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 const uint32_t BranchProbability::D; 23 24 raw_ostream &BranchProbability::print(raw_ostream &OS) const { 25 if (isUnknown()) 26 return OS << "?%"; 27 28 // Get a percentage rounded to two decimal digits. This avoids 29 // implementation-defined rounding inside printf. 30 double Percent = rint(((double)N / D) * 100.0 * 100.0) / 100.0; 31 return OS << format("0x%08" PRIx32 " / 0x%08" PRIx32 " = %.2f%%", N, D, 32 Percent); 33 } 34 35 LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; } 36 37 BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) { 38 assert(Denominator > 0 && "Denominator cannot be 0!"); 39 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!"); 40 if (Denominator == D) 41 N = Numerator; 42 else { 43 uint64_t Prob64 = 44 (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator; 45 N = static_cast<uint32_t>(Prob64); 46 } 47 } 48 49 BranchProbability 50 BranchProbability::getBranchProbability(uint64_t Numerator, 51 uint64_t Denominator) { 52 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!"); 53 // Scale down Denominator to fit in a 32-bit integer. 54 int Scale = 0; 55 while (Denominator > UINT32_MAX) { 56 Denominator >>= 1; 57 Scale++; 58 } 59 return BranchProbability(Numerator >> Scale, Denominator); 60 } 61 62 // If ConstD is not zero, then replace D by ConstD so that division and modulo 63 // operations by D can be optimized, in case this function is not inlined by the 64 // compiler. 65 template <uint32_t ConstD> 66 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) { 67 if (ConstD > 0) 68 D = ConstD; 69 70 assert(D && "divide by 0"); 71 72 // Fast path for multiplying by 1.0. 73 if (!Num || D == N) 74 return Num; 75 76 // Split Num into upper and lower parts to multiply, then recombine. 77 uint64_t ProductHigh = (Num >> 32) * N; 78 uint64_t ProductLow = (Num & UINT32_MAX) * N; 79 80 // Split into 32-bit digits. 81 uint32_t Upper32 = ProductHigh >> 32; 82 uint32_t Lower32 = ProductLow & UINT32_MAX; 83 uint32_t Mid32Partial = ProductHigh & UINT32_MAX; 84 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32); 85 86 // Carry. 87 Upper32 += Mid32 < Mid32Partial; 88 89 // Check for overflow. 90 if (Upper32 >= D) 91 return UINT64_MAX; 92 93 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32; 94 uint64_t UpperQ = Rem / D; 95 96 // Check for overflow. 97 if (UpperQ > UINT32_MAX) 98 return UINT64_MAX; 99 100 Rem = ((Rem % D) << 32) | Lower32; 101 uint64_t LowerQ = Rem / D; 102 uint64_t Q = (UpperQ << 32) + LowerQ; 103 104 // Check for overflow. 105 return Q < LowerQ ? UINT64_MAX : Q; 106 } 107 108 uint64_t BranchProbability::scale(uint64_t Num) const { 109 return ::scale<D>(Num, N, D); 110 } 111 112 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const { 113 return ::scale<0>(Num, D, N); 114 } 115
