There even was a ghc branch with partial work towards implementing this as part of fgaz’s gsoc. I’m happy to help out if any spare cycles are needed to work through the details On Fri, May 6, 2022 at 5:26 AM Simon Peyton Jones < simon.peytonjones@gmail.com> wrote:

There is a (stale) ghc-proposal for that,

...

https://github.com/ghc-proposals/ghc-proposals/pull/357

So there is! Thank you.

Gergo: would you like to take over this proposal, revise it if necessary in the light of the comments, and submit it?

Simon

On Fri, 6 May 2022 at 10:08, Oleg Grenrus wrote:

...

There is a (stale) ghc-proposal for that, https://github.com/ghc-proposals/ghc-proposals/pull/357

- Oleg

On 6.5.2022 12.04, Simon Peyton Jones wrote:

...

Dear devs

At the moment the INLINEABLE pragma means "capture my right-hand side, regardless of how big it is, so that it can be type-class-specialised, including in other modules". But it /also /says "feel free to inline me".

Some users (eg Gergo) want to say NOINLINE on some functions. But for these they'd still like to generate type-class-specialised versions. After all, if we aren't going to inline them, specialising is the next best thing.

But we have no way to say both "specialise me" and "don't inline me", because you can't say both INLINEABLE and NOINLINE. (That would look silly.)

I think we should probably just bite the bullet and add a SPECIALISABLE pragma, /orthogonal to INLINE/NOINLNE/, which say "capture my right-hand side, regardless of how big it is, so that it can be type-class-specialised, including in other modules". It behaves exactly like INLINEABLE except that you can specify it along with INLINE/NOINLINE.

Any thoughts? Do you think this needs a GHC proposal?

See #21036 < https://gitlab.haskell.org/ghc/ghc/-/issues/21036#note_407930>

Simon

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I can look into this, sure, but it wouldn’t exactly solve my original problem, which is that I would like to turn this on wholesale, not definition by definition.

What is "this" that you want to turn on, precisely? why would I ever not want to specialize a definition

I think the only downside is compilation time and code bloat. I think you are concerned about cross-module specialisation. There are two things in play: 1. Whether the defining module exposes the definition 2. Whether the importing module specialises the thus-exposed definition For (1) there are two choices: - (1a) Currently INLINEABLE captures the RHS of the function *exactly as the user wrote it*, and allows that to be specialised. - (1b) On the other hand, -fexpose-all-unfoldings does not attempt to capture the functions the user wrote; instead, it exposes the *post-optimisation *RHSs of all functions, regardless of per-function pragmas. I believe that (1b) is closer to what you want. For (2) one might wonder whether to - (2a) specialise every imported (type-class-overloaded) function whose unfolding we can see - (2b) specialise only imported functions with a SPECIALISABLE pragma - (2c) specialise imported functions only with -fspecialise-aggressively I think GHC currently does (2c). Maybe this taxonomy helps you a bit? Simon On Mon, 9 May 2022 at 02:38, Erdi, Gergo wrote:

PUBLIC

I can look into this, sure, but it wouldn’t exactly solve my original problem, which is that I would like to turn this on wholesale, not definition by definition. It seems that all past discussion about this was in the context of a per-definition pragma (and sadly, a large part of that was bikeshedding over the name of the pragma…). But is the reason for that spelled out explicitly somewhere? In other words, what is the cost of specialisation, why would I ever not want to specialize a definition (inlinable or not)? I’d like to understand this first before reviving the proposal.

*From:* ghc-devs *On Behalf Of *Simon Peyton Jones *Sent:* Friday, May 6, 2022 5:26 PM *To:* Oleg Grenrus ; ÉRDI Gergő *Cc:* GHC developers *Subject:* [External] Re: Specialising NOINLINE functions

There is a (stale) ghc-proposal for that, https://github.com/ghc-proposals/ghc-proposals/pull/357 https://clicktime.symantec.com/3NuNFMzg65dA5k5kXHX5U196xU?u=https%3A%2F%2Fgi...

So there is! Thank you.

Gergo: would you like to take over this proposal, revise it if necessary in the light of the comments, and submit it?

Simon

On Fri, 6 May 2022 at 10:08, Oleg Grenrus wrote:

There is a (stale) ghc-proposal for that, https://github.com/ghc-proposals/ghc-proposals/pull/357 https://clicktime.symantec.com/3NuNFMzg65dA5k5kXHX5U196xU?u=https%3A%2F%2Fgi...

- Oleg

On 6.5.2022 12.04, Simon Peyton Jones wrote:

...

Dear devs

At the moment the INLINEABLE pragma means "capture my right-hand side, regardless of how big it is, so that it can be type-class-specialised, including in other modules". But it /also /says "feel free to inline me".

Some users (eg Gergo) want to say NOINLINE on some functions. But for these they'd still like to generate type-class-specialised versions. After all, if we aren't going to inline them, specialising is the next best thing.

But we have no way to say both "specialise me" and "don't inline me", because you can't say both INLINEABLE and NOINLINE. (That would look silly.)

I think we should probably just bite the bullet and add a SPECIALISABLE pragma, /orthogonal to INLINE/NOINLNE/, which say "capture my right-hand side, regardless of how big it is, so that it can be type-class-specialised, including in other modules". It behaves exactly like INLINEABLE except that you can specify it along with INLINE/NOINLINE.

Any thoughts? Do you think this needs a GHC proposal?

See #21036 < https://gitlab.haskell.org/ghc/ghc/-/issues/21036#note_407930 https://clicktime.symantec.com/3SB6vTf6r7gWFXH7FGMko9a6xU?u=https%3A%2F%2Fgi...

Simon

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