[AIE] Dump critical path when failing

llvm/lib/Target/AIE/AIEPostPipeliner.cpp

@@ -93,6 +93,16 @@ llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const SlotCounts &Val) {
   return OS;
 }
 
+namespace {
+void dumpEarliestChain(const std::vector<NodeInfo> &Info, int N) {
+  int Prev = Info[N].LastEarliestPusher;
+  if (Prev >= 0) {
+    dumpEarliestChain(Info, Prev);
+  }
+  dbgs() << "  --> " << N << " @" << Info[N].Cycle << "\n";
+}
+} // namespace
+
 // The core of the PostPipeliner is simple. We are presented with a DAG that
 // represents enough copies of the body to reach the steady state of the loop.
 // NInstr is the number of instructions in the original body, the number of
@@ -197,6 +207,7 @@ void PostPipeliner::scheduleNode(SUnit &SU, int Cycle) {
     const int SNum = Succ->NodeNum;
     const int NewEarliest = Cycle + Latency;
     if (NewEarliest > Info[SNum].Earliest) {
+      Info[SNum].LastEarliestPusher = SU.NodeNum;
       Info[SNum].Earliest = NewEarliest;
       LLVM_DEBUG(dbgs() << SNum << " to " << Info[SNum].Earliest << " -; ");
     }
@@ -210,6 +221,7 @@ void PostPipeliner::scheduleNode(SUnit &SU, int Cycle) {
     const int PNum = Pred->NodeNum;
     const int NewLatest = Cycle - Latency;
     if (NewLatest < Info[PNum].Latest) {
+      Info[PNum].LastLatestPusher = SU.NodeNum;
       Info[PNum].Latest = NewLatest;
       LLVM_DEBUG(dbgs() << PNum << " to - " << Info[PNum].Latest << "; ");
     }
@@ -453,17 +465,19 @@ int PostPipeliner::mostUrgent(PostPipelinerStrategy &Strategy) {
 
 void PostPipeliner::resetSchedule() {
   Scoreboard.clear();
-  for (int K = 0; K < NInstr; K++) {
-    auto &N = Info[K];
-    N.Earliest = N.StaticEarliest;
-    N.Latest = N.StaticLatest;
-    N.Cycle = 0;
-    N.Scheduled = false;
-  }
-  for (int K = NInstr; K < NTotalInstrs; K++) {
+  for (int K = 0; K < NTotalInstrs; K++) {
     auto &N = Info[K];
-    N.Earliest = 0;
-    N.Latest = -1;
+    N.LastEarliestPusher = -1;
+    N.LastLatestPusher = -1;
+    if (K < NInstr) {
+      N.Earliest = N.StaticEarliest;
+      N.Latest = N.StaticLatest;
+      N.Cycle = 0;
+      N.Scheduled = false;
+    } else {
+      N.Earliest = 0;
+      N.Latest = -1;
+    }
   }
 
   FirstUnscheduled = 0;
@@ -527,8 +541,9 @@ bool PostPipeliner::scheduleOtherIterations() {
 
       // All iterations following the first one should fit exactly
       if (Earliest > Insert) {
-        LLVM_DEBUG(dbgs() << "  Latency not met (Earliest=" << Earliest
-                          << ")\n");
+        LLVM_DEBUG(dbgs() << "  Latency not met for " << N
+                          << "(Earliest=" << Earliest << ")\n";
+                   dumpEarliestChain(Info, N););
         return false;
       }
 

llvm/lib/Target/AIE/AIEPostPipeliner.h

@@ -92,6 +92,10 @@ class NodeInfo {
   // implies a minimum stagecount.
   int Latest = -1;
 
+  // Record critical path components
+  int LastEarliestPusher = -1;
+  int LastLatestPusher = -1;
+
   // Latest corrected taking Earliest of an LCD successor into account
   int LCDLatest = -1;