1 | // |
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2 | // Cforall Version 1.0.0 Copyright (C) 2015 University of Waterloo |
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3 | // |
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4 | // The contents of this file are covered under the licence agreement in the |
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5 | // file "LICENCE" distributed with Cforall. |
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6 | // |
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7 | // ResolveAssertions.cc -- |
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8 | // |
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9 | // Author : Aaron B. Moss |
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10 | // Created On : Fri Oct 05 13:46:00 2018 |
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11 | // Last Modified By : Aaron B. Moss |
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12 | // Last Modified On : Fri Oct 05 13:46:00 2018 |
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13 | // Update Count : 1 |
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14 | // |
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15 | |
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16 | #include "ResolveAssertions.h" |
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17 | |
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18 | #include <cassert> // for assertf |
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19 | #include <list> // for list |
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20 | #include <unordered_map> // for unordered_map |
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21 | #include <utility> // for move |
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22 | #include <vector> // for vector |
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23 | |
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24 | #include "Alternative.h" // for Alternative, AssertionItem |
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25 | #include "Common/FilterCombos.h" // for filterCombos |
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26 | #include "Common/utility.h" // for sort_mins |
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27 | #include "SymTab/Indexer.h" // for Indexer |
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28 | #include "TypeEnvironment.h" // for TypeEnvironment, etc. |
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29 | #include "typeops.h" // for adjustExprType |
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30 | #include "Unify.h" // for unify |
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31 | |
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32 | namespace ResolvExpr { |
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33 | /// Unified assertion candidate |
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34 | struct AssnCandidate { |
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35 | SymTab::Indexer::IdData cdata; ///< Satisfying declaration |
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36 | Type* adjType; ///< Satisfying type |
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37 | TypeEnvironment env; ///< Post-unification environment |
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38 | AssertionSet have; ///< Post-unification have-set |
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39 | AssertionSet need; ///< Post-unification need-set |
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40 | OpenVarSet openVars; ///< Post-unification open-var set |
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41 | |
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42 | AssnCandidate( const SymTab::Indexer::IdData& cdata, Type* adjType, TypeEnvironment&& env, |
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43 | AssertionSet&& have, AssertionSet&& need, OpenVarSet&& openVars ) |
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44 | : cdata(cdata), adjType(adjType), env(std::move(env)), have(std::move(have)), |
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45 | need(std::move(need)), openVars(std::move(openVars)) {} |
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46 | }; |
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47 | |
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48 | /// List of candidate assertion resolutions |
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49 | using CandidateList = std::vector<AssnCandidate>; |
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50 | |
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51 | /// Reference to single deferred item |
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52 | struct DeferRef { |
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53 | const DeclarationWithType* decl; |
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54 | const AssertionSetValue& info; |
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55 | const AssnCandidate& match; |
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56 | }; |
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57 | |
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58 | /// Wrapper for the deferred items from a single assertion resolution. |
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59 | /// Acts like indexed list of DeferRef |
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60 | struct DeferItem { |
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61 | DeclarationWithType* decl; |
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62 | AssertionSetValue info; |
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63 | CandidateList matches; |
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64 | |
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65 | DeferItem( DeclarationWithType* decl, const AssertionSetValue& info, |
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66 | CandidateList&& matches ) |
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67 | : decl(decl), info(info), matches(std::move(matches)) {} |
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68 | |
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69 | bool empty() const { return matches.empty(); } |
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70 | |
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71 | CandidateList::size_type size() const { return matches.size(); } |
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72 | |
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73 | DeferRef operator[] ( unsigned i ) const { return { decl, info, matches[i] }; } |
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74 | }; |
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75 | |
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76 | /// List of deferred resolution items |
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77 | using DeferList = std::vector<DeferItem>; |
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78 | |
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79 | /// Combo iterator that combines candidates into an output list, merging their environments. |
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80 | /// Rejects an appended candidate if the environments cannot be merged. |
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81 | class CandidateEnvMerger { |
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82 | /// Current list of merged candidates |
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83 | std::vector<DeferRef> crnt; |
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84 | /// Stack of environments to support backtracking |
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85 | std::vector<TypeEnvironment> envs; |
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86 | /// Stack of open variables to support backtracking |
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87 | std::vector<OpenVarSet> varSets; |
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88 | /// Indexer to use for merges |
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89 | const SymTab::Indexer& indexer; |
