[llvm] [MemCpyOpt] Forward `memcpy` based on the actual copy memory location. (PR #87190)

[Nikita Popov via llvm-commits]

================

----------------
nikic wrote:

Please make the bulk of the coverage not copy back into the same allocation, but into a separate (noalias) destination. The same-allocation case is a confusing edge-case where we should only verify that we switch to memmove in that case.

https://github.com/llvm/llvm-project/pull/87190