µopt ideas

[masklinn]

µopt probably make the most sense for the matcher (atoms_to_re / propagate_match) as that's where the bulk of the runtime would be spent aside from matching regexps.

use bitvec

• matched_atom_ids is currently an IntSet, I think the main point is that it prevents the same entry being added twice while we can keep iterating on new atoms. The same thing could be done via a bitset and a vec (vecdeque?)... although technically this could be done by using a bitset for the "sparse array" as it's only used to know whether the input is already in the set...
• making regexps into a bitset would avoid the need to sort it, iter_ones would hand out the indexes we need

uncount

• See how common it is for entries to have propagate_up_at_count > 1, and if it could make sense to keep that information a round and not allocate count when it's 0.
• Support variable-width count, or even lower it entirely: can an AND node have more than 256 children?