c-collect-line-comments is a compiled Lisp function in `cc-engine.el'.

(c-collect-line-comments RANGE)

If the argument is a cons of two buffer positions (such as returned by
`c-literal-limits'), and that range contains a C++ style line comment,
then an extended range is returned that contains all adjacent line
comments (i.e. all comments that starts in the same column with no
empty lines or non-whitespace characters between them). Otherwise the
argument is returned.

Note that this function might do hidden buffer changes. See the
comment at the start of cc-engine.el for more info.