[llvm] [llvm] Win x64 Unwind V2 1/n: Mark beginning and end of epilogs (PR #110024)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

> @efriedma-quic did you want the full documentation on learn.microsoft.com, or would updating readobj/objdump to handle the new unwind codes be sufficient?

I'd prefer real documentation if you have it... but given I'm pretty familiar with unwinding on Windows, probably I can figure out what's going on just from reading llvm-readobj dumps.

>Does code generated by LLVM fulfill these criteria at the moment, and are those rules documented anywhere?

https://learn.microsoft.com/en-us/cpp/build/prolog-and-epilog?view=msvc-170 has the rules... I think LLVM follows them?  Maybe not in some edge cases; I don't think there's a verifier or anything like that.

https://github.com/llvm/llvm-project/pull/110024