LLVM  8.0.0svn
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/Config/llvm-config.h"
16 #include "llvm/Support/Debug.h"
17 #include "llvm/Support/Format.h"
19 #include <cassert>
20 
21 using namespace llvm;
22 
23 const uint32_t BranchProbability::D;
24 
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 
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 
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  // Check for overflow.
93  if (Upper32 >= D)
94  return UINT64_MAX;
95 
96  uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
97  uint64_t UpperQ = Rem / D;
98 
99  // Check for overflow.
100  if (UpperQ > UINT32_MAX)
101  return UINT64_MAX;
102 
103  Rem = ((Rem % D) << 32) | Lower32;
104  uint64_t LowerQ = Rem / D;
105  uint64_t Q = (UpperQ << 32) + LowerQ;
106 
107  // Check for overflow.
108  return Q < LowerQ ? UINT64_MAX : Q;
109 }
110 
111 uint64_t BranchProbability::scale(uint64_t Num) const {
112  return ::scale<D>(Num, N, D);
113 }
114 
115 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
116  return ::scale<0>(Num, D, N);
117 }
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
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.
#define LLVM_DUMP_METHOD
Definition: Compiler.h:74
#define UINT64_MAX
Definition: DataTypes.h:83
static BranchProbability getBranchProbability(uint64_t Numerator, uint64_t Denominator)
uint64_t scale(uint64_t Num) const
Scale a large integer.
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dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:133
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
raw_ostream & print(raw_ostream &OS) const
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Definition: raw_ostream.h:46