[Bug tree-optimization/66726] missed optimization, factor conversion out of COND_EXPR

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66726

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Comment on attachment 35888
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35888
untested prototype patch

I thought pre does this already and that seems like a better place than
phi-opt. Oh wait pre does the opposite and really you should handle more than
two arguments to phis.