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90 | |
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91 | public: |
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92 | /// The merged environment/open variables and the list of candidates |
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93 | struct OutType { |
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94 | TypeEnvironment env; |
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95 | OpenVarSet openVars; |
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96 | std::vector<DeferRef> assns; |
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97 | |
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98 | OutType( const TypeEnvironment& env, const OpenVarSet& openVars, |
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99 | const std::vector<DeferRef>& assns ) |
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100 | : env(env), openVars(openVars), assns(assns) {} |
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101 | }; |
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102 | |
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103 | CandidateEnvMerger( const TypeEnvironment& env, const OpenVarSet& openVars, |
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104 | const SymTab::Indexer& indexer ) |
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105 | : crnt(), envs{ env }, varSets{ openVars }, indexer(indexer) {} |
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106 | |
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107 | bool append( DeferRef i ) { |
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108 | TypeEnvironment env = envs.back(); |
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109 | OpenVarSet openVars = varSets.back(); |
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110 | mergeOpenVars( openVars, i.match.openVars ); |
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111 | |
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112 | if ( ! env.combine( i.match.env, openVars, indexer ) ) return false; |
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113 | |
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114 | crnt.emplace_back( i ); |
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115 | envs.emplace_back( env ); |
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116 | varSets.emplace_back( openVars ); |
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117 | return true; |
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118 | } |
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119 | |
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120 | void backtrack() { |
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121 | crnt.pop_back(); |
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122 | envs.pop_back(); |
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123 | varSets.pop_back(); |
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124 | } |
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125 | |
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126 | OutType finalize() { return { envs.back(), varSets.back(), crnt }; } |
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127 | }; |
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128 | |
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129 | /// Comparator for CandidateEnvMerger outputs that sums their costs and caches the stored |
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130 | /// sums |
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131 | struct CandidateCost { |
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132 | using Element = CandidateEnvMerger::OutType; |
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133 | private: |
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134 | using Memo = std::unordered_map<const Element*, Cost>; |
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135 | mutable Memo cache; ///< cache of element costs |
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136 | const SymTab::Indexer& indexer; ///< Indexer for costing |
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137 | |
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138 | public: |
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139 | CandidateCost( const SymTab::Indexer& indexer ) : indexer(indexer) {} |
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140 | |
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141 | /// reports the cost of an element |
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142 | Cost get( const Element& x ) const { |
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143 | Memo::const_iterator it = cache.find( &x ); |
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144 | if ( it == cache.end() ) { |
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145 | Cost k = Cost::zero; |
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146 | for ( const auto& assn : x.assns ) { |
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147 | k += computeConversionCost( |
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148 | assn.match.adjType, assn.decl->get_type(), indexer, x.env ); |
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149 | } |
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150 | it = cache.emplace_hint( it, &x, k ); |
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151 | } |
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152 | return it->second; |
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153 | } |
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154 | |
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155 | /// compares elements by cost |
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156 | bool operator() ( const Element& a, const Element& b ) const { |
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157 | return get( a ) < get( b ); |
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158 | } |
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159 | }; |
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160 | |
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161 | /// Flag for state iteration |
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162 | enum IterateFlag { IterateState }; |
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163 | |
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164 | /// State needed to resolve a set of assertions |
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165 | struct ResnState { |
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166 | Alternative alt; ///< Alternative assertion is rooted on |
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167 | std::vector<AssertionItem> need; ///< Assertions to find |
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168 | AssertionSet newNeed; ///< New assertions for current resolutions |
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169 | DeferList deferred; ///< Deferred matches |
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170 | SymTab::Indexer& indexer; ///< Name lookup (depends on previous assertions) |
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171 | |
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172 | /// Initial resolution state for an alternative |
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173 | ResnState( Alternative& a, SymTab::Indexer& indexer ) |
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174 | : alt(a), need(), newNeed(), deferred(), indexer(indexer) { |
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175 | need.swap( a.need ); |
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176 | } |
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177 | |
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178 | /// Updated resolution state with new need-list |
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179 | ResnState( ResnState&& o, IterateFlag ) |
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180 | : alt(std::move(o.alt)), need(o.newNeed.begin(), o.newNeed.end()), newNeed(), deferred(), |
