>perl -E"$_ = qq{execu\x{e7}\x{e3}o}; utf8::downgrade($_); say $_ eq unpack('A*', $_) ?1:0"
1

>perl -E"$_ = qq{execu\x{e7}\x{e3}o}; utf8::upgrade($_); say $_ eq unpack('A*', $_) ?1:0"
1