https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66266
--- Comment #1 from Bruno Manganelli <bruno.manga95 at gmail dot com> --- Probably another symptom of https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64969 as inverting the arguments for auto_sum does not cause the assertion to fail. Apologies for the duplicate.
