Index: include/llvm/Analysis/IteratedDominanceFrontier.h
===================================================================
--- include/llvm/Analysis/IteratedDominanceFrontier.h
+++ include/llvm/Analysis/IteratedDominanceFrontier.h
@@ -40,6 +40,9 @@
 /// This algorithm is a linear time computation of Iterated Dominance Frontiers,
 /// pruned using the live-in set.
 /// By default, liveness is not used to prune the IDF computation.
+/// The template parameters should be either BasicBlock* or Inverse<BasicBlock
+/// *>, depending on if you want the forward or reverse IDF.
+template <class NodeTy>
 class IDFCalculator {
 
 public:
@@ -88,5 +91,7 @@
   const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
   SmallVector<BasicBlock *, 32> PHIBlocks;
 };
+typedef IDFCalculator<BasicBlock *> ForwardIDFCalculator;
+typedef IDFCalculator<Inverse<BasicBlock *>> ReverseIDFCalculator;
 }
 #endif
Index: lib/Analysis/IteratedDominanceFrontier.cpp
===================================================================
--- lib/Analysis/IteratedDominanceFrontier.cpp
+++ lib/Analysis/IteratedDominanceFrontier.cpp
@@ -16,9 +16,10 @@
 #include "llvm/IR/Dominators.h"
 #include <queue>
 
-using namespace llvm;
-
-void IDFCalculator::calculate(SmallVectorImpl<BasicBlock *> &PHIBlocks) {
+namespace llvm {
+template <class NodeTy>
+void IDFCalculator<NodeTy>::calculate(
+    SmallVectorImpl<BasicBlock *> &PHIBlocks) {
   // If we haven't computed dominator tree levels, do so now.
   if (DomLevels.empty()) {
     for (auto DFI = df_begin(DT.getRootNode()), DFE = df_end(DT.getRootNode());
@@ -61,8 +62,12 @@
     while (!Worklist.empty()) {
       DomTreeNode *Node = Worklist.pop_back_val();
       BasicBlock *BB = Node->getBlock();
-
-      for (auto Succ : successors(BB)) {
+      // Succ is the successor in the direction we are calculating IDF, so it is
+      // successor for IDF, and predecessor for Reverse IDF.
+      for (auto SuccIter = GraphTraits<NodeTy>::child_begin(BB),
+                End = GraphTraits<NodeTy>::child_end(BB);
+           SuccIter != End; ++SuccIter) {
+        BasicBlock *Succ = *SuccIter;
         DomTreeNode *SuccNode = DT.getNode(Succ);
 
         // Quickly skip all CFG edges that are also dominator tree edges instead
@@ -93,3 +98,7 @@
     }
   }
 }
+
+template class IDFCalculator<BasicBlock *>;
+template class IDFCalculator<Inverse<BasicBlock *>>;
+}
Index: lib/Transforms/Utils/MemorySSA.cpp
===================================================================
--- lib/Transforms/Utils/MemorySSA.cpp
+++ lib/Transforms/Utils/MemorySSA.cpp
@@ -304,7 +304,7 @@
   }
 
   // Determine where our MemoryPhi's should go
-  IDFCalculator IDFs(*DT);
+  ForwardIDFCalculator IDFs(*DT);
   IDFs.setDefiningBlocks(DefiningBlocks);
   IDFs.setLiveInBlocks(LiveInBlocks);
   SmallVector<BasicBlock *, 32> IDFBlocks;
Index: lib/Transforms/Utils/PromoteMemoryToRegister.cpp
===================================================================
--- lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -523,7 +523,7 @@
 
   AllocaInfo Info;
   LargeBlockInfo LBI;
-  IDFCalculator IDF(DT);
+  ForwardIDFCalculator IDF(DT);
 
   for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
     AllocaInst *AI = Allocas[AllocaNum];