https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101927
--- Comment #1 from Drea Pinski <pinskia at gcc dot gnu.org> ---
Note GCC does vectorize:
```
#include <stdlib.h>
#include <stdint.h>
size_t hd (const uint8_t *restrict a,
const uint8_t *restrict b,
size_t l) {
unsigned char r = 0;
size_t x;
for (x = 0; x < l; x++)
r += __builtin_popcount (a[x] ^ b[x]);
return r;
}
```
Just not widening of the addition from popcount it seems.
