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

[Craig Topper via llvm-commits]

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@@ -262,15 +262,21 @@ namespace {
     void HoistOutOfLoop(MachineDomTreeNode *HeaderN, MachineLoop *CurLoop,
                         MachineBasicBlock *CurPreheader);
 
-    void InitRegPressure(MachineBasicBlock *BB);
+    void InitRegPressure(MachineBasicBlock *BB, const MachineLoop *Loop);
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topperc wrote:

There was no single virtual register corresponding to each Callee Saved Register. The PrologEpilogEmitter approach looks after regalloc to see which callee saved registers are used in the function and spills/restores them.

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