[PATCH] D47233: [CodeGen] Emit MSVC RTTI for Obj-C EH types

[Shoaib Meenai via Phabricator via cfe-commits]

smeenai added inline comments.


================
Comment at: lib/CodeGen/CGObjCMac.cpp:7457-7460
 CGObjCNonFragileABIMac::GetEHType(QualType T) {
   // There's a particular fixed type info for 'id'.
   if (T->isObjCIdType() || T->isObjCQualifiedIdType()) {
+    if (CGM.getTriple().isWindowsMSVCEnvironment())
----------------
smeenai wrote:
> rjmccall wrote:
> > smeenai wrote:
> > > rjmccall wrote:
> > > > rnk wrote:
> > > > > @rjmccall how should this be organized in the long run? At this point, the naming seems totally wrong. Is the non-fragile ABI sort of the canonical way forward for Obj-C, i.e. it's what a new platform would want to use to best stay in sync with the future of obj-c?
> > > > For Darwin, yes, absolutely.
> > > > 
> > > > I think this method should probably just completely delegate to the `CGCXXABI` using a new `getAddrOfObjCRTTIDescriptor` method.
> > > To be clear, you'd want the entirety of the EHType emission logic to be shifted to CGCXXABI? I think that would make sense, and I can look into it.
> > Right.
> Sorry, getting back to this now.
> 
> What did you have in mind for handling the different Obj-C runtimes? Were you envisioning the new getAddrOfObjCRTTIDescriptor method supporting just the non-fragile Mac ABI or all of them?
Looked into this more. ItaniumRTTIBuilder already has a BuildObjCObjectTypeInfo, which confused me for a bit until I realized it's only ever used for the fragile ABI, and even then only when using C++ try/catch (instead of Obj-C style @try/@catch), which is a bit strange. Everything else does its own thing.

>From what I've been able to make out, these are the current possibilities for generating Obj-C RTTI for the Itanium ABI:
* Fragile macOS runtime using Obj-C @try/@catch: doesn't actually seem to generate any RTTI as far as I can tell, and uses `objc_exception_match` instead.
* Fragile macOS runtime using C++ try/catch: goes through `ItaniumRTTIBuilder::BuildObjCObjectTypeInfo`, which generates C++ compatible RTTI referencing a C++ class type info.
* Non-fragile macOS runtime: generates its own C++ compatible RTTI referencing `objc_ehtype_vtable`.
* GNUStep for Objective-C++: generates its own C++ compatible RTTI referencing `_ZTVN7gnustep7libobjc22__objc_class_type_infoE`.
* All other GNU runtimes (including GNUStep for Objective-C): just uses the identifier name string of the interface as its "RTTI".

I think it makes sense to only have the new `getAddrOfObjCRTTIDescriptor` method handle the non-fragile macOS runtime for now, and perhaps `ItaniumRTTIBuilder::BuildObjCObjectTypeInfo` should be renamed (or at least have a comment added) to indicate that it's only used for the fragile macOS runtime when catching an Obj-C type with C++ catch.


Repository:
  rC Clang

https://reviews.llvm.org/D47233