[NFC][Scheduler] Refactor tryCandidate to return boolean

This patch changes return type of tryCandidate from void to bool:

1. Methods in some targets already follow this convention.
2. This would help if some target wants to re-use generic code.
3. It looks more intuitive if these try-method returns the same type.

We may need to change return type of them from bool to some enum
further, to make it less confusing.

Reviewed By: foad

Differential Revision: https://reviews.llvm.org/D103951

Author: ecnelises

llvm/include/llvm/CodeGen/MachineScheduler.h

@@ -1012,7 +1012,7 @@ class GenericScheduler : public GenericSchedulerBase {
                      const RegPressureTracker &RPTracker,
                      RegPressureTracker &TempTracker);
 
-  virtual void tryCandidate(SchedCandidate &Cand, SchedCandidate &TryCand,
+  virtual bool tryCandidate(SchedCandidate &Cand, SchedCandidate &TryCand,
                             SchedBoundary *Zone) const;
 
   SUnit *pickNodeBidirectional(bool &IsTopNode);
@@ -1075,7 +1075,7 @@ class PostGenericScheduler : public GenericSchedulerBase {
   }
 
 protected:
-  virtual void tryCandidate(SchedCandidate &Cand, SchedCandidate &TryCand);
+  virtual bool tryCandidate(SchedCandidate &Cand, SchedCandidate &TryCand);
 
   void pickNodeFromQueue(SchedCandidate &Cand);
 };

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -2818,6 +2818,8 @@ void GenericSchedulerBase::traceCandidate(const SchedCandidate &Cand) {
 
 namespace llvm {
 /// Return true if this heuristic determines order.
+/// TODO: Consider refactor return type of these functions as integer or enum,
+/// as we may need to differentiate whether TryCand is better than Cand.
 bool tryLess(int TryVal, int CandVal,
              GenericSchedulerBase::SchedCandidate &TryCand,
              GenericSchedulerBase::SchedCandidate &Cand,
@@ -3176,34 +3178,35 @@ void GenericScheduler::initCandidate(SchedCandidate &Cand, SUnit *SU,
 /// \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.
-void GenericScheduler::tryCandidate(SchedCandidate &Cand,
+///             if Cand is from a different zone than TryCand.
+/// \return \c true if TryCand is better than Cand (Reason is NOT NoCand)
+bool GenericScheduler::tryCandidate(SchedCandidate &Cand,
                                     SchedCandidate &TryCand,
                                     SchedBoundary *Zone) const {
   // Initialize the candidate if needed.
   if (!Cand.isValid()) {
     TryCand.Reason = NodeOrder;
-    return;
+    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;
+    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;
+    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;
+    return TryCand.Reason != NoCand;
 
   // We only compare a subset of features when comparing nodes between
   // Top and Bottom boundary. Some properties are simply incomparable, in many
@@ -3217,12 +3220,12 @@ void GenericScheduler::tryCandidate(SchedCandidate &Cand,
     // heuristics to take precedence.
     if (Rem.IsAcyclicLatencyLimited && !Zone->getCurrMOps() &&
         tryLatency(TryCand, Cand, *Zone))
-      return;
+      return TryCand.Reason != NoCand;
 
     // Prioritize instructions that read unbuffered resources by stall cycles.
     if (tryLess(Zone->getLatencyStallCycles(TryCand.SU),
                 Zone->getLatencyStallCycles(Cand.SU), TryCand, Cand, Stall))
-      return;
+      return TryCand.Reason != NoCand;
   }
 
   // Keep clustered nodes together to encourage downstream peephole
@@ -3238,46 +3241,49 @@ void GenericScheduler::tryCandidate(SchedCandidate &Cand,
   if (tryGreater(TryCand.SU == TryCandNextClusterSU,
                  Cand.SU == CandNextClusterSU,
                  TryCand, Cand, Cluster))
-    return;
+    return TryCand.Reason != NoCand;
 
   if (SameBoundary) {
     // Weak edges are for clustering and other constraints.
     if (tryLess(getWeakLeft(TryCand.SU, TryCand.AtTop),
                 getWeakLeft(Cand.SU, Cand.AtTop),
                 TryCand, Cand, Weak))
-      return;
+      return TryCand.Reason != NoCand;
   }
 
   // Avoid increasing the max pressure of the entire region.
   if (DAG->isTrackingPressure() && tryPressure(TryCand.RPDelta.CurrentMax,
                                                Cand.RPDelta.CurrentMax,
                                                TryCand, Cand, RegMax, TRI,
                                                DAG->MF))
-    return;
+    return TryCand.Reason != NoCand;
 
   if (SameBoundary) {
     // Avoid critical resource consumption and balance the schedule.
     TryCand.initResourceDelta(DAG, SchedModel);
     if (tryLess(TryCand.ResDelta.CritResources, Cand.ResDelta.CritResources,
                 TryCand, Cand, ResourceReduce))
-      return;
+      return TryCand.Reason != NoCand;
     if (tryGreater(TryCand.ResDelta.DemandedResources,
                    Cand.ResDelta.DemandedResources,
                    TryCand, Cand, ResourceDemand))
-      return;
+      return TryCand.Reason != NoCand;
 
