Specialisation doesn't kick in -- NOW WITH MINIMAL WORKING EXAMPLE (RE: Instantiation of overloaded definition *in Core*)

[Simon Peyton Jones]

Yes I have a full build.  No it was not built with Hadrian.  I did not realise that your system relied not only on GHC as a library, but also on the build system that you use to build GHC.

I guess I can try that, but probably not today.  But what is “settings”?

Simon

PS: I am leaving Microsoft at the end of November 2021, at which point simonpj at microsoft.com<mailto:simonpj at microsoft.com> will cease to work.  Use simon.peytonjones at gmail.com<mailto:simon.peytonjones at gmail.com> instead.  (For now, it just forwards to simonpj at microsoft.com.)

From: Erdi, Gergo <Gergo.Erdi at sc.com>
Sent: 19 October 2021 09:03
To: Simon Peyton Jones <simonpj at microsoft.com>; 'Matthew Pickering' <matthewtpickering at gmail.com>
Cc: Montelatici, Raphael Laurent <Raphael.Montelatici at sc.com>; 'GHC' <ghc-devs at haskell.org>
Subject: RE: Specialisation doesn't kick in -- NOW WITH MINIMAL WORKING EXAMPLE (RE: Instantiation of overloaded definition *in Core*)


PUBLIC


PUBLIC

Do you have a full GHC build there? Are you using Hadrian? Did you set `libDir`’s definition in the source file to where you have GHC built? I just tried, and if I remove the files from my GHC build, I am able to rebuild them:

mi at localhost[ghc] $ for i in settings llvm-passes llvm-targets; do rm ~/prog/ghc/_build/stage1/lib/$i; done
mi at localhost[ghc] $ for i in settings llvm-passes llvm-targets; do ./hadrian/build-stack _build/stage1/lib/$i; done
| Successfully generated _build/stage1/lib/settings.
Build completed in 0.41s

| Copy file: llvm-passes => _build/stage1/lib/llvm-passes
Build completed in 0.40s

| Copy file: llvm-targets => _build/stage1/lib/llvm-targets
Build completed in 0.52s



From: Simon Peyton Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>>
Sent: Tuesday, October 19, 2021 3:54 PM
To: Erdi, Gergo <Gergo.Erdi at sc.com<mailto:Gergo.Erdi at sc.com>>; 'Matthew Pickering' <matthewtpickering at gmail.com<mailto:matthewtpickering at gmail.com>>
Cc: Montelatici, Raphael Laurent <Raphael.Montelatici at sc.com<mailto:Raphael.Montelatici at sc.com>>; 'GHC' <ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>>
Subject: [External] RE: Specialisation doesn't kick in -- NOW WITH MINIMAL WORKING EXAMPLE (RE: Instantiation of overloaded definition *in Core*)

As for opening a ticket – a big part of the problem is that I don’t even know yet if I’m doing something wrong, or GHC is! So it’s not clear what the ticket would even be for – “I’m using the GHC API wrongly” is not a strong bug report 😊

Plenty of tickets turn out to be non-bugs.  But they are still searchable, and form a permanent record that may help others, perhaps in unexpected ways.  So I encourage you to do so.

I successfully compiled the attached Main.hs with HEAD, passing ‘-package ghc’ as a command line argument.

When I run it I get

simonpj at MSRC-3645512:~/tmp$ ./gergo

Missing file: /home/simonpj/code/HEAD-1/compiler/stage1/build/settings

So now I’m stuck again.

Simon

PS: I am leaving Microsoft at the end of November 2021, at which point simonpj at microsoft.com<mailto:simonpj at microsoft.com> will cease to work.  Use simon.peytonjones at gmail.com<mailto:simon.peytonjones at gmail.com> instead.  (For now, it just forwards to simonpj at microsoft.com<mailto:simonpj at microsoft.com>.)

From: Erdi, Gergo <Gergo.Erdi at sc.com<mailto:Gergo.Erdi at sc.com>>
Sent: 19 October 2021 02:57
To: Simon Peyton Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>>; 'Matthew Pickering' <matthewtpickering at gmail.com<mailto:matthewtpickering at gmail.com>>
Cc: Montelatici, Raphael Laurent <Raphael.Montelatici at sc.com<mailto:Raphael.Montelatici at sc.com>>; 'GHC' <ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>>
Subject: RE: Specialisation doesn't kick in -- NOW WITH MINIMAL WORKING EXAMPLE (RE: Instantiation of overloaded definition *in Core*)


PUBLIC


PUBLIC

Thanks for looking into this!

