LLVM  4.0.0
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 LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; }
36 
38  assert(Denominator > 0 && "Denominator cannot be 0!");
39  assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
40  if (Denominator == D)
41  N = Numerator;
42  else {
43  uint64_t Prob64 =
44  (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator;
45  N = static_cast<uint32_t>(Prob64);
46  }
47 }
48 
51  uint64_t Denominator) {
52  assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
53  // Scale down Denominator to fit in a 32-bit integer.
54  int Scale = 0;
55  while (Denominator > UINT32_MAX) {
56  Denominator >>= 1;
57  Scale++;
58  }
59  return BranchProbability(Numerator >> Scale, Denominator);
60 }
61 
62 // If ConstD is not zero, then replace D by ConstD so that division and modulo
63 // operations by D can be optimized, in case this function is not inlined by the
64 // compiler.
65 template <uint32_t ConstD>
66 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
67  if (ConstD > 0)
68  D = ConstD;
69 
70  assert(D && "divide by 0");
71 
72  // Fast path for multiplying by 1.0.
73  if (!Num || D == N)
74  return Num;
75 
76  // Split Num into upper and lower parts to multiply, then recombine.
77  uint64_t ProductHigh = (Num >> 32) * N;
78  uint64_t ProductLow = (Num & UINT32_MAX) * N;
79 
80  // Split into 32-bit digits.
81  uint32_t Upper32 = ProductHigh >> 32;
82  uint32_t Lower32 = ProductLow & UINT32_MAX;
83  uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
84  uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
85 
86  // Carry.
87  Upper32 += Mid32 < Mid32Partial;
88 
89  // Check for overflow.
90  if (Upper32 >= D)
91  return UINT64_MAX;
92 
93  uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
94  uint64_t UpperQ = Rem / D;
95 
96  // Check for overflow.
97  if (UpperQ > UINT32_MAX)
98  return UINT64_MAX;
99 
100  Rem = ((Rem % D) << 32) | Lower32;
101  uint64_t LowerQ = Rem / D;
102  uint64_t Q = (UpperQ << 32) + LowerQ;
103 
104  // Check for overflow.
105  return Q < LowerQ ? UINT64_MAX : Q;
106 }
107 
108 uint64_t BranchProbability::scale(uint64_t Num) const {
109  return ::scale<D>(Num, N, D);
110 }
111 
112 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
113  return ::scale<0>(Num, D, N);
114 }
#define LLVM_DUMP_METHOD
Mark debug helper function definitions like dump() that should not be stripped from debug builds...
Definition: Compiler.h:450
static GCRegistry::Add< StatepointGC > D("statepoint-example","an example strategy for statepoint")
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 uint64_t scale(uint64_t Num, uint32_t N, uint32_t D)
raw_ostream & print(raw_ostream &OS) const
static BranchProbability getBranchProbability(uint64_t Numerator, uint64_t Denominator)
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
uint64_t scale(uint64_t Num) const
Scale a large integer.
#define N
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:44