     // Avoid serializing long latency dependence chains.
     // For acyclic path limited loops, latency was already checked above.
     if (!RegionPolicy.DisableLatencyHeuristic && TryCand.Policy.ReduceLatency &&
         !Rem.IsAcyclicLatencyLimited && tryLatency(TryCand, Cand, *Zone))
-      return;
+      return TryCand.Reason != NoCand;
 
     // Fall through to original instruction order.
     if ((Zone->isTop() && TryCand.SU->NodeNum < Cand.SU->NodeNum)
         || (!Zone->isTop() && TryCand.SU->NodeNum > Cand.SU->NodeNum)) {
       TryCand.Reason = NodeOrder;
+      return true;
     }
   }
+
+  return false;
 }
 
 /// Pick the best candidate from the queue.
@@ -3299,8 +3305,7 @@ void GenericScheduler::pickNodeFromQueue(SchedBoundary &Zone,
     initCandidate(TryCand, SU, Zone.isTop(), RPTracker, TempTracker);
     // Pass SchedBoundary only when comparing nodes from the same boundary.
     SchedBoundary *ZoneArg = Cand.AtTop == TryCand.AtTop ? &Zone : nullptr;
-    tryCandidate(Cand, TryCand, ZoneArg);
-    if (TryCand.Reason != NoCand) {
+    if (tryCandidate(Cand, TryCand, ZoneArg)) {
       // Initialize resource delta if needed in case future heuristics query it.
       if (TryCand.ResDelta == SchedResourceDelta())
         TryCand.initResourceDelta(DAG, SchedModel);
@@ -3378,8 +3383,7 @@ SUnit *GenericScheduler::pickNodeBidirectional(bool &IsTopNode) {
   assert(TopCand.isValid());
   SchedCandidate Cand = BotCand;
   TopCand.Reason = NoCand;
-  tryCandidate(Cand, TopCand, nullptr);
-  if (TopCand.Reason != NoCand) {
+  if (tryCandidate(Cand, TopCand, nullptr)) {
     Cand.setBest(TopCand);
     LLVM_DEBUG(traceCandidate(Cand));
   }
@@ -3543,42 +3547,47 @@ void PostGenericScheduler::registerRoots() {
 ///
 /// \param Cand provides the policy and current best candidate.
 /// \param TryCand refers to the next SUnit candidate, otherwise uninitialized.
-void PostGenericScheduler::tryCandidate(SchedCandidate &Cand,
+/// \return \c true if TryCand is better than Cand (Reason is NOT NoCand)
+bool PostGenericScheduler::tryCandidate(SchedCandidate &Cand,
                                         SchedCandidate &TryCand) {
   // Initialize the candidate if needed.
   if (!Cand.isValid()) {
     TryCand.Reason = NodeOrder;
-    return;
+    return true;
   }
 
   // Prioritize instructions that read unbuffered resources by stall cycles.
   if (tryLess(Top.getLatencyStallCycles(TryCand.SU),
               Top.getLatencyStallCycles(Cand.SU), TryCand, Cand, Stall))
-    return;
+    return TryCand.Reason != NoCand;
 
   // Keep clustered nodes together.
   if (tryGreater(TryCand.SU == DAG->getNextClusterSucc(),
                  Cand.SU == DAG->getNextClusterSucc(),
                  TryCand, Cand, Cluster))
-    return;
+    return TryCand.Reason != NoCand;
 
   // Avoid critical resource consumption and balance the schedule.
   if (tryLess(TryCand.ResDelta.CritResources, Cand.ResDelta.CritResources,
               TryCand, Cand, ResourceReduce))
-    return;
+    return TryCand.Reason != NoCand;
   if (tryGreater(TryCand.ResDelta.DemandedResources,
                  Cand.ResDelta.DemandedResources,
                  TryCand, Cand, ResourceDemand))
-    return;
+    return TryCand.Reason != NoCand;
 
   // Avoid serializing long latency dependence chains.
   if (Cand.Policy.ReduceLatency && tryLatency(TryCand, Cand, Top)) {
-    return;
+    return TryCand.Reason != NoCand;
   }
 
   // Fall through to original instruction order.
-  if (TryCand.SU->NodeNum < Cand.SU->NodeNum)
+  if (TryCand.SU->NodeNum < Cand.SU->NodeNum) {
     TryCand.Reason = NodeOrder;
+    return true;
+  }
+
+  return false;
 }
 
 void PostGenericScheduler::pickNodeFromQueue(SchedCandidate &Cand) {
@@ -3588,8 +3597,7 @@ void PostGenericScheduler::pickNodeFromQueue(SchedCandidate &Cand) {
     TryCand.SU = SU;
     TryCand.AtTop = true;
     TryCand.initResourceDelta(DAG, SchedModel);
-    tryCandidate(Cand, TryCand);
-    if (TryCand.Reason != NoCand) {
+    if (tryCandidate(Cand, TryCand)) {
       Cand.setBest(TryCand);
       LLVM_DEBUG(traceCandidate(Cand));
     }