[Bug tree-optimization/94589] Optimize (i<=>0)>0 to i>0

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94589

--- Comment #12 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to rguenther@suse.de from comment #11)

> For PR99997
> I have prototyped a forwprop patch to try constant folding
> stmts with all-constant PHIs, thus in this case c$_M_value_2 > 0,
> when there's only a single use of it

Maybe we could handle any case where trying to fold the single use (counting
x*x as a single use of x) with each possible value satisfies is_gimple_val (or
whatever the condition is to be allowed in a PHI, and without introducing a use
of a ssa_name before it is defined), so that things like PHI<X,0> & X would
simplify. But the constant case is indeed the most important, and should allow
the optimization in this PR before the vectorizer using reassoc1.