[llvm] [AArch64] Reland merge index address with large offset into base address (PR #79951)

[Thurston Dang via llvm-commits]

thurstond wrote:

> > FYI: I reverted [43ffe2e](https://github.com/llvm/llvm-project/commit/43ffe2eed0d9f73789dbe213023733d164999306) because of a buildbot breakage ([324b676](https://github.com/llvm/llvm-project/commit/324b676a3d0449add8d4e24047680125f9b9a716))
> 
> Thanks for your report, I'll take a look at it .would you please show how to build the above llvm ? My change doesn't touch the ppc target, and it is a little supprise to affact the ppc64-nest.ll under target PowerPC.

The crash is in the aarch64 clang compiler running on Linux (not PPC) while compiling the ppc64-nest.ll, so it's just a coincidence that the input file is ppc64-.

Here's the repro instructions:
```
mkdir scratch_dir
cd scratch_dir
git clone https://github.com/llvm/llvm-zorg.git
BUILDBOT_REVISION=43ffe2eed0d9f73789dbe213023733d164999306 llvm-zorg/zorg/buildbot/builders/sanitizers/buildbot_bootstrap_ubsan.sh
```
(based on https://github.com/google/sanitizers/wiki/SanitizerBotReproduceBuild but with your commit revision and the ubsan script)

Thanks!

https://github.com/llvm/llvm-project/pull/79951