[Bug tree-optimization/122086] [16 regression] Alignment in expand lost from __builtin_assume_aligned after r16-4081

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122086

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note this patch I went for:
```
The second way is to prevent forwprop for proping the ssa names from a
lower alignment and replacing the higher one.
That would fix -Og once I finish with set of patches.
```
This is based on the s390 issue.