Index: include/llvm/CodeGen/MachineFunction.h
===================================================================
--- include/llvm/CodeGen/MachineFunction.h
+++ include/llvm/CodeGen/MachineFunction.h
@@ -228,6 +228,10 @@
   // Allocation management for pseudo source values.
   std::unique_ptr<PseudoSourceValueManager> PSVManager;
 
+  /// Mark a basic block after which the function is cold.
+  /// This is null if no such fragment exists or has been computed.
+  const MachineBasicBlock *ColdFragmentStart;
+
   MachineFunction(const MachineFunction &) = delete;
   void operator=(const MachineFunction&) = delete;
 public:
@@ -346,6 +350,17 @@
   const MachineFunctionProperties &getProperties() const { return Properties; }
   MachineFunctionProperties &getProperties() { return Properties; }
 
+  /// Get the start of the cold fragment. null if none exists or was conputed.
+  const MachineBasicBlock *getColdFragmentStart() const {
+    return ColdFragmentStart;
+  }
+
+  /// Set the start of the cold fragment.
+  void setColdFragmentStart(const MachineBasicBlock *CFS) {
+    assert(!CFS || CFS->getParent() == this);
+    ColdFragmentStart = CFS;
+  }
+
   /// getInfo - Keep track of various per-function pieces of information for
   /// backends that would like to do so.
   ///
Index: lib/CodeGen/MachineBlockPlacement.cpp
===================================================================
--- lib/CodeGen/MachineBlockPlacement.cpp
+++ lib/CodeGen/MachineBlockPlacement.cpp
@@ -41,6 +41,7 @@
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/ScaledNumber.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetLowering.h"
@@ -588,6 +589,25 @@
     BestFreq = CandidateFreq;
   }
 
+  if (!BestBlock)
+    return nullptr;
+
+  auto *MF = BestBlock->getParent();
+  if (MF->getColdFragmentStart())
+    return BestBlock;
+
+  bool IsCold = IsEHPad;
+  if (!IsCold) {
+    typedef ScaledNumber<uint64_t> Scaled64;
+    Scaled64 B(BestFreq.getFrequency(), 5);
+    Scaled64 E(MBFI->getEntryFreq(), 0);
+
+    IsCold = (B / E) < 1;
+  }
+
+  if (IsCold)
+    MF->setColdFragmentStart(BestBlock);
+
   return BestBlock;
 }
 
@@ -1258,6 +1278,10 @@
   for (MachineBasicBlock &MBB : F)
     fillWorkLists(&MBB, UpdatedPreds, BlockWorkList, EHPadWorkList);
 
+  // We are reordering blocks, make sure we reset the cold fragment
+  // start and reset it where apropriate.
+  F.setColdFragmentStart(nullptr);
+
   BlockChain &FunctionChain = *BlockToChain[&F.front()];
   buildChain(&F.front(), FunctionChain, BlockWorkList, EHPadWorkList);
 
Index: lib/CodeGen/MachineFunction.cpp
===================================================================
--- lib/CodeGen/MachineFunction.cpp
+++ lib/CodeGen/MachineFunction.cpp
@@ -133,6 +133,7 @@
 
   FunctionNumber = FunctionNum;
   JumpTableInfo = nullptr;
+  ColdFragmentStart = nullptr;
 
   if (isFuncletEHPersonality(classifyEHPersonality(
           F->hasPersonalityFn() ? F->getPersonalityFn() : nullptr))) {