What optimizations would hypothetically be allowed and what optimizations the compiler actually has enough information to be allowed to perform are very differe

What optimizations would hypothetically be allowed and what optimizations the compiler actually has enough information to be allowed to perform are very different. A compiler is hypothetically allowed to convert array-of-struct into struct-of-array, but to actually be allowed to do that it would need to understand every single use of pointers in the entire program. That is extremely challenging, if not impossible.