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ref:cde9a383711a11544ce7e107a78147fb96cc4029

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diff --git a/contrib/libs/llvm12/include/llvm/Analysis/BlockFrequencyInfoImpl.h b/contrib/libs/llvm12/include/llvm/Analysis/BlockFrequencyInfoImpl.h
new file mode 100644
index 0000000000..f5c9294263
--- /dev/null
+++ b/contrib/libs/llvm12/include/llvm/Analysis/BlockFrequencyInfoImpl.h
@@ -0,0 +1,1604 @@
+#pragma once
+
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+#endif
+
+//==- BlockFrequencyInfoImpl.h - Block Frequency Implementation --*- C++ -*-==//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Shared implementation of BlockFrequency for IR and Machine Instructions.
+// See the documentation below for BlockFrequencyInfoImpl for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_BLOCKFREQUENCYINFOIMPL_H
+#define LLVM_ANALYSIS_BLOCKFREQUENCYINFOIMPL_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/GraphTraits.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/SparseBitVector.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/ValueHandle.h"
+#include "llvm/Support/BlockFrequency.h"
+#include "llvm/Support/BranchProbability.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/DOTGraphTraits.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/Format.h"
+#include "llvm/Support/ScaledNumber.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <deque>
+#include <iterator>
+#include <limits>
+#include <list>
+#include <string>
+#include <utility>
+#include <vector>
+
+#define DEBUG_TYPE "block-freq"
+
+extern llvm::cl::opt<bool> CheckBFIUnknownBlockQueries;
+
+namespace llvm {
+
+class BranchProbabilityInfo;
+class Function;
+class Loop;
+class LoopInfo;
+class MachineBasicBlock;
+class MachineBranchProbabilityInfo;
+class MachineFunction;
+class MachineLoop;
+class MachineLoopInfo;
+
+namespace bfi_detail {
+
+struct IrreducibleGraph;
+
+// This is part of a workaround for a GCC 4.7 crash on lambdas.
+template <class BT> struct BlockEdgesAdder;
+
+/// Mass of a block.
+///
+/// This class implements a sort of fixed-point fraction always between 0.0 and
+/// 1.0.  getMass() == std::numeric_limits<uint64_t>::max() indicates a value of
+/// 1.0.
+///
+/// Masses can be added and subtracted.  Simple saturation arithmetic is used,
+/// so arithmetic operations never overflow or underflow.
+///
+/// Masses can be multiplied.  Multiplication treats full mass as 1.0 and uses
+/// an inexpensive floating-point algorithm that's off-by-one (almost, but not
+/// quite, maximum precision).
+///
+/// Masses can be scaled by \a BranchProbability at maximum precision.
+class BlockMass {
+  uint64_t Mass = 0;
+
+public:
+  BlockMass() = default;
+  explicit BlockMass(uint64_t Mass) : Mass(Mass) {}
+
+  static BlockMass getEmpty() { return BlockMass(); }
+
+  static BlockMass getFull() {
+    return BlockMass(std::numeric_limits<uint64_t>::max());
+  }
+
+  uint64_t getMass() const { return Mass; }
+
+  bool isFull() const { return Mass == std::numeric_limits<uint64_t>::max(); }
+  bool isEmpty() const { return !Mass; }
+
+  bool operator!() const { return isEmpty(); }
+
+  /// Add another mass.
+  ///
+  /// Adds another mass, saturating at \a isFull() rather than overflowing.
+  BlockMass &operator+=(BlockMass X) {
+    uint64_t Sum = Mass + X.Mass;
+    Mass = Sum < Mass ? std::numeric_limits<uint64_t>::max() : Sum;
+    return *this;
+  }
+
+  /// Subtract another mass.
+  ///
+  /// Subtracts another mass, saturating at \a isEmpty() rather than
+  /// undeflowing.
+  BlockMass &operator-=(BlockMass X) {
+    uint64_t Diff = Mass - X.Mass;
+    Mass = Diff > Mass ? 0 : Diff;
+    return *this;
+  }
+
+  BlockMass &operator*=(BranchProbability P) {
+    Mass = P.scale(Mass);
+    return *this;
+  }
+
+  bool operator==(BlockMass X) const { return Mass == X.Mass; }
+  bool operator!=(BlockMass X) const { return Mass != X.Mass; }
+  bool operator<=(BlockMass X) const { return Mass <= X.Mass; }
+  bool operator>=(BlockMass X) const { return Mass >= X.Mass; }
+  bool operator<(BlockMass X) const { return Mass < X.Mass; }
+  bool operator>(BlockMass X) const { return Mass > X.Mass; }
+
+  /// Convert to scaled number.
+  ///
+  /// Convert to \a ScaledNumber.  \a isFull() gives 1.0, while \a isEmpty()
+  /// gives slightly above 0.0.
+  ScaledNumber<uint64_t> toScaled() const;
+
+  void dump() const;
+  raw_ostream &print(raw_ostream &OS) const;
+};
+
+inline BlockMass operator+(BlockMass L, BlockMass R) {
+  return BlockMass(L) += R;
+}
+inline BlockMass operator-(BlockMass L, BlockMass R) {
+  return BlockMass(L) -= R;
+}
+inline BlockMass operator*(BlockMass L, BranchProbability R) {
+  return BlockMass(L) *= R;
+}
+inline BlockMass operator*(BranchProbability L, BlockMass R) {
+  return BlockMass(R) *= L;
+}
+
+inline raw_ostream &operator<<(raw_ostream &OS, BlockMass X) {
+  return X.print(OS);
+}
+
+} // end namespace bfi_detail
+
+/// Base class for BlockFrequencyInfoImpl
+///
+/// BlockFrequencyInfoImplBase has supporting data structures and some
+/// algorithms for BlockFrequencyInfoImplBase.  Only algorithms that depend on
+/// the block type (or that call such algorithms) are skipped here.
+///
+/// Nevertheless, the majority of the overall algorithm documentation lives with
+/// BlockFrequencyInfoImpl.  See there for details.
+class BlockFrequencyInfoImplBase {
+public:
+  using Scaled64 = ScaledNumber<uint64_t>;
+  using BlockMass = bfi_detail::BlockMass;
+
+  /// Representative of a block.
+  ///
+  /// This is a simple wrapper around an index into the reverse-post-order
+  /// traversal of the blocks.
+  ///
+  /// Unlike a block pointer, its order has meaning (location in the
+  /// topological sort) and it's class is the same regardless of block type.
+  struct BlockNode {
+    using IndexType = uint32_t;
+
+    IndexType Index;
+
+    BlockNode() : Index(std::numeric_limits<uint32_t>::max()) {}
+    BlockNode(IndexType Index) : Index(Index) {}
+
+    bool operator==(const BlockNode &X) const { return Index == X.Index; }
+    bool operator!=(const BlockNode &X) const { return Index != X.Index; }
+    bool operator<=(const BlockNode &X) const { return Index <= X.Index; }
+    bool operator>=(const BlockNode &X) const { return Index >= X.Index; }
+    bool operator<(const BlockNode &X) const { return Index < X.Index; }
+    bool operator>(const BlockNode &X) const { return Index > X.Index; }
+
+    bool isValid() const { return Index <= getMaxIndex(); }
+
+    static size_t getMaxIndex() {
+       return std::numeric_limits<uint32_t>::max() - 1;
+    }
+  };
+
+  /// Stats about a block itself.
+  struct FrequencyData {
+    Scaled64 Scaled;
+    uint64_t Integer;
+  };
+
+  /// Data about a loop.
+  ///
+  /// Contains the data necessary to represent a loop as a pseudo-node once it's
+  /// packaged.
+  struct LoopData {
+    using ExitMap = SmallVector<std::pair<BlockNode, BlockMass>, 4>;
+    using NodeList = SmallVector<BlockNode, 4>;
+    using HeaderMassList = SmallVector<BlockMass, 1>;
+
+    LoopData *Parent;            ///< The parent loop.
+    bool IsPackaged = false;     ///< Whether this has been packaged.
+    uint32_t NumHeaders = 1;     ///< Number of headers.
+    ExitMap Exits;               ///< Successor edges (and weights).
