Index: include/llvm/Analysis/BlockFrequencyInfo.h
===================================================================
--- include/llvm/Analysis/BlockFrequencyInfo.h
+++ include/llvm/Analysis/BlockFrequencyInfo.h
@@ -51,6 +51,10 @@
   /// floating points.
   BlockFrequency getBlockFreq(const BasicBlock *BB) const;
 
+  // Set the frequency of the given basic block. Return true if it succeeds and
+  // false otherwise.
+  bool setBlockFreq(const BasicBlock *BB, uint64_t Freq);
+
   // Print the block frequency Freq to OS using the current functions entry
   // frequency to convert freq into a relative decimal form.
   raw_ostream &printBlockFreq(raw_ostream &OS, const BlockFrequency Freq) const;
Index: include/llvm/Analysis/BlockFrequencyInfoImpl.h
===================================================================
--- include/llvm/Analysis/BlockFrequencyInfoImpl.h
+++ include/llvm/Analysis/BlockFrequencyInfoImpl.h
@@ -456,6 +456,8 @@
 
   BlockFrequency getBlockFreq(const BlockNode &Node) const;
 
+  bool setBlockFreq(const BlockNode &Node, uint64_t Freq);
+
   raw_ostream &printBlockFreq(raw_ostream &OS, const BlockNode &Node) const;
   raw_ostream &printBlockFreq(raw_ostream &OS,
                               const BlockFrequency &Freq) const;
@@ -886,6 +888,7 @@
   BlockFrequency getBlockFreq(const BlockT *BB) const {
     return BlockFrequencyInfoImplBase::getBlockFreq(getNode(BB));
   }
+  bool setBlockFreq(const BlockT *BB, uint64_t Freq);
   Scaled64 getFloatingBlockFreq(const BlockT *BB) const {
     return BlockFrequencyInfoImplBase::getFloatingBlockFreq(getNode(BB));
   }
@@ -938,6 +941,21 @@
   finalizeMetrics();
 }
 
+template <class BT>
+bool BlockFrequencyInfoImpl<BT>::setBlockFreq(const BlockT *BB, uint64_t Freq) {
+  if (Nodes.count(BB))
+    return BlockFrequencyInfoImplBase::setBlockFreq(getNode(BB), Freq);
+  else {
+    // If BB is a newly added block after BFI is done, we need to create a new
+    // BlockNode for it assigned with a new index. The index can be determined
+    // by the size of Freqs.
+    BlockNode NewNode(Freqs.size());
+    Nodes[BB] = NewNode;
+    Freqs.emplace_back();
+    return BlockFrequencyInfoImplBase::setBlockFreq(NewNode, Freq);
+  }
+}
+
 template <class BT> void BlockFrequencyInfoImpl<BT>::initializeRPOT() {
   const BlockT *Entry = F->begin();
   RPOT.reserve(F->size());
Index: lib/Analysis/BlockFrequencyInfo.cpp
===================================================================
--- lib/Analysis/BlockFrequencyInfo.cpp
+++ lib/Analysis/BlockFrequencyInfo.cpp
@@ -150,6 +150,11 @@
   return BFI ? BFI->getBlockFreq(BB) : 0;
 }
 
+bool BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB,
+                                      uint64_t Freq) {
+  return BFI ? BFI->setBlockFreq(BB, Freq) : false;
+}
+
 /// Pop up a ghostview window with the current block frequency propagation
 /// rendered using dot.
 void BlockFrequencyInfo::view() const {
Index: lib/Analysis/BlockFrequencyInfoImpl.cpp
===================================================================
--- lib/Analysis/BlockFrequencyInfoImpl.cpp
+++ lib/Analysis/BlockFrequencyInfoImpl.cpp
@@ -527,6 +527,14 @@
   return Freqs[Node.Index].Scaled;
 }
 
+bool BlockFrequencyInfoImplBase::setBlockFreq(const BlockNode &Node,
+                                              uint64_t Freq) {
+  if (!Node.isValid())
+    return false;
+  Freqs[Node.Index].Integer = Freq;
+  return true;
+}
+
 std::string
 BlockFrequencyInfoImplBase::getBlockName(const BlockNode &Node) const {
   return std::string();