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 | // MultiLevelExit.cpp -- Replaces CFA's local control flow with C's versions. |
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8 | // |
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9 | // Author : Andrew Beach |
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10 | // Created On : Mon Nov 1 13:48:00 2021 |
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11 | // Last Modified By : Peter A. Buhr |
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12 | // Last Modified On : Thu Dec 14 17:34:12 2023 |
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13 | // Update Count : 39 |
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14 | // |
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15 | |
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16 | #include "MultiLevelExit.hpp" |
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17 | |
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18 | #include <set> |
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19 | |
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20 | #include "AST/Pass.hpp" |
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21 | #include "AST/Stmt.hpp" |
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22 | #include "LabelGenerator.hpp" |
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23 | |
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24 | using namespace std; |
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25 | using namespace ast; |
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26 | |
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27 | namespace ControlStruct { |
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28 | |
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29 | namespace { |
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30 | |
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31 | /// The return context is used to remember if returns are allowed and if |
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32 | /// not, why not. It is the nearest local control flow blocking construct. |
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33 | enum ReturnContext { |
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34 | MayReturn, |
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35 | InTryWithHandler, |
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36 | InResumeHandler, |
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37 | InFinally, |
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38 | }; |
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39 | |
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40 | class Entry { |
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41 | public: |
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42 | const Stmt * stmt; |
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43 | private: |
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44 | // Organized like a manual ADT. Avoids creating a bunch of dead data. |
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45 | struct Target { |
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46 | Label label; |
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47 | bool used = false; |
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48 | Target( const Label & label ) : label( label ) {} |
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49 | Target() : label( CodeLocation(), "" ) {} |
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50 | }; |
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51 | Target firstTarget; |
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52 | Target secondTarget; |
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53 | |
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54 | enum Kind { |
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55 | ForStmtK, WhileDoStmtK, CompoundStmtK, IfStmtK, CaseClauseK, SwitchStmtK, TryStmtK |
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56 | } kind; |
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57 | |
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58 | bool fallDefaultValid = true; |
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59 | |
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60 | static Label & useTarget( Target & target ) { |
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61 | target.used = true; |
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62 | return target.label; |
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63 | } |
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64 | public: |
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65 | Entry( const ForStmt * stmt, Label breakExit, Label contExit ) : |
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66 | stmt( stmt ), firstTarget( breakExit ), secondTarget( contExit ), kind( ForStmtK ) {} |
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67 | Entry( const WhileDoStmt * stmt, Label breakExit, Label contExit ) : |
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68 | stmt( stmt ), firstTarget( breakExit ), secondTarget( contExit ), kind( WhileDoStmtK ) {} |
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69 | Entry( const CompoundStmt *stmt, Label breakExit ) : |
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70 | stmt( stmt ), firstTarget( breakExit ), secondTarget(), kind( CompoundStmtK ) {} |
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71 | Entry( const IfStmt *stmt, Label breakExit ) : |
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72 | stmt( stmt ), firstTarget( breakExit ), secondTarget(), kind( IfStmtK ) {} |
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73 | Entry( const CaseClause *, const CompoundStmt *stmt, Label fallExit ) : |
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74 | stmt( stmt ), firstTarget( fallExit ), secondTarget(), kind( CaseClauseK ) {} |
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75 | Entry( const SwitchStmt *stmt, Label breakExit, Label fallDefaultExit ) : |
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76 | stmt( stmt ), firstTarget( breakExit ), secondTarget( fallDefaultExit ), kind( SwitchStmtK ) {} |
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77 | Entry( const TryStmt *stmt, Label breakExit ) : |
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78 | stmt( stmt ), firstTarget( breakExit ), secondTarget(), kind( TryStmtK ) {} |
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79 | |
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80 | // Check if this entry can be the target of the given type of control flow. |
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81 | bool isContTarget() const { return kind <= WhileDoStmtK; } |
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82 | bool isBreakTarget() const { return kind != CaseClauseK; } |
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83 | bool isFallTarget() const { return kind == CaseClauseK; } |
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84 | bool isFallDefaultTarget() const { return kind == SwitchStmtK; } |
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85 | |
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86 | // Check if this entry can be the target of an unlabelled break. |
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87 | bool isUnlabelledBreakTarget() const { return kind <= WhileDoStmtK || kind == SwitchStmtK; } |
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88 | |
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89 | // These routines set a target as being "used" by a BranchStmt |
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90 | Label useContExit() { assert( kind <= WhileDoStmtK ); return useTarget(secondTarget); } |
