#1746: GADT bug with -O2
-----------------------+----------------------------------------------------
Reporter: igloo | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 6.8.1
Component: Compiler | Version: 6.8
Severity: normal | Keywords:
Difficulty: Unknown | Os: Unknown
Testcase: | Architecture: Unknown
-----------------------+----------------------------------------------------
Reported by Daniel Gorín in
http://www.haskell.org/pipermail/glasgow-haskell-
users/2007-September/013178.html
This module:
{{{
{-# OPTIONS_GHC -fglasgow-exts #-}
module T where
data T a where T :: T a -> T [a]
class C a where
f :: a -> ()
instance C (T [a]) where
f (T x@(T _)) = f x
}}}
gives a compiler panic when compiled with `-O2`. With `-dcore-lint` we
get:
{{{
$ ghc -c -O2 e.hs -dcore-lint
rm: cannot remove `e.o': No such file or directory
rm: cannot remove `e.hi': No such file or directory
*** Core Lint Errors: in result of SpecConstr ***
<no location info>:
[in body of lambda with binder co_a5Z :: [a_a5t] ~ [a_a5X]]
a_a5X is out of scope
*** Offending Program ***
Rec {
$sa_s6U :: forall a_a5t a_a60.
([a_a5t] ~ [a_a5X], a_a5t ~ [a_a60]) =>
T.T a_a60 -> ()
[]
$sa_s6U =
\ (@ a_a5t) (@ co_a5Z) (@ a_a60) (@ co_a62) (ds_d69 [Just B] :: T.T
a_a60) ->
case (T.T @ a_a5t @ a_a60 @ co_a62 ds_d69)
`cast` (trans
(T.T (right co_a5Z)) (trans (T.T (right (sym co_a5Z)))
(T.T co_a62))
:: T.T a_a5t ~ T.T [a_a60])
of wild_B1 [Just B] { T.T @ a_a5X @ co_X68 ds_d67 [Just X] ->
case ds_d67 `cast` (T.T (right (sym co_X68)) :: T.T a_a5X ~ T.T a_a60)
of wild_Xc [Just X] { T.T @ a_X6c @ co_X6f ds_X6n [Just B] ->
a_s6j
@ a_X6c
(wild_Xc
`cast` (trans
(T.T (right co_X68)) (trans (T.T (right (sym co_X68)))
(T.T co_X6f))
:: T.T a_a60 ~ T.T [a_X6c]))
}
}
a_s6j [LoopBreaker Nothing] :: forall a_a5t. T.T [a_a5t] -> ()
[Arity 1
Str: DmdType Sb
RULES: "SC:a_s6j0" [0]
forall {@ a_a5t @ co_a5Z @ a_a60 @ co_a62 ds_d69 [Just B] ::
T.T a_a60}
a_s6j @ a_a60
((T.T @ a_a5t @ a_a60 @ co_a62 ds_d69)
`cast` (trans
(T.T (right co_a5Z)) (trans (T.T (right
(sym co_a5Z))) (T.T co_a62))
:: T.T a_a5t ~ T.T [a_a60]))
= $sa_s6U @ a_a5t @ co_a5Z @ a_a60 @ co_a62 ds_d69]
a_s6j =
\ (@ a_a5t) (ds_X6c :: T.T [a_a5t]) ->
case ds_X6c of wild_B1 [Just B] { T.T @ a_a5X @ co_a5Z ds_d67 [Just X]
->
case ds_d67 `cast` (T.T (right (sym co_a5Z)) :: T.T a_a5X ~ T.T a_a5t)
of wild_Xc [Just X] { T.T @ a_a60 @ co_a62 ds_d69 [Just B] ->
a_s6j
@ a_a60
(wild_Xc
`cast` (trans
(T.T (right co_a5Z)) (trans (T.T (right (sym co_a5Z)))
(T.T co_a62))
:: T.T a_a5t ~ T.T [a_a60]))
}
}
end Rec }
T.$f1 :: forall a_a5t. T.C (T.T [a_a5t])
[Exported]
[Arity 1
Str: DmdType Sb]
T.$f1 =
\ (@ a_a5t) ->
(a_s6j @ a_a5t)
`cast` (sym ((T.:Co:TC) (T.T [a_a5t]))
:: T.T [a_a5t] -> () ~ (T.:TC) (T.T [a_a5t]))
*** End of Offense ***
<no location info>:
Compilation had errors
}}}
This is a regression since 6.6.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1746>
GHC <http://www.haskell.org/ghc/>
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