1 //===- BranchProbability.h - Branch Probability Wrapper ---------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Definition of BranchProbability shared by IR and Machine Instructions.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_SUPPORT_BRANCHPROBABILITY_H
15 #define LLVM_SUPPORT_BRANCHPROBABILITY_H
17 #include "llvm/Support/DataTypes.h"
24 // This class represents Branch Probability as a non-negative fraction that is
25 // no greater than 1. It uses a fixed-point-like implementation, in which the
26 // denominator is always a constant value (here we use 1<<31 for maximum
28 class BranchProbability {
32 // Denominator, which is a constant value.
33 static const uint32_t D = 1u << 31;
35 // Construct a BranchProbability with only numerator assuming the denominator
36 // is 1<<31. For internal use only.
37 explicit BranchProbability(uint32_t n) : N(n) {}
40 BranchProbability() : N(0) {}
41 BranchProbability(uint32_t Numerator, uint32_t Denominator);
43 bool isZero() const { return N == 0; }
45 static BranchProbability getZero() { return BranchProbability(0); }
46 static BranchProbability getOne() { return BranchProbability(D); }
47 // Create a BranchProbability object with the given numerator and 1<<31
49 static BranchProbability getRaw(uint32_t N) { return BranchProbability(N); }
51 // Normalize given probabilties so that the sum of them becomes approximate
53 template <class ProbabilityList>
54 static void normalizeProbabilities(ProbabilityList &Probs);
56 uint32_t getNumerator() const { return N; }
57 static uint32_t getDenominator() { return D; }
59 // Return (1 - Probability).
60 BranchProbability getCompl() const { return BranchProbability(D - N); }
62 raw_ostream &print(raw_ostream &OS) const;
66 /// \brief Scale a large integer.
68 /// Scales \c Num. Guarantees full precision. Returns the floor of the
71 /// \return \c Num times \c this.
72 uint64_t scale(uint64_t Num) const;
74 /// \brief Scale a large integer by the inverse.
76 /// Scales \c Num by the inverse of \c this. Guarantees full precision.
77 /// Returns the floor of the result.
79 /// \return \c Num divided by \c this.
80 uint64_t scaleByInverse(uint64_t Num) const;
82 BranchProbability &operator+=(BranchProbability RHS);
83 BranchProbability &operator-=(BranchProbability RHS);
84 BranchProbability &operator*=(BranchProbability RHS) {
85 N = (static_cast<uint64_t>(N) * RHS.N + D / 2) / D;
89 BranchProbability operator+(BranchProbability RHS) const {
90 BranchProbability Prob(*this);
94 BranchProbability operator-(BranchProbability RHS) const {
95 BranchProbability Prob(*this);
99 BranchProbability operator*(BranchProbability RHS) const {
100 BranchProbability Prob(*this);
104 bool operator==(BranchProbability RHS) const { return N == RHS.N; }
105 bool operator!=(BranchProbability RHS) const { return !(*this == RHS); }
106 bool operator<(BranchProbability RHS) const { return N < RHS.N; }
107 bool operator>(BranchProbability RHS) const { return RHS < *this; }
108 bool operator<=(BranchProbability RHS) const { return !(RHS < *this); }
109 bool operator>=(BranchProbability RHS) const { return !(*this < RHS); }
112 inline raw_ostream &operator<<(raw_ostream &OS, BranchProbability Prob) {
113 return Prob.print(OS);
116 template <class ProbabilityList>
117 void BranchProbability::normalizeProbabilities(ProbabilityList &Probs) {
119 for (auto Prob : Probs)
122 for (auto &Prob : Probs)
123 Prob.N = (Prob.N * uint64_t(D) + Sum / 2) / Sum;