Use of the VHDL "alias" command statement may result in syntax error VSS-1081 in FPGA Express versions up to and including 3.3. FPGA Express may also crash without this error.
解决方案
The "alias" command statement is not supported by FPGA Express 3.3 and earlier.
Workaround: Create a new signal with the name you wish to use as an alias and connect the "aliased" and original signals together.