INLINABLE pragma and newtype wrappers prevent inlining

In #5327 (closed), we allowed case-of-known constructor to see through bindings that were marked as INLINABLE and used newtypes. However, this works only if the newtype does not have a wrapper. The following code, which is the same as T5237 except for the extra type parameters in Size, does not cause the optimization to fire.

{-# LANGUAGE GADTs, ExplicitForAll #-}
module T16254 where

newtype Size a b where
  Size :: forall b a. Int -> Size a b

{-# INLINABLE val2 #-}
val2 = Size 17

f n = case val2 of Size s -> s + s > n

The reason is that exprIsConApp_maybe sees $WSize (I# 17#), which is an application with a nontrivial argument. In general, this could cause duplication of work, but in this case we're dealing with a newtype wrapper, so this is safe.

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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