[Q] Inlining done: evtRead

[Gabor Greif]

I think you have to follow this:

-- | Data is available to be read.
evtRead :: Event
evtRead = Event 1
{-# INLINE evtRead #-}


On 1/8/19, Simon Peyton Jones <simonpj at microsoft.com> wrote:
> Are you sure?   GHC.Event isn't used on Windows, so I did this:
>
> =================
> module Bar where
>
> newtype Evt = Evt Int
>
> evtRead :: Evt
> evtRead = Evt 33
>
> instance Show Evt where
>   show = showEvt
>
> showEvt :: Evt -> String
> {-# NOINLINE showEvt #-}
> showEvt (Evt x) = show x
> ============
>
> module Foo where
>
> import Bar
>
> main = print evtRead
> ===============
>
> And indeed when I compile these with -O I get
>
> Foo.main1
>   = showEvt (Bar.evtRead1 `cast` (Sym (Bar.N:Evt[0]) :: Int ~R# Evt))
>
> where Bar.evtRead1 is the static (I# 33) box.
>
> No duplication.
>
> Can you give me a repro case that isn't OS-specific?  (I suppose I can try
> on Linux tomorrow, but I'm sure that the OS is only accidentally involved
> here.)
>
> Simon
>
> | -----Original Message-----
> | From: Gabor Greif <ggreif at gmail.com>
> | Sent: 07 January 2019 23:28
> | To: Simon Peyton Jones <simonpj at microsoft.com>
> | Cc: ghc-devs <ghc-devs at haskell.org>
> | Subject: [Q] Inlining done: evtRead
> |
> | Hi Simon,
> |
> | a simplifier question...
> |
> | Roughly a year ago I started learning about imported Ids, their
> unfoldings
> | etc.
> |
> | I have very small example program that compiles on Linux.
> |
> | ```haskell
> | import GHC.Event
> |
> | main = print evtRead
> | ```
> |
> | `evtRead` is a newtype-wrapped Int. When you compile above program
> | with HEAD GHC without optimisation, you'll see that `evtRead` gets
> | passed directly to `show`.
> |
> | But with -O1 it's unfolding will be inlined, floated to toplevel, and
> | dumped as static global data into the using Main module. This was not
> | the case in GHC 8.4. Not sure about 8.6 (will check). Anyway here is
> | the inlining notice that the simplifier gave me (-ddump-inlinings
> | -dverbose-core2core)
> |
> | > Inlining done: GHC.Event.Internal.evtRead
> | >     Inlined fn:  (GHC.Types.I# 1#)
> | >                  `cast` (Sym (GHC.Event.Internal.N:Event[0])
> | >                          :: GHC.Types.Coercible GHC.Types.Int
> | > GHC.Event.Internal.Event)
> | >     Cont:   Stop[BoringCtxt] GHC.Event.Internal.Event
> | >
> |
> | I believe this is a regression, as copies of global data can pop up in
> | potentially many different modules.
> |
> | What do you think? Which change could have caused this?
> |
> | Cheers,
> |
> |     Gabor
>