1 //===-------------- lib/Support/BranchProbability.cpp -----------*- 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 // This file implements Branch Probability class. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/Support/BranchProbability.h" 14 #include "llvm/Config/llvm-config.h" 15 #include "llvm/Support/Debug.h" 16 #include "llvm/Support/Format.h" 17 #include "llvm/Support/raw_ostream.h" 18 #include <cassert> 19 #include <cmath> 20 21 using namespace llvm; 22 23 constexpr uint32_t BranchProbability::D; 24 25 raw_ostream &BranchProbability::print(raw_ostream &OS) const { 26 if (isUnknown()) 27 return OS << "?%"; 28 29 // Get a percentage rounded to two decimal digits. This avoids 30 // implementation-defined rounding inside printf. 31 double Percent = rint(((double)N / D) * 100.0 * 100.0) / 100.0; 32 return OS << format("0x%08" PRIx32 " / 0x%08" PRIx32 " = %.2f%%", N, D, 33 Percent); 34 } 35 36 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 37 LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; } 38 #endif 39 40 BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) { 41 assert(Denominator > 0 && "Denominator cannot be 0!"); 42 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!"); 43 if (Denominator == D) 44 N = Numerator; 45 else { 46 uint64_t Prob64 = 47 (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator; 48 N = static_cast<uint32_t>(Prob64); 49 } 50 } 51 52 BranchProbability 53 BranchProbability::getBranchProbability(uint64_t Numerator, 54 uint64_t Denominator) { 55 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!"); 56 // Scale down Denominator to fit in a 32-bit integer. 57 int Scale = 0; 58 while (Denominator > UINT32_MAX) { 59 Denominator >>= 1; 60 Scale++; 61 } 62 return BranchProbability(Numerator >> Scale, Denominator); 63 } 64 65 // If ConstD is not zero, then replace D by ConstD so that division and modulo 66 // operations by D can be optimized, in case this function is not inlined by the 67 // compiler. 68 template <uint32_t ConstD> 69 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) { 70 if (ConstD > 0) 71 D = ConstD; 72 73 assert(D && "divide by 0"); 74 75 // Fast path for multiplying by 1.0. 76 if (!Num || D == N) 77 return Num; 78 79 // Split Num into upper and lower parts to multiply, then recombine. 80 uint64_t ProductHigh = (Num >> 32) * N; 81 uint64_t ProductLow = (Num & UINT32_MAX) * N; 82 83 // Split into 32-bit digits. 84 uint32_t Upper32 = ProductHigh >> 32; 85 uint32_t Lower32 = ProductLow & UINT32_MAX; 86 uint32_t Mid32Partial = ProductHigh & UINT32_MAX; 87 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32); 88 89 // Carry. 90 Upper32 += Mid32 < Mid32Partial; 91 92 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32; 93 uint64_t UpperQ = Rem / D; 94 95 // Check for overflow. 96 if (UpperQ > UINT32_MAX) 97 return UINT64_MAX; 98 99 Rem = ((Rem % D) << 32) | Lower32; 100 uint64_t LowerQ = Rem / D; 101 uint64_t Q = (UpperQ << 32) + LowerQ; 102 103 // Check for overflow. 104 return Q < LowerQ ? UINT64_MAX : Q; 105 } 106 107 uint64_t BranchProbability::scale(uint64_t Num) const { 108 return ::scale<D>(Num, N, D); 109 } 110 111 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const { 112 return ::scale<0>(Num, D, N); 113 } 114