[GHC] #10176: Invalid core generated with GHC 7.10 RC3

[GHC]

#10176: Invalid core generated with GHC 7.10 RC3
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        Reporter:  NeilMitchell      |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  high              |               Milestone:  7.10.1
       Component:  Compiler          |                 Version:  7.10.1-rc3
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by nomeata):

 After adding a lint check as suggested by SPJ, I simplified your example
 to
 {{{
 module Buggy(buggy) where

 {-# NOINLINE error1Arg #-}
 error1Arg :: () -> a
 error1Arg _ = undefined

 {-# NOINLINE buggy #-}
 buggy :: a
 buggy = error1Arg () ()
 }}}
 but I’m not sure if the lint check is actually correct here, as this is
 the core it complains about:
 {{{
 *** Core Lint errors : in result of Simplifier ***
 Buggy.hs:9:10: Warning:
     [in body of lambda with binder a_an8 :: *]
     No alternatives for HNF scrutinee error1Arg @ (() -> a_an8) ()
 *** Offending Program ***
 error1Arg [InlPrag=NOINLINE] :: forall a_an0. () -> a_an0
 [LclId, Arity=2, CallArity=2, Str=DmdType <B,A>b]
 error1Arg =
   \ (@ a_anf) _ [Occ=Dead, Dmd=<B,A>] -> undefined @ a_anf

 buggy [InlPrag=NOINLINE] :: forall a_amZ. a_amZ
 [LclIdX, Str=DmdType b]
 buggy =
   \ (@ a_an8) -> case error1Arg @ (() -> a_an8) () of wild_00 { }

 *** End of Offense ***
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10176#comment:6>
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