[llvm] [SystemZ] Improve handling of memmoves. (PR #196285)

[Nikita Popov via llvm-commits]

nikic wrote:

@JonPsson1 I think that's pretty much expected. In practice, memmove can either be converted to memcpy because we can prove they don't alias, or else we don't know anything about the relation of the pointers. Overlapping memmove within the same buffer seems like something that would be very rare.

https://github.com/llvm/llvm-project/pull/196285