[PATCH] D135091: Create storage for the `_cmd` argument to the helper function for generated getters/setters of `direct` Objective-C properties.

[Nuno Lopes via Phabricator via cfe-commits]

nlopes added inline comments.


================
Comment at: clang/lib/CodeGen/CGObjC.cpp:1125
+    llvm::Type *selType = CGF.ConvertType(CGF.getContext().getObjCSelType());
+    return llvm::UndefValue::get(selType);
+  }
----------------
mwyman wrote:
> nlopes wrote:
> > Please consider using PoisonValue here instead (if appropriate). We are trying to get rid of undef.
> > Thank you!
> > A poison value is a result of an erroneous operation.
> 
> I could very well be misunderstanding, but based on this description from LangRef.html `PoisonValue` doesn't seem appropriate here; this is not "erroneous" behavior: it is just continuing the behavior prior to removing the `_cmd` implicit argument from the ABI, which was that the value was `undef` from the generated getter/setter's caller.
> 
> https://github.com/llvm/llvm-project/blob/49acab3f1408be9439a57833aa7b67678c9a05ba/clang/lib/CodeGen/CGObjCMac.cpp#L2142
> 
> Since this is (essentially) replicating that behavior, I'm not sure `PoisonValue` is what we want.
If the value is not used, then it can be poison.
If it gets used somehow then it depends on the callers. I don't know anything about ObjC to know what the right answer is here.
As we want to remove undef, the fewer the uses the better. Thank you!


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D135091/new/

https://reviews.llvm.org/D135091