Opencv dependency question

I am building opencv, and it will automatically detect dependency, I noticed this

– Could not find OpenBLAS include. Turning OpenBLAS_FOUND off

– Could not find OpenBLAS lib. Turning OpenBLAS_FOUND off

It looks like no matter it can find OpenBLAS or not, it always can be built, how do I know if this dependency will be used or not?

For example, I am benchmarking performance of dnn using opencv_perf_dnn