[Bug tree-optimization/79622] [6/7/8 Regression] Wrong code w/ -O2 -floop-nest-optimize

[spop at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79622

--- Comment #4 from Sebastian Pop <spop at gcc dot gnu.org> ---
Yes, that phi node looks like a reduction.  We need to handle the phi as a
write to expose the loop carried reduction variable to the dependence analysis.
I think your change goes in the right direction.  Thanks!