[llvm] [AMDGPU] Add MaxMemoryClauseSchedStrategy (PR #114957)

[Matt Arsenault via llvm-commits]

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@@ -615,6 +615,138 @@ bool GCNMaxILPSchedStrategy::tryCandidate(SchedCandidate &Cand,
   return false;
 }
 
+GCNMaxMemoryClauseSchedStrategy::GCNMaxMemoryClauseSchedStrategy(
+    const MachineSchedContext *C)
+    : GCNSchedStrategy(C) {
+  SchedStages.push_back(GCNSchedStageID::MemoryClauseInitialSchedule);
+}
+
+/// GCNMaxMemoryClauseSchedStrategy tries best to clause memory instructions as
+/// much as possible. This is achieved by:
+//  1. Prioritize clustered operations before stall latency heuristic.
+//  2. Prioritize long-latency-load before stall latency heuristic.
+///
+/// \param Cand provides the policy and current best candidate.
+/// \param TryCand refers to the next SUnit candidate, otherwise uninitialized.
+/// \param Zone describes the scheduled zone that we are extending, or nullptr
+///             if Cand is from a different zone than TryCand.
+/// \return \c true if TryCand is better than Cand (Reason is NOT NoCand)
+bool GCNMaxMemoryClauseSchedStrategy::tryCandidate(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;
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arsenm wrote:

Put these under one isTrackingPressure check 

https://github.com/llvm/llvm-project/pull/114957