[ScheduleDAG] Fix unfolding of SUnits to already existent nodes.

Summary:
If unfolding an SUnit results in both load or the operation using it which
already exist in the DAG, abort the unfold if they are already scheduled.
If not, make sure we don't add duplicate dependencies.

This fixes PR37916.

Reviewers: davide, eli.friedman, fhahn, bogner

Subscribers: MatzeB, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D48666

llvm-svn: 337409

1 files changed, 30 insertions, 18 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
index 73f855f8f84..43e8ffd3839 100644
--- a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
@@ -1010,6 +1010,34 @@ SUnit *ScheduleDAGRRList::TryUnfoldSU(SUnit *SU) {
     computeLatency(LoadSU);
   }
 
+  bool isNewN = true;
+  SUnit *NewSU;
+  // This can only happen when isNewLoad is false.
+  if (N->getNodeId() != -1) {
+    NewSU = &SUnits[N->getNodeId()];
+    // If NewSU has already been scheduled, we need to clone it, but this
+    // negates the benefit to unfolding so just return SU.
+    if (NewSU->isScheduled)
+      return SU;
+    isNewN = false;
+  } else {
+    NewSU = CreateNewSUnit(N);
+    N->setNodeId(NewSU->NodeNum);
+
+    const MCInstrDesc &MCID = TII->get(N->getMachineOpcode());
+    for (unsigned i = 0; i != MCID.getNumOperands(); ++i) {
+      if (MCID.getOperandConstraint(i, MCOI::TIED_TO) != -1) {
+        NewSU->isTwoAddress = true;
+        break;
+      }
+    }
+    if (MCID.isCommutable())
+      NewSU->isCommutable = true;
+
+    InitNumRegDefsLeft(NewSU);
+    computeLatency(NewSU);
+  }
+
   LLVM_DEBUG(dbgs() << "Unfolding SU #" << SU->NodeNum << "\n");
 
   // Now that we are committed to unfolding replace DAG Uses.
@@ -1018,23 +1046,6 @@ SUnit *ScheduleDAGRRList::TryUnfoldSU(SUnit *SU) {
   DAG->ReplaceAllUsesOfValueWith(SDValue(SU->getNode(), OldNumVals - 1),
                                  SDValue(LoadNode, 1));
 
-  SUnit *NewSU = CreateNewSUnit(N);
-  assert(N->getNodeId() == -1 && "Node already inserted!");
-  N->setNodeId(NewSU->NodeNum);
-
-  const MCInstrDesc &MCID = TII->get(N->getMachineOpcode());
-  for (unsigned i = 0; i != MCID.getNumOperands(); ++i) {
-    if (MCID.getOperandConstraint(i, MCOI::TIED_TO) != -1) {
-      NewSU->isTwoAddress = true;
-      break;
-    }
-  }
-  if (MCID.isCommutable())
-    NewSU->isCommutable = true;
-
-  InitNumRegDefsLeft(NewSU);
-  computeLatency(NewSU);
-
   // Record all the edges to and from the old SU, by category.
   SmallVector<SDep, 4> ChainPreds;
   SmallVector<SDep, 4> ChainSuccs;
@@ -1100,7 +1111,8 @@ SUnit *ScheduleDAGRRList::TryUnfoldSU(SUnit *SU) {
 
   if (isNewLoad)
     AvailableQueue->addNode(LoadSU);
-  AvailableQueue->addNode(NewSU);
+  if (isNewN)
+    AvailableQueue->addNode(NewSU);
 
   ++NumUnfolds;