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91 | Label useBreakExit() { assert( kind != CaseClauseK ); return useTarget(firstTarget); } |
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92 | Label useFallExit() { assert( kind == CaseClauseK ); return useTarget(firstTarget); } |
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93 | Label useFallDefaultExit() { assert( kind == SwitchStmtK ); return useTarget(secondTarget); } |
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94 | |
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95 | // These routines check if a specific label for a statement is used by a BranchStmt |
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96 | bool isContUsed() const { assert( kind <= WhileDoStmtK ); return secondTarget.used; } |
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97 | bool isBreakUsed() const { assert( kind != CaseClauseK ); return firstTarget.used; } |
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98 | bool isFallUsed() const { assert( kind == CaseClauseK ); return firstTarget.used; } |
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99 | bool isFallDefaultUsed() const { assert( kind == SwitchStmtK ); return secondTarget.used; } |
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100 | void seenDefault() { fallDefaultValid = false; } |
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101 | bool isFallDefaultValid() const { return fallDefaultValid; } |
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102 | }; |
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103 | |
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104 | // Helper predicates used in find_if calls (it doesn't take methods): |
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105 | bool isBreakTarget( const Entry & entry ) { |
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106 | return entry.isBreakTarget(); |
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107 | } |
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108 | |
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109 | bool isContinueTarget( const Entry & entry ) { |
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110 | return entry.isContTarget(); |
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111 | } |
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112 | |
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113 | bool isFallthroughTarget( const Entry & entry ) { |
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114 | return entry.isFallTarget(); |
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115 | } |
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116 | |
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117 | bool isFallthroughDefaultTarget( const Entry & entry ) { |
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118 | return entry.isFallDefaultTarget(); |
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119 | } |
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120 | |
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121 | bool isUnlabelledBreakTarget( const Entry & entry ) { |
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122 | return entry.isUnlabelledBreakTarget(); |
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123 | } |
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124 | |
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125 | struct MultiLevelExitCore final : |
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126 | public WithVisitorRef<MultiLevelExitCore>, |
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127 | public WithShortCircuiting, public WithGuards { |
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128 | MultiLevelExitCore( const LabelToStmt & lt ); |
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129 | |
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130 | void previsit( const FunctionDecl * ); |
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131 | |
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132 | const CompoundStmt * previsit( const CompoundStmt * ); |
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133 | const BranchStmt * postvisit( const BranchStmt * ); |
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134 | void previsit( const WhileDoStmt * ); |
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135 | const WhileDoStmt * postvisit( const WhileDoStmt * ); |
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136 | void previsit( const ForStmt * ); |
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137 | const ForStmt * postvisit( const ForStmt * ); |
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138 | const CaseClause * previsit( const CaseClause * ); |
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139 | void previsit( const IfStmt * ); |
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140 | const IfStmt * postvisit( const IfStmt * ); |
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141 | void previsit( const SwitchStmt * ); |
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142 | const SwitchStmt * postvisit( const SwitchStmt * ); |
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143 | void previsit( const ReturnStmt * ); |
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144 | void previsit( const TryStmt * ); |
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145 | void postvisit( const TryStmt * ); |
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146 | void previsit( const CatchClause * ); |
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147 | void previsit( const FinallyClause * ); |
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148 | |
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149 | const Stmt * mutateLoop( const Stmt * body, Entry& ); |
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150 | |
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151 | const LabelToStmt & target_table; |
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152 | set<Label> fallthrough_labels; |
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153 | vector<Entry> enclosing_control_structures; |
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154 | Label break_label; |
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155 | ReturnContext ret_context; |
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156 | |
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157 | template<typename LoopNode> |
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158 | void prehandleLoopStmt( const LoopNode * loopStmt ); |
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159 | template<typename LoopNode> |
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160 | const LoopNode * posthandleLoopStmt( const LoopNode * loopStmt ); |
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161 | |
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162 | list<ptr<Stmt>> fixBlock( |
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163 | const list<ptr<Stmt>> & kids, bool caseClause ); |
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164 | |
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165 | void enterSealedContext( ReturnContext ); |
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166 | |
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167 | template<typename UnaryPredicate> |
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168 | auto findEnclosingControlStructure( UnaryPredicate pred ) { |
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169 | return find_if( enclosing_control_structures.rbegin(), |
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170 | enclosing_control_structures.rend(), pred ); |
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171 | } |
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172 | }; |
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173 | |
