[llvm] [PowerPC] provide CFI for ELF32 to unwind cr2, cr3, cr4 (PR #83098)

[Chen Zheng via llvm-commits]

https://github.com/chenzheng1030 approved this pull request.

This looks correct to me. `MustSaveCR` does not reflect the situation that whether cr2 ~ cr4 is spilled or not for SVR4 32-bit. So we can not depend on `MustSaveCR` to decide whether the CFI instruction should be generated. And for SVR4 32-bit, the non volatile CRs are stored related to frame-related slot, just below the GPR save area, so it is OK we use the common CFI generation logic at line 1222 instead of a customization one like the one for SVR4 64-bit. For SVR4 64-bit, the non volatile CSRs are saved at a fixed address.

I will add some PPC reviewers. Please wait for some days before you commit this.

Thanks very much for fixing this.

https://github.com/llvm/llvm-project/pull/83098