Since git 2.9 there is another experimental, opt-in, improvement to git diff that results in more readable diffs: Heuristics that try to capture the logical changes better. By default git tries to delay the start of diffs as long as possible leading to bogus highlighting of e.g. doc comments (slash star star).

See https://github.com/blog/2188-git-2-9-has-been-released (section Beautiful diffs) for an example and http://blog.deveo.com/whats-new-in-git-2-11/#experimentalheu... for another similar option that I did not try yet.