XILINX_SIMULATOR is a Verilog predefined-macro. The value of this macro is 1. Predefined macros perform tool-specific functions, or identify which tool to use in a design flow. The following is an example usage:
`ifdef VCS
// VCS specific code
`endif
`ifdef INCA
// NCSIM specific code
`endif
`ifdef MODEL_TECH
// MODELSIM specific code
`endif
`ifdef XILINX_ISIM
// ISE Simulator (ISim) specific code
`endif
`ifdef XILINX_SIMULATOR
// Vivado Simulator (XSim) specific code
`endif
`ifdef _VCP
//Aldec specific code
`endif