[Bug tree-optimization/64992] More optimize opportunity

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64992

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
if a was signed, then a * 2 == 0 just becomes a == 0 as if a * 2 overflows that
would become undefined
For unsigned, if a has a range of [0,(unsigned)INT_MAX] then a * 2 == 0 can be
optimized to a == 0.