Low performance when simulating large netlists

[jorkrohn]

I noticed that when including a large netlist in the design, the simulation performance dropped significantly. This didn't happen with ModelSim and GHDL. I did a speed comparison running the same test where I commented in and out the netlist from the design:

	ModelSim	GHDL	NVC
Without Netlist:	2.1 s	5.1 s	2.4 s
With Netlist:	2.7 s	7.1 s	3 min 34.7 s

This is a large (118000 lines) netlist from Xilinx which instantiates around 10000 unisim library components.

I'm running version 1.18.1

[nickg]

This is probably the same as issue #1331. I am working on some improvements.