[Bug tree-optimization/101668] BB vectorizer doesn't handle lowpart of existing vector

[crazylht at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101668

--- Comment #4 from Hongtao.liu <crazylht at gmail dot com> ---
Guess we need to extend backend hook to handle different input and output
modes.