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annotate lib/CodeGen/MachineBranchProbabilityInfo.cpp @ 89:9020ffd06b8b

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Create prototype declaration automatically (only support direct continuation)
author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Tue, 14 Apr 2015 03:55:39 +0900
parents 54457678186b
children 7d135dc70f03
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1 //===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===//
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2 //
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3 // The LLVM Compiler Infrastructure
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4 //
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5 // This file is distributed under the University of Illinois Open Source
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6 // License. See LICENSE.TXT for details.
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7 //
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8 //===----------------------------------------------------------------------===//
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9 //
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10 // This analysis uses probability info stored in Machine Basic Blocks.
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11 //
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12 //===----------------------------------------------------------------------===//
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13
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14 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
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15 #include "llvm/CodeGen/MachineBasicBlock.h"
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16 #include "llvm/IR/Instructions.h"
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17 #include "llvm/Support/Debug.h"
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18 #include "llvm/Support/raw_ostream.h"
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19
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20 using namespace llvm;
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21
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22 INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob",
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23 "Machine Branch Probability Analysis", false, true)
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24 INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob",
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25 "Machine Branch Probability Analysis", false, true)
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26
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27 char MachineBranchProbabilityInfo::ID = 0;
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28
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29 void MachineBranchProbabilityInfo::anchor() { }
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30
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31 uint32_t MachineBranchProbabilityInfo::
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32 getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const {
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33 // First we compute the sum with 64-bits of precision, ensuring that cannot
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34 // overflow by bounding the number of weights considered. Hopefully no one
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35 // actually needs 2^32 successors.
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36 assert(MBB->succ_size() < UINT32_MAX);
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37 uint64_t Sum = 0;
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38 Scale = 1;
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39 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
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40 E = MBB->succ_end(); I != E; ++I) {
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41 uint32_t Weight = getEdgeWeight(MBB, I);
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42 Sum += Weight;
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43 }
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44
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45 // If the computed sum fits in 32-bits, we're done.
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46 if (Sum <= UINT32_MAX)
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47 return Sum;
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48
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49 // Otherwise, compute the scale necessary to cause the weights to fit, and
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50 // re-sum with that scale applied.
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51 assert((Sum / UINT32_MAX) < UINT32_MAX);
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52 Scale = (Sum / UINT32_MAX) + 1;
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53 Sum = 0;
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54 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
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55 E = MBB->succ_end(); I != E; ++I) {
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56 uint32_t Weight = getEdgeWeight(MBB, I);
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57 Sum += Weight / Scale;
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58 }
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59 assert(Sum <= UINT32_MAX);
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60 return Sum;
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61 }
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62
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63 uint32_t MachineBranchProbabilityInfo::
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64 getEdgeWeight(const MachineBasicBlock *Src,
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65 MachineBasicBlock::const_succ_iterator Dst) const {
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66 uint32_t Weight = Src->getSuccWeight(Dst);
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67 if (!Weight)
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68 return DEFAULT_WEIGHT;
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69 return Weight;
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70 }
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71
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72 uint32_t MachineBranchProbabilityInfo::
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73 getEdgeWeight(const MachineBasicBlock *Src,
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74 const MachineBasicBlock *Dst) const {
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75 // This is a linear search. Try to use the const_succ_iterator version when
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76 // possible.
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77 return getEdgeWeight(Src, std::find(Src->succ_begin(), Src->succ_end(), Dst));
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78 }
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79
77
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80 bool
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81 MachineBranchProbabilityInfo::isEdgeHot(const MachineBasicBlock *Src,
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82 const MachineBasicBlock *Dst) const {
0
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83 // Hot probability is at least 4/5 = 80%
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84 // FIXME: Compare against a static "hot" BranchProbability.
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85 return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
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86 }
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87
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88 MachineBasicBlock *
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89 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
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90 uint32_t MaxWeight = 0;
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91 MachineBasicBlock *MaxSucc = nullptr;
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92 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
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93 E = MBB->succ_end(); I != E; ++I) {
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94 uint32_t Weight = getEdgeWeight(MBB, I);
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95 if (Weight > MaxWeight) {
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96 MaxWeight = Weight;
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97 MaxSucc = *I;
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98 }
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99 }
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100
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101 if (getEdgeProbability(MBB, MaxSucc) >= BranchProbability(4, 5))
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102 return MaxSucc;
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103
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104 return nullptr;
0
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105 }
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106
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107 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
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108 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
0
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109 uint32_t Scale = 1;
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110 uint32_t D = getSumForBlock(Src, Scale);
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111 uint32_t N = getEdgeWeight(Src, Dst) / Scale;
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112
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113 return BranchProbability(N, D);
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114 }
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115
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116 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
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117 raw_ostream &OS, const MachineBasicBlock *Src,
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118 const MachineBasicBlock *Dst) const {
0
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119
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120 const BranchProbability Prob = getEdgeProbability(Src, Dst);
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121 OS << "edge MBB#" << Src->getNumber() << " -> MBB#" << Dst->getNumber()
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122 << " probability is " << Prob
0
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123 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
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124
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125 return OS;
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126 }