-Note. When the "-C" option is used, git-diff-cache and
-git-diff-file commands feed not just modified filepairs but
-unmodified ones to diffcore mechanism as well. This lets the
-copy detector consider unmodified files as copy source
-candidates at the expense of making it slower. Currently
-git-diff-tree does not feed unmodified filepairs even when the
-"-C" option is used, so it can detect copies only if the file
-that was copied happened to have been modified in the same
-changeset.
+Note. When the "-C" option is used with --find-copies-harder
+option, git-diff-* commands feed unmodified filepairs to
+diffcore mechanism as well as modified ones. This lets the copy
+detector consider unmodified files as copy source candidates at
+the expense of making it slower. Without --find-copies-harder,
+git-diff-* commands can detect copies only if the file that was
+copied happened to have been modified in the same changeset.