[Bug middle-end/107891] Redudant "double" permutation from PR97832

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107891

--- Comment #1 from Hongtao.liu <crazylht at gmail dot com> ---
commemt25 from PR97832

I guess that's possible but the SLP vectorizer has a permute optimization
phase (and SLP discovery itself), it would be nice to see why the former
doesn't elide the permutes here.