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

[via llvm-commits]

dyung wrote:

Hi @DianQK, we started to see an assertion failure in some of our internal tests which I bisected back to your change. I have put a repro in #98726, can you take a look?

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