-XStrict prevents code inlining.

Hi, let's consider the following code:

{-# LANGUAGE Strict #-}  -- Comment/uncommenting this
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}

module K where

import Control.Monad.Trans
import qualified Control.Monad.State.Strict as S
import Control.Monad.Primitive

newtype StateT s m a = StateT (S.StateT s m a) -- S is Control.Monad.State.Strict
  deriving (Functor, Applicative, Monad, MonadTrans)

instance PrimMonad m => PrimMonad (StateT s m) where
  type PrimState (StateT s m) = PrimState m
  primitive ~a = lift (primitive a) ; {-# INLINE primitive #-}

If compiled with -XStrict this code is not inlined properly and it badly affects the performance. While discussing it on Haskell IRC lyxia helped very much with discovering the CORE differences. The lazy version has couple of things which the strict version is missing in form of [InlPrag=INLINE (sat-args=0)] on toplevel identifiers.

Core: https://gist.github.com/Lysxia/34684c9ca9fe4772ea38a5065414f542