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

Matthew Pickering matthewtpickering at gmail.com
Fri Oct 22 13:29:51 UTC 2021


Hi,

If there is a ticket then I can look into it next week.

Cheers,

Matt

On Fri, Oct 22, 2021 at 12:11 PM Simon Peyton Jones
<simonpj at microsoft.com> wrote:
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> I’m out of cycles.  Do please open a ticket. You are more likely to get attention that way.
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> Matthew: maybe you can help with reproducing this?
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> SImon
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> PS: I am leaving Microsoft at the end of November 2021, at which point simonpj at microsoft.com will cease to work.  Use simon.peytonjones at gmail.com instead.  (For now, it just forwards to simonpj at microsoft.com.)
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>
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> From: Erdi, Gergo <Gergo.Erdi at sc.com>
> Sent: 19 October 2021 09:36
> 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*)
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> PUBLIC
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> PUBLIC
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> “settings”? Honestly, I have no idea. GHC looks at these files in the directory passed to runGhc, and in my local setup I have some convoluted ghc-lib-based system to persist these files and also the base package.db into a Stack/cabal-installable package, but these are only needed for environments where there’s no bona-fide GHC build directory.
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> I am sure even without Hadrian, you should have these files somewhere under your build directory, since otherwise the same same runGhc function (used inside the GHC executable as well…) wouldn’t work. Maybe someone else with non-Hadrian knowledge can tell you where these files are put in the non-Hadrian build.
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> From: Simon Peyton Jones <simonpj at microsoft.com>
> Sent: Tuesday, October 19, 2021 4:08 PM
> To: Erdi, Gergo <Gergo.Erdi at sc.com>; 'Matthew Pickering' <matthewtpickering at gmail.com>
> Cc: Montelatici, Raphael Laurent <Raphael.Montelatici at sc.com>; 'GHC' <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*)
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> 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.
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> I guess I can try that, but probably not today.  But what is “settings”?
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> Simon
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> PS: I am leaving Microsoft at the end of November 2021, at which point simonpj at microsoft.com will cease to work.  Use simon.peytonjones at gmail.com instead.  (For now, it just forwards to simonpj at microsoft.com.)
>
>
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> 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*)
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> PUBLIC
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> PUBLIC
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> 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:
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> mi at localhost[ghc] $ for i in settings llvm-passes llvm-targets; do rm ~/prog/ghc/_build/stage1/lib/$i; done
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> mi at localhost[ghc] $ for i in settings llvm-passes llvm-targets; do ./hadrian/build-stack _build/stage1/lib/$i; done
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> | Successfully generated _build/stage1/lib/settings.
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> Build completed in 0.41s
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> | Copy file: llvm-passes => _build/stage1/lib/llvm-passes
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> Build completed in 0.40s
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> | Copy file: llvm-targets => _build/stage1/lib/llvm-targets
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> Build completed in 0.52s
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> From: Simon Peyton Jones <simonpj at microsoft.com>
> Sent: Tuesday, October 19, 2021 3:54 PM
> To: Erdi, Gergo <Gergo.Erdi at sc.com>; 'Matthew Pickering' <matthewtpickering at gmail.com>
> Cc: Montelatici, Raphael Laurent <Raphael.Montelatici at sc.com>; 'GHC' <ghc-devs at haskell.org>
> Subject: [External] RE: Specialisation doesn't kick in -- NOW WITH MINIMAL WORKING EXAMPLE (RE: Instantiation of overloaded definition *in Core*)
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> As for opening a ticket – a big part of the problem is that I don’t even know yet if I’m doing something wrong, or GHC is! So it’s not clear what the ticket would even be for – “I’m using the GHC API wrongly” is not a strong bug report 😊
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> Plenty of tickets turn out to be non-bugs.  But they are still searchable, and form a permanent record that may help others, perhaps in unexpected ways.  So I encourage you to do so.
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> I successfully compiled the attached Main.hs with HEAD, passing ‘-package ghc’ as a command line argument.
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> When I run it I get
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> simonpj at MSRC-3645512:~/tmp$ ./gergo
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> Missing file: /home/simonpj/code/HEAD-1/compiler/stage1/build/settings
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> So now I’m stuck again.
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> Simon
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> PS: I am leaving Microsoft at the end of November 2021, at which point simonpj at microsoft.com will cease to work.  Use simon.peytonjones at gmail.com instead.  (For now, it just forwards to simonpj at microsoft.com.)
>
>
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> From: Erdi, Gergo <Gergo.Erdi at sc.com>
> Sent: 19 October 2021 02:57
> 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*)
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> PUBLIC
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> PUBLIC
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> Thanks for looking into this!
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> `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.
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> 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 😊
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> From: Simon Peyton Jones <simonpj at microsoft.com>
> Sent: Saturday, October 16, 2021 12:52 AM
> To: Erdi, Gergo <Gergo.Erdi at sc.com>; 'Matthew Pickering' <matthewtpickering at gmail.com>
> Cc: Montelatici, Raphael Laurent <Raphael.Montelatici at sc.com>; 'GHC' <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*)
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> I could not compile Main.hs:
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> ~/code/HEAD-1/inplace/bin/ghc-stage1 -c Gergo.hs -package ghc
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> Gergo.hs:4:1: error:
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>     Could not find module ‘Paths_ghc_lib’
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>     Use -v (or `:set -v` in ghci) to see a list of the files searched for.
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>   |
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> 4 | import qualified Paths_ghc_lib as GHC
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>   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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> simonpj at MSRC-3645512:~/tmp$
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> Would you like to open a ticket rather than do this by email?
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> Simon
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> PS: I am leaving Microsoft at the end of November 2021, at which point simonpj at microsoft.com will cease to work.  Use 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: 15 October 2021 05:35
> 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*)
>
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> PUBLIC
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> PUBLIC
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> 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):
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> seq :: forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
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> seq
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>   = \ (@(m :: * -> *)) (v_srS [Occ=Once1!] :: Monad m) ->
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>       case v_srS of { C:Monad _ [Occ=Dead] v_srV [Occ=Once1] -> v_srV }
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> $dmseq :: forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
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> $dmseq
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>   = \ (@(m :: * -> *))
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>       ($dMonad [Occ=Once1] :: Monad m)
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>       (@a)
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>       (@b)
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>       (ma [Occ=Once1] :: m a)
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>       (mb [Occ=OnceL1] :: m b) ->
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>       let {
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>         sat_ss0 [Occ=Once1] :: a -> m b
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>         [LclId]
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>         sat_ss0 = \ _ [Occ=Dead] -> mb } in
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>       bind @m $dMonad @a @b ma sat_ss0
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> $fMonadIO :: Monad IO
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> $fMonadIO = C:Monad @IO bindIO $fMonadIO_$cseq;
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> $fMonadIO_$cseq :: forall a b. IO a -> IO b -> IO b
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> $fMonadIO_$cseq = \ (@a) (@b) -> $dmseq @IO $fMonadIO @a @b;
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> foo :: IO ()
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> foo = seq @IO $fMonadIO @() @() ioA ioA
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> 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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