1) A register must be added to the input to enable Design Compiler's optimization of the first part of the circuit.

2) Design Compiler crashes if the optimization problem becomes too difficult.
This can be solved by compiling smaller parts of the design and restart the tool after each compilation of multiplier_x, and/or relaxing the optimization effort by using the option -map_effort <high/medium/low>

3) Do not load the module mentor when using Cosmoscope since this module stops Cosmoscope from obtaining a license.

4) Some Nanosim components are missing. Exclude those from use with the Design Compiler command "set_dont_use {<lib/cell1> <lib/cell2> ...}", e.g.
set_dont_use {c35_CORELIB/MUX24 c35_CORELIB/MUX26 c35_CORELIB/MUX32 c35_CORELIB/NOR33}