compiler: fix crash on struct that embeds pointer type

    
    The type verification code that enforces rules about the types of
    embedded struct fields was not properly handling the case where the
    pointed-to type is a pointer type, e.g.
    
      type s *struct{ C int }
      type t struct{ *s }
    
    which is illegal according to the spec. Tweak the verifier to catch
    this case, and add a guard in the lowering pass to make sure that we
    don't crash on invalid accesses to field "C" in type "t" above.
    
    Fixes golang/go#22050
    
    Reviewed-on: https://go-review.googlesource.com/66530

From-SVN: r253236

gcc/go/gofrontend/MERGE

-cdf1f58c7578980e1d1949680c7e404961b7c153
+11b7dae7de94215e92eb46e703cfecd76c0a3282
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/types.cc

@@ -5842,7 +5842,9 @@ Struct_type::do_verify()
       Type* t = p->type();
       if (p->is_anonymous())
 	{
-	  if (t->named_type() != NULL && t->points_to() != NULL)
+	  if ((t->named_type() != NULL && t->points_to() != NULL)
+              || (t->named_type() == NULL && t->points_to() != NULL
+                  && t->points_to()->points_to() != NULL))
 	    {
 	      go_error_at(p->location(), "embedded type may not be a pointer");
 	      p->set_type(Type::make_error_type());
@@ -11848,6 +11850,12 @@ Type::bind_field_or_method(Gogo* gogo, const Type* type, Expression* expr,
 	      go_assert(expr->type()->struct_type() == st);
 	    }
 	  ret = st->field_reference(expr, name, location);
+          if (ret == NULL)
+            {
+              go_error_at(location, "type has no field %qs",
+                          Gogo::message_name(name).c_str());
+              return Expression::make_error(location);
+            }
 	}
       else if (it != NULL && it->find_method(name) != NULL)
 	ret = Expression::make_interface_field_reference(expr, name,