Function faiss_index_cpu_to_gpu 

pub unsafe extern "C" fn faiss_index_cpu_to_gpu(
    provider: *mut FaissGpuResourcesProvider,
    device: c_int,
    index: *const FaissIndex,
    p_out: *mut *mut FaissGpuIndex,
) -> c_int

converts any CPU index that can be converted to GPU