Andreas Kling 614713ed08 LibJS: Replace IndexedProperties with inline Packed/Holey/Dictionary ...

Replace the OwnPtr<IndexedPropertyStorage> indirection with inline
indexed element storage directly on Object. This eliminates virtual
dispatch and reduces indirection for indexed property access.

The new system uses three storage kinds tracked by IndexedStorageKind:

- Packed: Dense array, no holes. Elements stored in a malloced Value*
  array with capacity header (same layout as named properties).
- Holey: Dense array with possible holes marked by empty sentinel.
  Same physical layout as Packed.
- Dictionary: Sparse storage using GenericIndexedPropertyStorage,
  type-punned into the m_indexed_elements pointer.

Transitions: None->Packed->Holey->Dictionary (mostly monotonic).
Dictionary mode triggers on non-default attributes or sparse arrays.

Object keeps the same 48-byte size since m_indexed_elements (8 bytes)
replaces IndexedProperties (8 bytes), and the storage kind + array
size fit in existing padding alongside m_flags.

The asm interpreter benefits from one fewer indirection: it now reads
the element pointer and array size directly from Object fields instead
of chasing through OwnPtr -> IndexedPropertyStorage -> Vector.

Removes: IndexedProperties, SimpleIndexedPropertyStorage,
IndexedPropertyStorage, IndexedPropertyIterator.
Keeps: GenericIndexedPropertyStorage (for Dictionary mode).

2026-03-17 22:28:35 -05:00

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