Loads and store of values with type like <2 x p0> currently don't get imported because SelectionDAG has no knowledge of pointer types. To leverage the existing support for vector load/stores, we can bitcast the value to have s64 element types instead. We do this as a custom legalization.
This patch also adds support for general loads of <2 x s64>, and relaxes some type conditions on selecting G_BITCAST.