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

[Michael Maitland 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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michaelmaitland wrote:

> I basically copied that pass from the existing one CodeGen/CFIInstrInserter.cpp and modified it.

Is it possible to modify `CodeGen/CFIInstrInserter.cpp` instead of having a RISC-V specific copy? 

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