[Bug target/125636] [missed optimization] HImode byte-extend from memory causes partial-register-write stall on modern x86-64

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125636

--- Comment #6 from Drea Pinski <pinskia at gcc dot gnu.org> ---
See movqi_internal which does the full zero extend from qi to si.
So you just need to do the full extend in extendqihi2 for memory case I think.