Growing widens L1PointerMask without touching the table, so an entry whose
address has the new mask bit set sits where InvalidateCache no longer looks,
and a later shrink hands it back to the JIT. Wipe [0, old) on grow, the way
the shrink wipes [new, MAX); the still-valid entries go with it.
Hojun-Cho
7e3e4f81ac