[Bug target/113079] [x86] Fails to generate dot_prod instructions for 64-bit vector.

[liuhongt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113079

--- Comment #1 from Hongtao Liu <liuhongt at gcc dot gnu.org> ---
(In reply to Hongtao Liu from comment #0)
> int
> foo (int n, unsigned char* p, char* pi)
> {
>     int sum = 0;
>     for (int i = 0; i != 8; i++)
>     {
>         sum += p[i] * pi[i];
>     }
>     return sum;
> }
> 
> We can use 128-bit dot_prod instruction + clean upper 64 bits. Currently,
clean upper is not needed since it's integral operations, no side effect from
upper 64-bits operations.