GHC.Event.Thread.eventManager has a lot of indirections

Current eventManager:

eventManager :: IORef (IOArray Int (Maybe (ThreadId, EventManager)))
eventManager = unsafePerformIO $ do
...

That's a lot of indirections just to grab your thread's event manager.

Consider the following, which I believe would improve the performance of this:

data UnliftedIORef :: TYPE 'UnliftedRep -> Type where
  UnliftedIORef :: MutVar# RealWorld a -> UnliftedIORef a

eventManager :: UnliftedIORef (MutableArray# RealWorld Things)

data Things = Things !ThreadId !EventManager

I think the Maybe can be eliminated. I'm unsure. What makes me think it can be is the following snippet:

getSystemEventManager :: IO (Maybe EventManager)
getSystemEventManager = do
  t <- myThreadId
  (cap, _) <- threadCapability t
  eventManagerArray <- readIORef eventManager
  mmgr <- readIOArray eventManagerArray cap
  return $ fmap snd mmgr

getSystemEventManager_ :: IO EventManager
getSystemEventManager_ = do
  Just mgr <- getSystemEventManager
  return mgr
{-# INLINE getSystemEventManager_ #-}

Trac metadata

Trac field	Value
Version	8.6.2
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
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