[llvm] [InstCombine] fold `sub(zext(ptrtoint), zext(ptrtoint))` (PR #115369)

[Nikolay Panchenko via llvm-commits]

npanchen wrote:

@nikic please take a look again. The pattern should be similar to https://alive2.llvm.org/ce/z/v4Pyqg

https://github.com/llvm/llvm-project/pull/115369