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174 | NullStmt * labelledNullStmt( const CodeLocation & cl, const Label & label ) { |
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175 | return new NullStmt( cl, vector<Label>{ label } ); |
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176 | } |
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177 | |
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178 | MultiLevelExitCore::MultiLevelExitCore( const LabelToStmt & lt ) : |
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179 | target_table( lt ), break_label( CodeLocation(), "" ), |
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180 | ret_context( ReturnContext::MayReturn ) |
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181 | {} |
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182 | |
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183 | void MultiLevelExitCore::previsit( const FunctionDecl * ) { |
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184 | visit_children = false; |
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185 | } |
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186 | |
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187 | const CompoundStmt * MultiLevelExitCore::previsit( |
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188 | const CompoundStmt * stmt ) { |
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189 | visit_children = false; |
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190 | |
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191 | // if the stmt is labelled then generate a label to check in postvisit if the label is used |
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192 | bool isLabeled = ! stmt->labels.empty(); |
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193 | if ( isLabeled ) { |
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194 | Label breakLabel = newLabel( "blockBreak", stmt ); |
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195 | enclosing_control_structures.emplace_back( stmt, breakLabel ); |
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196 | GuardAction( [this]() { enclosing_control_structures.pop_back(); } ); |
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197 | } |
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198 | |
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199 | auto mutStmt = mutate( stmt ); |
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200 | // A child statement may set the break label. |
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201 | mutStmt->kids = fixBlock( stmt->kids, false ); |
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202 | |
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203 | if ( isLabeled ) { |
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204 | assert( ! enclosing_control_structures.empty() ); |
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205 | Entry & entry = enclosing_control_structures.back(); |
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206 | if ( ! entry.useBreakExit().empty() ) { |
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207 | break_label = entry.useBreakExit(); |
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208 | } |
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209 | } |
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210 | return mutStmt; |
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211 | } |
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212 | |
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213 | size_t getUnusedIndex( const Stmt * stmt, const Label & originalTarget ) { |
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214 | const size_t size = stmt->labels.size(); |
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215 | |
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216 | // If the label is empty, do not add unused attribute. |
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217 | if ( originalTarget.empty() ) return size; |
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218 | |
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219 | // Search for a label that matches the originalTarget. |
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220 | for ( size_t i = 0 ; i < size ; ++i ) { |
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221 | const Label & label = stmt->labels[i]; |
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222 | if ( label == originalTarget ) { |
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223 | for ( const Attribute * attr : label.attributes ) { |
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224 | if ( attr->name == "unused" ) return size; |
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225 | } |
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226 | return i; |
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227 | } |
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228 | } |
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229 | assertf( false, "CFA internal error: could not find label '%s' on statement %s", |
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230 | originalTarget.name.c_str(), toString( stmt ).c_str() ); |
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231 | } |
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232 | |
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233 | const Stmt * addUnused( const Stmt * stmt, const Label & originalTarget ) { |
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234 | size_t i = getUnusedIndex( stmt, originalTarget ); |
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235 | if ( i == stmt->labels.size() ) { |
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236 | return stmt; |
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237 | } |
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238 | Stmt * mutStmt = mutate( stmt ); |
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239 | mutStmt->labels[i].attributes.push_back( new Attribute( "unused" ) ); |
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240 | return mutStmt; |
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241 | } |
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242 | |
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243 | // This routine updates targets on enclosing control structures to indicate which |
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244 | // label is used by the BranchStmt that is passed |
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245 | const BranchStmt * MultiLevelExitCore::postvisit( const BranchStmt * stmt ) { |
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246 | vector<Entry>::reverse_iterator targetEntry = |
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247 | enclosing_control_structures.rend(); |
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248 | |
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249 | // Labels on different stmts require different approaches to access |
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250 | switch ( stmt->kind ) { |
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251 | case BranchStmt::Goto: |
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252 | return stmt; |
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253 | case BranchStmt::Continue: |
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254 | case BranchStmt::Break: { |
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255 | bool isContinue = stmt->kind == BranchStmt::Continue; |
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256 | // Handle unlabeled continue. |
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257 | if ( isContinue && stmt->target.empty() ) { |
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258 | targetEntry = findEnclosingControlStructure( isContinueTarget ); |
