[llvm] [CGP] Reassociate GEPs to separate scalar and vector indexing (PR #146379)

[Philip Reames via llvm-commits]

preames wrote:

JFYI - https://github.com/llvm/llvm-project/pull/146719 touches some of the same test cases in terms of impact, and should probably go first.  It''s conceptually simpler.  I think this change (or some variation) is still going to be needed though.  

https://github.com/llvm/llvm-project/pull/146379