[Bug target/117818] [13/14/15/16 regression] vec_add incorrectly generates vadduwm for vector char const inputs.

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117818

--- Comment #13 from Segher Boessenkool <segher at gcc dot gnu.org> ---
BTWQ, vsl and vsr always were (and still are) implemented just like the vslv
and vsrv instructions.  But it is only defined (in the arch) what it does when
all lanes hold the same number.