no way to talk about unpacking sum types / unpacking tuples

Suppose I have the following Haskell module:

{-# LANGUAGE BangPatterns #-}

-- strict 'Maybe'
data StrictMaybe a = SNothing | SJust !a

-- lazy 'Maybe'
data Maybe a = Nothing | Just a

data BoxedInner = BoxedInner
  !Int
  !(Maybe Int)

data StillBoxedInner = StillBoxedInner
  !Int
  !(StrictMaybe Int)

mBoxed :: BoxedInner
mBoxed = BoxedInner 0 (Just 0)

mWantThisToUnbox :: StillBoxedInner
mWantThisToUnbox = StillBoxedInner 1 (Just 1)

the 'StrictMaybe' can unbox the first 'Int' into 1#, but the 1 inside of the just cannot unbox. When compiled to core with -O2 what I'd want to see is something like:

mWantThisToUnbox = StillBoxedInner 0# (# | 1# #)

(where (# (# #) | a #) is an unboxed sum type with two constructors, one nullary and one unary)

but instead the Int inside 'SJust' remains boxed.

Even with something like the following:

{-# LANGUAGE UnboxedSums #-}
data UMaybe a = (# (# #) | a #)

something like 'UMaybe Int' would still result in 'Int' being boxed.

This same thing occurs with unpacked tuples, consider something like:

data StrictTuple = StrictTuple
  !Int
  !(Int, Int)

Anything inside the (Int, Int) tuple will not unbox, despite having a bang pattern there.

Trac metadata

Trac field	Value
Version	8.4.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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CC	andrewthad, osa1
Operating system
Architecture