[sv-ec] handling x's in expressions in constrants

I've doubts on how x's should be handled by solver. LRM say only that
x's are illegal in constraints but give no more detail on complex expr
behaviour

Please see examples - my questions are in comments

    class C;
      rand reg[1:0] a,b;
      constraint c1{(a/b==1) || (b==0);};
      function void post_randomize;
        $display("%d %d",a,b);
      endfunction
    endclass

    module top;
       C c =new;
       initial begin
         repeat (15)//should solver allow b==0 to be randomized or
    should not (bcos of x result in 2nd part of expr - a/b==1)??
           assert(c.randomize) else $display("failure");
         c.b=0;
         repeat (15) //should fail immediately bcos of x's or only x's
    on top level expr should results in runtime failure???
           assert(c.randomize(a)) else $display("failure");
       end
    endmodule

DANiel

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