Passing only Fc max to pin to track map function

[saaramahmoudi]

Current Behaviour

While we want to create connection blocks (pin->track and track->pin connections), we first loop over segments and calculate the maximum Fc over all pins of one block and this segment type (rr_graph.cpp, line 3253):

/* determine the maximum Fc to this segment type across all pins */
  int max_Fc = 0;
  for (int pin_index = 0; pin_index < Type->num_pins; ++pin_index) {
      int pin_class = Type->pin_class[pin_index];
      if (Fc[pin_index][seg_inf[iseg].seg_index] > max_Fc && Type->class_inf[pin_class].type == pin_type) {
          max_Fc = Fc[pin_index][seg_inf[iseg].seg_index];
      }
  }

Afterward, we use max_Fc calculated to pass through the pin_to_seg_type_map to create connections based on max_Fc:

/* get pin connections to tracks of the current segment type */
auto pin_to_seg_type_map = alloc_and_load_pin_to_seg_type(pin_type, num_seg_type_tracks, max_Fc, Type, type_layer, perturb_switch_pattern[seg_inf[iseg].seg_index], directionality);

Although we use the maximum Fc value, we can override some pins (such as the carry chain) with Fc 0. However, assuming one pin has 4 connections to this segment and the other has 6 connections to this segment, we connect both pins 6 times since the max_Fc would be 6. Here is the comment for the mentioned function (rr_graph.cpp, line 3298):

/* Note: currently a single value of Fc is used across each pin. In the future
     * the looping below will have to be modified if we want to account for pin-based
     * Fc values 
*/

@vaughnbetz If you agree that it is better to account for pin-based Fc values, I can implement and keep this issue to track the progress. If there is a specific reason for this implementation, I can add more comments to the function to avoid confusion.