[llvm] [RISCV] Remove CalleeSavedInfo for Zcmp/save-restore-libcalls registers (PR #79535)

[Visoiu Mistrih Francis via llvm-commits]

francisvm wrote:

> Could this patch affect Inter Procedural Register Allocation? I'm seeing a regression and I'm guess this could be related.

hmm, PEI runs post-ra, right? I don't know how IPRA works and what is the state of each function when it runs, but this should only be apparent post-PEI.

It does seem like `LiveRegUnits` uses `MFI.getCalleeSavedInfo` for pristine registers, so maybe there is something related there?

```
llvm/lib/CodeGen/LiveRegUnits.cpp
102:    const auto &CSI = MFI.getCalleeSavedInfo();
122:    for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
133:  for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
```

https://github.com/llvm/llvm-project/pull/79535