[llvm] [AMDGPU] Initialize FrameOffsetReg for amdgpu_cs_chain functions (PR #165518)

[via llvm-commits]

jofrn wrote:

> This should definitely work on GFX12 and -O0! If you feel like the issues are not related to your patch, let me know and I can look into fixing them. Thanks :)

It can fail with or without -O0; I had a typo, clarified above.

The current issue occurs from the fp_all test case. The original patch for recurse requires only

`return !MF.getInfo<SIMachineFunctionInfo>()->isChainFunction() &&
         (frameTriviallyRequiresSP(MFI) || MFI.isFrameAddressTaken() ...`

fp_all requires perhaps the additional modifications to `SIFrameLowering::emitEpilogue`.

https://github.com/llvm/llvm-project/pull/165518