`Paths_ghc_lib` is referenced just because I am using GHC via ghc-lib. You can of course instead use a local full build of GHC for the libDir. Please find an updated version attached that does that – you’ll just have to adapt the definition of `libDir` to your environment.

As for opening a ticket – a big part of the problem is that I don’t even know yet if I’m doing something wrong, or GHC is! So it’s not clear what the ticket would even be for – “I’m using the GHC API wrongly” is not a strong bug report 😊


From: Simon Peyton Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>>
Sent: Saturday, October 16, 2021 12:52 AM
To: Erdi, Gergo <Gergo.Erdi at sc.com<mailto:Gergo.Erdi at sc.com>>; 'Matthew Pickering' <matthewtpickering at gmail.com<mailto:matthewtpickering at gmail.com>>
Cc: Montelatici, Raphael Laurent <Raphael.Montelatici at sc.com<mailto:Raphael.Montelatici at sc.com>>; 'GHC' <ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>>
Subject: [External] RE: Specialisation doesn't kick in -- NOW WITH MINIMAL WORKING EXAMPLE (RE: Instantiation of overloaded definition *in Core*)

I could not compile Main.hs:

~/code/HEAD-1/inplace/bin/ghc-stage1 -c Gergo.hs -package ghc



Gergo.hs:4:1: error:

    Could not find module ‘Paths_ghc_lib’

    Use -v (or `:set -v` in ghci) to see a list of the files searched for.

  |

4 | import qualified Paths_ghc_lib as GHC

  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

simonpj at MSRC-3645512:~/tmp$

Would you like to open a ticket rather than do this by email?

Simon

PS: I am leaving Microsoft at the end of November 2021, at which point simonpj at microsoft.com<mailto:simonpj at microsoft.com> will cease to work.  Use simon.peytonjones at gmail.com<mailto:simon.peytonjones at gmail.com> instead.  (For now, it just forwards to simonpj at microsoft.com<mailto:simonpj at microsoft.com>.)

From: Erdi, Gergo <Gergo.Erdi at sc.com<mailto:Gergo.Erdi at sc.com>>
Sent: 15 October 2021 05:35
To: Simon Peyton Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>>; 'Matthew Pickering' <matthewtpickering at gmail.com<mailto:matthewtpickering at gmail.com>>
Cc: Montelatici, Raphael Laurent <Raphael.Montelatici at sc.com<mailto:Raphael.Montelatici at sc.com>>; 'GHC' <ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>>
Subject: RE: Specialisation doesn't kick in -- NOW WITH MINIMAL WORKING EXAMPLE (RE: Instantiation of overloaded definition *in Core*)


PUBLIC


PUBLIC

OK I now have a standalone demonstrator that shows, at least, that the default method implementation is not specialized. With the attached input programs, the resulting Core (using GHC e46edfcf47d674731935b2ea1443cc7927e071fb) is as follows (only showing the relevant parts):

seq :: forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
seq
  = \ (@(m :: * -> *)) (v_srS [Occ=Once1!] :: Monad m) ->
      case v_srS of { C:Monad _ [Occ=Dead] v_srV [Occ=Once1] -> v_srV }

$dmseq :: forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
$dmseq
  = \ (@(m :: * -> *))
      ($dMonad [Occ=Once1] :: Monad m)
      (@a)
      (@b)
      (ma [Occ=Once1] :: m a)
      (mb [Occ=OnceL1] :: m b) ->
      let {
        sat_ss0 [Occ=Once1] :: a -> m b
        [LclId]
        sat_ss0 = \ _ [Occ=Dead] -> mb } in
      bind @m $dMonad @a @b ma sat_ss0

$fMonadIO :: Monad IO
$fMonadIO = C:Monad @IO bindIO $fMonadIO_$cseq;

$fMonadIO_$cseq :: forall a b. IO a -> IO b -> IO b
$fMonadIO_$cseq = \ (@a) (@b) -> $dmseq @IO $fMonadIO @a @b;

foo :: IO ()
foo = seq @IO $fMonadIO @() @() ioA ioA

If I turn on Opt_D_dump_spec, I can see that specializer *is* running, it just doesn’t *do* anything.



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