Vivado hangs on power operations with large exponents

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.

History:
2019-01-15 Initial description of bug.