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diff --git a/contrib/llvm/lib/Analysis/IteratedDominanceFrontier.cpp b/contrib/llvm/lib/Analysis/IteratedDominanceFrontier.cpp
new file mode 100644
index 0000000..9f1edd2
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+++ b/contrib/llvm/lib/Analysis/IteratedDominanceFrontier.cpp
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+//===- IteratedDominanceFrontier.cpp - Compute IDF ------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/IteratedDominanceFrontier.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Dominators.h"
+#include <queue>
+
+using namespace llvm;
+
+void IDFCalculator::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());
+         DFI != DFE; ++DFI) {
+      DomLevels[*DFI] = DFI.getPathLength() - 1;
+    }
+  }
+
+  // Use a priority queue keyed on dominator tree level so that inserted nodes
+  // are handled from the bottom of the dominator tree upwards.
+  typedef std::pair<DomTreeNode *, unsigned> DomTreeNodePair;
+  typedef std::priority_queue<DomTreeNodePair, SmallVector<DomTreeNodePair, 32>,
+                              less_second> IDFPriorityQueue;
+  IDFPriorityQueue PQ;
+
+  for (BasicBlock *BB : *DefBlocks) {
+    if (DomTreeNode *Node = DT.getNode(BB))
+      PQ.push(std::make_pair(Node, DomLevels.lookup(Node)));
+  }
+
+  SmallVector<DomTreeNode *, 32> Worklist;
+  SmallPtrSet<DomTreeNode *, 32> VisitedPQ;
+  SmallPtrSet<DomTreeNode *, 32> VisitedWorklist;
+
+  while (!PQ.empty()) {
+    DomTreeNodePair RootPair = PQ.top();
+    PQ.pop();
+    DomTreeNode *Root = RootPair.first;
+    unsigned RootLevel = RootPair.second;
+
+    // Walk all dominator tree children of Root, inspecting their CFG edges with
+    // targets elsewhere on the dominator tree. Only targets whose level is at
+    // most Root's level are added to the iterated dominance frontier of the
+    // definition set.
+
+    Worklist.clear();
+    Worklist.push_back(Root);
+    VisitedWorklist.insert(Root);
+
+    while (!Worklist.empty()) {
+      DomTreeNode *Node = Worklist.pop_back_val();
+      BasicBlock *BB = Node->getBlock();
+
+      for (auto Succ : successors(BB)) {
+        DomTreeNode *SuccNode = DT.getNode(Succ);
+
+        // Quickly skip all CFG edges that are also dominator tree edges instead
+        // of catching them below.
+        if (SuccNode->getIDom() == Node)
+          continue;
+
+        unsigned SuccLevel = DomLevels.lookup(SuccNode);
+        if (SuccLevel > RootLevel)
+          continue;
+
+        if (!VisitedPQ.insert(SuccNode).second)
+          continue;
+
+        BasicBlock *SuccBB = SuccNode->getBlock();
+        if (useLiveIn && !LiveInBlocks->count(SuccBB))
+          continue;
+
+        PHIBlocks.emplace_back(SuccBB);
+        if (!DefBlocks->count(SuccBB))
+          PQ.push(std::make_pair(SuccNode, SuccLevel));
+      }
+
+      for (auto DomChild : *Node) {
+        if (VisitedWorklist.insert(DomChild).second)
+          Worklist.push_back(DomChild);
+      }
+    }
+  }
+}