+    NodeList Nodes;              ///< Header and the members of the loop.
+    HeaderMassList BackedgeMass; ///< Mass returned to each loop header.
+    BlockMass Mass;
+    Scaled64 Scale;
+
+    LoopData(LoopData *Parent, const BlockNode &Header)
+      : Parent(Parent), Nodes(1, Header), BackedgeMass(1) {}
+
+    template <class It1, class It2>
+    LoopData(LoopData *Parent, It1 FirstHeader, It1 LastHeader, It2 FirstOther,
+             It2 LastOther)
+        : Parent(Parent), Nodes(FirstHeader, LastHeader) {
+      NumHeaders = Nodes.size();
+      Nodes.insert(Nodes.end(), FirstOther, LastOther);
+      BackedgeMass.resize(NumHeaders);
+    }
+
+    bool isHeader(const BlockNode &Node) const {
+      if (isIrreducible())
+        return std::binary_search(Nodes.begin(), Nodes.begin() + NumHeaders,
+                                  Node);
+      return Node == Nodes[0];
+    }
+
+    BlockNode getHeader() const { return Nodes[0]; }
+    bool isIrreducible() const { return NumHeaders > 1; }
+
+    HeaderMassList::difference_type getHeaderIndex(const BlockNode &B) {
+      assert(isHeader(B) && "this is only valid on loop header blocks");
+      if (isIrreducible())
+        return std::lower_bound(Nodes.begin(), Nodes.begin() + NumHeaders, B) -
+               Nodes.begin();
+      return 0;
+    }
+
+    NodeList::const_iterator members_begin() const {
+      return Nodes.begin() + NumHeaders;
+    }
+
+    NodeList::const_iterator members_end() const { return Nodes.end(); }
+    iterator_range<NodeList::const_iterator> members() const {
+      return make_range(members_begin(), members_end());
+    }
+  };
+
+  /// Index of loop information.
+  struct WorkingData {
+    BlockNode Node;           ///< This node.
+    LoopData *Loop = nullptr; ///< The loop this block is inside.
+    BlockMass Mass;           ///< Mass distribution from the entry block.
+
+    WorkingData(const BlockNode &Node) : Node(Node) {}
+
+    bool isLoopHeader() const { return Loop && Loop->isHeader(Node); }
+
+    bool isDoubleLoopHeader() const {
+      return isLoopHeader() && Loop->Parent && Loop->Parent->isIrreducible() &&
+             Loop->Parent->isHeader(Node);
+    }
+
+    LoopData *getContainingLoop() const {
+      if (!isLoopHeader())
+        return Loop;
+      if (!isDoubleLoopHeader())
+        return Loop->Parent;
+      return Loop->Parent->Parent;
+    }
+
+    /// Resolve a node to its representative.
+    ///
+    /// Get the node currently representing Node, which could be a containing
+    /// loop.
+    ///
+    /// This function should only be called when distributing mass.  As long as
+    /// there are no irreducible edges to Node, then it will have complexity
+    /// O(1) in this context.
+    ///
+    /// In general, the complexity is O(L), where L is the number of loop
+    /// headers Node has been packaged into.  Since this method is called in
+    /// the context of distributing mass, L will be the number of loop headers
+    /// an early exit edge jumps out of.
+    BlockNode getResolvedNode() const {
+      auto L = getPackagedLoop();
+      return L ? L->getHeader() : Node;
+    }
+
+    LoopData *getPackagedLoop() const {
+      if (!Loop || !Loop->IsPackaged)
+        return nullptr;
+      auto L = Loop;
+      while (L->Parent && L->Parent->IsPackaged)
+        L = L->Parent;
+      return L;
+    }
+
+    /// Get the appropriate mass for a node.
+    ///
+    /// Get appropriate mass for Node.  If Node is a loop-header (whose loop
+    /// has been packaged), returns the mass of its pseudo-node.  If it's a
+    /// node inside a packaged loop, it returns the loop's mass.
+    BlockMass &getMass() {
+      if (!isAPackage())
+        return Mass;
+      if (!isADoublePackage())
+        return Loop->Mass;
+      return Loop->Parent->Mass;
+    }
+
+    /// Has ContainingLoop been packaged up?
+    bool isPackaged() const { return getResolvedNode() != Node; }
+
+    /// Has Loop been packaged up?
+    bool isAPackage() const { return isLoopHeader() && Loop->IsPackaged; }
+
+    /// Has Loop been packaged up twice?
+    bool isADoublePackage() const {
+      return isDoubleLoopHeader() && Loop->Parent->IsPackaged;
+    }
+  };
+
+  /// Unscaled probability weight.
+  ///
+  /// Probability weight for an edge in the graph (including the
+  /// successor/target node).
+  ///
+  /// All edges in the original function are 32-bit.  However, exit edges from
+  /// loop packages are taken from 64-bit exit masses, so we need 64-bits of
+  /// space in general.
+  ///
+  /// In addition to the raw weight amount, Weight stores the type of the edge
+  /// in the current context (i.e., the context of the loop being processed).
+  /// Is this a local edge within the loop, an exit from the loop, or a
+  /// backedge to the loop header?
+  struct Weight {
+    enum DistType { Local, Exit, Backedge };
+    DistType Type = Local;
+    BlockNode TargetNode;
+    uint64_t Amount = 0;
+
+    Weight() = default;
+    Weight(DistType Type, BlockNode TargetNode, uint64_t Amount)
+        : Type(Type), TargetNode(TargetNode), Amount(Amount) {}
+  };
+
+  /// Distribution of unscaled probability weight.
+  ///
+  /// Distribution of unscaled probability weight to a set of successors.
+  ///
+  /// This class collates the successor edge weights for later processing.
+  ///
+  /// \a DidOverflow indicates whether \a Total did overflow while adding to
+  /// the distribution.  It should never overflow twice.
+  struct Distribution {
+    using WeightList = SmallVector<Weight, 4>;
+
+    WeightList Weights;       ///< Individual successor weights.
+    uint64_t Total = 0;       ///< Sum of all weights.
+    bool DidOverflow = false; ///< Whether \a Total did overflow.
+
+    Distribution() = default;
+
+    void addLocal(const BlockNode &Node, uint64_t Amount) {
+      add(Node, Amount, Weight::Local);
+    }
+
+    void addExit(const BlockNode &Node, uint64_t Amount) {
+      add(Node, Amount, Weight::Exit);
+    }
+
+    void addBackedge(const BlockNode &Node, uint64_t Amount) {
+      add(Node, Amount, Weight::Backedge);
+    }
+
+    /// Normalize the distribution.
+    ///
+    /// Combines multiple edges to the same \a Weight::TargetNode and scales
+    /// down so that \a Total fits into 32-bits.
+    ///
+    /// This is linear in the size of \a Weights.  For the vast majority of
+    /// cases, adjacent edge weights are combined by sorting WeightList and
+    /// combining adjacent weights.  However, for very large edge lists an
+    /// auxiliary hash table is used.
+    void normalize();
+
+  private:
+    void add(const BlockNode &Node, uint64_t Amount, Weight::DistType Type);
+  };
+
+  /// Data about each block.  This is used downstream.
+  std::vector<FrequencyData> Freqs;
+
+  /// Whether each block is an irreducible loop header.
+  /// This is used downstream.
+  SparseBitVector<> IsIrrLoopHeader;
+
+  /// Loop data: see initializeLoops().
+  std::vector<WorkingData> Working;
+
+  /// Indexed information about loops.
+  std::list<LoopData> Loops;
+
+  /// Virtual destructor.
+  ///
+  /// Need a virtual destructor to mask the compiler warning about
+  /// getBlockName().
+  virtual ~BlockFrequencyInfoImplBase() = default;
+
+  /// Add all edges out of a packaged loop to the distribution.
+  ///
+  /// Adds all edges from LocalLoopHead to Dist.  Calls addToDist() to add each
+  /// successor edge.
+  ///
+  /// \return \c true unless there's an irreducible backedge.
+  bool addLoopSuccessorsToDist(const LoopData *OuterLoop, LoopData &Loop,
+                               Distribution &Dist);
+
+  /// Add an edge to the distribution.
