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

[Mikhail Gudim via llvm-commits]

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@@ -21874,6 +21874,108 @@ bool RISCVTargetLowering::fallBackToDAGISel(const Instruction &Inst) const {
   return false;
 }
 
+static MachineInstr *findInstrWhichNeedAllCSRs(MachineBasicBlock &MBB) {
+  // Some instructions may require (implicitly) all CSRs to be saved.
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mgudim wrote:

> Is it possible that there are other functions in addition to these functions that need all CSRs to be saved? Is it possible that there can be multiple MI in MBB that need this kind of handling?

It's possible, I only added the ones I know.

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