[Bug target/94962] Suboptimal AVX2 code for _mm256_zextsi128_si256(_mm_set1_epi8(-1))

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94962

--- Comment #3 from Hongtao.liu <crazylht at gmail dot com> ---
You're right, from intel SDM: 
VEX.128 encoded version: Bits (MAXVL-1:128) of the destination register are
zeroed.