[Bug tree-optimization/125567] SLP build misses operand swapping for a commutative scalar-vector add pattern

[chenzhongyao.hit at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125567

--- Comment #6 from Zhongyao Chen <chenzhongyao.hit at gmail dot com> ---
Created attachment 64621
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=64621&action=edit
proposed patch

Proposed patch attached. If it looks good, I can post it to the mailing list.

My local tests show no regression for vect.exp, only a few for rvv.exp, 
but those are reasonable, just need update test expectations.