+  ///
+  /// Adds an edge to Succ to Dist.  If \c LoopHead.isValid(), then whether the
+  /// edge is local/exit/backedge is in the context of LoopHead.  Otherwise,
+  /// every edge should be a local edge (since all the loops are packaged up).
+  ///
+  /// \return \c true unless aborted due to an irreducible backedge.
+  bool addToDist(Distribution &Dist, const LoopData *OuterLoop,
+                 const BlockNode &Pred, const BlockNode &Succ, uint64_t Weight);
+
+  LoopData &getLoopPackage(const BlockNode &Head) {
+    assert(Head.Index < Working.size());
+    assert(Working[Head.Index].isLoopHeader());
+    return *Working[Head.Index].Loop;
+  }
+
+  /// Analyze irreducible SCCs.
+  ///
+  /// Separate irreducible SCCs from \c G, which is an explicit graph of \c
+  /// OuterLoop (or the top-level function, if \c OuterLoop is \c nullptr).
+  /// Insert them into \a Loops before \c Insert.
+  ///
+  /// \return the \c LoopData nodes representing the irreducible SCCs.
+  iterator_range<std::list<LoopData>::iterator>
+  analyzeIrreducible(const bfi_detail::IrreducibleGraph &G, LoopData *OuterLoop,
+                     std::list<LoopData>::iterator Insert);
+
+  /// Update a loop after packaging irreducible SCCs inside of it.
+  ///
+  /// Update \c OuterLoop.  Before finding irreducible control flow, it was
+  /// partway through \a computeMassInLoop(), so \a LoopData::Exits and \a
+  /// LoopData::BackedgeMass need to be reset.  Also, nodes that were packaged
+  /// up need to be removed from \a OuterLoop::Nodes.
+  void updateLoopWithIrreducible(LoopData &OuterLoop);
+
+  /// Distribute mass according to a distribution.
+  ///
+  /// Distributes the mass in Source according to Dist.  If LoopHead.isValid(),
+  /// backedges and exits are stored in its entry in Loops.
+  ///
+  /// Mass is distributed in parallel from two copies of the source mass.
+  void distributeMass(const BlockNode &Source, LoopData *OuterLoop,
+                      Distribution &Dist);
+
+  /// Compute the loop scale for a loop.
+  void computeLoopScale(LoopData &Loop);
+
+  /// Adjust the mass of all headers in an irreducible loop.
+  ///
+  /// Initially, irreducible loops are assumed to distribute their mass
+  /// equally among its headers. This can lead to wrong frequency estimates
+  /// since some headers may be executed more frequently than others.
+  ///
+  /// This adjusts header mass distribution so it matches the weights of
+  /// the backedges going into each of the loop headers.
+  void adjustLoopHeaderMass(LoopData &Loop);
+
+  void distributeIrrLoopHeaderMass(Distribution &Dist);
+
+  /// Package up a loop.
+  void packageLoop(LoopData &Loop);
+
+  /// Unwrap loops.
+  void unwrapLoops();
+
+  /// Finalize frequency metrics.
+  ///
+  /// Calculates final frequencies and cleans up no-longer-needed data
+  /// structures.
+  void finalizeMetrics();
+
+  /// Clear all memory.
+  void clear();
+
+  virtual std::string getBlockName(const BlockNode &Node) const;
+  std::string getLoopName(const LoopData &Loop) const;
+
+  virtual raw_ostream &print(raw_ostream &OS) const { return OS; }
+  void dump() const { print(dbgs()); }
+
+  Scaled64 getFloatingBlockFreq(const BlockNode &Node) const;
+
+  BlockFrequency getBlockFreq(const BlockNode &Node) const;
+  Optional<uint64_t> getBlockProfileCount(const Function &F,
+                                          const BlockNode &Node,
+                                          bool AllowSynthetic = false) const;
+  Optional<uint64_t> getProfileCountFromFreq(const Function &F,
+                                             uint64_t Freq,
+                                             bool AllowSynthetic = false) const;
+  bool isIrrLoopHeader(const BlockNode &Node);
+
+  void 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;
+
+  uint64_t getEntryFreq() const {
+    assert(!Freqs.empty());
+    return Freqs[0].Integer;
+  }
+};
+
+namespace bfi_detail {
+
+template <class BlockT> struct TypeMap {};
+template <> struct TypeMap<BasicBlock> {
+  using BlockT = BasicBlock;
+  using BlockKeyT = AssertingVH<const BasicBlock>;
+  using FunctionT = Function;
+  using BranchProbabilityInfoT = BranchProbabilityInfo;
+  using LoopT = Loop;
+  using LoopInfoT = LoopInfo;
+};
+template <> struct TypeMap<MachineBasicBlock> {
+  using BlockT = MachineBasicBlock;
+  using BlockKeyT = const MachineBasicBlock *;
+  using FunctionT = MachineFunction;
+  using BranchProbabilityInfoT = MachineBranchProbabilityInfo;
+  using LoopT = MachineLoop;
+  using LoopInfoT = MachineLoopInfo;
+};
+
+template <class BlockT, class BFIImplT>
+class BFICallbackVH;
+
+/// Get the name of a MachineBasicBlock.
+///
+/// Get the name of a MachineBasicBlock.  It's templated so that including from
+/// CodeGen is unnecessary (that would be a layering issue).
+///
+/// This is used mainly for debug output.  The name is similar to
+/// MachineBasicBlock::getFullName(), but skips the name of the function.
+template <class BlockT> std::string getBlockName(const BlockT *BB) {
+  assert(BB && "Unexpected nullptr");
+  auto MachineName = "BB" + Twine(BB->getNumber());
+  if (BB->getBasicBlock())
+    return (MachineName + "[" + BB->getName() + "]").str();
+  return MachineName.str();
+}
+/// Get the name of a BasicBlock.
+template <> inline std::string getBlockName(const BasicBlock *BB) {
+  assert(BB && "Unexpected nullptr");
+  return BB->getName().str();
+}
+
+/// Graph of irreducible control flow.
+///
+/// This graph is used for determining the SCCs in a loop (or top-level
+/// function) that has irreducible control flow.
+///
+/// During the block frequency algorithm, the local graphs are defined in a
+/// light-weight way, deferring to the \a BasicBlock or \a MachineBasicBlock
+/// graphs for most edges, but getting others from \a LoopData::ExitMap.  The
+/// latter only has successor information.
+///
+/// \a IrreducibleGraph makes this graph explicit.  It's in a form that can use
+/// \a GraphTraits (so that \a analyzeIrreducible() can use \a scc_iterator),
+/// and it explicitly lists predecessors and successors.  The initialization
+/// that relies on \c MachineBasicBlock is defined in the header.
+struct IrreducibleGraph {
+  using BFIBase = BlockFrequencyInfoImplBase;
+
+  BFIBase &BFI;
+
+  using BlockNode = BFIBase::BlockNode;
+  struct IrrNode {
+    BlockNode Node;
+    unsigned NumIn = 0;
+    std::deque<const IrrNode *> Edges;
+
+    IrrNode(const BlockNode &Node) : Node(Node) {}
+
+    using iterator = std::deque<const IrrNode *>::const_iterator;
+
+    iterator pred_begin() const { return Edges.begin(); }
+    iterator succ_begin() const { return Edges.begin() + NumIn; }
+    iterator pred_end() const { return succ_begin(); }
+    iterator succ_end() const { return Edges.end(); }
+  };
+  BlockNode Start;
+  const IrrNode *StartIrr = nullptr;
+  std::vector<IrrNode> Nodes;
+  SmallDenseMap<uint32_t, IrrNode *, 4> Lookup;
+
+  /// Construct an explicit graph containing irreducible control flow.
+  ///
+  /// Construct an explicit graph of the control flow in \c OuterLoop (or the
+  /// top-level function, if \c OuterLoop is \c nullptr).  Uses \c
+  /// addBlockEdges to add block successors that have not been packaged into
+  /// loops.
+  ///
+  /// \a BlockFrequencyInfoImpl::computeIrreducibleMass() is the only expected
+  /// user of this.
