In reply to KillSteal:
There is a problem when you have multiple randc variables with interconnected constraints. The solver has to order randc variable and that could cause randomize() to fail. Notice in the results you are getting for the values of
end_addr are not cyclic. If the
repeat loop gets extended, you notice that none of the variables have cyclic values. So it seems some tools are ignoring the randc modifier and just making the variables rand.