[Q] Inlining done: evtRead

[Gabor Greif]

Hmm, yes. So why wasn't GHC 8.4 doing this? Did some commit fix the
inliner to respect the pragma?

Thanks and cheers,

    Gabor

On 1/8/19, Simon Peyton Jones <simonpj at microsoft.com> wrote:
> Oh well, your INLINE pragma is saying "please inline evtRead at every call
> site". And so GHC does exactly that.
>
> That seems like obeying the pragma doesn't it?
>
> Simon
>
> | -----Original Message-----
> | From: Gabor Greif <ggreif at gmail.com>
> | Sent: 08 January 2019 00:06
> | To: Simon Peyton Jones <simonpj at microsoft.com>
> | Cc: ghc-devs <ghc-devs at haskell.org>
> | Subject: Re: [Q] Inlining done: evtRead
> |
> | 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
> | >
>