Why do I receive "ncelab: *W,RXNORX: Some design units are compiled with "-RELAX" option, and others without it" when I elaborate designs?
I see this even if I am not using the -RELAX switch.
The -RELAX switch is used with NCSIM to make it compliant with ModelSim.
Due to differences in LRM interpretations, Xilinx uses the -RELAX switch with CompXLib when compiling the Xilinx ISE libraries. This is why the message will be there when doing an elaboration of designs. This warning is safe to ignore.
Xilinx is working on clearing up all the simulation discrepancies between MTI and NCSIM so this switch can be removed in a future release of CompXLib.