1 //===-------------- lib/Support/BranchProbability.cpp -----------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file implements Branch Probability class. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/Support/BranchProbability.h" 15 #include "llvm/Support/Debug.h" 16 #include "llvm/Support/Format.h" 17 #include "llvm/Support/raw_ostream.h" 18 #include <cassert> 19 20 using namespace llvm; 21 22 raw_ostream &BranchProbability::print(raw_ostream &OS) const { 23 auto GetHexDigit = [](int Val) -> char { 24 assert(Val < 16); 25 if (Val < 10) 26 return '0' + Val; 27 return 'a' + Val - 10; 28 }; 29 OS << "0x"; 30 for (int Digits = 0; Digits < 8; ++Digits) 31 OS << GetHexDigit(N >> (28 - Digits * 4) & 0xf); 32 OS << " / 0x"; 33 for (int Digits = 0; Digits < 8; ++Digits) 34 OS << GetHexDigit(D >> (28 - Digits * 4) & 0xf); 35 OS << " = " << format("%.2f%%", ((double)N / D) * 100.0); 36 return OS; 37 } 38 39 void BranchProbability::dump() const { print(dbgs()) << '\n'; } 40 41 BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) { 42 assert(Denominator > 0 && "Denominator cannot be 0!"); 43 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!"); 44 if (Denominator == D) 45 N = Numerator; 46 else { 47 uint64_t Prob64 = 48 (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator; 49 N = static_cast<uint32_t>(Prob64); 50 } 51 } 52 53 BranchProbability &BranchProbability::operator+=(BranchProbability RHS) { 54 assert(N <= D - RHS.N && 55 "The sum of branch probabilities should not exceed one!"); 56 N += RHS.N; 57 return *this; 58 } 59 60 BranchProbability &BranchProbability::operator-=(BranchProbability RHS) { 61 assert(N >= RHS.N && 62 "Can only subtract a smaller probability from a larger one!"); 63 N -= RHS.N; 64 return *this; 65 } 66 67 // If ConstD is not zero, then replace D by ConstD so that division and modulo 68 // operations by D can be optimized, in case this function is not inlined by the 69 // compiler. 70 template <uint32_t ConstD> 71 inline uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) { 72 if (ConstD > 0) 73 D = ConstD; 74 75 assert(D && "divide by 0"); 76 77 // Fast path for multiplying by 1.0. 78 if (!Num || D == N) 79 return Num; 80 81 // Split Num into upper and lower parts to multiply, then recombine. 82 uint64_t ProductHigh = (Num >> 32) * N; 83 uint64_t ProductLow = (Num & UINT32_MAX) * N; 84 85 // Split into 32-bit digits. 86 uint32_t Upper32 = ProductHigh >> 32; 87 uint32_t Lower32 = ProductLow & UINT32_MAX; 88 uint32_t Mid32Partial = ProductHigh & UINT32_MAX; 89 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32); 90 91 // Carry. 92 Upper32 += Mid32 < Mid32Partial; 93 94 // Check for overflow. 95 if (Upper32 >= D) 96 return UINT64_MAX; 97 98 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32; 99 uint64_t UpperQ = Rem / D; 100 101 // Check for overflow. 102 if (UpperQ > UINT32_MAX) 103 return UINT64_MAX; 104 105 Rem = ((Rem % D) << 32) | Lower32; 106 uint64_t LowerQ = Rem / D; 107 uint64_t Q = (UpperQ << 32) + LowerQ; 108 109 // Check for overflow. 110 return Q < LowerQ ? UINT64_MAX : Q; 111 } 112 113 uint64_t BranchProbability::scale(uint64_t Num) const { 114 return ::scale<D>(Num, N, D); 115 } 116 117 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const { 118 return ::scale<0>(Num, D, N); 119 } 120