%Error: 3.sv:1: Unsupported: $ expression
tri[$^'{}dreg;end
     ^
%Error: 3.sv:1: Unsupported: Empty '{}
tri[$^'{}dreg;end
       ^~
%Error: Internal Error: 3.sv:1: ../V3Ast.cpp:359: Null item passed to setOp2p
tri[$^'{}dreg;end
      ^
                         ... See the manual and http://www.veripool.org/verilator for more assistance.