https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90204
--- Comment #2 from Hongtao.liu <crazylht at gmail dot com> ---
It seems such code generation is r254855's intention.
/* Use 256-bit AVX instructions instead of 512-bit AVX
instructions
4695 in the auto-vectorizer. */
4696 if (ix86_tune_features[X86_TUNE_AVX256_OPTIMAL]
4697 && !(opts_set->x_ix86_target_flags &
OPTION_MASK_PREFER_AVX256))
4698 opts->x_ix86_target_flags |= OPTION_MASK_PREFER_AVX256;
I know there is a frequency reduction issue when many zmm registers are used,
but i don't know what exact situation did r254855 deal with?
