[llvm] [PowerPC] Spill non-volatile registers required for traceback table (PR #71115)

[Chen Zheng via llvm-commits]

chenzheng1030 wrote:

> I missed your ping, sorry Zheng.

No worries at all. Thanks very much for working on this.

I still confused by the `nounwind` attribute changes. I thought you were adding this attribute to suppress some CFI instructions. But I tested this patch locally, without this attribute changes, all the impacted LITs are still good. So I don't think we need the `nounwind` attribute change, right? The CSR should always backup/restore till 31 without considering the nounwind attribute?

https://github.com/llvm/llvm-project/pull/71115