const int MAX_RETRIES = 5;

void login()

{

  for ( int idx = 0; idx < MAX_RETRIES; ++idx)

    if ( internal_login() == true)

      // we have a successful login

      return;

  throw "could not login";

}

If MAX_RETRIES is a compile-time constant, a modern compiler could "unroll" the above loop, somewhat like this:

void unrolled_login()

{

  if ( internal_login() == true) return;

  if ( internal_login() == true) return;

  if ( internal_login() == true) return;

  if ( internal_login() == true) return;

  if ( internal_login() == true) return;

  throw "could not login";

}

If MAX_RETRIES is a run-time constant, the compiler cannot optimize anything, since MAX_RETRIES could be any value