Index: llvm/trunk/include/llvm/IR/Dominators.h
===================================================================
--- llvm/trunk/include/llvm/IR/Dominators.h
+++ llvm/trunk/include/llvm/IR/Dominators.h
@@ -46,6 +46,9 @@
 using BBUpdates = ArrayRef<llvm::cfg::Update<BasicBlock *>>;
 
 extern template void Calculate<BBDomTree>(BBDomTree &DT);
+extern template void CalculateWithUpdates<BBDomTree>(BBDomTree &DT,
+                                                     BBUpdates U);
+
 extern template void Calculate<BBPostDomTree>(BBPostDomTree &DT);
 
 extern template void InsertEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From,
@@ -145,6 +148,9 @@
 
   DominatorTree() = default;
   explicit DominatorTree(Function &F) { recalculate(F); }
+  explicit DominatorTree(DominatorTree &DT, DomTreeBuilder::BBUpdates U) {
+    recalculate(*DT.Parent, U);
+  }
 
   /// Handle invalidation explicitly.
   bool invalidate(Function &F, const PreservedAnalyses &PA,
Index: llvm/trunk/include/llvm/Support/GenericDomTree.h
===================================================================
--- llvm/trunk/include/llvm/Support/GenericDomTree.h
+++ llvm/trunk/include/llvm/Support/GenericDomTree.h
@@ -193,6 +193,10 @@
 void Calculate(DomTreeT &DT);
 
 template <typename DomTreeT>
+void CalculateWithUpdates(DomTreeT &DT,
+                          ArrayRef<typename DomTreeT::UpdateType> Updates);
+
+template <typename DomTreeT>
 void InsertEdge(DomTreeT &DT, typename DomTreeT::NodePtr From,
                 typename DomTreeT::NodePtr To);
 
@@ -730,6 +734,11 @@
     DomTreeBuilder::Calculate(*this);
   }
 
+  void recalculate(ParentType &Func, ArrayRef<UpdateType> Updates) {
+    Parent = &Func;
+    DomTreeBuilder::CalculateWithUpdates(*this, Updates);
+  }
+
   /// verify - checks if the tree is correct. There are 3 level of verification:
   ///  - Full --  verifies if the tree is correct by making sure all the
   ///             properties (including the parent and the sibling property)
Index: llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
===================================================================
--- llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
+++ llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
@@ -1576,6 +1576,25 @@
   SemiNCAInfo<DomTreeT>::CalculateFromScratch(DT, nullptr);
 }
 
+template <typename DomTreeT>
+void CalculateWithUpdates(DomTreeT &DT,
+                          ArrayRef<typename DomTreeT::UpdateType> Updates) {
+  // TODO: Move BUI creation in common method, reuse in ApplyUpdates.
+  typename SemiNCAInfo<DomTreeT>::BatchUpdateInfo BUI;
+  LLVM_DEBUG(dbgs() << "Legalizing " << BUI.Updates.size() << " updates\n");
+  cfg::LegalizeUpdates<typename DomTreeT::NodePtr>(Updates, BUI.Updates,
+                                                   DomTreeT::IsPostDominator);
+  const size_t NumLegalized = BUI.Updates.size();
+  BUI.FutureSuccessors.reserve(NumLegalized);
+  BUI.FuturePredecessors.reserve(NumLegalized);
+  for (auto &U : BUI.Updates) {
+    BUI.FutureSuccessors[U.getFrom()].push_back({U.getTo(), U.getKind()});
+    BUI.FuturePredecessors[U.getTo()].push_back({U.getFrom(), U.getKind()});
+  }
+
+  SemiNCAInfo<DomTreeT>::CalculateFromScratch(DT, &BUI);
+}
+
 template <class DomTreeT>
 void InsertEdge(DomTreeT &DT, typename DomTreeT::NodePtr From,
                 typename DomTreeT::NodePtr To) {
Index: llvm/trunk/lib/IR/Dominators.cpp
===================================================================
--- llvm/trunk/lib/IR/Dominators.cpp
+++ llvm/trunk/lib/IR/Dominators.cpp
@@ -71,8 +71,13 @@
 
 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree>(
     DomTreeBuilder::BBDomTree &DT);
+template void
+llvm::DomTreeBuilder::CalculateWithUpdates<DomTreeBuilder::BBDomTree>(
+    DomTreeBuilder::BBDomTree &DT, BBUpdates U);
+
 template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>(
     DomTreeBuilder::BBPostDomTree &DT);
+// No CalculateWithUpdates<PostDomTree> instantiation, unless a usecase arises.
 
 template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>(
     DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);