LLVM  6.0.0svn
BranchProbability.cpp
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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 
15 #include "llvm/Support/Debug.h"
16 #include "llvm/Support/Format.h"
18 #include <cassert>
19 
20 using namespace llvm;
21 
22 const uint32_t BranchProbability::D;
23 
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 
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 
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  // Check for overflow.
92  if (Upper32 >= D)
93  return UINT64_MAX;
94 
95  uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
96  uint64_t UpperQ = Rem / D;
97 
98  // Check for overflow.
99  if (UpperQ > UINT32_MAX)
100  return UINT64_MAX;
101 
102  Rem = ((Rem % D) << 32) | Lower32;
103  uint64_t LowerQ = Rem / D;
104  uint64_t Q = (UpperQ << 32) + LowerQ;
105 
106  // Check for overflow.
107  return Q < LowerQ ? UINT64_MAX : Q;
108 }
109 
110 uint64_t BranchProbability::scale(uint64_t Num) const {
111  return ::scale<D>(Num, N, D);
112 }
113 
114 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
115  return ::scale<0>(Num, D, N);
116 }
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Definition: AllocatorList.h:24
#define LLVM_DUMP_METHOD
Mark debug helper function definitions like dump() that should not be stripped from debug builds...
Definition: Compiler.h:449
format_object< Ts... > format(const char *Fmt, const Ts &... Vals)
These are helper functions used to produce formatted output.
Definition: Format.h:124
uint64_t scaleByInverse(uint64_t Num) const
Scale a large integer by the inverse.
static BranchProbability getBranchProbability(uint64_t Numerator, uint64_t Denominator)
uint64_t scale(uint64_t Num) const
Scale a large integer.
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Definition: Debug.cpp:132
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raw_ostream & print(raw_ostream &OS) const
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Definition: raw_ostream.h:44