In the simpler version of the link-eval data structure that we use in dominator

computation, the Ancestor field is always set to the Parent, so we can remove
the explicit link entirely and merge the Parent and Ancestor fields. Instead of
checking for whether an ancestor exists for a node or not, we simply check
whether the node has already been processed. This is simpler if Compress is
inlined into Eval, so I did that as well.

This is about a 3% speedup running -domtree on test-suite + SPEC2000 & SPEC2006,
but it also opens up some opportunities for further improvement.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124061 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 23 insertions, 38 deletions

diff --git a/include/llvm/Analysis/DominatorInternals.h b/include/llvm/Analysis/DominatorInternals.h
index 7f468836d2..125836a6a3 100644
--- a/include/llvm/Analysis/DominatorInternals.h
+++ b/include/llvm/Analysis/DominatorInternals.h
@@ -42,7 +42,6 @@ unsigned DFSPass(DominatorTreeBase<typename GraphT::NodeType>& DT,
   VInfo.Label = V;
 
   Vertex.push_back(V);        // Vertex[n] = V;
-  //Info[V].Ancestor = 0;     // Ancestor[n] = 0
 
   for (succ_iterator SI = succ_begin(V), E = succ_end(V); SI != E; ++SI) {
     InfoRec &SuccVInfo = DT.Info[*SI];
@@ -70,7 +69,6 @@ unsigned DFSPass(DominatorTreeBase<typename GraphT::NodeType>& DT,
       BBInfo.Label = BB;
 
       DT.Vertex.push_back(BB);       // Vertex[n] = V;
-      //BBInfo[V].Ancestor = 0;   // Ancestor[n] = 0
 
       if (IsChildOfArtificialExit)
         BBInfo.Parent = 1;
@@ -106,53 +104,47 @@ unsigned DFSPass(DominatorTreeBase<typename GraphT::NodeType>& DT,
 }
 
 template<class GraphT>
-void Compress(DominatorTreeBase<typename GraphT::NodeType>& DT,
-              typename GraphT::NodeType *VIn) {
+typename GraphT::NodeType* 
+Eval(DominatorTreeBase<typename GraphT::NodeType>& DT,
+     typename GraphT::NodeType *VIn, unsigned LastLinked) {
+  typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInInfo =
+                                                                  DT.Info[VIn];
+  if (VInInfo.DFSNum < LastLinked)
+    return VIn;
+
   SmallVector<typename GraphT::NodeType*, 32> Work;
   SmallPtrSet<typename GraphT::NodeType*, 32> Visited;
-  typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInVAInfo =
-                                      DT.Info[DT.Vertex[DT.Info[VIn].Ancestor]];
 
-  if (VInVAInfo.Ancestor != 0)
+  if (VInInfo.Parent >= LastLinked)
     Work.push_back(VIn);
   
   while (!Work.empty()) {
     typename GraphT::NodeType* V = Work.back();
     typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInfo =
                                                                      DT.Info[V];
-    typename GraphT::NodeType* VAncestor = DT.Vertex[VInfo.Ancestor];
-    typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VAInfo =
-                                                             DT.Info[VAncestor];
+    typename GraphT::NodeType* VAncestor = DT.Vertex[VInfo.Parent];
 
     // Process Ancestor first
-    if (Visited.insert(VAncestor) &&
-        VAInfo.Ancestor != 0) {
+    if (Visited.insert(VAncestor) && VInfo.Parent >= LastLinked) {
       Work.push_back(VAncestor);
       continue;
     } 
     Work.pop_back(); 
 
     // Update VInfo based on Ancestor info
-    if (VAInfo.Ancestor == 0)
+    if (VInfo.Parent < LastLinked)
       continue;
+
+    typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VAInfo =
+                                                             DT.Info[VAncestor];
     typename GraphT::NodeType* VAncestorLabel = VAInfo.Label;
     typename GraphT::NodeType* VLabel = VInfo.Label;
     if (DT.Info[VAncestorLabel].Semi < DT.Info[VLabel].Semi)
       VInfo.Label = VAncestorLabel;
-    VInfo.Ancestor = VAInfo.Ancestor;
+    VInfo.Parent = VAInfo.Parent;
   }
-}
 
