Avoid using a loop in ReleasePred and ReleaseSucc methods to compute the

new CycleBound value. Instead, just update CycleBound on each call.
Also, make ReleasePred and ReleaseSucc methods more consistent accross
the various schedulers.

This also happens to make ScheduleDAGRRList's CycleBound computation
somewhat more interesting, though it still doesn't have any noticeable
effect, because no current targets that use the register-pressure
reduction scheduler provide pipeline models.

llvm-svn: 59475

1 files changed, 26 insertions, 28 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
index 4611ec1c597..1bce96727dd 100644
--- a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
@@ -78,7 +78,7 @@ public:
   void Schedule();
 
 private:
-  void ReleaseSucc(SUnit *SuccSU, bool isChain);
+  void ReleaseSucc(SUnit *SU, SUnit *SuccSU, bool isChain);
   void ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle);
   void ListScheduleTopDown();
 };
@@ -106,35 +106,33 @@ void ScheduleDAGList::Schedule() {
 //===----------------------------------------------------------------------===//
 
 /// ReleaseSucc - Decrement the NumPredsLeft count of a successor. Add it to
-/// the PendingQueue if the count reaches zero.
-void ScheduleDAGList::ReleaseSucc(SUnit *SuccSU, bool isChain) {
-  SuccSU->NumPredsLeft--;
+/// the PendingQueue if the count reaches zero. Also update its cycle bound.
+void ScheduleDAGList::ReleaseSucc(SUnit *SU, SUnit *SuccSU, bool isChain) {
+  --SuccSU->NumPredsLeft;
   
-  assert(SuccSU->NumPredsLeft >= 0 &&
-         "List scheduling internal error");
+#ifndef NDEBUG
+  if (SuccSU->NumPredsLeft < 0) {
+    cerr << "*** Scheduling failed! ***\n";
+    SuccSU->dump(DAG);
+    cerr << " has been released too many times!\n";
+    assert(0);
+  }
+#endif
+  
+  // Compute how many cycles it will be before this actually becomes
+  // available.  This is the max of the start time of all predecessors plus
+  // their latencies.
+  // If this is a token edge, we don't need to wait for the latency of the
+  // preceeding instruction (e.g. a long-latency load) unless there is also
+  // some other data dependence.
+  unsigned PredDoneCycle = SU->Cycle;
+  if (!isChain)
+    PredDoneCycle += SU->Latency;
+  else if (SU->Latency)
+    PredDoneCycle += 1;
+  SuccSU->CycleBound = std::max(SuccSU->CycleBound, PredDoneCycle);
   
   if (SuccSU->NumPredsLeft == 0) {
-    // Compute how many cycles it will be before this actually becomes
-    // available.  This is the max of the start time of all predecessors plus
-    // their latencies.
-    unsigned AvailableCycle = 0;
-    for (SUnit::pred_iterator I = SuccSU->Preds.begin(),
-         E = SuccSU->Preds.end(); I != E; ++I) {
-      // If this is a token edge, we don't need to wait for the latency of the
-      // preceeding instruction (e.g. a long-latency load) unless there is also
-      // some other data dependence.
-      SUnit &Pred = *I->Dep;
-      unsigned PredDoneCycle = Pred.Cycle;
-      if (!I->isCtrl)
-        PredDoneCycle += Pred.Latency;
-      else if (Pred.Latency)
-        PredDoneCycle += 1;
-
-      AvailableCycle = std::max(AvailableCycle, PredDoneCycle);
-    }
-    
-    assert(SuccSU->CycleBound == 0 && "CycleBound already assigned!");
-    SuccSU->CycleBound = AvailableCycle;
     PendingQueue.push_back(SuccSU);
   }
 }
@@ -152,7 +150,7 @@ void ScheduleDAGList::ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle) {
   // Top down: release successors.
   for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
        I != E; ++I)
-    ReleaseSucc(I->Dep, I->isCtrl);
+    ReleaseSucc(SU, I->Dep, I->isCtrl);
 
   SU->isScheduled = true;
   AvailableQueue->ScheduledNode(SU);