[llvm] [llvm] Fix behavior of llvm.objectsize in presence of negative / large offset (PR #115504)

[via llvm-commits]

serge-sans-paille wrote:

@hvdijk : Are you fine with me landing this as part of https://github.com/llvm/llvm-project/pull/115522 ?
We can elaborate on the negative gep composition aspects in a later patch.

https://github.com/llvm/llvm-project/pull/115504