If someone were to do a C-based API server, does Postgres have an API to interface with it at the PLAN or EXECUTE level, to save from long query processing? Say

If someone were to do a C-based API server, does Postgres have an API to interface with it at the PLAN or EXECUTE level, to save from long query processing? Say, a query with dozens of joins and columns, and you want to shave off 500 microseconds? Libpq doesn't seem to have something like that.