+  template <class BlockEdgesAdder>
+  IrreducibleGraph(BFIBase &BFI, const BFIBase::LoopData *OuterLoop,
+                   BlockEdgesAdder addBlockEdges) : BFI(BFI) {
+    initialize(OuterLoop, addBlockEdges);
+  }
+
+  template <class BlockEdgesAdder>
+  void initialize(const BFIBase::LoopData *OuterLoop,
+                  BlockEdgesAdder addBlockEdges);
+  void addNodesInLoop(const BFIBase::LoopData &OuterLoop);
+  void addNodesInFunction();
+
+  void addNode(const BlockNode &Node) {
+    Nodes.emplace_back(Node);
+    BFI.Working[Node.Index].getMass() = BlockMass::getEmpty();
+  }
+
+  void indexNodes();
+  template <class BlockEdgesAdder>
+  void addEdges(const BlockNode &Node, const BFIBase::LoopData *OuterLoop,
+                BlockEdgesAdder addBlockEdges);
+  void addEdge(IrrNode &Irr, const BlockNode &Succ,
+               const BFIBase::LoopData *OuterLoop);
+};
+
+template <class BlockEdgesAdder>
+void IrreducibleGraph::initialize(const BFIBase::LoopData *OuterLoop,
+                                  BlockEdgesAdder addBlockEdges) {
+  if (OuterLoop) {
+    addNodesInLoop(*OuterLoop);
+    for (auto N : OuterLoop->Nodes)
+      addEdges(N, OuterLoop, addBlockEdges);
+  } else {
+    addNodesInFunction();
+    for (uint32_t Index = 0; Index < BFI.Working.size(); ++Index)
+      addEdges(Index, OuterLoop, addBlockEdges);
+  }
+  StartIrr = Lookup[Start.Index];
+}
+
+template <class BlockEdgesAdder>
+void IrreducibleGraph::addEdges(const BlockNode &Node,
+                                const BFIBase::LoopData *OuterLoop,
+                                BlockEdgesAdder addBlockEdges) {
+  auto L = Lookup.find(Node.Index);
+  if (L == Lookup.end())
+    return;
+  IrrNode &Irr = *L->second;
+  const auto &Working = BFI.Working[Node.Index];
+
+  if (Working.isAPackage())
+    for (const auto &I : Working.Loop->Exits)
+      addEdge(Irr, I.first, OuterLoop);
+  else
+    addBlockEdges(*this, Irr, OuterLoop);
+}
+
+} // end namespace bfi_detail
+
+/// Shared implementation for block frequency analysis.
+///
+/// This is a shared implementation of BlockFrequencyInfo and
+/// MachineBlockFrequencyInfo, and calculates the relative frequencies of
+/// blocks.
+///
+/// LoopInfo defines a loop as a "non-trivial" SCC dominated by a single block,
+/// which is called the header.  A given loop, L, can have sub-loops, which are
+/// loops within the subgraph of L that exclude its header.  (A "trivial" SCC
+/// consists of a single block that does not have a self-edge.)
+///
+/// In addition to loops, this algorithm has limited support for irreducible
+/// SCCs, which are SCCs with multiple entry blocks.  Irreducible SCCs are
+/// discovered on the fly, and modelled as loops with multiple headers.
+///
+/// The headers of irreducible sub-SCCs consist of its entry blocks and all
+/// nodes that are targets of a backedge within it (excluding backedges within
+/// true sub-loops).  Block frequency calculations act as if a block is
+/// inserted that intercepts all the edges to the headers.  All backedges and
+/// entries point to this block.  Its successors are the headers, which split
+/// the frequency evenly.
+///
+/// This algorithm leverages BlockMass and ScaledNumber to maintain precision,
+/// separates mass distribution from loop scaling, and dithers to eliminate
+/// probability mass loss.
+///
+/// The implementation is split between BlockFrequencyInfoImpl, which knows the
+/// type of graph being modelled (BasicBlock vs. MachineBasicBlock), and
+/// BlockFrequencyInfoImplBase, which doesn't.  The base class uses \a
+/// BlockNode, a wrapper around a uint32_t.  BlockNode is numbered from 0 in
+/// reverse-post order.  This gives two advantages:  it's easy to compare the
+/// relative ordering of two nodes, and maps keyed on BlockT can be represented
+/// by vectors.
+///
+/// This algorithm is O(V+E), unless there is irreducible control flow, in
+/// which case it's O(V*E) in the worst case.
+///
+/// These are the main stages:
+///
+///  0. Reverse post-order traversal (\a initializeRPOT()).
+///
+///     Run a single post-order traversal and save it (in reverse) in RPOT.
+///     All other stages make use of this ordering.  Save a lookup from BlockT
+///     to BlockNode (the index into RPOT) in Nodes.
+///
+///  1. Loop initialization (\a initializeLoops()).
+///
+///     Translate LoopInfo/MachineLoopInfo into a form suitable for the rest of
+///     the algorithm.  In particular, store the immediate members of each loop
+///     in reverse post-order.
+///
+///  2. Calculate mass and scale in loops (\a computeMassInLoops()).
+///
+///     For each loop (bottom-up), distribute mass through the DAG resulting
+///     from ignoring backedges and treating sub-loops as a single pseudo-node.
+///     Track the backedge mass distributed to the loop header, and use it to
+///     calculate the loop scale (number of loop iterations).  Immediate
+///     members that represent sub-loops will already have been visited and
+///     packaged into a pseudo-node.
+///
+///     Distributing mass in a loop is a reverse-post-order traversal through
+///     the loop.  Start by assigning full mass to the Loop header.  For each
+///     node in the loop:
+///
+///         - Fetch and categorize the weight distribution for its successors.
+///           If this is a packaged-subloop, the weight distribution is stored
+///           in \a LoopData::Exits.  Otherwise, fetch it from
+///           BranchProbabilityInfo.
+///
+///         - Each successor is categorized as \a Weight::Local, a local edge
+///           within the current loop, \a Weight::Backedge, a backedge to the
+///           loop header, or \a Weight::Exit, any successor outside the loop.
+///           The weight, the successor, and its category are stored in \a
+///           Distribution.  There can be multiple edges to each successor.
+///
+///         - If there's a backedge to a non-header, there's an irreducible SCC.
+///           The usual flow is temporarily aborted.  \a
+///           computeIrreducibleMass() finds the irreducible SCCs within the
+///           loop, packages them up, and restarts the flow.
+///
+///         - Normalize the distribution:  scale weights down so that their sum
+///           is 32-bits, and coalesce multiple edges to the same node.
+///
+///         - Distribute the mass accordingly, dithering to minimize mass loss,
+///           as described in \a distributeMass().
+///
+///     In the case of irreducible loops, instead of a single loop header,
+///     there will be several. The computation of backedge masses is similar
+///     but instead of having a single backedge mass, there will be one
+///     backedge per loop header. In these cases, each backedge will carry
+///     a mass proportional to the edge weights along the corresponding
+///     path.
+///
+///     At the end of propagation, the full mass assigned to the loop will be
+///     distributed among the loop headers proportionally according to the
+///     mass flowing through their backedges.
+///
+///     Finally, calculate the loop scale from the accumulated backedge mass.
+///
+///  3. Distribute mass in the function (\a computeMassInFunction()).
+///
+///     Finally, distribute mass through the DAG resulting from packaging all
+///     loops in the function.  This uses the same algorithm as distributing
+///     mass in a loop, except that there are no exit or backedge edges.
+///
+///  4. Unpackage loops (\a unwrapLoops()).
+///
+///     Initialize each block's frequency to a floating point representation of
+///     its mass.
+///
+///     Visit loops top-down, scaling the frequencies of its immediate members
+///     by the loop's pseudo-node's frequency.
+///
+///  5. Convert frequencies to a 64-bit range (\a finalizeMetrics()).
+///
+///     Using the min and max frequencies as a guide, translate floating point
+///     frequencies to an appropriate range in uint64_t.
+///
+/// It has some known flaws.
+///
+///   - The model of irreducible control flow is a rough approximation.
+///
+///     Modelling irreducible control flow exactly involves setting up and
+///     solving a group of infinite geometric series.  Such precision is
+///     unlikely to be worthwhile, since most of our algorithms give up on
+///     irreducible control flow anyway.
