cache

This is one possible fix for [bug 1427681](https://bugzilla.mozilla.org/show_bug.cgi?id=1427681) which tries to skip some rule nodes when using rule cache.

Try push for correctness: https://treeherder.mozilla.org/#/jobs?repo=try&revision=74e3941e2cfc5fba4bce839f2518af8a5a8b7411

It doesn't really show much memory saving on awsy. It only shows several KB save on fresh start memory. But since conceptually it's simple, I guess it's worth taking.

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components/style/properties/declaration_block.rs

@@ -283,6 +283,12 @@ impl PropertyDeclarationBlock {
         self.longhands.contains(id)
     }
 
+    /// Returns whether this block contains any reset longhand.
+    #[inline]
+    pub fn contains_any_reset(&self) -> bool {
+        self.longhands.contains_any_reset()
+    }
+
     /// Get a declaration for a given property.
     ///
     /// NOTE: This is linear time.

components/style/properties/properties.mako.rs

@@ -309,6 +309,16 @@ impl LonghandIdSet {
         true
     }
 
+    /// Returns whether this set contains any longhand that `other` also contains.
+    pub fn contains_any(&self, other: &Self) -> bool {
+        for (self_cell, other_cell) in self.storage.iter().zip(other.storage.iter()) {
+            if (*self_cell & *other_cell) != 0 {
+                return true;
+            }
+        }
+        false
+    }
+
     /// Create an empty set
     #[inline]
     pub fn new() -> LonghandIdSet {
@@ -322,6 +332,13 @@ impl LonghandIdSet {
         (self.storage[bit / 32] & (1 << (bit % 32))) != 0
     }
 
+    /// Return whether this set contains any reset longhand.
+    #[inline]
+    pub fn contains_any_reset(&self) -> bool {
+        ${static_longhand_id_set("RESET", lambda p: not p.style_struct.inherited)}
+        self.contains_any(&RESET)
+    }
+
     /// Add the given property to the set
     #[inline]
     pub fn insert(&mut self, id: LonghandId) {
@@ -3157,6 +3174,7 @@ pub fn cascade(
         device,
         pseudo,
         rule_node,
+        guards,
         iter_declarations,
         parent_style,
         parent_style_ignoring_first_line,
@@ -3176,6 +3194,7 @@ pub fn apply_declarations<'a, F, I>(
     device: &Device,
     pseudo: Option<<&PseudoElement>,
     rules: &StrongRuleNode,
+    guards: &StylesheetGuards,
     iter_declarations: F,
     parent_style: Option<<&ComputedValues>,
     parent_style_ignoring_first_line: Option<<&ComputedValues>,
@@ -3478,7 +3497,7 @@ where
             % endif
             }
 
-            if let Some(style) = rule_cache.and_then(|c| c.find(&context.builder)) {
+            if let Some(style) = rule_cache.and_then(|c| c.find(guards, &context.builder)) {
                 context.builder.copy_reset_from(style);
                 apply_reset = false;
             }