[GHC] #8714: ExistentialQuantification plus DeriveDataTypeable leads to core lint error

[GHC]

#8714: ExistentialQuantification plus DeriveDataTypeable leads to core lint error
----------------------------------+-------------------------------------
       Reporter:  CoreyOConnor    |             Owner:
           Type:  bug             |            Status:  new
       Priority:  normal          |         Milestone:
      Component:  Compiler        |           Version:  7.6.3
       Keywords:                  |  Operating System:  Unknown/Multiple
   Architecture:  x86_64 (amd64)  |   Type of failure:  None/Unknown
     Difficulty:  Unknown         |         Test Case:
     Blocked By:                  |          Blocking:
Related Tickets:                  |
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 The attached program produces an core lint error when compiling with
 optimization.

 {{{
 $ ghc -O -debug -dcore-lint Main
 [1 of 1] Compiling Main             ( Main.hs, Main.o )
 *** Core Lint errors : in result of Float out(FOS {Lam = Just 0,
                                                    Consts = True,
                                                    PAPs = True}) ***
 <no location info>: Warning:
     In the type ‛cache_s16y’
     @ cache_s16y is out of scope
 *** Offending Program ***
 Main.focusAst
   :: forall syntax_aB4.
      GHC.Types.Int
      -> Main.BufferImpl syntax_aB4 -> Main.BufferImpl syntax_aB4
 [LclIdX,
  Arity=2,
  Str=DmdType <L,U><S(S),1*U(U)>m,
  Unf=Unf{Src=InlineStable, TopLvl=True, Arity=2, Value=True,
          ConLike=True, WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(unsat_ok=True,boring_ok=False)
          Tmpl= \ (@ syntax_aMw)
                  (r_aB5 [Occ=Once] :: GHC.Types.Int)
                  (b_aB6 [Occ=Once!] :: Main.BufferImpl syntax_aMw) ->
                  case b_aB6
                  of _ [Occ=Dead, Dmd=<L,A>]
                  { Main.FBufferData ds_dOP [Occ=Once!, Dmd=<S,U>] ->
                  case ds_dOP
                  of _ [Occ=Dead, Dmd=<L,A>]
                  { Main.HLState @ cache_s16y dt_s16z [Dmd=<C(C(S)),U>]
                                 cache_s16A [Occ=Once, Dmd=<S,U>] ->
                  case dt_s16z r_aB5 cache_s16A of dt_XBQ { __DEFAULT ->
                  Main.FBufferData
                    @ syntax_aMw
                    (Main.HLState @ syntax_aMw @ cache_s16y dt_s16z dt_XBQ)
                  }
                  }
                  }}]
 Main.focusAst =
   \ (@ syntax_aMw)
     (r_aB5 :: GHC.Types.Int)
     (b_aB6 :: Main.BufferImpl syntax_aMw) ->
     case b_aB6
     of _ [Occ=Dead, Dmd=<L,A>] { Main.FBufferData ds_dOP [Dmd=<S,U>] ->
     case ds_dOP
     of _ [Occ=Dead] { Main.HLState @ cache_s220 dt_s221 cache_s222 ->
     case dt_s221 r_aB5 cache_s222 of dt_XBQ { __DEFAULT ->
     Main.FBufferData
       @ syntax_aMw
       (Main.HLState @ syntax_aMw @ cache_s220 dt_s221 dt_XBQ)
     }
     }
     }
 <snip>
 }}}

 The full log is attached.

 The same error occurs with a GHC HEAD build from 2012/12/12. I will check
 with a latest HEAD.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8714>
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