[DAG] Set up infrastructure to avoid smart constructor-based dangling nodes

Summary:
Various SelectionDAG non-combine operations (e.g. the getNode smart
constructor and legalization) may leave dangling nodes by applying
optimizations without fully pruning unused result values. This results
in nodes that are never added to the worklist and therefore can not be
pruned.

Add a node inserter for the combiner to make sure such nodes have the
chance of being pruned. This allows a number of additional peephole
optimizations.

Reviewers: efriedma, RKSimon, craig.topper, jyknight

Reviewed By: jyknight

Subscribers: msearles, jyknight, sdardis, nemanjai, javed.absar, hiraditya, jrtc27, atanasyan, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58068

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357279 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/SelectionDAG.h b/include/llvm/CodeGen/SelectionDAG.h
index 44eaff5d096ceca70e0e3695c7a6a5322b4020eb..aac3e0f0c66faa2cb6913eb2f3aa2588cb27acc6 100644 (file)
--- a/include/llvm/CodeGen/SelectionDAG.h
+++ b/include/llvm/CodeGen/SelectionDAG.h
@@ -297,6 +297,9 @@ public:
 
     /// The node N that was updated.
     virtual void NodeUpdated(SDNode *N);
+
+    /// The node N that was inserted.
+    virtual void NodeInserted(SDNode *N);
   };
 
   struct DAGNodeDeletedListener : public DAGUpdateListener {

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 5dad16f43e058e44265911219f231e34e6d67bee..ec8949071e8451acb6fce176d1990a71c7f8e435 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -647,6 +647,17 @@ public:
   }
 };
 
+class WorklistInserter : public SelectionDAG::DAGUpdateListener {
+  DAGCombiner &DC;
+
+public:
+  explicit WorklistInserter(DAGCombiner &dc)
+      : SelectionDAG::DAGUpdateListener(dc.getDAG()), DC(dc) {}
+
+  // This should eventually be pruning.
+  void NodeInserted(SDNode *N) override { }
+};
+
 } // end anonymous namespace
 
 //===----------------------------------------------------------------------===//
@@ -1399,6 +1410,8 @@ void DAGCombiner::Run(CombineLevel AtLevel) {
   LegalOperations = Level >= AfterLegalizeVectorOps;
   LegalTypes = Level >= AfterLegalizeTypes;
 
+  WorklistInserter AddNodes(*this);
+
   // Add all the dag nodes to the worklist.
   for (SDNode &Node : DAG.allnodes())
     AddToWorklist(&Node);

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 3cd08271f264dcb38c49c6c161b383fd17430170..0ee308b99443174a413e730dacc7a9e4605557bb 100644 (file)
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -85,6 +85,7 @@ static SDVTList makeVTList(const EVT *VTs, unsigned NumVTs) {
 // Default null implementations of the callbacks.
 void SelectionDAG::DAGUpdateListener::NodeDeleted(SDNode*, SDNode*) {}
 void SelectionDAG::DAGUpdateListener::NodeUpdated(SDNode*) {}
+void SelectionDAG::DAGUpdateListener::NodeInserted(SDNode *) {}
 
 void SelectionDAG::DAGNodeDeletedListener::anchor() {}
 
@@ -840,6 +841,8 @@ void SelectionDAG::InsertNode(SDNode *N) {
   N->PersistentId = NextPersistentId++;
   VerifySDNode(N);
 #endif
+  for (DAGUpdateListener *DUL = UpdateListeners; DUL; DUL = DUL->Next)
+    DUL->NodeInserted(N);
 }
 
 /// RemoveNodeFromCSEMaps - Take the specified node out of the CSE map that