vc-diff

vc-diff is an interactive autoloaded compiled Lisp function in `vc.el'.

It is bound to C-x v =, <menu-bar> <tools> <vc> <vc-diff>.

(vc-diff &optional HISTORIC NOT-URGENT)

Display diffs between file revisions.
Normally this compares the currently selected fileset with their
working revisions. With a prefix argument HISTORIC, it reads two revision
designators specifying which revisions to compare.

The optional argument NOT-URGENT non-nil means it is ok to say no to
saving the buffer.