https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122014
--- Comment #3 from Kang-Che Sung <Explorer09 at gmail dot com> --- Acknowledge the popcount_8_bp and popcount_16_bp case. The point is to recognize the don't-care so that gcc won't need to mask the upper bits in order to constrain the values to `uint8_t` or `uint16_t`. Also, because the ADDV instruction adds the values of *all* lanes in a vector, for the 16-bit case, it would be better to use UADDLP instead as UADDLP would effectively make the upper bit ignored after extracting the sum of lane 0.
