Node contains cycle

[TwentyFlight]

[edit] Problem solved : in order to get rid of this problem (which is actually a combinational loop), just put the code within a clocked process.

Hello,

I've got this piece of code, within a process, where a signal "foo" is tested and then reassigned :

case foo is
when "000" => foo <= "111";
when "001" => foo <= "101";
...
...
end case;

Compilation completes successfully, but Lattice gives me warnings like this : Node foo_1__un0_n contains cycle, will not be collapsed away

What does it mean? Should I be worried about it or not? My code works fine when using a simulator.

Thanks