1//===-------------- lib/Support/BranchProbability.cpp -----------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements Branch Probability class.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/Support/BranchProbability.h"
14#include "llvm/Config/llvm-config.h"
15#include "llvm/Support/Debug.h"
16#include "llvm/Support/Format.h"
17#include "llvm/Support/raw_ostream.h"
18#include <cassert>
19#include <cmath>
20
21using namespace llvm;
22
23constexpr uint32_t BranchProbability::D;
24
25raw_ostream &BranchProbability::print(raw_ostream &OS) const {
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)
37LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; }
38#endif
39
40BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) {
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
52BranchProbability
53BranchProbability::getBranchProbability(uint64_t Numerator,
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.
68template <uint32_t ConstD>
69static 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  uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
93  uint64_t UpperQ = Rem / D;
94
95  // Check for overflow.
96  if (UpperQ > UINT32_MAX)
97    return UINT64_MAX;
98
99  Rem = ((Rem % D) << 32) | Lower32;
100  uint64_t LowerQ = Rem / D;
101  uint64_t Q = (UpperQ << 32) + LowerQ;
102
103  // Check for overflow.
104  return Q < LowerQ ? UINT64_MAX : Q;
105}
106
107uint64_t BranchProbability::scale(uint64_t Num) const {
108  return ::scale<D>(Num, N, D);
109}
110
111uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
112  return ::scale<0>(Num, D, N);
113}
114