Severe performance degradation in GHC 8.0.1 compared to GHC 7.10.x
While working on a project, I have noticed that GHC 8 takes too long to run my test suite on CI server, see for example here:
GHC 8 finished in 370 [seconds](https://travis-ci.org/mrkkrp/zip/jobs/113059197\#L599), while GHC
- 10.3 in
[82 seconds](https://travis-ci.org/mrkkrp/zip/jobs/113059195\#L608), 7.10.2 and 7.10.1 demonstrated similar results (77 seconds).
There are minor differences in versions of libraries used, mainly those that are shipped with GHC, I read their changelogs and it seems like it's not likely that this sort of slow-down (× 4.5) happened because of one of those libraries.
Note that due to the nature of the project I test it does fair amount of IO in temporary directories, I'll be happy to provide more information if you like. BTW, here is the test suite: