Ways to make a sim.do use previuosly compiled sources?

In reply to chim20air:

2 options spring to mind:

a) Use qrun command to compile/optimize and launch simulation

Incremental compilation and optimization works really well with qrun
There is a seperare qrun user guide that comes with the install

b) Create a PDU (Pre-optimized Design Unit) for the DUT

This optimizes the DUT so that if you are only making changes to the testbench, then it doesn't have to re-compile or optimize your RTL code.
e.g.
vlog -work dut_lib -f dut_files.f
vopt -pdu +acc dut_top -o dut_top_pdu +cover=sbfec+dut_top.

vlog -work tb_lib -f tb_files.f
vopt testbench +acc -o testbench_opt -L dut_lib
vsim -t -ps -coverage testbench_opt

Once your DUT PDU has been created, you only rerun the last 3 commands
Only recompile and re-generate the DUT PDU if you modify the RTL code