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

[Michael Maitland via llvm-commits]

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@@ -138,6 +141,9 @@ class ReachingDefAnalysis : public MachineFunctionPass {
   DenseMap<MachineInstr *, int> InstIds;
 
   MBBReachingDefsInfo MBBReachingDefs;
+  using MBBFrameObjsReachingDefsInfo =
+      std::vector<std::vector<std::vector<int>>>;
+  MBBFrameObjsReachingDefsInfo MBBFrameObjsReachingDefs;
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michaelmaitland wrote:

It would be nice to add a docstring that describes this object. My understanding is that this is representing a map of MBBNumber -> Frame Object Index -> reaching def instruction numbers, since it is not clear by the data type definition.

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