Create a smart cross-reference to a line in an 'algorithmic' environment using \autoref

The line counter is hidden from hyperref's \autoref because the counter is stepped using \addtocounter{ALG@line}{1} instead of \refstepcounter{ALG@line}. The following patch corrects this, allowing you to define \ALG@lineautorefname:

\documentclass{article}

\usepackage{algorithm,algpseudocode}
\usepackage{hyperref,etoolbox}

\makeatletter
\patchcmd{\ALG@step}{\addtocounter{ALG@line}{1}}{\refstepcounter{ALG@line}}{}{}
\newcommand{\ALG@lineautorefname}{Line}
\makeatother

\newcommand{\algorithmautorefname}{Algorithm}

\begin{document}  

See \autoref{alg:myalg}, specifically \autoref{algl:y}.

\begin{algorithm}
  \caption{An algorithm}\label{alg:myalg}
  \begin{algorithmic}[1]
    \State Do X 
    \State Do Y \label{algl:y}
    \State $x = y + z$
  \end{algorithmic}
\end{algorithm}

\end{document}

The following is a cleveref-based solution. Note: \cref (the main user macro of the cleveref package) works very much like \autoref, except that it's actually far more powerful and flexible than \autoref. For instance, \cref can take multiple arguments; see the code below for an example. Further good news: cleveref is programmed "out of the box" to know that lines in an algorithmic environment should be called, well, "lines" -- no need to provide this setup yourself.

\documentclass{article}
\usepackage{algorithm,algpseudocode}
\usepackage[colorlinks]{hyperref}
\usepackage[noabbrev,capitalize,nameinlink]{cleveref}
\begin{document}

\begin{algorithm}
\caption{Baseline}\label{ALG_baseline}
\begin{algorithmic}[1]
  \State Do X 
  \State Do Y        \label{algl:y}
  \State $x = y + z$ \label{algl:sum}
\end{algorithmic}
\end{algorithm}
\cref{algl:y} in \cref{ALG_baseline} is \dots

\cref{algl:y,algl:sum} of the algorithm are based on \dots
\end{document}