1 //====--------------- lib/Support/BlockFrequency.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 Block Frequency class. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/Support/BranchProbability.h" 15 #include "llvm/Support/BlockFrequency.h" 16 #include "llvm/Support/raw_ostream.h" 17 #include <cassert> 18 19 using namespace llvm; 20 21 /// Multiply FREQ by N and store result in W array. 22 static void mult96bit(uint64_t freq, uint32_t N, uint64_t W[2]) { 23 uint64_t u0 = freq & UINT32_MAX; 24 uint64_t u1 = freq >> 32; 25 26 // Represent 96-bit value as w[2]:w[1]:w[0]; 27 uint32_t w[3] = { 0, 0, 0 }; 28 29 uint64_t t = u0 * N; 30 uint64_t k = t >> 32; 31 w[0] = t; 32 t = u1 * N + k; 33 w[1] = t; 34 w[2] = t >> 32; 35 36 // W[1] - higher bits. 37 // W[0] - lower bits. 38 W[0] = w[0] + ((uint64_t) w[1] << 32); 39 W[1] = w[2]; 40 } 41 42 43 /// Divide 96-bit value stored in W array by D. 44 /// Return 64-bit quotient, saturated to UINT64_MAX on overflow. 45 static uint64_t div96bit(uint64_t W[2], uint32_t D) { 46 uint64_t y = W[0]; 47 uint64_t x = W[1]; 48 unsigned i; 49 50 assert(x != 0 && "This is really a 64-bit division"); 51 52 // This long division algorithm automatically saturates on overflow. 53 for (i = 0; i < 64 && x; ++i) { 54 uint32_t t = -((x >> 31) & 1); // Splat bit 31 to bits 0-31. 55 x = (x << 1) | (y >> 63); 56 y = y << 1; 57 if ((x | t) >= D) { 58 x -= D; 59 ++y; 60 } 61 } 62 63 return y << (64 - i); 64 } 65 66 67 void BlockFrequency::scale(uint32_t N, uint32_t D) { 68 assert(D != 0 && "Division by zero"); 69 70 // Calculate Frequency * N. 71 uint64_t MulLo = (Frequency & UINT32_MAX) * N; 72 uint64_t MulHi = (Frequency >> 32) * N; 73 uint64_t MulRes = (MulHi << 32) + MulLo; 74 75 // If the product fits in 64 bits, just use built-in division. 76 if (MulHi <= UINT32_MAX && MulRes >= MulLo) { 77 Frequency = MulRes / D; 78 return; 79 } 80 81 // Product overflowed, use 96-bit operations. 82 // 96-bit value represented as W[1]:W[0]. 83 uint64_t W[2]; 84 mult96bit(Frequency, N, W); 85 Frequency = div96bit(W, D); 86 return; 87 } 88 89 BlockFrequency &BlockFrequency::operator*=(const BranchProbability &Prob) { 90 scale(Prob.getNumerator(), Prob.getDenominator()); 91 return *this; 92 } 93 94 const BlockFrequency 95 BlockFrequency::operator*(const BranchProbability &Prob) const { 96 BlockFrequency Freq(Frequency); 97 Freq *= Prob; 98 return Freq; 99 } 100 101 BlockFrequency &BlockFrequency::operator/=(const BranchProbability &Prob) { 102 scale(Prob.getDenominator(), Prob.getNumerator()); 103 return *this; 104 } 105 106 BlockFrequency BlockFrequency::operator/(const BranchProbability &Prob) const { 107 BlockFrequency Freq(Frequency); 108 Freq /= Prob; 109 return Freq; 110 } 111 112 BlockFrequency &BlockFrequency::operator+=(const BlockFrequency &Freq) { 113 uint64_t Before = Freq.Frequency; 114 Frequency += Freq.Frequency; 115 116 // If overflow, set frequency to the maximum value. 117 if (Frequency < Before) 118 Frequency = UINT64_MAX; 119 120 return *this; 121 } 122 123 const BlockFrequency 124 BlockFrequency::operator+(const BlockFrequency &Prob) const { 125 BlockFrequency Freq(Frequency); 126 Freq += Prob; 127 return Freq; 128 } 129 130 void BlockFrequency::print(raw_ostream &OS) const { 131 // Convert fixed-point number to decimal. 132 OS << Frequency / getEntryFrequency() << "."; 133 uint64_t Rem = Frequency % getEntryFrequency(); 134 uint64_t Eps = 1; 135 do { 136 Rem *= 10; 137 Eps *= 10; 138 OS << Rem / getEntryFrequency(); 139 Rem = Rem % getEntryFrequency(); 140 } while (Rem >= Eps/2); 141 } 142 143 namespace llvm { 144 145 raw_ostream &operator<<(raw_ostream &OS, const BlockFrequency &Freq) { 146 Freq.print(OS); 147 return OS; 148 } 149 150 } 151