[Bug tree-optimization/97770] [ICELAKE]Missing vectorization for vpopcnt

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97770

--- Comment #17 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Richard Biener from comment #16)
> Changing the signature will not help given we don't want to regress other
> cases.
> Instead we have to somehow remove the pro- and demotions with the help of
> patterns.  I think using .POPCOUNT should work there.

I'm thinking of reimplementing _mm_popcnt_u64 with a backend builtin like
__builtin_ia32_popcountll which is defined as ULONGLONG_FTYPE_ULONGLONG, and
handle that in TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION.