[cfe-dev] Clang/LLVM Member Function Pointers size and behavior?

[Nico Weber]

On Tue, Oct 16, 2012 at 11:53 AM, John McCall <rjmccall at apple.com> wrote:
> On Oct 16, 2012, at 11:26 AM, Devid wrote:
>>> I'm confused.  You need compatibility with MSVC about the size of member
>>> function pointers, but you don't care about compatibility of, say, class
>>> layout
>>> or vtables or anything like that?
>>
>> Well it would be great that this will be compatible too but for now member
>> function pointers compatibility is probably enough.
>> For example I just do not use virtual functions for now.
>
> If you're not using virtual functions, manglings will matter, and the
> Itanium manglings are totally different from the MSVC manglings.
> So I really doubt that you're actually going to get any real sort of
> compatibility without turning on the MSVC compatibility stuff.
>
> (I'm not actually certain how to do that at the driver level, because I
> mostly just code-review this work rather than take advantage of it.
> But other people on the list should be able to help, or you can check
> the archives to find where it's been discussed before.)

-fms-compatibility and -fms-extensions for language extensions (but
those are on by default for win32 targets), and -Xclang -cxx-abi
-Xclang microsoft (this doesn't have a nicer parameter because the ms
abi isn't really usable yet).

>
> The good news is that, if you're not using virtual functions or bases,
> there aren't any known, major problems (besides member pointers)
> that you're going to run into.
>
>>> You'll have to also hack code generation so that
>> Any tips where to start doing this ?
>
> The right thing to do is to go to MicrosoftCXXABI.cpp and start adding
> real implementations of the various member-pointer APIs.
>
>>> These are just private changes and you're not hoping to upstream them,
>>> right?
>> This is dependent. If I will be able to find proper solution then upstream
>> them would be great.
>> But for now it appears for me like a Ugly Hack that nobody really need,
>> except of me.
>
> Yeah, we definitely would not accept anything modifying the Itanium ABI
> code.  The right solution is to continue to flesh out the dedicated Microsoft
> ABI support.
>
> John.
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