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LibWeb: Make CSS::StyleProperties copy-on-write internally

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This makes the way we've implemented the CSS `revert` keyword a lot less
expensive.

Until now, we were making a deep copy of all property values at the
start of each cascade origin. (Those are the values that `revert` would
bring us back to if encountered.)

With this patch, the revert property set becomes a shallow copy, and we
only clone the property set if the cascade ends up writing something.

This knocks a 5% profile item down to 1.3% on https://tailwindcss.com
This commit is contained in:
Andreas Kling 2024-09-10 11:46:32 +02:00 • committed by Andreas Kling
commit e399b472e9
Notes: github-actions[bot] 2024-09-10 11:52:22 +00:00
3 changed files with 74 additions and 57 deletions
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12
Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
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@ -887,7 +887,7 @@ void StyleComputer::set_property_expanding_shorthands(StyleProperties& style, CS
{
for_each_property_expanding_shorthands(property_id, value, AllowUnresolved::No, [&](PropertyID shorthand_id, CSSStyleValue const& shorthand_value) {
if (shorthand_value.is_revert()) {
auto const& property_in_previous_cascade_origin = style_for_revert.m_property_values[to_underlying(shorthand_id)];
auto const& property_in_previous_cascade_origin = style_for_revert.m_data->m_property_values[to_underlying(shorthand_id)];
if (property_in_previous_cascade_origin) {
style.set_property(shorthand_id, *property_in_previous_cascade_origin, StyleProperties::Inherited::No, important);
if (shorthand_id == CSS::PropertyID::AnimationName)
@ -1826,7 +1826,7 @@ void StyleComputer::compute_cascaded_values(StyleProperties& style, DOM::Element
// FIXME: This is not very efficient, we should only resolve the custom properties that are actually used.
for (auto i = to_underlying(CSS::first_property_id); i <= to_underlying(CSS::last_property_id); ++i) {
auto property_id = (CSS::PropertyID)i;
auto& property = style.m_property_values[i];
auto& property = style.m_data->m_property_values[i];
if (property && property->is_unresolved())
property = Parser::Parser::resolve_unresolved_style_value(Parser::ParsingContext { document() }, element, pseudo_element, property_id, property->as_unresolved());
}
@ -1939,7 +1939,7 @@ void StyleComputer::compute_defaulted_property_value(StyleProperties& style, DOM
{
// FIXME: If we don't know the correct initial value for a property, we fall back to `initial`.
auto& value_slot = style.m_property_values[to_underlying(property_id)];
auto& value_slot = style.m_data->m_property_values[to_underlying(property_id)];
if (!value_slot) {
if (is_inherited_property(property_id)) {
style.set_property(
@ -2410,7 +2410,7 @@ void StyleComputer::absolutize_values(StyleProperties& style) const
// We have to resolve them right away, so that the *computed* line-height is ready for inheritance.
// We can't simply absolutize *all* percentage values against the font size,
// because most percentages are relative to containing block metrics.
auto& line_height_value_slot = style.m_property_values[to_underlying(CSS::PropertyID::LineHeight)];
auto& line_height_value_slot = style.m_data->m_property_values[to_underlying(CSS::PropertyID::LineHeight)];
if (line_height_value_slot && line_height_value_slot->is_percentage()) {
line_height_value_slot = LengthStyleValue::create(
Length::make_px(CSSPixels::nearest_value_for(font_size * static_cast<double>(line_height_value_slot->as_percentage().percentage().as_fraction()))));
@ -2423,8 +2423,8 @@ void StyleComputer::absolutize_values(StyleProperties& style) const
if (line_height_value_slot && line_height_value_slot->is_length())
line_height_value_slot = LengthStyleValue::create(Length::make_px(line_height));
for (size_t i = 0; i < style.m_property_values.size(); ++i) {
auto& value_slot = style.m_property_values[i];
for (size_t i = 0; i < style.m_data->m_property_values.size(); ++i) {
auto& value_slot = style.m_data->m_property_values[i];
if (!value_slot)
continue;
value_slot = value_slot->absolutized(viewport_rect(), font_metrics, m_root_element_font_metrics);