diff --git a/include/llvm/Analysis/Dominators.h b/include/llvm/Analysis/Dominators.h
index f0b4672..0740f72 100644
--- a/include/llvm/Analysis/Dominators.h
+++ b/include/llvm/Analysis/Dominators.h
@@ -23,6 +23,7 @@
 
 #include "llvm/Pass.h"
 #include <set>
+#include "llvm/ADT/DenseMap.h"
 
 namespace llvm {
 
@@ -103,7 +104,7 @@
 
 protected:
   void reset();
-  typedef std::map<BasicBlock*, DomTreeNode*> DomTreeNodeMapType;
+  typedef DenseMap<BasicBlock*, DomTreeNode*> DomTreeNodeMapType;
   DomTreeNodeMapType DomTreeNodes;
   DomTreeNode *RootNode;
 
@@ -120,7 +121,7 @@
     InfoRec() : Semi(0), Size(0), Label(0), Parent(0), Child(0), Ancestor(0){}
   };
 
-  std::map<BasicBlock*, BasicBlock*> IDoms;
+  DenseMap<BasicBlock*, BasicBlock*> IDoms;
 
   // Vertex - Map the DFS number to the BasicBlock*
   std::vector<BasicBlock*> Vertex;
@@ -141,8 +142,8 @@
   /// block.  This is the same as using operator[] on this class.
   ///
   inline DomTreeNode *getNode(BasicBlock *BB) const {
-    DomTreeNodeMapType::const_iterator i = DomTreeNodes.find(BB);
-    return (i != DomTreeNodes.end()) ? i->second : 0;
+    DomTreeNodeMapType::const_iterator I = DomTreeNodes.find(BB);
+    return I != DomTreeNodes.end() ? I->second : 0;
   }
 
   inline DomTreeNode *operator[](BasicBlock *BB) const {
@@ -302,9 +303,9 @@
   BasicBlock *Eval(BasicBlock *v);
   void Link(BasicBlock *V, BasicBlock *W, InfoRec &WInfo);
   inline BasicBlock *getIDom(BasicBlock *BB) const {
-      std::map<BasicBlock*, BasicBlock*>::const_iterator I = IDoms.find(BB);
-      return I != IDoms.end() ? I->second : 0;
-    }
+    DenseMap<BasicBlock*, BasicBlock*>::const_iterator I = IDoms.find(BB);
+    return I != IDoms.end() ? I->second : 0;
+  }
 };
 
 //===-------------------------------------
diff --git a/include/llvm/Analysis/PostDominators.h b/include/llvm/Analysis/PostDominators.h
index 091925e..5841da3 100644
--- a/include/llvm/Analysis/PostDominators.h
+++ b/include/llvm/Analysis/PostDominators.h
@@ -45,7 +45,7 @@
   void Link(BasicBlock *V, BasicBlock *W, InfoRec &WInfo);
 
   inline BasicBlock *getIDom(BasicBlock *BB) const {
-    std::map<BasicBlock*, BasicBlock*>::const_iterator I = IDoms.find(BB);
+    DenseMap<BasicBlock*, BasicBlock*>::const_iterator I = IDoms.find(BB);
     return I != IDoms.end() ? I->second : 0;
   }
 };
diff --git a/lib/Analysis/PostDominators.cpp b/lib/Analysis/PostDominators.cpp
index 1188cff..e3169a5 100644
--- a/lib/Analysis/PostDominators.cpp
+++ b/lib/Analysis/PostDominators.cpp
@@ -28,7 +28,7 @@
 F("postdomtree", "Post-Dominator Tree Construction", true);
 
 unsigned PostDominatorTree::DFSPass(BasicBlock *V, InfoRec &VInfo,
-                                          unsigned N) {
+                                    unsigned N) {
   std::vector<std::pair<BasicBlock *, InfoRec *> > workStack;
   std::set<BasicBlock *> visited;
   workStack.push_back(std::make_pair(V, &VInfo));
@@ -111,13 +111,18 @@
   // Step #0: Scan the function looking for the root nodes of the post-dominance
   // relationships.  These blocks, which have no successors, end with return and
   // unwind instructions.
-  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
-    if (succ_begin(I) == succ_end(I)) {
-      Instruction *Insn = I->getTerminator();
+  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
+    TerminatorInst *Insn = I->getTerminator();
+    if (Insn->getNumSuccessors() == 0) {
       // Unreachable block is not a root node.
       if (!isa<UnreachableInst>(Insn))
         Roots.push_back(I);
     }
+    
+    // Prepopulate maps so that we don't get iterator invalidation issues later.
+    IDoms[I] = 0;
+    DomTreeNodes[I] = 0;
+  }
   
   Vertex.push_back(0);
   
diff --git a/lib/VMCore/Dominators.cpp b/lib/VMCore/Dominators.cpp
index 91b422c..9b36e1d 100644
--- a/lib/VMCore/Dominators.cpp
+++ b/lib/VMCore/Dominators.cpp
@@ -212,8 +212,7 @@
 
   std::vector<BasicBlock *> Work;
   std::set<BasicBlock *> Visited;
-  InfoRec &VInInfo = Info[VIn];
-  BasicBlock *VInAncestor = VInInfo.Ancestor;
+  BasicBlock *VInAncestor = Info[VIn].Ancestor;
   InfoRec &VInVAInfo = Info[VInAncestor];
 
   if (VInVAInfo.Ancestor != 0)
@@ -233,7 +232,7 @@
     } 
     Work.pop_back(); 
 
-    // Update VINfo based on Ancestor info
+    // Update VInfo based on Ancestor info
     if (VAInfo.Ancestor == 0)
       continue;
     BasicBlock *VAncestorLabel = VAInfo.Label;
@@ -366,17 +365,16 @@
   // Loop over all of the reachable blocks in the function...
   for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
     if (BasicBlock *ImmDom = getIDom(I)) {  // Reachable block.
-      DomTreeNode *&BBNode = DomTreeNodes[I];
-      if (!BBNode) {  // Haven't calculated this node yet?
-        // Get or calculate the node for the immediate dominator
-        DomTreeNode *IDomNode = getNodeForBlock(ImmDom);
+      DomTreeNode *BBNode = DomTreeNodes[I];
+      if (BBNode) continue;  // Haven't calculated this node yet?
 
-        // Add a new tree node for this BasicBlock, and link it as a child of
-        // IDomNode
-        DomTreeNode *C = new DomTreeNode(I, IDomNode);
-        DomTreeNodes[I] = C;
-        BBNode = IDomNode->addChild(C);
-      }
+      // Get or calculate the node for the immediate dominator
+      DomTreeNode *IDomNode = getNodeForBlock(ImmDom);
+
+      // Add a new tree node for this BasicBlock, and link it as a child of
+      // IDomNode
+      DomTreeNode *C = new DomTreeNode(I, IDomNode);
+      DomTreeNodes[I] = IDomNode->addChild(C);
     }
 
   // Free temporary memory used to construct idom's
@@ -387,8 +385,7 @@
   updateDFSNumbers();
 }
 
-void DominatorTreeBase::updateDFSNumbers()
-{
+void DominatorTreeBase::updateDFSNumbers() {
   int dfsnum = 0;
   // Iterate over all nodes in depth first order.
   for (unsigned i = 0, e = Roots.size(); i != e; ++i)