[llvm] [InstCombine] Merge one-use GEP offsets during expansion (PR #147263)

[Nikita Popov via llvm-commits]

nikic wrote:

A downside of this approach is that we can't preserve all GEP flags when round-tripping gep+gep -> gep+add -> gep+gep. So if extra uses get removed and we restore the gep+gep form, we may lose flags.

https://github.com/llvm/llvm-project/pull/147263