[llvm] [AArch64] merge index address with large offset into base address (PR #75343)

[David Green via llvm-commits]

davemgreen wrote:

It looks like this is causing #79756 too. I hadn't realised that it was committed in separate commits and then only partially reverted. I'll remove the LDRBBroX part too to make sure we don't see problems on the llvm-19 branch.

@vfdff there is a test case in #79756 that looks useful for figuring out at least one of the problems going on.

https://github.com/llvm/llvm-project/pull/75343