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module Main (main) where
{- This program is designed to check that case-of-known-constructor
fires even if an application of a DataCon wrapper is floated out:
* The early FloatOut pass will float `D False` out of `g`, since
it’s a constant, non-trivial expression.
* But since `D` is strict, the floated-out expression will actually
be `$WD False`.
* In simplifier phase 2, `f` will be inlined into `g`, leading to a
case expression that scrutinizes the floated-out binding.
* If case-of-known-constructor fires, we’ll end up with `notRule
False`, the RULE will fire, and we get True.
* If it doesn’t fire at phase 2, it will fire later at phase 0 when
we inline the DataCon wrapper. But now the RULE is inactive, so
we’ll end up with False instead.
We want case-of-known-constructor to fire early, so we want the output
to be True. See #18012 for more details. -}
main :: IO ()
main = print (g ())
data T = D !Bool
notRule :: Bool -> Bool
notRule x = x
{-# INLINE [0] notRule #-}
{-# RULES "notRule/False" [~0] notRule False = True #-}
f :: T -> () -> Bool
f (D a) () = notRule a
{-# INLINE [100] f #-} -- so it isn’t inlined before FloatOut
g :: () -> Bool
g x = f (D False) x
{-# NOINLINE g #-}
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