Compile time regression in GHC 8.
This bug is entirely reproducible but unfortunately takes some setup. I don't have a minimal example.
The regression is happening in FLTKHS (https://github.com/deech/fltkhs), the Haskell bindings to the FLTK(http://fltk.org) toolkit, and in particular to this GUI (https://github.com/deech/fltkhs/blob/master/images/tree-complex-windows.png). In GHC 7.8, it taks 5-9 seconds to compile and link in 7.10.3, that goes up to 12-15 seconds and finally in GHC 8 it shoots up to 45 seconds. While these numbers come from my i7, 16GB RAM Linux laptop, the compile time regression is proportionally reproducible across machines and operating systems.
Here are the steps to reproduce it
Please follow the instructions here (https://github.com/deech/fltkhs\#linux-and-bsd) but only the first set which is about installing FLTK 1.3.
Clone the repo with the offending application:
git clone https://github.com/deech/fltkhs-fluid-demos
Build the application and reproduce the problem:
cabal install c2hs
cabal install fltkhs
At the root of the repo do
cabal build fltkhs-fluid-tree