-template<class GraphT>
-typename GraphT::NodeType* 
-Eval(DominatorTreeBase<typename GraphT::NodeType>& DT,
-     typename GraphT::NodeType *V) {
-  typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInfo =
-                                                                     DT.Info[V];
-  if (VInfo.Ancestor == 0)
-    return V;
-  Compress<GraphT>(DT, V);
-  return VInfo.Label;
+  return VInInfo.Label;
 }
 
 template<class FuncT, class NodeT>
@@ -169,7 +161,6 @@ void Calculate(DominatorTreeBase<typename GraphTraits<NodeT>::NodeType>& DT,
     BBInfo.Label = NULL;
 
     DT.Vertex.push_back(NULL);       // Vertex[n] = V;
-      //BBInfo[V].Ancestor = 0;   // Ancestor[n] = 0
   }
 
   // Step #1: Number blocks in depth-first order and initialize variables used
@@ -205,7 +196,7 @@ void Calculate(DominatorTreeBase<typename GraphTraits<NodeT>::NodeType>& DT,
     // Step #2: Implicitly define the immediate dominator of vertices
     for (unsigned j = i; Buckets[j] != i; j = Buckets[j]) {
       typename GraphT::NodeType* V = DT.Vertex[Buckets[j]];
-      typename GraphT::NodeType* U = Eval<GraphT>(DT, V);
+      typename GraphT::NodeType* U = Eval<GraphT>(DT, V, i + 1);
       DT.IDoms[V] = DT.Info[U].Semi < i ? U : W;
     }
 
@@ -219,7 +210,7 @@ void Calculate(DominatorTreeBase<typename GraphTraits<NodeT>::NodeType>& DT,
          E = InvTraits::child_end(W); CI != E; ++CI) {
       typename InvTraits::NodeType *N = *CI;
       if (DT.Info.count(N)) {  // Only if this predecessor is reachable!
-        unsigned SemiU = DT.Info[Eval<GraphT>(DT, N)].Semi;
+        unsigned SemiU = DT.Info[Eval<GraphT>(DT, N, i + 1)].Semi;
         if (SemiU < WInfo.Semi)
           WInfo.Semi = SemiU;
       }
@@ -234,9 +225,6 @@ void Calculate(DominatorTreeBase<typename GraphTraits<NodeT>::NodeType>& DT,
       Buckets[i] = Buckets[WInfo.Semi];
       Buckets[WInfo.Semi] = i;
     }
-
-    // Link W to its DFS tree parent.
-    WInfo.Ancestor = WInfo.Parent;
   }
 
   if (N >= 1) {
diff --git a/include/llvm/Analysis/Dominators.h b/include/llvm/Analysis/Dominators.h
index 133e1231f9..230e83d301 100644
--- a/include/llvm/Analysis/Dominators.h
+++ b/include/llvm/Analysis/Dominators.h
@@ -195,11 +195,11 @@ protected:
   // Information record used during immediate dominators computation.
   struct InfoRec {
     unsigned DFSNum;
+    unsigned Parent;
     unsigned Semi;
     NodeT *Label;
-    unsigned Parent, Ancestor;
 
-    InfoRec() : DFSNum(0), Semi(0), Label(0), Parent(0), Ancestor(0) {}
+    InfoRec() : DFSNum(0), Parent(0), Semi(0), Label(0) {}
   };
 
   DenseMap<NodeT*, NodeT*> IDoms;
@@ -564,13 +564,10 @@ public:
 
 protected:
   template<class GraphT>
-  friend void Compress(DominatorTreeBase<typename GraphT::NodeType>& DT,
-                       typename GraphT::NodeType* VIn);
-
-  template<class GraphT>
   friend typename GraphT::NodeType* Eval(
                                DominatorTreeBase<typename GraphT::NodeType>& DT,
-                                         typename GraphT::NodeType* V);
+                                         typename GraphT::NodeType* V,
+                                         unsigned LastLinked);
 
   template<class GraphT>
   friend unsigned DFSPass(DominatorTreeBase<typename GraphT::NodeType>& DT,