[llvm] [llvm] Use LazyValueInfo to improve llvm.objectsize computation (PR #114673)

[Harald van Dijk via llvm-commits]

hvdijk wrote:

It feels a bit risky to use `llvm.assume` to optimise away `llvm.objectsize`, since the former means it's UB if the assumption is false, and the latter is used to detect various forms of UB. Your PR might be fine, but it is difficult to be sure: we would not want the presence of UB to result in diagnostics for UB being suppressed. I will look in more detail later.

https://github.com/llvm/llvm-project/pull/114673