[llvm] [CVP] Remove Zero-Index GEP (PR #144831)

[Nikita Popov via llvm-commits]

https://github.com/nikic requested changes to this pull request.

There is nothing really GEP specific here -- this just uses LVI to determine whether values are constant. However, there is a reason why we don't actually do this very obvious optimization: Unlike SCCP (which *does* perform this type of optimization), LVI is very, very slow and we need to keep the number of values we query small.

Compile-time: https://llvm-compile-time-tracker.com/compare.php?from=a9a71b6d311892d6add6aab3790b20fe945cca38&to=f4918da327f8d1cb43fb6aa181c948f0f9e37979&stat=instructions:u

https://github.com/llvm/llvm-project/pull/144831