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181 | indexer(o.indexer) {} |
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182 | }; |
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183 | |
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184 | /// Binds a single assertion, updating resolution state |
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185 | void bindAssertion( const DeclarationWithType* decl, AssertionSetValue info, Alternative& alt, |
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186 | AssnCandidate& match ) { |
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187 | |
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188 | DeclarationWithType* candidate = match.cdata.id; |
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189 | assertf( candidate->get_uniqueId(), "Assertion candidate does not have a unique ID: %s", toString( candidate ).c_str() ); |
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190 | |
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191 | Expression* varExpr = match.cdata.combine( alt.cvtCost ); |
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192 | delete varExpr->result; |
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193 | varExpr->result = match.adjType->clone(); |
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194 | |
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195 | // follow the current assertion's ID chain to find the correct set of inferred parameters |
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196 | // to add the candidate o (i.e. the set of inferred parameters belonging to the entity |
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197 | // which requested the assertion parameter) |
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198 | InferredParams* inferParams = &alt.expr->inferParams; |
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199 | for ( UniqueId id : info.idChain ) { |
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200 | inferParams = (*inferParams)[ id ].inferParams.get(); |
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201 | } |
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202 | |
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203 | (*inferParams)[ decl->get_uniqueId() ] = ParamEntry{ |
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204 | candidate->get_uniqueId(), match.adjType, decl->get_type()->clone(), varExpr }; |
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205 | } |
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206 | |
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207 | /// Adds a captured assertion to the symbol table |
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208 | void addToIndexer( AssertionSet &assertSet, SymTab::Indexer &indexer ) { |
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209 | for ( AssertionSet::iterator i = assertSet.begin(); i != assertSet.end(); ++i ) { |
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210 | if ( i->second.isUsed ) { |
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211 | indexer.addId( i->first ); |
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212 | } |
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213 | } |
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214 | } |
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215 | |
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216 | /// Resolve a single assertion, in context |
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217 | bool resolveAssertion( AssertionItem& assn, ResnState& resn ) { |
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218 | // skip unused assertions |
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219 | if ( ! assn.info.isUsed ) return true; |
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220 | |
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221 | // lookup candidates for this assertion |
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222 | std::list< SymTab::Indexer::IdData > candidates; |
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223 | resn.indexer.lookupId( assn.decl->name, candidates ); |
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224 | |
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225 | // find the candidates that unify with the desired type |
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226 | CandidateList matches; |
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227 | for ( const auto& cdata : candidates ) { |
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228 | DeclarationWithType* candidate = cdata.id; |
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229 | |
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230 | // build independent unification context for candidate |
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231 | AssertionSet have, newNeed; |
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232 | TypeEnvironment newEnv{ resn.alt.env }; |
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233 | OpenVarSet newOpenVars{ resn.alt.openVars }; |
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234 | Type* adjType = candidate->get_type()->clone(); |
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235 | adjustExprType( adjType, newEnv, resn.indexer ); |
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236 | |
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237 | // keep unifying candidates |
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238 | if ( unify( assn.decl->get_type(), adjType, newEnv, newNeed, have, newOpenVars, |
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239 | resn.indexer ) ) { |
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240 | // set up idChain on new assertions |
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241 | for ( auto& a : newNeed ) { |
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242 | a.second.idChain = assn.info.idChain; |
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243 | a.second.idChain.push_back( assn.decl->get_uniqueId() ); |
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244 | } |
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245 | |
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246 | matches.emplace_back( cdata, adjType, std::move(newEnv), std::move(have), |
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247 | std::move(newNeed), std::move(newOpenVars) ); |
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248 | } else { |
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249 | delete adjType; |
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250 | } |
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251 | } |
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252 | |
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253 | // break if no suitable assertion |
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254 | if ( matches.empty() ) return false; |
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255 | |
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256 | // defer if too many suitable assertions |
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257 | if ( matches.size() > 1 ) { |
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258 | resn.deferred.emplace_back( assn.decl, assn.info, std::move(matches) ); |
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259 | return true; |
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260 | } |
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261 | |
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262 | // otherwise bind current match in ongoing scope |
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263 | AssnCandidate& match = matches.front(); |
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264 | addToIndexer( match.have, resn.indexer ); |
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265 | resn.newNeed.insert( match.need.begin(), match.need.end() ); |
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266 | resn.alt.env = std::move(match.env); |
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267 | resn.alt.openVars = std::move(match.openVars); |
