[cfe-dev] [RFC] Warning for large Objective C runtime encodings (-Wobjc-encodings-larger-than=)

[Dave MacLachlan via cfe-dev]

Thanks Nat!

I'll look into it once this hopefully gets checked in.

Cheers,
Dave

On Tue, Dec 11, 2018 at 12:44 PM Nat! via cfe-dev <cfe-dev at lists.llvm.org>
wrote:

>
> On 11.12.18 05:06, Dave MacLachlan via cfe-dev wrote:
> > Hey esteemed colleagues,
> >
> > We recently noticed that we were generating some incredibly large
> > Objective C runtime encodings in some of our apps that are using
> > Objective C++ and passing C++ types in Objective C methods, or have
> > C++ types as instance variables. Templates are especially notorious
> > for generating huge amounts of Objective C runtime information. I did
> > a write up on it here:
> >
> > https://medium.com/@dmaclach/objective-c-encoding-and-you-866624cc02de
> >
> > but am looking for a better solution than my hacky "smart pointers".
> > As a first step I wanted to have a warning I could control to
> > understand where my problem spots are.
> >
> > I would appreciate any thoughts on
> >
> > https://reviews.llvm.org/D55544
> >
> > It is my first real foray into clang coding, so I expect my
> > implementation is naïve.
> >
> > Tracking bug:
> >
> > https://bugs.llvm.org/show_bug.cgi?id=38346
> >
> > Cheers,
> > Dave
> >
>
> Hi
>
> This is a an idea, that may or may not be useful, depending on your
> circumstances.
>
> What you could do is turn off the "bool EncodeBlockParameters, bool
> EncodeClassNames, bool EncodePointerToObjCTypedef" (especially the
> latter) flags passed to ASTContext::getObjCEncodingForTypeImpl,
> depending on a newly introduced compiler flag in `Options.td`. The
> resulting encodings are much smaller yet remain compatible. The amount
> of code out there that actually correctly introspects C++ type @encodes
> is probably extremely close to zero.
>
> Usually the decision to use extended or traditional @encode is made at
> the runtime level. My runtime
> (https://github.com/mulle-objc/mulle-objc-runtime) uses extended format,
> but I don't support C++ anyway :) I could see a warning or compiler
> option like this as being useful, especially if the type is used in a
> lot of methods. But then this could also be part of the runtime...
>
> I also can't help but comment, that mixing C++ and Objective-C gets you
> the worst of both worlds. :)
>
> Ciao
>
>     Nat!
>
>
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