[llvm] [EarlyCSE] Fix improper icmp simplification (PR #122043)

[via llvm-commits]

llvmssh wrote:

> > https://godbolt.org/z/1MfndEMMs
> 
> In this case, `%4` is passed into `_ZN1A5valueEv` which has `noundef` and `nonnull/dereferenceable` parameter attributes. The optimizer will assume `%4` is nonnull in the subsequent execution path.
> 
> Without `noundef` and `nonnull/dereferenceable`, the icmp will not be optimized out: https://godbolt.org/z/chhxE3Txr

Yes, icmp is simplified with its information. Should we add the check of volatile to icmp simplify?

https://github.com/llvm/llvm-project/pull/122043