+///
+///     Nevertheless, we might find that we need to get closer.  Here's a sort
+///     of TODO list for the model with diminishing returns, to be completed as
+///     necessary.
+///
+///       - The headers for the \a LoopData representing an irreducible SCC
+///         include non-entry blocks.  When these extra blocks exist, they
+///         indicate a self-contained irreducible sub-SCC.  We could treat them
+///         as sub-loops, rather than arbitrarily shoving the problematic
+///         blocks into the headers of the main irreducible SCC.
+///
+///       - Entry frequencies are assumed to be evenly split between the
+///         headers of a given irreducible SCC, which is the only option if we
+///         need to compute mass in the SCC before its parent loop.  Instead,
+///         we could partially compute mass in the parent loop, and stop when
+///         we get to the SCC.  Here, we have the correct ratio of entry
+///         masses, which we can use to adjust their relative frequencies.
+///         Compute mass in the SCC, and then continue propagation in the
+///         parent.
+///
+///       - We can propagate mass iteratively through the SCC, for some fixed
+///         number of iterations.  Each iteration starts by assigning the entry
+///         blocks their backedge mass from the prior iteration.  The final
+///         mass for each block (and each exit, and the total backedge mass
+///         used for computing loop scale) is the sum of all iterations.
+///         (Running this until fixed point would "solve" the geometric
+///         series by simulation.)
+template <class BT> class BlockFrequencyInfoImpl : BlockFrequencyInfoImplBase {
+  // This is part of a workaround for a GCC 4.7 crash on lambdas.
+  friend struct bfi_detail::BlockEdgesAdder<BT>;
+
+  using BlockT = typename bfi_detail::TypeMap<BT>::BlockT;
+  using BlockKeyT = typename bfi_detail::TypeMap<BT>::BlockKeyT;
+  using FunctionT = typename bfi_detail::TypeMap<BT>::FunctionT;
+  using BranchProbabilityInfoT =
+      typename bfi_detail::TypeMap<BT>::BranchProbabilityInfoT;
+  using LoopT = typename bfi_detail::TypeMap<BT>::LoopT;
+  using LoopInfoT = typename bfi_detail::TypeMap<BT>::LoopInfoT;
+  using Successor = GraphTraits<const BlockT *>;
+  using Predecessor = GraphTraits<Inverse<const BlockT *>>;
+  using BFICallbackVH =
+      bfi_detail::BFICallbackVH<BlockT, BlockFrequencyInfoImpl>;
+
+  const BranchProbabilityInfoT *BPI = nullptr;
+  const LoopInfoT *LI = nullptr;
+  const FunctionT *F = nullptr;
+
+  // All blocks in reverse postorder.
+  std::vector<const BlockT *> RPOT;
+  DenseMap<BlockKeyT, std::pair<BlockNode, BFICallbackVH>> Nodes;
+
+  using rpot_iterator = typename std::vector<const BlockT *>::const_iterator;
+
+  rpot_iterator rpot_begin() const { return RPOT.begin(); }
+  rpot_iterator rpot_end() const { return RPOT.end(); }
+
+  size_t getIndex(const rpot_iterator &I) const { return I - rpot_begin(); }
+
+  BlockNode getNode(const rpot_iterator &I) const {
+    return BlockNode(getIndex(I));
+  }
+
+  BlockNode getNode(const BlockT *BB) const { return Nodes.lookup(BB).first; }
+
+  const BlockT *getBlock(const BlockNode &Node) const {
+    assert(Node.Index < RPOT.size());
+    return RPOT[Node.Index];
+  }
+
+  /// Run (and save) a post-order traversal.
+  ///
+  /// Saves a reverse post-order traversal of all the nodes in \a F.
+  void initializeRPOT();
+
+  /// Initialize loop data.
+  ///
+  /// Build up \a Loops using \a LoopInfo.  \a LoopInfo gives us a mapping from
+  /// each block to the deepest loop it's in, but we need the inverse.  For each
+  /// loop, we store in reverse post-order its "immediate" members, defined as
+  /// the header, the headers of immediate sub-loops, and all other blocks in
+  /// the loop that are not in sub-loops.
+  void initializeLoops();
+
+  /// Propagate to a block's successors.
+  ///
+  /// In the context of distributing mass through \c OuterLoop, divide the mass
+  /// currently assigned to \c Node between its successors.
+  ///
+  /// \return \c true unless there's an irreducible backedge.
+  bool propagateMassToSuccessors(LoopData *OuterLoop, const BlockNode &Node);
+
+  /// Compute mass in a particular loop.
+  ///
+  /// Assign mass to \c Loop's header, and then for each block in \c Loop in
+  /// reverse post-order, distribute mass to its successors.  Only visits nodes
+  /// that have not been packaged into sub-loops.
+  ///
+  /// \pre \a computeMassInLoop() has been called for each subloop of \c Loop.
+  /// \return \c true unless there's an irreducible backedge.
+  bool computeMassInLoop(LoopData &Loop);
+
+  /// Try to compute mass in the top-level function.
+  ///
+  /// Assign mass to the entry block, and then for each block in reverse
+  /// post-order, distribute mass to its successors.  Skips nodes that have
+  /// been packaged into loops.
+  ///
+  /// \pre \a computeMassInLoops() has been called.
+  /// \return \c true unless there's an irreducible backedge.
+  bool tryToComputeMassInFunction();
+
+  /// Compute mass in (and package up) irreducible SCCs.
+  ///
+  /// Find the irreducible SCCs in \c OuterLoop, add them to \a Loops (in front
+  /// of \c Insert), and call \a computeMassInLoop() on each of them.
+  ///
+  /// If \c OuterLoop is \c nullptr, it refers to the top-level function.
+  ///
+  /// \pre \a computeMassInLoop() has been called for each subloop of \c
+  /// OuterLoop.
+  /// \pre \c Insert points at the last loop successfully processed by \a
+  /// computeMassInLoop().
+  /// \pre \c OuterLoop has irreducible SCCs.
+  void computeIrreducibleMass(LoopData *OuterLoop,
+                              std::list<LoopData>::iterator Insert);
+
+  /// Compute mass in all loops.
+  ///
+  /// For each loop bottom-up, call \a computeMassInLoop().
+  ///
+  /// \a computeMassInLoop() aborts (and returns \c false) on loops that
+  /// contain a irreducible sub-SCCs.  Use \a computeIrreducibleMass() and then
+  /// re-enter \a computeMassInLoop().
+  ///
+  /// \post \a computeMassInLoop() has returned \c true for every loop.
+  void computeMassInLoops();
+
+  /// Compute mass in the top-level function.
+  ///
+  /// Uses \a tryToComputeMassInFunction() and \a computeIrreducibleMass() to
+  /// compute mass in the top-level function.
+  ///
+  /// \post \a tryToComputeMassInFunction() has returned \c true.
+  void computeMassInFunction();
+
+  std::string getBlockName(const BlockNode &Node) const override {
+    return bfi_detail::getBlockName(getBlock(Node));
+  }
+
+public:
+  BlockFrequencyInfoImpl() = default;
+
+  const FunctionT *getFunction() const { return F; }
+
+  void calculate(const FunctionT &F, const BranchProbabilityInfoT &BPI,
+                 const LoopInfoT &LI);
+
+  using BlockFrequencyInfoImplBase::getEntryFreq;
+
+  BlockFrequency getBlockFreq(const BlockT *BB) const {
+    return BlockFrequencyInfoImplBase::getBlockFreq(getNode(BB));
+  }
+
+  Optional<uint64_t> getBlockProfileCount(const Function &F,
+                                          const BlockT *BB,
+                                          bool AllowSynthetic = false) const {
+    return BlockFrequencyInfoImplBase::getBlockProfileCount(F, getNode(BB),
+                                                            AllowSynthetic);
+  }
+
+  Optional<uint64_t> getProfileCountFromFreq(const Function &F,
+                                             uint64_t Freq,
+                                             bool AllowSynthetic = false) const {
+    return BlockFrequencyInfoImplBase::getProfileCountFromFreq(F, Freq,
+                                                               AllowSynthetic);
+  }
+
+  bool isIrrLoopHeader(const BlockT *BB) {
+    return BlockFrequencyInfoImplBase::isIrrLoopHeader(getNode(BB));
+  }
+
+  void setBlockFreq(const BlockT *BB, uint64_t Freq);
+
+  void forgetBlock(const BlockT *BB) {
+    // We don't erase corresponding items from `Freqs`, `RPOT` and other to
+    // avoid invalidating indices. Doing so would have saved some memory, but
+    // it's not worth it.
