LLVM  9.0.0svn
BranchProbability.h
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1 //===- BranchProbability.h - Branch Probability Wrapper ---------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Definition of BranchProbability shared by IR and Machine Instructions.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_SUPPORT_BRANCHPROBABILITY_H
14 #define LLVM_SUPPORT_BRANCHPROBABILITY_H
15 
16 #include "llvm/Support/DataTypes.h"
17 #include <algorithm>
18 #include <cassert>
19 #include <climits>
20 #include <numeric>
21 
22 namespace llvm {
23 
24 class raw_ostream;
25 
26 // This class represents Branch Probability as a non-negative fraction that is
27 // no greater than 1. It uses a fixed-point-like implementation, in which the
28 // denominator is always a constant value (here we use 1<<31 for maximum
29 // precision).
31  // Numerator
32  uint32_t N;
33 
34  // Denominator, which is a constant value.
35  static const uint32_t D = 1u << 31;
36  static const uint32_t UnknownN = UINT32_MAX;
37 
38  // Construct a BranchProbability with only numerator assuming the denominator
39  // is 1<<31. For internal use only.
40  explicit BranchProbability(uint32_t n) : N(n) {}
41 
42 public:
43  BranchProbability() : N(UnknownN) {}
44  BranchProbability(uint32_t Numerator, uint32_t Denominator);
45 
46  bool isZero() const { return N == 0; }
47  bool isUnknown() const { return N == UnknownN; }
48 
50  static BranchProbability getOne() { return BranchProbability(D); }
51  static BranchProbability getUnknown() { return BranchProbability(UnknownN); }
52  // Create a BranchProbability object with the given numerator and 1<<31
53  // as denominator.
55  // Create a BranchProbability object from 64-bit integers.
56  static BranchProbability getBranchProbability(uint64_t Numerator,
57  uint64_t Denominator);
58 
59  // Normalize given probabilties so that the sum of them becomes approximate
60  // one.
61  template <class ProbabilityIter>
62  static void normalizeProbabilities(ProbabilityIter Begin,
63  ProbabilityIter End);
64 
65  uint32_t getNumerator() const { return N; }
66  static uint32_t getDenominator() { return D; }
67 
68  // Return (1 - Probability).
69  BranchProbability getCompl() const { return BranchProbability(D - N); }
70 
71  raw_ostream &print(raw_ostream &OS) const;
72 
73  void dump() const;
74 
75  /// Scale a large integer.
76  ///
77  /// Scales \c Num. Guarantees full precision. Returns the floor of the
78  /// result.
79  ///
80  /// \return \c Num times \c this.
81  uint64_t scale(uint64_t Num) const;
82 
83  /// Scale a large integer by the inverse.
84  ///
85  /// Scales \c Num by the inverse of \c this. Guarantees full precision.
86  /// Returns the floor of the result.
87  ///
88  /// \return \c Num divided by \c this.
89  uint64_t scaleByInverse(uint64_t Num) const;
90 
92  assert(N != UnknownN && RHS.N != UnknownN &&
93  "Unknown probability cannot participate in arithmetics.");
94  // Saturate the result in case of overflow.
95  N = (uint64_t(N) + RHS.N > D) ? D : N + RHS.N;
96  return *this;
97  }
98 
100  assert(N != UnknownN && RHS.N != UnknownN &&
101  "Unknown probability cannot participate in arithmetics.");
102  // Saturate the result in case of underflow.
