[llvm] [AArch64] merge index address with large offset into base address (PR #72187)

[via llvm-commits]

vfdff wrote:

> It is probably best to split the CGP and DAG parts out into separate patches if we can. I'm seeing some failures in the test-suite, although the look like they might be post-isel so there might be something else going on. I'm still not 100% sure how to structure this without causing regressions in places.

hi @davemgreen, I spilt the 2nd patch into [pr74046](https://github.com/llvm/llvm-project/pull/74046) according your idea, and that I'll rebase this patch after that patch is merged because the `OneUse` checking can be avoid for the 1st patch if the 2nd is merged first.

https://github.com/llvm/llvm-project/pull/72187