+    Nodes.erase(BB);
+  }
+
+  Scaled64 getFloatingBlockFreq(const BlockT *BB) const {
+    return BlockFrequencyInfoImplBase::getFloatingBlockFreq(getNode(BB));
+  }
+
+  const BranchProbabilityInfoT &getBPI() const { return *BPI; }
+
+  /// Print the frequencies for the current function.
+  ///
+  /// Prints the frequencies for the blocks in the current function.
+  ///
+  /// Blocks are printed in the natural iteration order of the function, rather
+  /// than reverse post-order.  This provides two advantages:  writing -analyze
+  /// tests is easier (since blocks come out in source order), and even
+  /// unreachable blocks are printed.
+  ///
+  /// \a BlockFrequencyInfoImplBase::print() only knows reverse post-order, so
+  /// we need to override it here.
+  raw_ostream &print(raw_ostream &OS) const override;
+
+  using BlockFrequencyInfoImplBase::dump;
+  using BlockFrequencyInfoImplBase::printBlockFreq;
+
+  raw_ostream &printBlockFreq(raw_ostream &OS, const BlockT *BB) const {
+    return BlockFrequencyInfoImplBase::printBlockFreq(OS, getNode(BB));
+  }
+
+  void verifyMatch(BlockFrequencyInfoImpl<BT> &Other) const;
+};
+
+namespace bfi_detail {
+
+template <class BFIImplT>
+class BFICallbackVH<BasicBlock, BFIImplT> : public CallbackVH {
+  BFIImplT *BFIImpl;
+
+public:
+  BFICallbackVH() = default;
+
+  BFICallbackVH(const BasicBlock *BB, BFIImplT *BFIImpl)
+      : CallbackVH(BB), BFIImpl(BFIImpl) {}
+
+  virtual ~BFICallbackVH() = default;
+
+  void deleted() override {
+    BFIImpl->forgetBlock(cast<BasicBlock>(getValPtr()));
+  }
+};
+
+/// Dummy implementation since MachineBasicBlocks aren't Values, so ValueHandles
+/// don't apply to them.
+template <class BFIImplT>
+class BFICallbackVH<MachineBasicBlock, BFIImplT> {
+public:
+  BFICallbackVH() = default;
+  BFICallbackVH(const MachineBasicBlock *, BFIImplT *) {}
+};
+
+} // end namespace bfi_detail
+
+template <class BT>
+void BlockFrequencyInfoImpl<BT>::calculate(const FunctionT &F,
+                                           const BranchProbabilityInfoT &BPI,
+                                           const LoopInfoT &LI) {
+  // Save the parameters.
+  this->BPI = &BPI;
+  this->LI = &LI;
+  this->F = &F;
+
+  // Clean up left-over data structures.
+  BlockFrequencyInfoImplBase::clear();
+  RPOT.clear();
+  Nodes.clear();
+
+  // Initialize.
+  LLVM_DEBUG(dbgs() << "\nblock-frequency: " << F.getName()
+                    << "\n================="
+                    << std::string(F.getName().size(), '=') << "\n");
+  initializeRPOT();
+  initializeLoops();
+
+  // Visit loops in post-order to find the local mass distribution, and then do
+  // the full function.
+  computeMassInLoops();
+  computeMassInFunction();
+  unwrapLoops();
+  finalizeMetrics();
+
+  if (CheckBFIUnknownBlockQueries) {
+    // To detect BFI queries for unknown blocks, add entries for unreachable
+    // blocks, if any. This is to distinguish between known/existing unreachable
+    // blocks and unknown blocks.
+    for (const BlockT &BB : F)
+      if (!Nodes.count(&BB))
+        setBlockFreq(&BB, 0);
+  }
+}
+
+template <class BT>
+void BlockFrequencyInfoImpl<BT>::setBlockFreq(const BlockT *BB, uint64_t Freq) {
+  if (Nodes.count(BB))
+    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, BFICallbackVH(BB, this)};
+    Freqs.emplace_back();
+    BlockFrequencyInfoImplBase::setBlockFreq(NewNode, Freq);
+  }
+}
+
+template <class BT> void BlockFrequencyInfoImpl<BT>::initializeRPOT() {
+  const BlockT *Entry = &F->front();
+  RPOT.reserve(F->size());
+  std::copy(po_begin(Entry), po_end(Entry), std::back_inserter(RPOT));
+  std::reverse(RPOT.begin(), RPOT.end());
+
+  assert(RPOT.size() - 1 <= BlockNode::getMaxIndex() &&
+         "More nodes in function than Block Frequency Info supports");
+
+  LLVM_DEBUG(dbgs() << "reverse-post-order-traversal\n");
+  for (rpot_iterator I = rpot_begin(), E = rpot_end(); I != E; ++I) {
+    BlockNode Node = getNode(I);
+    LLVM_DEBUG(dbgs() << " - " << getIndex(I) << ": " << getBlockName(Node)
+                      << "\n");
+    Nodes[*I] = {Node, BFICallbackVH(*I, this)};
+  }
+
+  Working.reserve(RPOT.size());
+  for (size_t Index = 0; Index < RPOT.size(); ++Index)
+    Working.emplace_back(Index);
+  Freqs.resize(RPOT.size());
+}
+
+template <class BT> void BlockFrequencyInfoImpl<BT>::initializeLoops() {
+  LLVM_DEBUG(dbgs() << "loop-detection\n");
+  if (LI->empty())
+    return;
+
+  // Visit loops top down and assign them an index.
+  std::deque<std::pair<const LoopT *, LoopData *>> Q;
+  for (const LoopT *L : *LI)
+    Q.emplace_back(L, nullptr);
+  while (!Q.empty()) {
+    const LoopT *Loop = Q.front().first;
+    LoopData *Parent = Q.front().second;
+    Q.pop_front();
+
+    BlockNode Header = getNode(Loop->getHeader());
+    assert(Header.isValid());
+
+    Loops.emplace_back(Parent, Header);
+    Working[Header.Index].Loop = &Loops.back();
+    LLVM_DEBUG(dbgs() << " - loop = " << getBlockName(Header) << "\n");
+
+    for (const LoopT *L : *Loop)
+      Q.emplace_back(L, &Loops.back());
+  }
+
+  // Visit nodes in reverse post-order and add them to their deepest containing
+  // loop.
+  for (size_t Index = 0; Index < RPOT.size(); ++Index) {
+    // Loop headers have already been mostly mapped.
+    if (Working[Index].isLoopHeader()) {
+      LoopData *ContainingLoop = Working[Index].getContainingLoop();
+      if (ContainingLoop)
+        ContainingLoop->Nodes.push_back(Index);
+      continue;
+    }
+
+    const LoopT *Loop = LI->getLoopFor(RPOT[Index]);
+    if (!Loop)
+      continue;
+
+    // Add this node to its containing loop's member list.
+    BlockNode Header = getNode(Loop->getHeader());
+    assert(Header.isValid());
+    const auto &HeaderData = Working[Header.Index];
+    assert(HeaderData.isLoopHeader());
+
+    Working[Index].Loop = HeaderData.Loop;
+    HeaderData.Loop->Nodes.push_back(Index);
+    LLVM_DEBUG(dbgs() << " - loop = " << getBlockName(Header)
+                      << ": member = " << getBlockName(Index) << "\n");
+  }
+}
+
+template <class BT> void BlockFrequencyInfoImpl<BT>::computeMassInLoops() {
+  // Visit loops with the deepest first, and the top-level loops last.
