https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78436
--- Comment #4 from ktkachov at gcc dot gnu.org --- Assignment of negative values to signed bitfields has caused me some headaches in encode_tree_to_bitpos due to native_encode_expr sign-extending the value to GET_MODE_SIZE (TYPE_MODE (...)) bytes, making it necessary to truncate the excess padding introduced. Maybe there's a but g in that logic
