[llvm] [RISCV][WIP] Let RA do the CSR saves. (PR #90819)

[Mikhail Gudim via llvm-commits]

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@@ -1164,6 +1170,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &MF) {
 void PEI::insertPrologEpilogCode(MachineFunction &MF) {
   const TargetFrameLowering &TFI = *MF.getSubtarget().getFrameLowering();
 
+  TFI.emitCFIsForCSRsHandledByRA(MF, RDA);
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mgudim wrote:

In my code, only the registers added by `RISCVFrameLowering::determineMustCalleeSaves` will be handled the same way as before (with usual prologue / epilogue). 

https://github.com/llvm/llvm-project/pull/90819