From e4621704ceb5dd81d70eeab50c277bc469da9b7d Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Thu, 2 Nov 2023 07:48:51 +0100
Subject: [PATCH] LibWeb: Avoid unnecessary JS::Handles in
 Node::queue_mutation_record()

We don't need to make a list of the target node's ancestors before
iterating over them, since nothing happens while iterating them that
can disturb the list anyway (no arbitrary JS execution etc).

The incessant construction and destruction of handles here was showing
up in profiles of basically every website that uses JavaScript to build
some or all of their DOM tree.
---
 Userland/Libraries/LibWeb/DOM/Node.cpp | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/Userland/Libraries/LibWeb/DOM/Node.cpp b/Userland/Libraries/LibWeb/DOM/Node.cpp
index 2b775c197e..b619e749ca 100644
--- a/Userland/Libraries/LibWeb/DOM/Node.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Node.cpp
@@ -1544,14 +1544,8 @@ void Node::queue_mutation_record(FlyString const& type, Optional<DeprecatedStrin
     OrderedHashMap<MutationObserver*, Optional<DeprecatedString>> interested_observers;
 
     // 2. Let nodes be the inclusive ancestors of target.
-    Vector<JS::Handle<Node const>> nodes;
-    nodes.append(JS::make_handle(*this));
-
-    for (auto* parent_node = parent(); parent_node; parent_node = parent_node->parent())
-        nodes.append(JS::make_handle(*parent_node));
-
     // 3. For each node in nodes, and then for each registered of node’s registered observer list:
-    for (auto& node : nodes) {
+    for (auto* node = this; node; node = node->parent()) {
         for (auto& registered_observer : node->m_registered_observer_list) {
             // 1. Let options be registered’s options.
             auto& options = registered_observer->options();
@@ -1563,7 +1557,7 @@ void Node::queue_mutation_record(FlyString const& type, Optional<DeprecatedStrin
             //      - type is "characterData" and options["characterData"] either does not exist or is false
             //      - type is "childList" and options["childList"] is false
             //    then:
-            if (!(node.ptr() != this && !options.subtree)
+            if (!(node != this && !options.subtree)
                 && !(type == MutationType::attributes && (!options.attributes.has_value() || !options.attributes.value()))
                 && !(type == MutationType::attributes && options.attribute_filter.has_value() && (attribute_namespace.has_value() || !options.attribute_filter->contains_slow(attribute_name.value_or("").view())))
                 && !(type == MutationType::characterData && (!options.character_data.has_value() || !options.character_data.value()))