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

[Michael Maitland 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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michaelmaitland wrote:

Do we need to be worried about not handling cases that we don't currently know about? Do we need to solve this problem more generally?

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