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{-# LANGUAGE BangPatterns #-}
{-# OPTIONS_GHC -fdmd-unbox-width=0 #-} -- otherwise we'll optimistically unbox the arg to c
module T19398 where
data T a = MkT !a !a
f :: T a -> T a
f (MkT a b) = MkT b a
{-# NOINLINE f #-}
-- | Should *not* have the CPR property, even though the scrutinee is a
-- variable with the CPR property. It shows how Test (A) of
-- Historical Note [Optimistic field binder CPR] is unsound.
a :: Int -> Int
a n
| n == 0 = n
| even n = case q of MkT x y -> if x == y then x else y
| otherwise = case q of MkT x y -> if x == y then y else x
where
q = f $ f $ f $ f $ f $ f $ f $ MkT n n
-- | Should not have the CPR property, because 'x' will not be unboxed.
-- It shows how Test (C) of Historical Note [Optimistic field binder CPR] is
-- unsound.
c :: (Int, Int) -> Int
c (x,_) = x
|
