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LibWeb: Add specialized fast_is for lists

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Before:
  `is<HTMLOLListElement>` and other similar calls in this commit
  are resolved to `dynamic_cast`, which incurs runtime overhead
  for resolving the type. The Performance hit becomes apparent
  when rendering large lists. Callgrind analysis points to a
  significant performance hit from calls to `is<...>` in
  `Element::list_owner`.

Reference: Michael Gibbs and Bjarne Stroustrup (2006) Fast dynamic
casting. Softw. Pract. Exper. 2006; 36:139–156

After:
  Implement inline `fast_is` virtual method that immediately
  resolves the type. Results in noticeable performance improvement
  2x-ish for lists with 20K entries.

Bonus: Convert starting value for LI elements to signed integer
    The spec requires the start attribute and starting value to be
    "integer". Firefox and Chrome support a negative start attribute.

FIXME: At the time of this PR, about 134 other objects resolve
`is<...>` to `dynamic_cast`. It may be a good idea to coordinate
similar changes to at least [some of] the ones that my have impact
on performance (maybe open a new issue?).
This commit is contained in:
Manuel Zahariev
2025-04-23 07:06:11 -07:00
committed by Sam Atkins
parent 12c9da2d3f
commit d27b43c1ee
Notes: github-actions[bot] 2025-06-16 11:46:35 +00:00 
Author: https://github.com/manuel-za
Commit: https://github.com/LadybirdBrowser/ladybird/commit/d27b43c1eeb
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4442
Reviewed-by: https://github.com/AtkinsSJ ✅
Reviewed-by: https://github.com/InvalidUsernameException
Reviewed-by: https://github.com/R-Goc
Reviewed-by: https://github.com/skyz1 ✅
7 changed files with 52 additions and 5 deletions
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9
Libraries/LibWeb/HTML/HTMLMenuElement.h
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@@ -21,6 +21,8 @@ public:
// https://www.w3.org/TR/html-aria/#el-menu
virtual Optional<ARIA::Role> default_role() const override { return ARIA::Role::list; }
virtual bool is_html_menu_element() const override { return true; }
private:
HTMLMenuElement(DOM::Document&, DOM::QualifiedName);
@@ -28,3 +30,10 @@ private:
};
}
namespace Web::DOM {
template<>
inline bool Node::fast_is<Web::HTML::HTMLMenuElement>() const { return is_html_menu_element(); }
}