+  for (auto L = Loops.rbegin(), E = Loops.rend(); L != E; ++L) {
+    if (computeMassInLoop(*L))
+      continue;
+    auto Next = std::next(L);
+    computeIrreducibleMass(&*L, L.base());
+    L = std::prev(Next);
+    if (computeMassInLoop(*L))
+      continue;
+    llvm_unreachable("unhandled irreducible control flow");
+  }
+}
+
+template <class BT>
+bool BlockFrequencyInfoImpl<BT>::computeMassInLoop(LoopData &Loop) {
+  // Compute mass in loop.
+  LLVM_DEBUG(dbgs() << "compute-mass-in-loop: " << getLoopName(Loop) << "\n");
+
+  if (Loop.isIrreducible()) {
+    LLVM_DEBUG(dbgs() << "isIrreducible = true\n");
+    Distribution Dist;
+    unsigned NumHeadersWithWeight = 0;
+    Optional<uint64_t> MinHeaderWeight;
+    DenseSet<uint32_t> HeadersWithoutWeight;
+    HeadersWithoutWeight.reserve(Loop.NumHeaders);
+    for (uint32_t H = 0; H < Loop.NumHeaders; ++H) {
+      auto &HeaderNode = Loop.Nodes[H];
+      const BlockT *Block = getBlock(HeaderNode);
+      IsIrrLoopHeader.set(Loop.Nodes[H].Index);
+      Optional<uint64_t> HeaderWeight = Block->getIrrLoopHeaderWeight();
+      if (!HeaderWeight) {
+        LLVM_DEBUG(dbgs() << "Missing irr loop header metadata on "
+                          << getBlockName(HeaderNode) << "\n");
+        HeadersWithoutWeight.insert(H);
+        continue;
+      }
+      LLVM_DEBUG(dbgs() << getBlockName(HeaderNode)
+                        << " has irr loop header weight "
+                        << HeaderWeight.getValue() << "\n");
+      NumHeadersWithWeight++;
+      uint64_t HeaderWeightValue = HeaderWeight.getValue();
+      if (!MinHeaderWeight || HeaderWeightValue < MinHeaderWeight)
+        MinHeaderWeight = HeaderWeightValue;
+      if (HeaderWeightValue) {
+        Dist.addLocal(HeaderNode, HeaderWeightValue);
+      }
+    }
+    // As a heuristic, if some headers don't have a weight, give them the
+    // minimum weight seen (not to disrupt the existing trends too much by
+    // using a weight that's in the general range of the other headers' weights,
+    // and the minimum seems to perform better than the average.)
+    // FIXME: better update in the passes that drop the header weight.
+    // If no headers have a weight, give them even weight (use weight 1).
+    if (!MinHeaderWeight)
+      MinHeaderWeight = 1;
+    for (uint32_t H : HeadersWithoutWeight) {
+      auto &HeaderNode = Loop.Nodes[H];
+      assert(!getBlock(HeaderNode)->getIrrLoopHeaderWeight() &&
+             "Shouldn't have a weight metadata");
+      uint64_t MinWeight = MinHeaderWeight.getValue();
+      LLVM_DEBUG(dbgs() << "Giving weight " << MinWeight << " to "
+                        << getBlockName(HeaderNode) << "\n");
+      if (MinWeight)
+        Dist.addLocal(HeaderNode, MinWeight);
+    }
+    distributeIrrLoopHeaderMass(Dist);
+    for (const BlockNode &M : Loop.Nodes)
+      if (!propagateMassToSuccessors(&Loop, M))
+        llvm_unreachable("unhandled irreducible control flow");
+    if (NumHeadersWithWeight == 0)
+      // No headers have a metadata. Adjust header mass.
+      adjustLoopHeaderMass(Loop);
+  } else {
+    Working[Loop.getHeader().Index].getMass() = BlockMass::getFull();
+    if (!propagateMassToSuccessors(&Loop, Loop.getHeader()))
+      llvm_unreachable("irreducible control flow to loop header!?");
+    for (const BlockNode &M : Loop.members())
+      if (!propagateMassToSuccessors(&Loop, M))
+        // Irreducible backedge.
+        return false;
+  }
+
+  computeLoopScale(Loop);
+  packageLoop(Loop);
+  return true;
+}
+
+template <class BT>
+bool BlockFrequencyInfoImpl<BT>::tryToComputeMassInFunction() {
+  // Compute mass in function.
+  LLVM_DEBUG(dbgs() << "compute-mass-in-function\n");
+  assert(!Working.empty() && "no blocks in function");
+  assert(!Working[0].isLoopHeader() && "entry block is a loop header");
+
+  Working[0].getMass() = BlockMass::getFull();
+  for (rpot_iterator I = rpot_begin(), IE = rpot_end(); I != IE; ++I) {
+    // Check for nodes that have been packaged.
+    BlockNode Node = getNode(I);
+    if (Working[Node.Index].isPackaged())
+      continue;
+
+    if (!propagateMassToSuccessors(nullptr, Node))
+      return false;
+  }
+  return true;
+}
+
+template <class BT> void BlockFrequencyInfoImpl<BT>::computeMassInFunction() {
+  if (tryToComputeMassInFunction())
+    return;
+  computeIrreducibleMass(nullptr, Loops.begin());
+  if (tryToComputeMassInFunction())
+    return;
+  llvm_unreachable("unhandled irreducible control flow");
+}
+
+/// \note This should be a lambda, but that crashes GCC 4.7.
+namespace bfi_detail {
+
+template <class BT> struct BlockEdgesAdder {
+  using BlockT = BT;
+  using LoopData = BlockFrequencyInfoImplBase::LoopData;
+  using Successor = GraphTraits<const BlockT *>;
+
+  const BlockFrequencyInfoImpl<BT> &BFI;
+
+  explicit BlockEdgesAdder(const BlockFrequencyInfoImpl<BT> &BFI)
+      : BFI(BFI) {}
+
+  void operator()(IrreducibleGraph &G, IrreducibleGraph::IrrNode &Irr,
+                  const LoopData *OuterLoop) {
+    const BlockT *BB = BFI.RPOT[Irr.Node.Index];
+    for (const auto Succ : children<const BlockT *>(BB))
+      G.addEdge(Irr, BFI.getNode(Succ), OuterLoop);
+  }
+};
+
+} // end namespace bfi_detail
+
+template <class BT>
+void BlockFrequencyInfoImpl<BT>::computeIrreducibleMass(
+    LoopData *OuterLoop, std::list<LoopData>::iterator Insert) {
+  LLVM_DEBUG(dbgs() << "analyze-irreducible-in-";
+             if (OuterLoop) dbgs()
+             << "loop: " << getLoopName(*OuterLoop) << "\n";
+             else dbgs() << "function\n");
+
+  using namespace bfi_detail;
+
+  // Ideally, addBlockEdges() would be declared here as a lambda, but that
+  // crashes GCC 4.7.
+  BlockEdgesAdder<BT> addBlockEdges(*this);
+  IrreducibleGraph G(*this, OuterLoop, addBlockEdges);
+
+  for (auto &L : analyzeIrreducible(G, OuterLoop, Insert))
+    computeMassInLoop(L);
+
+  if (!OuterLoop)
+    return;
+  updateLoopWithIrreducible(*OuterLoop);
+}
+
+// A helper function that converts a branch probability into weight.
+inline uint32_t getWeightFromBranchProb(const BranchProbability Prob) {
+  return Prob.getNumerator();
+}
+
+template <class BT>
+bool
+BlockFrequencyInfoImpl<BT>::propagateMassToSuccessors(LoopData *OuterLoop,
+                                                      const BlockNode &Node) {
+  LLVM_DEBUG(dbgs() << " - node: " << getBlockName(Node) << "\n");
+  // Calculate probability for successors.
+  Distribution Dist;
+  if (auto *Loop = Working[Node.Index].getPackagedLoop()) {
+    assert(Loop != OuterLoop && "Cannot propagate mass in a packaged loop");
+    if (!addLoopSuccessorsToDist(OuterLoop, *Loop, Dist))
+      // Irreducible backedge.
