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 20 using namespace llvm; 21 22 constexpr 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 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 36 LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; } 37 #endif 38 39 BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) { 40 assert(Denominator > 0 && "Denominator cannot be 0!"); 41 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!"); 42 if (Denominator == D) 43 N = Numerator; 44 else { 45 uint64_t Prob64 = 46 (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator; 47 N = static_cast<uint32_t>(Prob64); 48 } 49 } 50 51 BranchProbability 52 BranchProbability::getBranchProbability(uint64_t Numerator, 53 uint64_t Denominator) { 54 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!"); 55 // Scale down Denominator to fit in a 32-bit integer. 56 int Scale = 0; 57 while (Denominator > UINT32_MAX) { 58 Denominator >>= 1; 59 Scale++; 60 } 61 return BranchProbability(Numerator >> Scale, Denominator); 62 } 63 64 // If ConstD is not zero, then replace D by ConstD so that division and modulo 65 // operations by D can be optimized, in case this function is not inlined by the 66 // compiler. 67 template <uint32_t ConstD> 68 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) { 69 if (ConstD > 0) 70 D = ConstD; 71 72 assert(D && "divide by 0"); 73 74 // Fast path for multiplying by 1.0. 75 if (!Num || D == N) 76 return Num; 77 78 // Split Num into upper and lower parts to multiply, then recombine. 79 uint64_t ProductHigh = (Num >> 32) * N; 80 uint64_t ProductLow = (Num & UINT32_MAX) * N; 81 82 // Split into 32-bit digits. 83 uint32_t Upper32 = ProductHigh >> 32; 84 uint32_t Lower32 = ProductLow & UINT32_MAX; 85 uint32_t Mid32Partial = ProductHigh & UINT32_MAX; 86 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32); 87 88 // Carry. 89 Upper32 += Mid32 < Mid32Partial; 90 91 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32; 92 uint64_t UpperQ = Rem / D; 93 94 // Check for overflow. 95 if (UpperQ > UINT32_MAX) 96 return UINT64_MAX; 97 98 Rem = ((Rem % D) << 32) | Lower32; 99 uint64_t LowerQ = Rem / D; 100 uint64_t Q = (UpperQ << 32) + LowerQ; 101 102 // Check for overflow. 103 return Q < LowerQ ? UINT64_MAX : Q; 104 } 105 106 uint64_t BranchProbability::scale(uint64_t Num) const { 107 return ::scale<D>(Num, N, D); 108 } 109 110 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const { 111 return ::scale<0>(Num, D, N); 112 } 113