https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63900
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to Segher Boessenkool from comment #3) > Reopened; this is a perfectly valid missed optimisation. > > Nothing here does a "full memory clobber"; instead, CSE simply doesn't > know how to handle a three-byte datum. That is because it is BLKmode. This is most likely going to be a won't fix really because it is too hard to implement for small benefit. Also in this case using memset would be better and optimize easier.
