[PATCH] D55850: [OpenCL] Allow address spaces as method qualifiers

[John McCall via Phabricator via cfe-commits]

rjmccall added inline comments.


================
Comment at: lib/Sema/SemaOverload.cpp:9279
+        (CandAS1 != LangAS::opencl_generic && CandAS1 != LangAS::Default))
+      return true;
+  }
----------------
Anastasia wrote:
> rjmccall wrote:
> > rjmccall wrote:
> > > This at least needs a comment explaining the rule you're trying to implement.
> > Okay, thanks for the clarification.  I think this should just be part of `CompareImplicitConversionSequence`, right?  It seems to me that you should prefer e.g. `int __private *` -> `int __private *` over `int __generic *`  as a normal argument conversion as well.
> > 
> > Also, can this be written in terms of `isAddressSpaceSupersetOf`?  I don't remember how `LangAS::Default` works in OpenCL C++ enough to understand how it fits in here.
> That's correct we should implement the same logic for the arguments too. I will create a helper function or do you think we should just call `CompareImplicitConversionSequence` on the method type too?
> 
> I think `isAddressSpaceSupersetOf` can't be used here because it determines compatibility of address spaces. However, the logic we are expressing is for the address space preference instead.
If I understand correctly, we already call `CompareImplicitConversionSequence` on the object-argument conversion above, as part of the `for (unsigned ArgIdx = StartArg; ArgIdx < NumArgs; ++ArgIdx) ` loop.

I think the address-space ordering rule can be reasonably based on compatibility.  In fact, I think it already is in our implementation.  The right rule is basically that (1) an exact match is better than a conversion and (2) a conversion to a subspace is better than a conversion to a superspace.  You can think of this as modifying the "proper subset" rule of [over.ics.rank]p3.2.5, which in implementation terms means `Qualifiers::isMoreQualifiedThan`, which already ends up using `isAddressSpaceSupersetOf`.  So if this ranking isn't working right, it's probably because we're incorrectly fast-pathing based on CVR qualifiers somewhere, and in fact I can see a pretty suspicious check like that in `CompareQualificationConversions`.


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  https://reviews.llvm.org/D55850/new/

https://reviews.llvm.org/D55850