Time Quest Warning

a warning is displayed when perform time quest analysis(post-map):

Warning: fs~reg0|fs could not be matched with a pin

My constraint:

create_generated_clock -name fs -source [get_ports {clk}] -divide_by 128 [get_pins fs~reg0|fs]

FYI, I have a top module that connects the clock divider and square wave(using clock enable method):

square_valid

sq_valid1

(

.clk(clk),

.reset(reset),

.sq_ena(sq_ena),

.clock_ena(fs),

.factor(factor),

.square_1(square),

.sq_valid(sq_valid)

);

mod128_counter

mod128count1

(

.clk(clk),

.reset(reset),

.fs(fs),

.two_fs(two_fs)

);

Besides, i have tried:

[get_pins fs]

[get_registers fs~reg0|fs] //fs~reg0, the name get from RTL viewer

[get_nets fs]

All have the same warning. I have no idea what is the problem..

thanks