AST: Refine recursive property checks on type alias types

lib/Sema/CSSimplify.cpp

@@ -4823,7 +4823,9 @@ performMemberLookup(ConstraintKind constraintKind, DeclName memberName,
     // to access the type with a protocol metatype base.
     } else if (instanceTy->isExistentialType() &&
                isa<TypeAliasDecl>(decl) &&
-               !cast<TypeAliasDecl>(decl)->getInterfaceType()->hasTypeParameter()) {
+               !cast<TypeAliasDecl>(decl)
+                  ->getUnderlyingType()->getCanonicalType()
+                    ->hasTypeParameter()) {
 
       /* We're OK */