BranchProbability.h

Go to the documentation of this file.

//===- BranchProbability.h - Branch Probability Wrapper ---------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Definition of BranchProbability shared by IR and Machine Instructions.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_BRANCHPROBABILITY_H
#define LLVM_SUPPORT_BRANCHPROBABILITY_H

#include "llvm/Support/DataTypes.h"
#include <cassert>

namespace llvm {

class raw_ostream;

// This class represents Branch Probability as a non-negative fraction.
class BranchProbability {
  // Numerator
  uint32_t N;

  // Denominator
  uint32_t D;

public:
  BranchProbability(uint32_t n, uint32_t d) : N(n), D(d) {
    assert(d > 0 && "Denomiator cannot be 0!");
    assert(n <= d && "Probability cannot be bigger than 1!");
  }

  static BranchProbability getZero() { return BranchProbability(0, 1); }
  static BranchProbability getOne() { return BranchProbability(1, 1); }

  uint32_t getNumerator() const { return N; }
  uint32_t getDenominator() const { return D; }

  // Return (1 - Probability).
  BranchProbability getCompl() const {
    return BranchProbability(D - N, D);
  }

  raw_ostream &print(raw_ostream &OS) const;

  void dump() const;

  /// \brief Scale a large integer.
  ///
  /// Scales \c Num.  Guarantees full precision.  Returns the floor of the
  /// result.
  ///
  /// \return \c Num times \c this.
  uint64_t scale(uint64_t Num) const;

  /// \brief Scale a large integer by the inverse.
  ///
  /// Scales \c Num by the inverse of \c this.  Guarantees full precision.
  /// Returns the floor of the result.
  ///
  /// \return \c Num divided by \c this.
  uint64_t scaleByInverse(uint64_t Num) const;

  bool operator==(BranchProbability RHS) const {
    return (uint64_t)N * RHS.D == (uint64_t)D * RHS.N;
  }
  bool operator!=(BranchProbability RHS) const {
    return !(*this == RHS);
  }
  bool operator<(BranchProbability RHS) const {
    return (uint64_t)N * RHS.D < (uint64_t)D * RHS.N;
  }
  bool operator>(BranchProbability RHS) const { return RHS < *this; }
  bool operator<=(BranchProbability RHS) const { return !(RHS < *this); }
  bool operator>=(BranchProbability RHS) const { return !(*this < RHS); }
};

inline raw_ostream &operator<<(raw_ostream &OS, const BranchProbability &Prob) {
  return Prob.print(OS);
}

}

#endif