Andreas Kling 9e8e568b43 LibWeb: Use structural sharing for CSS custom properties ...

Replace per-element OrderedHashMap storage for custom properties with
a RefCounted chain (CustomPropertyData) that enables structural
sharing. Each chain node stores only the properties declared directly
on its element, with a parent pointer to the inherited chain.

Elements that don't override any custom properties share the parent's
data directly (just a RefPtr copy). During cascade, only entries that
actually differ from the parent are stored in own_values - the rest
are inherited through the chain. During var() resolution, resolved
values are compared against the parent's and matching entries are
dropped, enabling further sharing.

The chain uses a depth limit (max 32) with flattening, plus
absorption of small parent nodes (threshold 8) to keep lookups fast.

This reduces custom property memory from ~79 MB to ~5.7 MB on
cloudflare.com.

2026-02-13 14:57:15 +01:00

1.4 KiB

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