[llvm] [IPSCCP] Do not attempt `tryToReplaceWithConstant` if may break invariants (PR #102820)

[Nikita Popov via llvm-commits]

nikic wrote:

It's even more obvious when you consider that the returned constant may just be a constant integer/float rather than a global. That can open up all kinds of optimizations, and is also something where rematerialization is more likely to be profitable.

https://github.com/llvm/llvm-project/pull/102820