#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 mbieleck): Thanks for the response. Replying to [comment:36 goldfire]:
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.
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
I realize that. I just picked any variant of `UnivCo` to quickly test if this has any chance of working (and actually improving compile times). Of course the right thing to do is to introduce a new `UnivCoProvenance` specifically for this case. the coercion a little earlier, we might have more luck. Yes, it might still create the coercion, but at least it will prevent the simplifier from processing it repeatedly later.
I don't think the simple solution here is quite the right approach that will continue to work in the long term.
Who said we can't make incremental improvements? If this would be put behind a flag, it should not harm anyone. For the record, here are some timing results (using Types.hs from the ticket): {{{ $ ./timing.sh GHC=inplace/bin/ghc-stage2 N old omit old_tail omit_tail 200 0m0.465s 0m0.404s 0m1.674s 0m0.445s 400 0m0.695s 0m0.504s 0m10.745s 0m0.645s 600 0m1.077s 0m0.614s 0m28.975s 0m0.985s 800 0m1.565s 0m0.755s timeout 0m1.446s 1000 0m2.225s 0m1.075s timeout 0m2.435s 1200 0m3.167s 0m1.426s timeout 0m3.575s 1400 0m4.236s 0m1.705s timeout 0m5.045s 1600 0m5.786s 0m1.654s timeout 0m4.775s 1800 0m5.756s 0m1.955s timeout 0m6.156s 2000 0m7.215s 0m3.106s timeout 0m9.865s }}} `old` is the default behavior, `omit` is my patch. `_tail` variants use the tail recursive type family. The reason I'm so desperate is that it greatly affects my code. I'm using extensible (Vinyl) records computed using some type families. For bigger records, GHC just runs out of memory. This patch helps. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8095#comment:37 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler