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 19 using namespace llvm; 20 21 raw_ostream &BranchProbability::print(raw_ostream &OS) const { 22 return OS << N << " / " << D << " = " 23 << format("%g%%", ((double)N / D) * 100.0); 24 } 25 26 void BranchProbability::dump() const { print(dbgs()) << '\n'; } 27 28 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) { 29 assert(D && "divide by 0"); 30 31 // Fast path for multiplying by 1.0. 32 if (!Num || D == N) 33 return Num; 34 35 // Split Num into upper and lower parts to multiply, then recombine. 36 uint64_t ProductHigh = (Num >> 32) * N; 37 uint64_t ProductLow = (Num & UINT32_MAX) * N; 38 39 // Split into 32-bit digits. 40 uint32_t Upper32 = ProductHigh >> 32; 41 uint32_t Lower32 = ProductLow & UINT32_MAX; 42 uint32_t Mid32Partial = ProductHigh & UINT32_MAX; 43 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32); 44 45 // Carry. 46 Upper32 += Mid32 < Mid32Partial; 47 48 // Check for overflow. 49 if (Upper32 >= D) 50 return UINT64_MAX; 51 52 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32; 53 uint64_t UpperQ = Rem / D; 54 55 // Check for overflow. 56 if (UpperQ > UINT32_MAX) 57 return UINT64_MAX; 58 59 Rem = ((Rem % D) << 32) | Lower32; 60 uint64_t LowerQ = Rem / D; 61 uint64_t Q = (UpperQ << 32) + LowerQ; 62 63 // Check for overflow. 64 return Q < LowerQ ? UINT64_MAX : Q; 65 } 66 67 uint64_t BranchProbability::scale(uint64_t Num) const { 68 return ::scale(Num, N, D); 69 } 70 71 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const { 72 return ::scale(Num, D, N); 73 } 74
