[llvm] [CodeGen][MachinePipeliner] Limit register pressure when scheduling (PR #74807)

[Leandro Lupori via llvm-commits]

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@@ -1102,6 +1121,359 @@ struct FuncUnitSorter {
   }
 };
 
+/// Calculate the maximum register pressure of the scheduled instructions stream
+class HighRegisterPressureDetector {
+  MachineBasicBlock *OrigMBB;
+  const MachineFunction &MF;
+  const MachineRegisterInfo &MRI;
+  const TargetRegisterInfo *TRI;
+
+  const unsigned PSetNum;
+
+  // Indexed by PSet ID
+  // InitSetPressure takes into account the register preesure of live-in
+  // registers. It's not depend on how the loop is scheduled, so it's enough to
+  // calculate them once at the begining.
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luporl wrote:

```suggestion
  // InitSetPressure takes into account the register pressure of live-in
  // registers. It's not depend on how the loop is scheduled, so it's enough to
  // calculate them once at the beginning.
```

https://github.com/llvm/llvm-project/pull/74807