Optimization: avoid expensive slicing when everything is concrete

[andreamattavelli]

[davidtr1037]

Can you please give more details?

[andreamattavelli]

@davidtr1037 Suppose that I want to skip function f(a,b). If both a and b are concrete, we don't need to skip the function, slice, etc. We can simply execute it.
Not easy to implement: we need to take into account also side effects on the function.