ExistentialQuantification plus DeriveDataTypeable leads to core lint error

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.

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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