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1 //===-------------- lib/Support/BranchProbability.cpp -----------*- C++ -*-===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8 //
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9 // This file implements Branch Probability class.
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10 //
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11 //===----------------------------------------------------------------------===//
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12
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13 #include "llvm/Support/BranchProbability.h"
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14 #include "llvm/Config/llvm-config.h"
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15 #include "llvm/Support/Debug.h"
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16 #include "llvm/Support/Format.h"
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17 #include "llvm/Support/raw_ostream.h"
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18 #include <cassert>
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19
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20 using namespace llvm;
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21
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173
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22 constexpr uint32_t BranchProbability::D;
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150
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23
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24 raw_ostream &BranchProbability::print(raw_ostream &OS) const {
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25 if (isUnknown())
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26 return OS << "?%";
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27
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28 // Get a percentage rounded to two decimal digits. This avoids
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29 // implementation-defined rounding inside printf.
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30 double Percent = rint(((double)N / D) * 100.0 * 100.0) / 100.0;
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31 return OS << format("0x%08" PRIx32 " / 0x%08" PRIx32 " = %.2f%%", N, D,
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32 Percent);
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33 }
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34
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35 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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36 LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; }
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37 #endif
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38
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39 BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) {
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40 assert(Denominator > 0 && "Denominator cannot be 0!");
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41 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
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42 if (Denominator == D)
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43 N = Numerator;
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44 else {
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45 uint64_t Prob64 =
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46 (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator;
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47 N = static_cast<uint32_t>(Prob64);
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48 }
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49 }
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50
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51 BranchProbability
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52 BranchProbability::getBranchProbability(uint64_t Numerator,
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53 uint64_t Denominator) {
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54 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
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55 // Scale down Denominator to fit in a 32-bit integer.
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56 int Scale = 0;
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57 while (Denominator > UINT32_MAX) {
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58 Denominator >>= 1;
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59 Scale++;
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60 }
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61 return BranchProbability(Numerator >> Scale, Denominator);
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62 }
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63
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64 // If ConstD is not zero, then replace D by ConstD so that division and modulo
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65 // operations by D can be optimized, in case this function is not inlined by the
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66 // compiler.
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67 template <uint32_t ConstD>
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68 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
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69 if (ConstD > 0)
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70 D = ConstD;
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71
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72 assert(D && "divide by 0");
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73
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74 // Fast path for multiplying by 1.0.
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75 if (!Num || D == N)
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76 return Num;
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77
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78 // Split Num into upper and lower parts to multiply, then recombine.
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79 uint64_t ProductHigh = (Num >> 32) * N;
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80 uint64_t ProductLow = (Num & UINT32_MAX) * N;
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81
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82 // Split into 32-bit digits.
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83 uint32_t Upper32 = ProductHigh >> 32;
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84 uint32_t Lower32 = ProductLow & UINT32_MAX;
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85 uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
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86 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
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87
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88 // Carry.
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89 Upper32 += Mid32 < Mid32Partial;
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90
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91 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
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92 uint64_t UpperQ = Rem / D;
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93
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94 // Check for overflow.
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95 if (UpperQ > UINT32_MAX)
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96 return UINT64_MAX;
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97
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98 Rem = ((Rem % D) << 32) | Lower32;
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99 uint64_t LowerQ = Rem / D;
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100 uint64_t Q = (UpperQ << 32) + LowerQ;
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101
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102 // Check for overflow.
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103 return Q < LowerQ ? UINT64_MAX : Q;
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104 }
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105
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106 uint64_t BranchProbability::scale(uint64_t Num) const {
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107 return ::scale<D>(Num, N, D);
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108 }
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109
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110 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
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111 return ::scale<0>(Num, D, N);
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112 }
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