[SROA] Teach SROA to perform no-op pointer conversion.
- When promoting a pointer from memory to register, SROA skips pointers from different address spaces. However, as ptrtoint and inttoptr are defined as no-op casts if that integer type has the same as the pointer value, generate the pair of ptrtoint/inttoptr (no-op cast) sequence to convert pointers from different address spaces if they have the same size.
Reviewers: arsenm, chandlerc, lebedev.ri
Differential Revision: https://reviews.llvm.org/D81943