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#include <cassert>
19
20using namespace llvm;
21
22const uint32_t BranchProbability::D;
23
24raw_ostream &BranchProbability::print(raw_ostream &OS) const {
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
35LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; }
36
37BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) {
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
49BranchProbability
50BranchProbability::getBranchProbability(uint64_t Numerator,
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.
65template <uint32_t ConstD>
66static 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
108uint64_t BranchProbability::scale(uint64_t Num) const {
109  return ::scale<D>(Num, N, D);
110}
111
112uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
113  return ::scale<0>(Num, D, N);
114}
115