The following module should set y to constant 6'b110011, but instead it just hangs Vivado 2018.3:
module issue_021(a, y); input [31:0] a; output [5:0] y; assign y = 6'd3 ** 123456789; endmodule
It seems as if Vivado tries to calculate the power by simply performing 123456789 (or rather 123456788) multiplications. But the power operator should of course be implemented using a proper power-modulus algorithm.
2019-01-15 Initial description of bug.