[llvm] [MemCpyOpt] Calculate the offset value to forward `memcpy` (PR #87190)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw commented:

Can you add some tests to demonstrate that the staging allocas will be eliminated after memcpy forwarding?


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