How to inline early in a GHC plugin?

[Conal Elliott]

Yes, thank you, Simon. I had not occurred to me that an inlining could
start working in a later phase due to loss of loop-breaker status, rather
than the relationship between the current phase and the identifier's
declared inlining phase.

-- Conal

On Tue, Dec 6, 2016 at 6:02 AM, Simon Peyton Jones <simonpj at microsoft.com>
wrote:

> *   To access an unfolding, is `maybeUnfoldingTemplate (idUnfolding v)`
> the recommended recipe?
>
> You can see by looking at the code that idUnfolding returns nothing for a
> loop breaker.  You have to decide if that’s what you want; if not, use
> realIdUnfolding.
>
>
>
> *   Is it the case that this recipe succeeds (`Just`) in some compiler
> phases and not others?
>
> It fails for loop breakers.  An Id might be a loop breaker in some phases
> but not others; e.g. the loop might be broken by some optimisation.
>
>
>
> *   Before an Id is ready for general inlining by the simplifier, can I
> get the Id's unfolding another way so that I can substitute it early?
>
>
>
> realIdUnfolding always works.  As the code shows
>
>
>
> idUnfolding :: Id -> Unfolding
>
> -- Do not expose the unfolding of a loop breaker!
>
> idUnfolding id
>
>   | isStrongLoopBreaker (occInfo info) = NoUnfolding
>
>   | otherwise                          = unfoldingInfo info
>
>   where
>
>     info = idInfo id
>
>
>
> realIdUnfolding :: Id -> Unfolding
>
> -- Expose the unfolding if there is one, including for loop breakers
>
> realIdUnfolding id = unfoldingInfo (idInfo id)
>
>
>
>
>
> Does that help?
>
>
>
> Simon
>
>
>
>
>
> *From:* conal.elliott at gmail.com [mailto:conal.elliott at gmail.com] *On
> Behalf Of *Conal Elliott
> *Sent:* 02 December 2016 18:13
> *To:* Simon Peyton Jones <simonpj at microsoft.com>
> *Cc:* ghc-devs at haskell.org
> *Subject:* Re: How to inline early in a GHC plugin?
>
>
>
> Thanks for the pointers, Simon. Some more specific questions:
>
>
>
> *   To access an unfolding, is `maybeUnfoldingTemplate (idUnfolding v)`
> the recommended recipe?
>
> *   Is it the case that this recipe succeeds (`Just`) in some compiler
> phases and not others?
>
>     If so, is this difference due to Ids being altered (presumably via
> `setUnfoldingInfo` being called between phases)?
>
> *   Before an Id is ready for general inlining by the simplifier, can I
> get the Id's unfolding another way so that I can substitute it early?
>
>
>
> A short Skype chat might easily clear up my questions and confusions if
> you have time and inclination.
>
>
>
> Regards, - Conal
>
>
>
> On Fri, Dec 2, 2016 at 9:07 AM, Simon Peyton Jones <simonpj at microsoft.com>
> wrote:
>
> I don’t really understand your question clearly.  So I’ll guess
>
>
>
> Unfoldings are added to Ids in Simplify.completeBind (look for
> setUnfoldingInfo).  Apart from INLINE pragmas, that’s about the only place
> it happens.
>
>
>
> Does that help?
>
>
>
> S
>
>
>
> *From:* ghc-devs [mailto:ghc-devs-bounces at haskell.org] *On Behalf Of *Conal
> Elliott
> *Sent:* 01 December 2016 21:51
> *To:* ghc-devs at haskell.org
> *Subject:* How to inline early in a GHC plugin?
>
>
>
> I'm implementing a GHC plugin that installs a `BuiltInRule` that does the
> work, and I'd like to learn how to inline more flexibly. Given an
> identifier `v`, I'm using `maybeUnfoldingTemplate (realIdUnfolding v)` to
> get a `Maybe CoreExpr`. Sometimes this recipe yields `Nothing` until a
> later compiler phase. Meanwhile, I guess my variable `v` has been replaced
> by one with inlining info. First, am I understanding this mechanism
> correctly? A GHC source pointer to how inlining is made available would
> help me. Second, can I access the inlining info before it's made available
> to the rest of the simplifier?
>
>
>
> Thanks,  - Conal
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-devs/attachments/20161207/7bb1fa91/attachment-0001.html>