Set env.var MODELICAUSERCFLAGS=-O3 or use setCFlags(getCFlags() + " -O3")
Or better yet, use -Os or -O2. That runs faster than O3 in most cases. Usually, the overall time is slower though (the simulation runtime is already optimized and it takes a lot of extra effort to optimize all of the generated code, some which is never run).

Thank you, I will do that.

I have a very large model that I need to simulate.  I am converting it from another format to Modelica, and just learning Modelica.  I would say there are about 250 differential equations and about 750 algebraic.  Out of curiosity, what would be your best-guess time to build the simulation?

https://test.openmodelica.org/libraries … rsive.html
https://test.openmodelica.org/libraries … ptions.err has 2404 states, around 4000 equations.Takes 1 minute to compile the C-code with -O0, and runs in 13 seconds.

https://test.openmodelica.org/libraries … rsive.html
https://test.openmodelica.org/libraries … yAdder.err on the other hand has 324 states, 1649 equations (some which are torn non-linear systems). 1m18s to compile the C-code with -O0, and runs into a timeout (on the same machine it would take around 9 minutes or so to finish). But the slowness here is that the non-linear solvers take long to converge. They are already optimized.

So... It depends a lot on other structures in your model.