Note that this fails under -fsanitize=align
Subject: [PATCH v5 2/6] Teach VACUUM to use visibility map snapshot.
performing post-bootstrap initialization ...
../src/backend/access/heap/visibilitymap.c:482:38: runtime error: load of misaligned address 0x5559e1352424 for type 'uint64', which requires 8 byte alignment
> *all_visible += pg_popcount64(umap[i] & VISIBLE_MASK64);