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268 | |
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269 | bindAssertion( assn.decl, assn.info, resn.alt, match ); |
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270 | return true; |
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271 | } |
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272 | |
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273 | ///< Limit to depth of recursion of assertion satisfaction |
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274 | static const int recursionLimit = /* 10 */ 4; |
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275 | |
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276 | void resolveAssertions( Alternative& alt, const SymTab::Indexer& indexer, AltList& out ) { |
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277 | // finish early if no assertions to resolve |
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278 | if ( alt.need.empty() ) { |
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279 | out.emplace_back( alt ); |
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280 | return; |
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281 | } |
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282 | |
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283 | // build list of possible resolutions |
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284 | using ResnList = std::vector<ResnState>; |
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285 | SymTab::Indexer root_indexer{ indexer }; |
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286 | ResnList resns{ ResnState{ alt, root_indexer } }; |
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287 | ResnList new_resns{}; |
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288 | |
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289 | // resolve assertions in breadth-first-order up to a limited number of levels deep |
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290 | for ( unsigned level = 0; level < recursionLimit; ++level ) { |
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291 | // scan over all mutually-compatible resolutions |
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292 | for ( auto& resn : resns ) { |
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293 | // make initial pass at matching assertions |
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294 | for ( auto& assn : resn.need ) { |
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295 | // fail early if any assertion is not resolvable |
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296 | if ( ! resolveAssertion( assn, resn ) ) goto nextResn; |
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297 | } |
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298 | |
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299 | if ( resn.deferred.empty() ) { |
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300 | // either add successful match or push back next state |
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301 | if ( resn.newNeed.empty() ) { |
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302 | out.emplace_back( resn.alt ); |
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303 | } else { |
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304 | new_resns.emplace_back( std::move(resn), IterateState ); |
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305 | } |
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306 | } else { |
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307 | // resolve deferred assertions by mutual compatibility and sort by cost |
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308 | std::vector<CandidateEnvMerger::OutType> compatible = filterCombos( |
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309 | resn.deferred, |
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310 | CandidateEnvMerger{ resn.alt.env, resn.alt.openVars, resn.indexer } ); |
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311 | auto lmin = sort_mins( compatible.begin(), compatible.end(), |
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312 | CandidateCost{resn.indexer} ); |
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313 | |
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314 | for ( auto it = compatible.begin(); it != lmin ; ++it ) { |
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315 | auto& compat = *it; |
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316 | ResnState new_resn = resn; |
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317 | |
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318 | // add compatible assertions to new resolution state |
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319 | for ( DeferRef r : compat.assns ) { |
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320 | AssnCandidate match = r.match; |
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321 | addToIndexer( match.have, new_resn.indexer ); |
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322 | new_resn.newNeed.insert( match.need.begin(), match.need.end() ); |
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323 | |
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324 | bindAssertion( r.decl, r.info, new_resn.alt, match ); |
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325 | } |
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326 | |
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327 | // set mutual environment into resolution state |
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328 | new_resn.alt.env = std::move(compat.env); |
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329 | new_resn.alt.openVars = std::move(compat.openVars); |
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330 | |
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331 | // either add sucessful match or push back next state |
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332 | if ( new_resn.newNeed.empty() ) { |
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333 | out.emplace_back( new_resn.alt ); |
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334 | } else { |
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335 | new_resns.emplace_back( std::move(new_resn), IterateState ); |
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336 | } |
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337 | } |
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338 | } |
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339 | nextResn:; } |
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340 | |
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341 | // finish or reset for next round |
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342 | if ( new_resns.empty() ) return; |
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343 | resns.swap( new_resns ); |
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344 | new_resns.clear(); |
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345 | } |
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346 | |
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347 | // exceeded recursion limit if reaches here |
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348 | if ( out.empty() ) { |
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349 | SemanticError( alt.expr->location, "Too many recursive assertions" ); |
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350 | } |
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351 | } |
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352 | } // namespace ResolvExpr |
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353 | |
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354 | // Local Variables: // |
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355 | // tab-width: 4 // |
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356 | // mode: c++ // |
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357 | // compile-command: "make install" // |
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358 | // End: // |
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