[m-rev.] for post-commit review: O(n^2) to O(n log n)

[Zoltan Somogyi]

On Mon, 10 Jan 2022 18:18:05 +1100, Peter Wang <novalazy at gmail.com> wrote:
> I don't understand that. Currently there is one .track_flags file per
> module.

Sorry, my bad. I was under the impression that there was one such file
per directory, like Mercury.options. I will fix the comment.

Zoltan.