Possible enhancements for memory accesses.

- Consolidate the detection of access independence.
- Hoist a load out of a loop if all inputs except the memory input are loop-invariants and all memory accesses in the loop are independent from that load. Can also hoist if the control input post-dominates the loop head.
- Hoist a store out of a loop if it post-dominates the loop head, the pointer and value inputs are loop-invariants, all accesses between the store and the loop head are independent from that store.