[PATCH] D50144: Add Windows support for the GNUstep Objective-C ABI V2.

[Shoaib Meenai via Phabricator via cfe-commits]

smeenai added inline comments.


================
Comment at: lib/AST/MicrosoftMangle.cpp:1886
   case BuiltinType::ObjCId:
-    mangleArtificalTagType(TTK_Struct, "objc_object");
+    mangleArtificalTagType(TTK_Struct, ".objc_object");
     break;
----------------
theraven wrote:
> compnerd wrote:
> > DHowett-MSFT wrote:
> > > I'm interested in @smeenai's take on this, as well.
> > Hmm, doesn't this break ObjC/ObjC++ interoperability?  I don't think that we should be changing the decoration here for the MS ABI case.
> No, this fixes ObjC++ interop.  Throwing an exception from a `@throw` and catching it with `catch` now works and we avoid the problem that a C++ compilation unit declares a `struct` that happens to have the same name as an Objective-C class (which is very common for wrapper code) may catch things of the wrong type.
I've seen a lot of code which does something like this in a header

```lang=cpp
#ifdef __OBJC__
@class I;
#else
struct I;
#endif

void f(I *);
```

You want `f` to be mangled consistently across C++ and Objective-C++, otherwise you'll get link errors if `f` is e.g. defined in a C++ TU and referenced in an Objective-C++ TU. This was the case before your change and isn't the case after your change, which is what @compnerd was pointing out. They are mangled consistently in the Itanium ABI, and we want them to be mangled consistently in the MS ABI as well.

Not wanting the catch mix-up is completely reasonable, of course, but it can be done in a more targeted way. I'll put up a patch that undoes this part of the change while still preventing incorrect catching.


Repository:
  rC Clang

https://reviews.llvm.org/D50144