[llvm] [GlobalOpt] Check if global gets compared to pointer of different obj. (PR #153789)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Have we explicitly said somewhere that icmp never exposes provenance?  I mean, we can make that call I guess, but it has some weird implications.  Like, we currently combine `ptrtoint(x) == ptrtoint(y)` to `x == y`.

I think this came out of the discussion on #125205; I don't know of any real-world testcase.

https://github.com/llvm/llvm-project/pull/153789