From 1242b9152e1ae9d8f40629d5fd5f15a94bcca014 Mon Sep 17 00:00:00 2001
From: Andreas Kling <andreas@ladybird.org>
Date: Mon, 21 Apr 2025 01:12:12 +0200
Subject: [PATCH] LibWeb: Turn Element.scroll(0, 0) into a no-op when possible

For unscrolled elements (already at 0, 0) that aren't eligible to be the
Document.scrollingElement, we can short-circuit here and avoid doing a
synchronous relayout of the page.

This avoids a bunch of synchronous layouts on Speedometer3's NewsSite
subtests.
---
 Libraries/LibWeb/DOM/Element.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Libraries/LibWeb/DOM/Element.cpp b/Libraries/LibWeb/DOM/Element.cpp
index 7ddcd37b06e..9af9b500461 100644
--- a/Libraries/LibWeb/DOM/Element.cpp
+++ b/Libraries/LibWeb/DOM/Element.cpp
@@ -2813,6 +2813,16 @@ void Element::scroll(double x, double y)
     if (document.document_element() == this && document.in_quirks_mode())
         return;
 
+    // OPTIMIZATION: Scrolling an unscrolled element to (0, 0) is a no-op as long
+    //               as the element is not eligible to be the Document.scrollingElement.
+    if (x == 0
+        && y == 0
+        && scroll_offset(ScrollOffsetFor::Self).is_zero()
+        && this != document.body()
+        && this != document.document_element()) {
+        return;
+    }
+
     // NOTE: Ensure that layout is up-to-date before looking at metrics.
     document.update_layout(UpdateLayoutReason::ElementScroll);