[MachineScheduler] improve reuse of 'releaseNode'method

The 'SchedBoundary::releaseNode' is merely invoked for releasing the Top/Bottom root nodes.
However,  'SchedBoundary::releasePending' uses its same logic to check if the Pending queue
has any releasable SUnit.
It is possible to slightly modify the body of the two, allowing re-use of the former ('releaseNode')
in the latter.

Patch by Lorenzo Casalino <lorenzo.casalino93@gmail.com>

Reviewers: MatzeB, fhahn, atrick

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D65506

include/llvm/CodeGen/MachineScheduler.h

@@ -757,7 +757,8 @@ public:
 
   unsigned getOtherResourceCount(unsigned &OtherCritIdx);
 
-  void releaseNode(SUnit *SU, unsigned ReadyCycle);
+  template <bool InPQueue>
+  void releaseNode(SUnit *SU, unsigned ReadyCycle, unsigned Idx = 0);
 
   void bumpCycle(unsigned NextCycle);
 
@@ -955,7 +956,7 @@ public:
     if (SU->isScheduled)
       return;
 
-    Top.releaseNode(SU, SU->TopReadyCycle);
+    Top.releaseNode<false>(SU, SU->TopReadyCycle);
     TopCand.SU = nullptr;
   }
 
@@ -963,7 +964,7 @@ public:
     if (SU->isScheduled)
       return;
 
-    Bot.releaseNode(SU, SU->BotReadyCycle);
+    Bot.releaseNode<false>(SU, SU->BotReadyCycle);
     BotCand.SU = nullptr;
   }
 
@@ -1043,7 +1044,7 @@ public:
   void releaseTopNode(SUnit *SU) override {
     if (SU->isScheduled)
       return;
-    Top.releaseNode(SU, SU->TopReadyCycle);
+    Top.releaseNode<false>(SU, SU->TopReadyCycle);
   }
 
   // Only called for roots.

lib/CodeGen/MachineScheduler.cpp

@@ -2088,7 +2088,8 @@ getOtherResourceCount(unsigned &OtherCritIdx) {
   return OtherCritCount;
 }
 
-void SchedBoundary::releaseNode(SUnit *SU, unsigned ReadyCycle) {
+template <bool InPQueue>
+void SchedBoundary::releaseNode(SUnit *SU, unsigned ReadyCycle, unsigned Idx) {
   assert(SU->getInstr() && "Scheduled SUnit must have instr");
 
 #ifndef NDEBUG
@@ -2105,11 +2106,19 @@ void SchedBoundary::releaseNode(SUnit *SU, unsigned ReadyCycle) {
   // Check for interlocks first. For the purpose of other heuristics, an
   // instruction that cannot issue appears as if it's not in the ReadyQueue.
   bool IsBuffered = SchedModel->getMicroOpBufferSize() != 0;
-  if ((!IsBuffered && ReadyCycle > CurrCycle) || checkHazard(SU) ||
-      Available.size() >= ReadyListLimit)
-    Pending.push(SU);
-  else
+  bool HazardDetected = (!IsBuffered && ReadyCycle > CurrCycle) ||
+                        checkHazard(SU) || (Available.size() >= ReadyListLimit);
+
+  if (!HazardDetected) {
     Available.push(SU);
+
+    if (InPQueue)
+      Pending.remove(Pending.begin() + Idx);
+    return;
+  }
+
+  if (!InPQueue)
+    Pending.push(SU);
 }
 
 /// Move the boundary of scheduled code by one cycle.
@@ -2349,26 +2358,21 @@ void SchedBoundary::releasePending() {
 
   // Check to see if any of the pending instructions are ready to issue.  If
   // so, add them to the available queue.
-  bool IsBuffered = SchedModel->getMicroOpBufferSize() != 0;
-  for (unsigned i = 0, e = Pending.size(); i != e; ++i) {
-    SUnit *SU = *(Pending.begin()+i);
+  for (unsigned I = 0, E = Pending.size(); I < E; ++I) {
+    SUnit *SU = *(Pending.begin() + I);
     unsigned ReadyCycle = isTop() ? SU->TopReadyCycle : SU->BotReadyCycle;
 
     if (ReadyCycle < MinReadyCycle)
       MinReadyCycle = ReadyCycle;
 
-    if (!IsBuffered && ReadyCycle > CurrCycle)
-      continue;
-
-    if (checkHazard(SU))
-      continue;
-
     if (Available.size() >= ReadyListLimit)
       break;
 
-    Available.push(SU);
-    Pending.remove(Pending.begin()+i);
-    --i; --e;
+    releaseNode<true>(SU, ReadyCycle, I);
+    if (E != Pending.size()) {
+      --I;
+      --E;
+    }
   }
   CheckPending = false;
 }