[llvm] [AMDGPU] Examine instructions in pending queues during scheduling (PR #147653)

[Jeffrey Byrnes via llvm-commits]

================
@@ -524,6 +619,47 @@ GCNSchedStageID GCNSchedStrategy::getNextStage() const {
   return *std::next(CurrentStage);
 }
 
+bool GCNSchedStrategy::tryPendingCandidate(SchedCandidate &Cand,
+                                           SchedCandidate &TryCand,
+                                           SchedBoundary *Zone) const {
+  // Initialize the candidate if needed.
+  if (!Cand.isValid()) {
+    TryCand.Reason = NodeOrder;
+    return true;
+  }
+
+  // Bias PhysReg Defs and copies to their uses and defined respectively.
+  if (tryGreater(biasPhysReg(TryCand.SU, TryCand.AtTop),
+                 biasPhysReg(Cand.SU, Cand.AtTop), TryCand, Cand, PhysReg))
+    return TryCand.Reason != NoCand;
+
+  // Avoid exceeding the target's limit.
+  if (DAG->isTrackingPressure() &&
+      tryPressure(TryCand.RPDelta.Excess, Cand.RPDelta.Excess, TryCand, Cand,
+                  RegExcess, TRI, DAG->MF))
+    return TryCand.Reason != NoCand;
+
+  // Avoid increasing the max critical pressure in the scheduled region.
+  if (DAG->isTrackingPressure() &&
+      tryPressure(TryCand.RPDelta.CriticalMax, Cand.RPDelta.CriticalMax,
+                  TryCand, Cand, RegCritical, TRI, DAG->MF))
+    return TryCand.Reason != NoCand;
+
+  bool SameBoundary = Zone != nullptr;
+  if (SameBoundary) {
+    TryCand.initResourceDelta(DAG, SchedModel);
+    if (tryLess(TryCand.ResDelta.CritResources, Cand.ResDelta.CritResources,
+                TryCand, Cand, ResourceReduce))
+      return TryCand.Reason != NoCand;
+    if (tryGreater(TryCand.ResDelta.DemandedResources,
+                   Cand.ResDelta.DemandedResources, TryCand, Cand,
+                   ResourceDemand))
+      return TryCand.Reason != NoCand;
+  }
+
+  return false;
----------------
jrbyrnes wrote:

Seems like there may be some cases which would benefit from using a stall cycle heuristic. Maybe as a follow-up.

https://github.com/llvm/llvm-project/pull/147653