Clean up rr_node_route_inf about vtr-verilog-to-routing

[AlexandreSinger]

The acc_cost and occ_ members appear to not be used in the maze expansion (against what the comment above this class is saying). We should separate out the per-iteration route info from the maze-expansion route info. Beyond organization, this would reduce the amount of data being stored in the cache during maze expansion and also reduce the number of global variables the maze expansion touches.

This would require creating a new struct to hold this "per-iteration" routing info and would require modifying the RoutingContext to also hold this information:

struct RoutingContext : public Context {
    // ...

    vtr::vector<RRNodeId, t_rr_node_route_inf> rr_node_route_inf; /* [0..device_ctx.num_rr_nodes-1] */

    // ...
};

Perhaps the new type could be named rr_node_per_iter_route_inf, but I am concerned the name might be too long.

@vaughnbetz What do you think about this change?

[amin1377]

@AlexandreSinger As discussed: The occ_ field is read in the connection router (maze expansion) to calculate the congestion cost (Link)

[vaughnbetz]

acc_cost is also read during the connection router (maze expansion); it just isn't written during maze expansion.

[AlexandreSinger]

The PR resolving this issue has been merged into master. Closing this issue. Since the occ and acc_cost are read during the wave expansion, it should be fine to keep them in this struct.