[Bug rtl-optimization/93565] Combine duplicates count trailing zero instructions

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93565

--- Comment #2 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Of course it first tried to do

Failed to match this instruction:
(parallel [
        (set (reg:DI 101 [ _9 ])
            (ctz:DI (reg/v:DI 98 [ x ])))
        (set (reg:DI 100)
            (ctz:DI (reg/v:DI 98 [ x ])))
    ])

so we could try to do that as just the ctz and then a register move,
and hope that move can be optimised away.  But this is more expensive
if it can *not* be optimised (higher latency).  Hrm.