[llvm] [InstCombine] Remove redundant alignment assumptions. (PR #123348)

[via llvm-commits]

goldsteinn wrote:

> > Can this ever delete unrecoverable information?
> 
> The main case where we can lose info is if we derive the alignment from an argument and later inline the function; then the align arg attribute will be gone. Updated to only do this for pointers not derived from an argument.
> 
Hmm, maybe we should re-emit alignment assumptions during inlining?

https://github.com/llvm/llvm-project/pull/123348