[llvm] [AMDGPU] Optionally Use GCNRPTrackers during scheduling (PR #93090)

[Jeffrey Byrnes via llvm-commits]

================
@@ -151,14 +157,42 @@ static bool canUsePressureDiffs(const SUnit &SU) {
 static void getRegisterPressures(bool AtTop,
                                  const RegPressureTracker &RPTracker, SUnit *SU,
                                  std::vector<unsigned> &Pressure,
-                                 std::vector<unsigned> &MaxPressure) {
+                                 std::vector<unsigned> &MaxPressure,
+                                 GCNDownwardRPTracker &DownwardTracker,
+                                 GCNUpwardRPTracker &UpwardTracker,
+                                 ScheduleDAGMI *DAG) {
   // getDownwardPressure() and getUpwardPressure() make temporary changes to
   // the tracker, so we need to pass those function a non-const copy.
   RegPressureTracker &TempTracker = const_cast<RegPressureTracker &>(RPTracker);
-  if (AtTop)
-    TempTracker.getDownwardPressure(SU->getInstr(), Pressure, MaxPressure);
-  else
-    TempTracker.getUpwardPressure(SU->getInstr(), Pressure, MaxPressure);
+  if (!GCNTrackers) {
+    if (AtTop)
+      TempTracker.getDownwardPressure(SU->getInstr(), Pressure, MaxPressure);
+    else
+      TempTracker.getUpwardPressure(SU->getInstr(), Pressure, MaxPressure);
+  } else {
+    Pressure.resize(4, 0);
+    if (AtTop) {
+      GCNDownwardRPTracker TempTopTracker(DownwardTracker);
+      auto MI = SU->getInstr();
+      TempTopTracker.advance(MI, false, DAG->getLIS());
+
+      Pressure[AMDGPU::RegisterPressureSets::SReg_32] =
----------------
jrbyrnes wrote:

Hi thanks for taking a look.

I'm not sure about this one.

In order to sink the Pressure assignments without introducing a ternary, we would need to do something like:


```
  // GCNTrackers
  Pressure.resize(4, 0);
  GCNRPTracker TempTracker(
      AtTop ? static_cast<GCNRPTracker>(DownwardTracker)
            : static_cast<GCNRPTracker>(UpwardTracker));
  MachineInstr *MI = SU->getInstr();
  AtTop ? (void)reinterpret_cast<GCNDownwardRPTracker *>(&TempTracker)
              ->advance(MI, false, DAG->getLIS())
        : reinterpret_cast<GCNUpwardRPTracker *>(&TempTracker)
              ->recede(*MI);

  Pressure[AMDGPU::RegisterPressureSets::SReg_32] =
      TempTracker.getPressure().getSGPRNum();
  Pressure[AMDGPU::RegisterPressureSets::VGPR_32] =
      TempTracker.getPressure().getVGPRNum(false);
```


 I'm not sure I prefer this over what we have now. But if you feel strongly about it, I will change.


https://github.com/llvm/llvm-project/pull/93090