+      return false;
+  } else {
+    const BlockT *BB = getBlock(Node);
+    for (auto SI = GraphTraits<const BlockT *>::child_begin(BB),
+              SE = GraphTraits<const BlockT *>::child_end(BB);
+         SI != SE; ++SI)
+      if (!addToDist(
+              Dist, OuterLoop, Node, getNode(*SI),
+              getWeightFromBranchProb(BPI->getEdgeProbability(BB, SI))))
+        // Irreducible backedge.
+        return false;
+  }
+
+  // Distribute mass to successors, saving exit and backedge data in the
+  // loop header.
+  distributeMass(Node, OuterLoop, Dist);
+  return true;
+}
+
+template <class BT>
+raw_ostream &BlockFrequencyInfoImpl<BT>::print(raw_ostream &OS) const {
+  if (!F)
+    return OS;
+  OS << "block-frequency-info: " << F->getName() << "\n";
+  for (const BlockT &BB : *F) {
+    OS << " - " << bfi_detail::getBlockName(&BB) << ": float = ";
+    getFloatingBlockFreq(&BB).print(OS, 5)
+        << ", int = " << getBlockFreq(&BB).getFrequency();
+    if (Optional<uint64_t> ProfileCount =
+        BlockFrequencyInfoImplBase::getBlockProfileCount(
+            F->getFunction(), getNode(&BB)))
+      OS << ", count = " << ProfileCount.getValue();
+    if (Optional<uint64_t> IrrLoopHeaderWeight =
+        BB.getIrrLoopHeaderWeight())
+      OS << ", irr_loop_header_weight = " << IrrLoopHeaderWeight.getValue();
+    OS << "\n";
+  }
+
+  // Add an extra newline for readability.
+  OS << "\n";
+  return OS;
+}
+
+template <class BT>
+void BlockFrequencyInfoImpl<BT>::verifyMatch(
+    BlockFrequencyInfoImpl<BT> &Other) const {
+  bool Match = true;
+  DenseMap<const BlockT *, BlockNode> ValidNodes;
+  DenseMap<const BlockT *, BlockNode> OtherValidNodes;
+  for (auto &Entry : Nodes) {
+    const BlockT *BB = Entry.first;
+    if (BB) {
+      ValidNodes[BB] = Entry.second.first;
+    }
+  }
+  for (auto &Entry : Other.Nodes) {
+    const BlockT *BB = Entry.first;
+    if (BB) {
+      OtherValidNodes[BB] = Entry.second.first;
+    }
+  }
+  unsigned NumValidNodes = ValidNodes.size();
+  unsigned NumOtherValidNodes = OtherValidNodes.size();
+  if (NumValidNodes != NumOtherValidNodes) {
+    Match = false;
+    dbgs() << "Number of blocks mismatch: " << NumValidNodes << " vs "
+           << NumOtherValidNodes << "\n";
+  } else {
+    for (auto &Entry : ValidNodes) {
+      const BlockT *BB = Entry.first;
+      BlockNode Node = Entry.second;
+      if (OtherValidNodes.count(BB)) {
+        BlockNode OtherNode = OtherValidNodes[BB];
+        const auto &Freq = Freqs[Node.Index];
+        const auto &OtherFreq = Other.Freqs[OtherNode.Index];
+        if (Freq.Integer != OtherFreq.Integer) {
+          Match = false;
+          dbgs() << "Freq mismatch: " << bfi_detail::getBlockName(BB) << " "
+                 << Freq.Integer << " vs " << OtherFreq.Integer << "\n";
+        }
+      } else {
+        Match = false;
+        dbgs() << "Block " << bfi_detail::getBlockName(BB) << " index "
+               << Node.Index << " does not exist in Other.\n";
+      }
+    }
+    // If there's a valid node in OtherValidNodes that's not in ValidNodes,
+    // either the above num check or the check on OtherValidNodes will fail.
+  }
+  if (!Match) {
+    dbgs() << "This\n";
+    print(dbgs());
+    dbgs() << "Other\n";
+    Other.print(dbgs());
+  }
+  assert(Match && "BFI mismatch");
+}
+
+// Graph trait base class for block frequency information graph
+// viewer.
+
+enum GVDAGType { GVDT_None, GVDT_Fraction, GVDT_Integer, GVDT_Count };
+
+template <class BlockFrequencyInfoT, class BranchProbabilityInfoT>
+struct BFIDOTGraphTraitsBase : public DefaultDOTGraphTraits {
+  using GTraits = GraphTraits<BlockFrequencyInfoT *>;
+  using NodeRef = typename GTraits::NodeRef;
+  using EdgeIter = typename GTraits::ChildIteratorType;
+  using NodeIter = typename GTraits::nodes_iterator;
+
+  uint64_t MaxFrequency = 0;
+
+  explicit BFIDOTGraphTraitsBase(bool isSimple = false)
+      : DefaultDOTGraphTraits(isSimple) {}
+
+  static StringRef getGraphName(const BlockFrequencyInfoT *G) {
+    return G->getFunction()->getName();
+  }
+
+  std::string getNodeAttributes(NodeRef Node, const BlockFrequencyInfoT *Graph,
+                                unsigned HotPercentThreshold = 0) {
+    std::string Result;
+    if (!HotPercentThreshold)
+      return Result;
+
+    // Compute MaxFrequency on the fly:
+    if (!MaxFrequency) {
+      for (NodeIter I = GTraits::nodes_begin(Graph),
+                    E = GTraits::nodes_end(Graph);
+           I != E; ++I) {
+        NodeRef N = *I;
+        MaxFrequency =
+            std::max(MaxFrequency, Graph->getBlockFreq(N).getFrequency());
+      }
+    }
+    BlockFrequency Freq = Graph->getBlockFreq(Node);
+    BlockFrequency HotFreq =
+        (BlockFrequency(MaxFrequency) *
+         BranchProbability::getBranchProbability(HotPercentThreshold, 100));
+
+    if (Freq < HotFreq)
+      return Result;
+
+    raw_string_ostream OS(Result);
+    OS << "color=\"red\"";
+    OS.flush();
+    return Result;
+  }
+
+  std::string getNodeLabel(NodeRef Node, const BlockFrequencyInfoT *Graph,
+                           GVDAGType GType, int layout_order = -1) {
+    std::string Result;
+    raw_string_ostream OS(Result);
+
+    if (layout_order != -1)
+      OS << Node->getName() << "[" << layout_order << "] : ";
+    else
+      OS << Node->getName() << " : ";
+    switch (GType) {
+    case GVDT_Fraction:
+      Graph->printBlockFreq(OS, Node);
+      break;
+    case GVDT_Integer:
+      OS << Graph->getBlockFreq(Node).getFrequency();
+      break;
+    case GVDT_Count: {
+      auto Count = Graph->getBlockProfileCount(Node);
+      if (Count)
+        OS << Count.getValue();
+      else
+        OS << "Unknown";
+      break;
+    }
+    case GVDT_None:
+      llvm_unreachable("If we are not supposed to render a graph we should "
+                       "never reach this point.");
+    }
+    return Result;
+  }
+
+  std::string getEdgeAttributes(NodeRef Node, EdgeIter EI,
+                                const BlockFrequencyInfoT *BFI,
+                                const BranchProbabilityInfoT *BPI,
+                                unsigned HotPercentThreshold = 0) {
+    std::string Str;
+    if (!BPI)
+      return Str;
+
+    BranchProbability BP = BPI->getEdgeProbability(Node, EI);
+    uint32_t N = BP.getNumerator();
+    uint32_t D = BP.getDenominator();
+    double Percent = 100.0 * N / D;
+    raw_string_ostream OS(Str);
+    OS << format("label=\"%.1f%%\"", Percent);
+
+    if (HotPercentThreshold) {
+      BlockFrequency EFreq = BFI->getBlockFreq(Node) * BP;
+      BlockFrequency HotFreq = BlockFrequency(MaxFrequency) *
+                               BranchProbability(HotPercentThreshold, 100);
+
+      if (EFreq >= HotFreq) {
+        OS << ",color=\"red\"";
+      }
+    }
+
+    OS.flush();
+    return Str;
+  }
+};
+
+} // end namespace llvm
+
+#undef DEBUG_TYPE
+
+#endif // LLVM_ANALYSIS_BLOCKFREQUENCYINFOIMPL_H
+
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif