sched: Avoid trivially redundant DAG edges. Take the one with higher latency.

llvm-svn: 158379

2 files changed, 27 insertions, 5 deletions

diff --git a/llvm/include/llvm/CodeGen/ScheduleDAG.h b/llvm/include/llvm/CodeGen/ScheduleDAG.h
index 3dd3c0c4673..85ab47beb6b 100644
--- a/llvm/include/llvm/CodeGen/ScheduleDAG.h
+++ b/llvm/include/llvm/CodeGen/ScheduleDAG.h
@@ -117,8 +117,9 @@ namespace llvm {
       }
     }
 
-    bool operator==(const SDep &Other) const {
-      if (Dep != Other.Dep || Latency != Other.Latency) return false;
+    /// Return true if the specified SDep is equivalent except for latency.
+    bool overlaps(const SDep &Other) const {
+      if (Dep != Other.Dep) return false;
       switch (Dep.getInt()) {
       case Data:
       case Anti:
@@ -133,6 +134,10 @@ namespace llvm {
       llvm_unreachable("Invalid dependency kind!");
     }
 
+    bool operator==(const SDep &Other) const {
+      return overlaps(Other) && Latency == Other.Latency;
+    }
+
     bool operator!=(const SDep &Other) const {
       return !operator==(Other);
     }
diff --git a/llvm/lib/CodeGen/ScheduleDAG.cpp b/llvm/lib/CodeGen/ScheduleDAG.cpp
index 8fd64265fda..752f8e40804 100644
--- a/llvm/lib/CodeGen/ScheduleDAG.cpp
+++ b/llvm/lib/CodeGen/ScheduleDAG.cpp
@@ -64,10 +64,27 @@ const MCInstrDesc *ScheduleDAG::getNodeDesc(const SDNode *Node) const {
 /// specified node.
 bool SUnit::addPred(const SDep &D) {
   // If this node already has this depenence, don't add a redundant one.
-  for (SmallVector<SDep, 4>::const_iterator I = Preds.begin(), E = Preds.end();
-       I != E; ++I)
-    if (*I == D)
+  for (SmallVector<SDep, 4>::iterator I = Preds.begin(), E = Preds.end();
+       I != E; ++I) {
+    if (I->overlaps(D)) {
+      // Extend the latency if needed. Equivalent to removePred(I) + addPred(D).
+      if (I->getLatency() < D.getLatency()) {
+        SUnit *PredSU = I->getSUnit();
+        // Find the corresponding successor in N.
+        SDep ForwardD = *I;
+        ForwardD.setSUnit(this);
+        for (SmallVector<SDep, 4>::iterator II = PredSU->Succs.begin(),
+               EE = PredSU->Succs.end(); II != EE; ++II) {
+          if (*II == ForwardD) {
+            II->setLatency(D.getLatency());
+            break;
+          }
+        }
+        I->setLatency(D.getLatency());
+      }
       return false;
+    }
+  }
   // Now add a corresponding succ to N.
   SDep P = D;
   P.setSUnit(this);