While reviewing a separate patch related to nbtree, I noticed that _bt_setup_array_cmp in nbtpreprocesskeys.c performs multiple redundant lookups of the operator family OID via rel->rd_opfamily[skey->sk_attno - 1].
The attached patch caches this value in a local opfamily variable. This matches the pattern used in several other functions within the same file (such as _bt_skiparray_strat_decrement, _bt_preprocess_array_keys, etc.), making the code more consistent and readable.
The assignment is placed after the early-return check for (elemtype == opcintype) to ensure we only perform the array indexing when the cross-type comparison logic is actually reached.
