[llvm] [MemCpyOpt] Drop dead `memmove` calls on `memset`'d source data (PR #101930)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> Is there any real-world code written like this?

While the usefulness of the patch is indeed questionable, dubious at the very least, I thought it could still make sense considering that the underlying optimization is quite trivial/basic per sé, and has a low compile-time. I feel like compilers should still perform at their best if possible, while clearly trading for efficiency. That said, I advocate for optimizations that turn out to be actually profitable, so I do not oppose if this is an unnecessary addition.

https://github.com/llvm/llvm-project/pull/101930