#15696: Derived Ord instance for enumerations with more than 8 elements seems to be incorrect -------------------------------------+------------------------------------- Reporter: mrkkrp | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.6.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Sometimes. Here is the thread that explains the bug: https://github.com/haskell/containers/issues/568 I originally reported this as a bug on `containers` issue tracker, but we seem to have concluded that this is probably a bug in the GHC optimizer itself. I think the shortest repro so far is this: {{{#!hs import qualified Data.Set as S main = print $ let {-# noinline f #-} f () = T2 in S.fromList [f (), f ()] data T = T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 deriving (Show, Read, Eq, Ord, Bounded, Enum) }}} which prints {{{#!hs fromList [T2,T2] }}} The person who derived this from my original repro says:
And as I said earlier, comment out the T9 constructor => prints fromList [T2] as it should.
Another interesting quote:
Can confirm. Tested with ghc-8.6.1, containers-0.6.0.1 and leancheck-0.7.5 (so it does not seem to depend on the testing framework). Error occurs:
* with ghc -O1 and -O2 (but not with -O0) * and if data type has at least 9 elements
So, likely a bug in ghc's optimizer.
in some cases, input has duplicates, but not always.
This is a bad one, makes GHC 8.6.1 totally unusable for me. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15696 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler