I curious about how an optimiser determines that a block of code can be vectorised. It's trivial to see this in the initial version of compute() but I'm not sur

I curious about how an optimiser determines that a block of code can be vectorised. It's trivial to see this in the initial version of compute() but I'm not sure how an optimiser does this. Is it as simple as checking that A, B, and C are cost? And how far would an optimiser typically take its analysis? For example, if B was defined inside the loop as (non -const) A * 2 ? Or as A * f() , where f() always returns 2, maybe using a constant or maybe a calculation etc. Seems like a very hard problem,