[Bug target/104371] [x86] Failure to use optimize pxor+pcmpeqb+pmovmskb+cmp 0xFFFF pattern to ptest

[crazylht at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104371

--- Comment #3 from Hongtao.liu <crazylht at gmail dot com> ---
Similar for

#include<immintrin.h>
bool is_zero256(__m256i x)
{
    return _mm256_movemask_epi8(_mm256_cmpeq_epi8(x, _mm256_setzero_si256()))
== 0xffffffff;
}