... BTW, a quick grep for other calls of PageIndexTupleDelete suggests
that SPGiST could make very good use of PageIndexTupleOverwrite, and
there may be use for it in GIN too.
I see one place in btree where there's a PageIndexTupleDelete and then
an insert, but it's unlikely to be worth touching because the page is
expected to be empty after the PageIndexTupleDelete; so there's no
data movement we could avoid in that case.
I don't plan to investigate these cases myself, but somebody should.
regards, tom lane
