[Bug middle-end/122715] Missed optimization of IFN_AVG_FLOOR (x, x) --> x

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122715

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to ktkachov from comment #1)
> It can be fixed by adding folding of IFN_AVG_FLOOR (x, x) in match.pd IMO

The aarch64 one can be fixed that way but the x86 one needs a backend change
first:
  _5 = __builtin_ia32_pavgb (_3, _3);