#8095: TypeFamilies painfully slow -------------------------------------+------------------------------------- Reporter: MikeIzbicki | Owner: goldfire Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler (Type | Version: 7.6.3 checker) | Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #5321, #11598, | Differential Rev(s): #12506 | Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): While I do think your proposed solution may fix the problem reported here -- slow compilation -- in my opinion it throws the baby out with the bathwater. Using `mkUnsafeCo` should happen only from `unsafeCoerce#`. There's nothing unsafe going on here, yet the Core code will be littered with what appear to be unsafe coercions. Instead of abusing the current unsafe coercions, the plan above is to introduce a new `OmittedCo` (controlled by `-f` flags) that is quite like `UnsafeCo` (but stores used coercion variables, for instance). Then, when reading the Core, we can tell the difference between the product of `unsafeCoerce#` and something omitted. By the way, I say "may fix" above because this approach might still create the coercion, only to throw it away. If we prevent the creation of the coercion a little earlier, we might have more luck. By the way, I'm sorry to rain on your parade a bit here. I do very much appreciate your just going in to fix this... but I don't think the simple solution here is quite the right approach that will continue to work in the long term. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8095#comment:36 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler