-funroll-loops and -ffast-math are useful optimisations because most of the computations which lpython intends to handle involve loops and math, so enabling both of these will speed up the code. In fact, enabling -O1, -O2 and -O3 speeds up the code significantly when the lpython decorated function doesn’t return arrays. As a user I would like to pass these flags via lpython decorator but since its a class based decorator , its not so easy to pass these flags.