Here is a new scan of regexp irregularities in the Emacs tree (master at 1ed7cd41db), using relint 1.13, xr 1.15.

Relint now finds more regexps, and the xr linting engine has a new subsumption check. This check finds pairs of repetitions, one made unnecessary by the other, like [ab]+a* or a*a*. The check is somewhat experimental, but is accurate enough and not only indicates possible mistakes and general waste but also potential slow regexps.

As an example of the last point, the running time of

(string-match "a*a*b" (make-string N ?a))

is cubical in N. (Not all mistakes are exponential, but it's bad enough.)