We might be able to just get away with replacing the Set with a flat array and doing the O(n) lookup time. The expanded sets are probably pretty small, all things considered. We could also generate a fresh Set for each state reduction. Still O(n), but then we aren't doing an additional O(n) search for each lookup. Finally, we could either implement or grab an existing persistent immutable set.

This patch replaces the mutable sets with Immutable.js sets. You'll need to apply the patch in 1253784 first. Try push: https://treeherder.mozilla.org/#/jobs?repo=try&revision=f87d7721084e

Comment on attachment 8731399 [details] [diff] [review] Bug1239436-immutable-set.patch --- Depends on 1253784 Review of attachment 8731399 [details] [diff] [review]: ----------------------------------------------------------------- Excellent!!! Thank you, Lin!

You're welcome :)

Shoot, forgot blocker