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+//===--- BranchProbabilityInfo.h - Branch Probability Analysis --*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass is used to evaluate branch probabilties.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
+#define LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/BranchProbability.h"
+
+namespace llvm {
+class LoopInfo;
+class raw_ostream;
+
+/// \brief Analysis pass providing branch probability information.
+///
+/// This is a function analysis pass which provides information on the relative
+/// probabilities of each "edge" in the function's CFG where such an edge is
+/// defined by a pair (PredBlock and an index in the successors). The
+/// probability of an edge from one block is always relative to the
+/// probabilities of other edges from the block. The probabilites of all edges
+/// from a block sum to exactly one (100%).
+/// We use a pair (PredBlock and an index in the successors) to uniquely
+/// identify an edge, since we can have multiple edges from Src to Dst.
+/// As an example, we can have a switch which jumps to Dst with value 0 and
+/// value 10.
+class BranchProbabilityInfo : public FunctionPass {
+public:
+  static char ID;
+
+  BranchProbabilityInfo() : FunctionPass(ID) {
+    initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+  bool runOnFunction(Function &F) override;
+  void print(raw_ostream &OS, const Module *M = nullptr) const override;
+
+  /// \brief Get an edge's probability, relative to other out-edges of the Src.
+  ///
+  /// This routine provides access to the fractional probability between zero
+  /// (0%) and one (100%) of this edge executing, relative to other edges
+  /// leaving the 'Src' block. The returned probability is never zero, and can
+  /// only be one if the source block has only one successor.
+  BranchProbability getEdgeProbability(const BasicBlock *Src,
+                                       unsigned IndexInSuccessors) const;
+
+  /// \brief Get the probability of going from Src to Dst.
+  ///
+  /// It returns the sum of all probabilities for edges from Src to Dst.
+  BranchProbability getEdgeProbability(const BasicBlock *Src,
+                                       const BasicBlock *Dst) const;
+
+  /// \brief Test if an edge is hot relative to other out-edges of the Src.
+  ///
+  /// Check whether this edge out of the source block is 'hot'. We define hot
+  /// as having a relative probability >= 80%.
+  bool isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const;
+
+  /// \brief Retrieve the hot successor of a block if one exists.
+  ///
+  /// Given a basic block, look through its successors and if one exists for
+  /// which \see isEdgeHot would return true, return that successor block.
+  BasicBlock *getHotSucc(BasicBlock *BB) const;
+
+  /// \brief Print an edge's probability.
+  ///
+  /// Retrieves an edge's probability similarly to \see getEdgeProbability, but
+  /// then prints that probability to the provided stream. That stream is then
+  /// returned.
+  raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src,
+                                    const BasicBlock *Dst) const;
+
+  /// \brief Get the raw edge weight calculated for the edge.
+  ///
+  /// This returns the raw edge weight. It is guaranteed to fall between 1 and
+  /// UINT32_MAX. Note that the raw edge weight is not meaningful in isolation.
+  /// This interface should be very carefully, and primarily by routines that
+  /// are updating the analysis by later calling setEdgeWeight.
+  uint32_t getEdgeWeight(const BasicBlock *Src,
+                         unsigned IndexInSuccessors) const;
+
+  /// \brief Get the raw edge weight calculated for the block pair.
+  ///
+  /// This returns the sum of all raw edge weights from Src to Dst.
+  /// It is guaranteed to fall between 1 and UINT32_MAX.
+  uint32_t getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const;
+
+  uint32_t getEdgeWeight(const BasicBlock *Src,
+                         succ_const_iterator Dst) const;
+
+  /// \brief Set the raw edge weight for a given edge.
+  ///
+  /// This allows a pass to explicitly set the edge weight for an edge. It can
+  /// be used when updating the CFG to update and preserve the branch
+  /// probability information. Read the implementation of how these edge
+  /// weights are calculated carefully before using!
+  void setEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors,
+                     uint32_t Weight);
+
+private:
+  // Since we allow duplicate edges from one basic block to another, we use
+  // a pair (PredBlock and an index in the successors) to specify an edge.
+  typedef std::pair<const BasicBlock *, unsigned> Edge;
+
+  // Default weight value. Used when we don't have information about the edge.
+  // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
+  // the successors have a weight yet. But it doesn't make sense when providing
+  // weight to an edge that may have siblings with non-zero weights. This can
+  // be handled various ways, but it's probably fine for an edge with unknown
+  // weight to just "inherit" the non-zero weight of an adjacent successor.
+  static const uint32_t DEFAULT_WEIGHT = 16;
+
+  DenseMap<Edge, uint32_t> Weights;
+
+  /// \brief Handle to the LoopInfo analysis.
+  LoopInfo *LI;
+
+  /// \brief Track the last function we run over for printing.
+  Function *LastF;
+
+  /// \brief Track the set of blocks directly succeeded by a returning block.
+  SmallPtrSet<BasicBlock *, 16> PostDominatedByUnreachable;
+
+  /// \brief Track the set of blocks that always lead to a cold call.
+  SmallPtrSet<BasicBlock *, 16> PostDominatedByColdCall;
+
+  /// \brief Get sum of the block successors' weights.
+  uint32_t getSumForBlock(const BasicBlock *BB) const;
+
+  bool calcUnreachableHeuristics(BasicBlock *BB);
+  bool calcMetadataWeights(BasicBlock *BB);
+  bool calcColdCallHeuristics(BasicBlock *BB);
+  bool calcPointerHeuristics(BasicBlock *BB);
+  bool calcLoopBranchHeuristics(BasicBlock *BB);
+  bool calcZeroHeuristics(BasicBlock *BB);
+  bool calcFloatingPointHeuristics(BasicBlock *BB);
+  bool calcInvokeHeuristics(BasicBlock *BB);
+};
+
+}
+
+#endif