[PATCH] D53417: [Clang][Sema][PowerPC] Choose a better candidate in overload function call if there is a compatible vector conversion instead of ambiguous call error

[Hubert Tong via Phabricator via cfe-commits]

hubert.reinterpretcast added inline comments.


================
Comment at: clang/lib/Sema/SemaOverload.cpp:3913
+        for (auto Type : Types) {
+          if (S.Context.getCanonicalType(Type)->getTypeClass() != Type::Vector)
+            return false;
----------------
hubert.reinterpretcast wrote:
> wuzish wrote:
> > hubert.reinterpretcast wrote:
> > > wuzish wrote:
> > > > hubert.reinterpretcast wrote:
> > > > > wuzish wrote:
> > > > > > hubert.reinterpretcast wrote:
> > > > > > > Considering that this is a local lambda called in one place, are we expecting cases where the canonical type is not something on which we can call getVectorKind()? If not, then we do not need this `if`.
> > > > > > Well, that's for ExtVectorType. I encounter some testcase failure because of that. So I just narrow the condition to only handle Type::Vector.
> > > > > > 
> > > > > > As the following comment said, so I treat it separately.
> > > > > > 
> > > > > > /// ExtVectorType - Extended vector type. This type is created using
> > > > > > /// __attribute__((ext_vector_type(n)), where "n" is the number of elements.
> > > > > > /// Unlike vector_size, ext_vector_type is only allowed on typedef's. This
> > > > > > /// class enables syntactic extensions, like Vector Components for accessing
> > > > > > /// points (as .xyzw), colors (as .rgba), and textures (modeled after OpenGL
> > > > > > /// Shading Language).
> > > > > An ExtVectorType is a VectorType, so what sort of failures are you hitting?
> > > > Yes. But the TypeClass of ExtVectorType is ExtVector.
> > > > 
> > > > some test points check the error report for ambiguous call because of too many implicit cast choices from ext_vector_type to vector type. Such as blow.
> > > > 
> > > > 
> > > > ```
> > > > typedef char char16 __attribute__ ((__vector_size__ (16)));
> > > > typedef long long longlong16 __attribute__ ((__vector_size__ (16)));
> > > > typedef char char16_e __attribute__ ((__ext_vector_type__ (16)));
> > > > typedef long long longlong16_e __attribute__ ((__ext_vector_type__ (2)));
> > > > 
> > > > 
> > > > void f1_test(char16 c16, longlong16 ll16, char16_e c16e, longlong16_e ll16e) {
> > > >   int &ir1 = f1(c16);
> > > >   float &fr1 = f1(ll16);
> > > >   f1(c16e); // expected-error{{call to 'f1' is ambiguous}}
> > > >   f1(ll16e); // expected-error{{call to 'f1' is ambiguous}}
> > > > }
> > > > ```
> > > > 
> > > > If we are gonna widen the condition, we can make a follow-up patch. Or we need include this condition and do this together in this patch?
> > > The widening that has occurred is in allowing the scope of the change to encompass cases where AltiVec vectors are not sufficiently involved. The change in behaviour makes sense, and perhaps the community may want to pursue it; however, the mandate to make that level of change has not been given.
> > > 
> > > I do not believe that requiring that the TypeClass be VectorType is the correct narrowing of the scope. Instead, we may want to consider requiring that for each `SCS` in { `SCS1`, `SCS2` }, there is one AltiVec type and one generic vector type in { `SCS.getFromType()`, `SCS.getToType(2)` }.
> > > 
> > The key point is that ExtVector is a kind of typeclass, **and** its vector kind is generic vector type.
> > 
> > So you think we should encompass ext_vector cases as a part of the scope of this patch? And modify the above cases' expected behavior (remove the **expected-error**)?
> I gave a concrete suggested narrowing of the scope that does not exclude ExtVectorType or other derived types of VectorType. It also does not change the behaviour of the `f1_test` case above. We could pursue additional discussion over that case (separable from the current patch) on the mailing list.
> 
> I believe my suggestion does do something about this case:
> ```
> typedef unsigned int GccType __attribute__((__ext_vector_type__(16)));
> typedef __vector unsigned int AltiVecType;
> 
> typedef float GccOtherType __attribute__((__vector_size__(16)));
> 
> void f(GccType);
> void f(GccOtherType);
> 
> void g(AltiVecType v) { f(v); }
> ```
> 
> I think that addressing the latter case is within the realm of things that we should consider for this patch. Either way, we should ensure that tests for AltiVec/__ext_vector_type__ conversions are available.
Sorry, typo in the above case:
```
typedef unsigned int GccType __attribute__((__ext_vector_type__(4)));
```



https://reviews.llvm.org/D53417