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diff --git a/include/llvm/Analysis/IteratedDominanceFrontier.h b/include/llvm/Analysis/IteratedDominanceFrontier.h
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+++ b/include/llvm/Analysis/IteratedDominanceFrontier.h
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+//===- IteratedDominanceFrontier.h - Calculate IDF --------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+/// \brief Compute iterated dominance frontiers using a linear time algorithm.
+///
+/// The algorithm used here is based on:
+///
+///   Sreedhar and Gao. A linear time algorithm for placing phi-nodes.
+///   In Proceedings of the 22nd ACM SIGPLAN-SIGACT Symposium on Principles of
+///   Programming Languages
+///   POPL '95. ACM, New York, NY, 62-73.
+///
+/// It has been modified to not explicitly use the DJ graph data structure and
+/// to directly compute pruned SSA using per-variable liveness information.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_IDF_H
+#define LLVM_ANALYSIS_IDF_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+
+namespace llvm {
+
+class BasicBlock;
+template <class T> class DomTreeNodeBase;
+typedef DomTreeNodeBase<BasicBlock> DomTreeNode;
+class DominatorTree;
+
+/// \brief Determine the iterated dominance frontier, given a set of defining
+/// blocks, and optionally, a set of live-in blocks.
+///
+/// In turn, the results can be used to place phi nodes.
+///
+/// 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.
+class IDFCalculator {
+
+public:
+  IDFCalculator(DominatorTree &DT) : DT(DT), useLiveIn(false) {}
+
+  /// \brief Give the IDF calculator the set of blocks in which the value is
+  /// defined.  This is equivalent to the set of starting blocks it should be
+  /// calculating the IDF for (though later gets pruned based on liveness).
+  ///
+  /// Note: This set *must* live for the entire lifetime of the IDF calculator.
+  void setDefiningBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
+    DefBlocks = &Blocks;
+  }
+
+  /// \brief Give the IDF calculator the set of blocks in which the value is
+  /// live on entry to the block.   This is used to prune the IDF calculation to
+  /// not include blocks where any phi insertion would be dead.
+  ///
+  /// Note: This set *must* live for the entire lifetime of the IDF calculator.
+
+  void setLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &Blocks) {
+    LiveInBlocks = &Blocks;
+    useLiveIn = true;
+  }
+
+  /// \brief Reset the live-in block set to be empty, and tell the IDF
+  /// calculator to not use liveness anymore.
+  void resetLiveInBlocks() {
+    LiveInBlocks = nullptr;
+    useLiveIn = false;
+  }
+
+  /// \brief Calculate iterated dominance frontiers
+  ///
+  /// This uses the linear-time phi algorithm based on DJ-graphs mentioned in
+  /// the file-level comment.  It performs DF->IDF pruning using the live-in
+  /// set, to avoid computing the IDF for blocks where an inserted PHI node
+  /// would be dead.
+  void calculate(SmallVectorImpl<BasicBlock *> &IDFBlocks);
+
+private:
+  DominatorTree &DT;
+  bool useLiveIn;
+  DenseMap<DomTreeNode *, unsigned> DomLevels;
+  const SmallPtrSetImpl<BasicBlock *> *LiveInBlocks;
+  const SmallPtrSetImpl<BasicBlock *> *DefBlocks;
+  SmallVector<BasicBlock *, 32> PHIBlocks;
+};
+}
+#endif