LLVM  14.0.0git
BranchProbability.cpp
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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 
14 #include "llvm/Config/llvm-config.h"
15 #include "llvm/Support/Debug.h"
16 #include "llvm/Support/Format.h"
18 #include <cassert>
19 #include <cmath>
20 
21 using namespace llvm;
22 
23 constexpr 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>
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 
108  return ::scale<D>(Num, N, D);
109 }
110 
112  return ::scale<0>(Num, D, N);
113 }
llvm::BranchProbability::scaleByInverse
uint64_t scaleByInverse(uint64_t Num) const
Scale a large integer by the inverse.
Definition: BranchProbability.cpp:111
LLVM_DUMP_METHOD
#define LLVM_DUMP_METHOD
Mark debug helper function definitions like dump() that should not be stripped from debug builds.
Definition: Compiler.h:506
llvm
This file implements support for optimizing divisions by a constant.
Definition: AllocatorList.h:23
llvm::BranchProbability::BranchProbability
BranchProbability()
Definition: BranchProbability.h:43
llvm::FloatStyle::Percent
@ Percent
llvm::BranchProbability::getBranchProbability
static BranchProbability getBranchProbability(uint64_t Numerator, uint64_t Denominator)
Definition: BranchProbability.cpp:53
llvm::BranchProbability::print
raw_ostream & print(raw_ostream &OS) const
Definition: BranchProbability.cpp:25
Format.h
llvm::BranchProbability::scale
uint64_t scale(uint64_t Num) const
Scale a large integer.
Definition: BranchProbability.cpp:107
llvm::dbgs
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
UINT64_MAX
#define UINT64_MAX
Definition: DataTypes.h:77
llvm::raw_ostream
This class implements an extremely fast bulk output stream that can only output to a stream.
Definition: raw_ostream.h:53
BranchProbability.h
llvm::BranchProbability::dump
void dump() const
Definition: BranchProbability.cpp:37
uint64_t
D
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
llvm::BranchProbability::isUnknown
bool isUnknown() const
Definition: BranchProbability.h:47
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
uint32_t
llvm::BranchProbability
Definition: BranchProbability.h:30
scale
static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D)
Definition: BranchProbability.cpp:69
llvm::format
format_object< Ts... > format(const char *Fmt, const Ts &... Vals)
These are helper functions used to produce formatted output.
Definition: Format.h:124
N
#define N
raw_ostream.h
Debug.h