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

[Jeffrey Byrnes via llvm-commits]

================
@@ -148,17 +154,44 @@ static bool canUsePressureDiffs(const SUnit &SU) {
   return true;
 }
 
-static void getRegisterPressures(bool AtTop,
-                                 const RegPressureTracker &RPTracker, SUnit *SU,
-                                 std::vector<unsigned> &Pressure,
-                                 std::vector<unsigned> &MaxPressure) {
+static void getRegisterPressures(
+    bool AtTop, const RegPressureTracker &RPTracker, SUnit *SU,
+    std::vector<unsigned> &Pressure, std::vector<unsigned> &MaxPressure,
+    GCNDownwardRPTracker &DownwardTracker, GCNUpwardRPTracker &UpwardTracker,
+    ScheduleDAGMI *DAG, const SIRegisterInfo *SRI) {
   // 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) {
+    AtTop
+        ? TempTracker.getDownwardPressure(SU->getInstr(), Pressure, MaxPressure)
+        : TempTracker.getUpwardPressure(SU->getInstr(), Pressure, MaxPressure);
+
+    return;
+  }
+
+  // GCNTrackers
+  Pressure.resize(4, 0);
+  MachineInstr *MI = SU->getInstr();
+  if (AtTop) {
+    GCNDownwardRPTracker TempDownwardTracker(DownwardTracker);
+    TempDownwardTracker.bumpDownwardPressure(MI, SRI);
+    Pressure[AMDGPU::RegisterPressureSets::SReg_32] =
+        TempDownwardTracker.getPressure().getSGPRNum();
+    Pressure[AMDGPU::RegisterPressureSets::VGPR_32] =
+        TempDownwardTracker.getPressure().getArchVGPRNum();
+    Pressure[AMDGPU::RegisterPressureSets::AGPR_32] =
+        TempDownwardTracker.getPressure().getAGPRNum();
+  } else {
+    GCNUpwardRPTracker TempUpwardTracker(UpwardTracker);
----------------
jrbyrnes wrote:

Unfortunately, it is not this easy for the upwardRPTracker

The method the upwardTracker uses to determine the use lane masks adds lanemasks from other subranges unrelated to the the subreg use in the instruction.

On the other hand, bumpUpwardPressure uses RegOpers.collect which simply uses TRI.getSubRegIndexLaneMask(SubRegIdx) to get the lane masks.

In short, recede and bumpupward are logically inconsistent for this usecase, and I would prefer to not change recede. This would result in introducing behavioral changes when trackers are disabled.

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