103  N = N < RHS.N ? 0 : N - RHS.N;
104  return *this;
105  }
106 
108  assert(N != UnknownN && RHS.N != UnknownN &&
109  "Unknown probability cannot participate in arithmetics.");
110  N = (static_cast<uint64_t>(N) * RHS.N + D / 2) / D;
111  return *this;
112  }
113 
115  assert(N != UnknownN &&
116  "Unknown probability cannot participate in arithmetics.");
117  N = (uint64_t(N) * RHS > D) ? D : N * RHS;
118  return *this;
119  }
120 
122  assert(N != UnknownN &&
123  "Unknown probability cannot participate in arithmetics.");
124  assert(RHS > 0 && "The divider cannot be zero.");
125  N /= RHS;
126  return *this;
127  }
128 
130  BranchProbability Prob(*this);
131  Prob += RHS;
132  return Prob;
133  }
134 
136  BranchProbability Prob(*this);
137  Prob -= RHS;
138  return Prob;
139  }
140 
142  BranchProbability Prob(*this);
143  Prob *= RHS;
144  return Prob;
145  }
146 
148  BranchProbability Prob(*this);
149  Prob *= RHS;
150  return Prob;
151  }
152 
154  BranchProbability Prob(*this);
155  Prob /= RHS;
156  return Prob;
157  }
158 
159  bool operator==(BranchProbability RHS) const { return N == RHS.N; }
160  bool operator!=(BranchProbability RHS) const { return !(*this == RHS); }
161 
162  bool operator<(BranchProbability RHS) const {
163  assert(N != UnknownN && RHS.N != UnknownN &&
164  "Unknown probability cannot participate in comparisons.");
165  return N < RHS.N;
166  }
167 
168  bool operator>(BranchProbability RHS) const {
169  assert(N != UnknownN && RHS.N != UnknownN &&
170  "Unknown probability cannot participate in comparisons.");
171  return RHS < *this;
172  }
173 
174  bool operator<=(BranchProbability RHS) const {
175  assert(N != UnknownN && RHS.N != UnknownN &&
176  "Unknown probability cannot participate in comparisons.");
177  return !(RHS < *this);
178  }
179 
180  bool operator>=(BranchProbability RHS) const {
181  assert(N != UnknownN && RHS.N != UnknownN &&
182  "Unknown probability cannot participate in comparisons.");
183  return !(*this < RHS);
184  }
185 };
186 
188  return Prob.print(OS);
189 }
190 
191 template <class ProbabilityIter>
192 void BranchProbability::normalizeProbabilities(ProbabilityIter Begin,
193  ProbabilityIter End) {
194  if (Begin == End)
195  return;
196 
197  unsigned UnknownProbCount = 0;
198  uint64_t Sum = std::accumulate(Begin, End, uint64_t(0),
199  [&](uint64_t S, const BranchProbability &BP) {
200  if (!BP.isUnknown())
201  return S + BP.N;
202  UnknownProbCount++;
203  return S;
204  });
205 
206  if (UnknownProbCount > 0) {
208  // If the sum of all known probabilities is less than one, evenly distribute
209  // the complement of sum to unknown probabilities. Otherwise, set unknown
210  // probabilities to zeros and continue to normalize known probabilities.
212  ProbForUnknown = BranchProbability::getRaw(
213  (BranchProbability::getDenominator() - Sum) / UnknownProbCount);
214 
215  std::replace_if(Begin, End,
216  [](const BranchProbability &BP) { return BP.isUnknown(); },
217  ProbForUnknown);
218 
220  return;
221  }
222 
223  if (Sum == 0) {
224  BranchProbability BP(1, std::distance(Begin, End));
225  std::fill(Begin, End, BP);
226  return;
227  }
228 
229  for (auto I = Begin; I != End; ++I)
230  I->N = (I->N * uint64_t(D) + Sum / 2) / Sum;
231 }
232 
233 }
234 
235 #endif
BranchProbability getCompl() const
bool operator<(BranchProbability RHS) const
This class represents lattice values for constants.
Definition: AllocatorList.h:23
bool operator>(BranchProbability RHS) const
static BranchProbability getRaw(uint32_t N)
static BranchProbability getOne()
BranchProbability operator/(uint32_t RHS) const
BranchProbability operator+(BranchProbability RHS) const
uint64_t scaleByInverse(uint64_t Num) const
Scale a large integer by the inverse.
BranchProbability operator*(uint32_t RHS) const
static void normalizeProbabilities(ProbabilityIter Begin, ProbabilityIter End)
BranchProbability & operator+=(BranchProbability RHS)
bool operator==(BranchProbability RHS) const
bool operator<=(BranchProbability RHS) const
static BranchProbability getUnknown()
static uint32_t getDenominator()
static BranchProbability getBranchProbability(uint64_t Numerator, uint64_t Denominator)
uint64_t scale(uint64_t Num) const
Scale a large integer.
BranchProbability & operator-=(BranchProbability RHS)
BranchProbability & operator/=(uint32_t RHS)
#define I(x, y, z)
Definition: MD5.cpp:58
BranchProbability operator-(BranchProbability RHS) const
bool operator>=(BranchProbability RHS) const
BranchProbability & operator*=(uint32_t RHS)
raw_ostream & operator<<(raw_ostream &OS, const APInt &I)
Definition: APInt.h:2038
BranchProbability & operator*=(BranchProbability RHS)
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
raw_ostream & print(raw_ostream &OS) const
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:45
static BranchProbability getZero()
BranchProbability operator*(BranchProbability RHS) const
bool operator!=(BranchProbability RHS) const
uint32_t getNumerator() const