Help on first ticket

[Richard Fung]

Awesome that's definitely very helpful! I'll be sure to ask again if/when I
get stuck.

Thanks!!

On Sat, Jun 4, 2016 at 3:20 PM, Ben Gamari <ben at smart-cactus.org> wrote:

> Richard Fung <minesasecret at gmail.com> writes:
>
> > Hello! I apologize if this isn't the right place to ask; if it isn't
> please
> > steer me in the right direction.
> >
> Hi Richard!
>
> > Would anyone be willing to advise me on my first ticket? I've been trying
> > to work on it on and off but haven't made much progress on my own.
> >
> > It's ticket #9370: https://ghc.haskell.org/trac/ghc/ticket/9370
> >
> Great, I'm happy to hear that someone has picked this one up. I think it
> is a nice choice for a self-contained newcomers project.
>
> > I think I understand the issue conceptually but I don't know where to
> look
> > for the code that needs to be changed..
> >
> I don't know where the code responsible for this is off the top of my
> head, however I can provide some pointers.
>
> So the unfoldings you are looking to preserve come from interface files.
> The machinery for all of this is in compiler/iface. IfaceSyn.hs is of
> particular interest and there you will find the definition of
> IfaceUnfolding, which is the unfolding representation which is stored in
> the interface file. Unfoldings live inside of IdInfo values, which hold
> various miscellaneous information which we need to preserve about a
> particular Id (identifier).
>
> There is a somewhat useful comment regarding how IdInfo is treated above
> the definition of IfaceIdInfo in IfaceSyn. In particular it seems that
> interface files for modules compiled with -O0 will have their IdInfo
> fields set to NoInfo. It's not clear what happens when an interface file
> is read. However, grepping for NoInfo reveals a use-site in
> TcIface.tcIdInfo which looks interesting (in particular the ignore_prags
> guard). I think this should be enough to get you going on the interface
> file part of this.
>
> The other part of this ticket is deciding whether to use an unfolding
> when considering whether to inline. This will be done in the simplifier
> (compiler/simplCore). Grepping for "inline" and "unfold" in
> simplCore/Simplify.hs (as well as reading the notes in that file) will
> likely be enough to get you started.
>
> Do let me know if you still feel lost or want to discuss this further. I
> look forward to hearing how it goes.
>
> Cheers,
>
> - Ben
>
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