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| //===- BranchProbability.h - Branch Probability Wrapper ---------*- 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
//
//===----------------------------------------------------------------------===//
//
// 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 <algorithm>
#include <cassert>
#include <climits>
#include <numeric>
namespace llvm {
class raw_ostream;
// This class represents Branch Probability as a non-negative fraction that is
// no greater than 1. It uses a fixed-point-like implementation, in which the
// denominator is always a constant value (here we use 1<<31 for maximum
// precision).
class BranchProbability {
// Numerator
uint32_t N;
// Denominator, which is a constant value.
static const uint32_t D = 1u << 31;
static const uint32_t UnknownN = UINT32_MAX;
// Construct a BranchProbability with only numerator assuming the denominator
// is 1<<31. For internal use only.
explicit BranchProbability(uint32_t n) : N(n) {}
public:
BranchProbability() : N(UnknownN) {}
BranchProbability(uint32_t Numerator, uint32_t Denominator);
bool isZero() const { return N == 0; }
bool isUnknown() const { return N == UnknownN; }
static BranchProbability getZero() { return BranchProbability(0); }
static BranchProbability getOne() { return BranchProbability(D); }
static BranchProbability getUnknown() { return BranchProbability(UnknownN); }
// Create a BranchProbability object with the given numerator and 1<<31
// as denominator.
static BranchProbability getRaw(uint32_t N) { return BranchProbability(N); }
// Create a BranchProbability object from 64-bit integers.
static BranchProbability getBranchProbability(uint64_t Numerator,
uint64_t Denominator);
// Normalize given probabilties so that the sum of them becomes approximate
// one.
template <class ProbabilityIter>
static void normalizeProbabilities(ProbabilityIter Begin,
ProbabilityIter End);
uint32_t getNumerator() const { return N; }
static uint32_t getDenominator() { return D; }
// Return (1 - Probability).
BranchProbability getCompl() const { return BranchProbability(D - N); }
raw_ostream &print(raw_ostream &OS) const;
void dump() const;
/// 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;
/// 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;
BranchProbability &operator+=(BranchProbability RHS) {
assert(N != UnknownN && RHS.N != UnknownN &&
"Unknown probability cannot participate in arithmetics.");
// Saturate the result in case of overflow.
N = (uint64_t(N) + RHS.N > D) ? D : N + RHS.N;
return *this;
}
BranchProbability &operator-=(BranchProbability RHS) {
assert(N != UnknownN && RHS.N != UnknownN &&
"Unknown probability cannot participate in arithmetics.");
// Saturate the result in case of underflow.
N = N < RHS.N ? 0 : N - RHS.N;
return *this;
}
BranchProbability &operator*=(BranchProbability RHS) {
assert(N != UnknownN && RHS.N != UnknownN &&
"Unknown probability cannot participate in arithmetics.");
N = (static_cast<uint64_t>(N) * RHS.N + D / 2) / D;
return *this;
}
BranchProbability &operator*=(uint32_t RHS) {
assert(N != UnknownN &&
"Unknown probability cannot participate in arithmetics.");
N = (uint64_t(N) * RHS > D) ? D : N * RHS;
return *this;
}
BranchProbability &operator/=(BranchProbability RHS) {
assert(N != UnknownN && RHS.N != UnknownN &&
"Unknown probability cannot participate in arithmetics.");
N = (static_cast<uint64_t>(N) * D + RHS.N / 2) / RHS.N;
return *this;
}
BranchProbability &operator/=(uint32_t RHS) {
assert(N != UnknownN &&
"Unknown probability cannot participate in arithmetics.");
assert(RHS > 0 && "The divider cannot be zero.");
N /= RHS;
return *this;
}
BranchProbability operator+(BranchProbability RHS) const {
BranchProbability Prob(*this);
Prob += RHS;
return Prob;
}
BranchProbability operator-(BranchProbability RHS) const {
BranchProbability Prob(*this);
Prob -= RHS;
return Prob;
}
BranchProbability operator*(BranchProbability RHS) const {
BranchProbability Prob(*this);
Prob *= RHS;
return Prob;
}
BranchProbability operator*(uint32_t RHS) const {
BranchProbability Prob(*this);
Prob *= RHS;
return Prob;
}
BranchProbability operator/(BranchProbability RHS) const {
BranchProbability Prob(*this);
Prob /= RHS;
return Prob;
}
BranchProbability operator/(uint32_t RHS) const {
BranchProbability Prob(*this);
Prob /= RHS;
return Prob;
}
bool operator==(BranchProbability RHS) const { return N == RHS.N; }
bool operator!=(BranchProbability RHS) const { return !(*this == RHS); }
bool operator<(BranchProbability RHS) const {
assert(N != UnknownN && RHS.N != UnknownN &&
"Unknown probability cannot participate in comparisons.");
return N < RHS.N;
}
bool operator>(BranchProbability RHS) const {
assert(N != UnknownN && RHS.N != UnknownN &&
"Unknown probability cannot participate in comparisons.");
return RHS < *this;
}
bool operator<=(BranchProbability RHS) const {
assert(N != UnknownN && RHS.N != UnknownN &&
"Unknown probability cannot participate in comparisons.");
return !(RHS < *this);
}
bool operator>=(BranchProbability RHS) const {
assert(N != UnknownN && RHS.N != UnknownN &&
"Unknown probability cannot participate in comparisons.");
return !(*this < RHS);
}
};
inline raw_ostream &operator<<(raw_ostream &OS, BranchProbability Prob) {
return Prob.print(OS);
}
template <class ProbabilityIter>
void BranchProbability::normalizeProbabilities(ProbabilityIter Begin,
ProbabilityIter End) {
if (Begin == End)
return;
unsigned UnknownProbCount = 0;
uint64_t Sum = std::accumulate(Begin, End, uint64_t(0),
[&](uint64_t S, const BranchProbability &BP) {
if (!BP.isUnknown())
return S + BP.N;
UnknownProbCount++;
return S;
});
if (UnknownProbCount > 0) {
BranchProbability ProbForUnknown = BranchProbability::getZero();
// If the sum of all known probabilities is less than one, evenly distribute
// the complement of sum to unknown probabilities. Otherwise, set unknown
// probabilities to zeros and continue to normalize known probabilities.
if (Sum < BranchProbability::getDenominator())
ProbForUnknown = BranchProbability::getRaw(
(BranchProbability::getDenominator() - Sum) / UnknownProbCount);
std::replace_if(Begin, End,
[](const BranchProbability &BP) { return BP.isUnknown(); },
ProbForUnknown);
if (Sum <= BranchProbability::getDenominator())
return;
}
if (Sum == 0) {
BranchProbability BP(1, std::distance(Begin, End));
std::fill(Begin, End, BP);
return;
}
for (auto I = Begin; I != End; ++I)
I->N = (I->N * uint64_t(D) + Sum / 2) / Sum;
}
}
#endif
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