GHC inliner doesn't

Compile this program

{-# OPTIONS_GHC -O2 -ddump-simpl #-}
module Foo where

class C a where
    to' :: a -> Int
    from' :: Int -> a

{-# NOINLINE to #-}
to :: (C a) => a -> Int
to = to'

{-# NOINLINE from #-}
from :: (C a) => Int -> a
from = from'

{-# INLINE foo #-}
foo :: (C a) => (Int -> Int) -> a -> a
foo f x = from (f (to x))

bar :: (C a) => (Int -> Int) -> a -> a
bar f = foo f . foo f
 

Study the output. It contains

...
Foo.foo =
  __inline_me (\ (@ a_a6n) ($dC_a6t :: Foo.C a_a6n) ->
...

and

...
Foo.bar =
  \ (@ a_a6w) ($dC_a6G :: Foo.C a_a6w) ->
    let {
      foo1_s7S [ALWAYS Just L] :: (GHC.Base.Int -> GHC.Base.Int) -> a_a6w -> a_a6w
      [Str: DmdType]
      foo1_s7S = Foo.foo @ a_a6w $dC_a6G
...

Why isn't foo inlined?

Note that if the export list is changed to only export bar, then foo does get inlined.

Trac metadata

Trac field	Value
Version	6.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	lennart@augustsson.net
Operating system	Unknown
Architecture	Unknown