[Sema] Fix assertion failure at vector comparison

[kevgs]

Summary

For for this bug report https://llvm.org/bugs/show_bug.cgi?id=27258

[rnk]

I think Sema::CheckVectorOperands isn't supposed to return a scalar type. Fixing that with http://reviews.llvm.org/D19123 also solves this problem. Richard, WDYT?

[rsmith]

I agree. In the example, the type of y == z should be vec, not int -- we should "promote" to the vector type.

lib/Sema/SemaExpr.cpp

   if (vType.isNull())
     return vType;
 
+  if (!vType->isVectorType())
+    return vType;
+
   QualType LHSType = LHS.get()->getType();
 
   // If AltiVec, the comparison results in a numeric type, i.e.

test/Sema/vector-cast.c

   v = ptr; // expected-error-re {{assigning to 'short_sizeof_pointer' (vector of {{[0-9]+}} 'short' values) from incompatible type 'void *'}}
   ptr = v; // expected-error {{assigning to 'void *' from incompatible type 'short_sizeof_pointer'}}
 }
+
+typedef int vec __attribute__((vector_size(4)));
+void f6(vec z, int y) {
+  y = y == z;
+}