restrict website to only specific ip addresses on same VS

You could create a data group with the allowed ip addresses, and then reference them in an iRule, that only matches if the host header is :

when HTTP_REQUEST {
    if { [HTTP::host] equals "www.example.com" } {

        Require client ip address to be present in datagroup (dg_example.com) for allowed source ip's
        if { ! [class match [IP::client_addr] eq dg_example.com] } {
            drop
            return
        }
    }

}