Congestion-Aware Initial Accumulated Cost

[soheilshahrouz]

This PR adds a new option to bias routing away from congested channels during early iterations by adjusting the initial accumulated cost based on estimated CHANX/CHANY utilization.

[soheilshahrouz]

To-do list

1. compute channel widths by iterating over RR nodes ---> done
2. support 3d ---> CHANX/CHANY utilization for all layers are computed. CHANX nodes that represent vertical connection are mistakenly initilized with acc_cost of the CHANX at that location.

[soheilshahrouz]

titan_quick_qor

channel width	place_time	wl	cpd	route_time	pack_time	heap_pops	total_swaps
300	1.0007	0.9991	0.9965	0.9993	0.9950	1.0067	1
270	1.0054	0.9984	1.0047	0.9615	0.9965	0.9914	1
250	0.9876	0.9981	1.0031	0.8403	0.9924	0.8510	1

In experiments with a channel width of 250, bitcoin_miner failed for both the master branch and this branch.

[soheilshahrouz]

The impact of increasing acc_fac to 1.1 on Titan benchmarks

W	place_time	wl	cpd	route_time	pack_time	heap_pops	total_swaps
250	1.017395588	1.001856283	1.00593143	1.043113712	1.000524706	1.054397302	1
270	1.008064369	1.000474773	1.004645215	0.9784847728	1.003675494	1.000754474	1

Comparison between this branch and master. Data collection in progress...

W	place_time	wl	cpd	route_time	pack_time	heap_pops	total_swaps
300	1.000709887	0.9990728234	0.9964754886	1.006605634	0.9989301366	1.006669728	1
270	1.007525117	0.9983562986	1.004650437	0.9699298169	0.9988696226	0.9913845767	1
250	1.008814692	0.9980936599	1.003070789	0.8505039119	0.9995534048	0.8510168759	1

Bitcoin miner failed on both branches when W=250.