__m256i version of _mm_test_all_zeros

Question

I know how to test if an _m128i register is all zero with the _mm_test_all_zeros intrinsic.

What is the AVX2 / __m256i version of this intrinsic? If one isn't available, what is the fastest way to test if all 256 bits in a SIMD register are zero?

Answer 1

The fastest is probably vptest instruction.

// Return 1 if `x` is all zeros, otherwise 0
inline int test_all_zeros( __m256i x )
{
    return _mm256_testz_si256( x, x );
}