autoref for algorithms

\autoref does only work completely with a corresponding \....autorefname macro, i.e. \sectionautorefname etc.

hyperref extracts the reference information from its specific label information, where the relevant counter name is stored as well.

This means, if the counter is named foo, \fooautorefname must exist -- otherwise it's ignored (and a warning shipped to the console).

The algorithm environment has a counter of the same name, so

\newcommand{\algorithmautorefname}{Algorithm}

will provide hyperref with the correct information.

\documentclass{article}

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

\newcommand{\algorithmautorefname}{Algorithm}

\begin{document}
\begin{algorithm}
\caption{Baseline}\label{ALG_baseline}
%\begin{algorithmic}[1]
%
%\end{algorithmic}
\end{algorithm}

\autoref{ALG_baseline} is simply linked to with a number.

\end{document}

Please note, that cleveref package provides a similar feature, however, the names must be setup as well, with \crefname{algorithm}{algorithm}{algorithms} etc.

Update

This addresses the comment by the O.P. about detecting names of counters.

An excerpt of the .log file:

The counter definitions are written to the .log file as c@foo=\countY, where Y is the number of a free counter register and not really important (apart from few exceptions.)

\@float@every@algorithm=\toks16
\c@algorithm=\count88

Later on, we find

\c@ALG@line=\count89
\c@ALG@rem=\count90
\c@ALG@nested=\count91
\ALG@tlm=\skip43
\ALG@thistlm=\skip44
\c@ALG@Lnr=\count92
\c@ALG@blocknr=\count93
\c@ALG@storecount=\count94
\c@ALG@tmpcounter=\count95
\ALG@tmplength=\skip45

This means, that ALG@line is (very likely) the line number counter.

However, it's a 'hidden' counter, due to @ usage in the name!

I took me half an our to figure out that I had to use \renewcommand{} instead of just \newcommand to overwrite the hyperref default algorithm name.