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259 | if ( targetEntry == enclosing_control_structures.rend() ) { |
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260 | SemanticError( stmt->location, |
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261 | "\"continue\" outside a loop" ); |
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262 | } |
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263 | // Handle unlabeled break. |
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264 | } else if ( stmt->target.empty() ) { |
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265 | targetEntry = findEnclosingControlStructure( isUnlabelledBreakTarget ); |
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266 | if ( targetEntry == enclosing_control_structures.rend() ) { |
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267 | SemanticError( stmt->location, |
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268 | "\"break\" outside a loop or \"switch\"" ); |
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269 | } |
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270 | // Handle labeled break and continue. |
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271 | } else { |
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272 | // Lookup label in table to find attached control structure. |
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273 | targetEntry = findEnclosingControlStructure( |
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274 | [ targetStmt = target_table.at(stmt->target) ](auto entry){ |
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275 | return entry.stmt == targetStmt; |
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276 | } ); |
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277 | // Ensure that selected target is valid. |
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278 | if ( targetEntry == enclosing_control_structures.rend() |
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279 | || ( isContinue ? !isContinueTarget( *targetEntry ) : !isBreakTarget( *targetEntry ) ) ) { |
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280 | SemanticError( stmt->location, toString( (isContinue ? "\"continue\"" : "\"break\""), |
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281 | " target must be an enclosing ", (isContinue ? "loop: " : "control structure: "), |
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282 | stmt->originalTarget ) ); |
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283 | } |
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284 | } |
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285 | break; |
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286 | } |
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287 | // handle fallthrough in case/switch stmts |
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288 | case BranchStmt::FallThrough: { |
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289 | targetEntry = findEnclosingControlStructure( isFallthroughTarget ); |
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290 | // Check that target is valid. |
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291 | if ( targetEntry == enclosing_control_structures.rend() ) { |
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292 | SemanticError( stmt->location, "\"fallthrough\" must be enclosed in a \"switch\" or \"choose\"" ); |
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293 | } |
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294 | if ( ! stmt->target.empty() ) { |
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295 | // Labelled fallthrough: target must be a valid fallthough label. |
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296 | if ( ! fallthrough_labels.count( stmt->target ) ) { |
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297 | SemanticError( stmt->location, toString( "\"fallthrough\" target must be a later case statement: ", |
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298 | stmt->originalTarget ) ); |
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299 | } |
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300 | return new BranchStmt( stmt->location, BranchStmt::Goto, stmt->originalTarget ); |
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301 | } |
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302 | break; |
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303 | } |
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304 | case BranchStmt::FallThroughDefault: { |
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305 | targetEntry = findEnclosingControlStructure( isFallthroughDefaultTarget ); |
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306 | |
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307 | // Check if in switch or choose statement. |
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308 | if ( targetEntry == enclosing_control_structures.rend() ) { |
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309 | SemanticError( stmt->location, "\"fallthrough\" must be enclosed in a \"switch\" or \"choose\"" ); |
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310 | } |
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311 | |
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312 | // Check if switch or choose has default clause. |
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313 | auto switchStmt = strict_dynamic_cast< const SwitchStmt * >( targetEntry->stmt ); |
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314 | bool foundDefault = false; |
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315 | for ( auto caseStmt : switchStmt->cases ) { |
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316 | if ( caseStmt->isDefault() ) { |
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317 | foundDefault = true; |
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318 | break; |
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319 | } |
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320 | } |
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321 | if ( ! foundDefault ) { |
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322 | SemanticError( stmt->location, "\"fallthrough default\" must be enclosed in a \"switch\" or \"choose\"" |
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323 | "control structure with a \"default\" clause" ); |
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324 | } |
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325 | break; |
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326 | } |
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327 | default: |
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328 | assert( false ); |
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329 | } |
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330 | |
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331 | // Branch error checks: get the appropriate label name, which is always replaced. |
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332 | Label exitLabel( CodeLocation(), "" ); |
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333 | switch ( stmt->kind ) { |
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334 | case BranchStmt::Break: |
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335 | assert( ! targetEntry->useBreakExit().empty() ); |
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336 | exitLabel = targetEntry->useBreakExit(); |
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337 | break; |
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338 | case BranchStmt::Continue: |
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339 | assert( ! targetEntry->useContExit().empty() ); |
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340 | exitLabel = targetEntry->useContExit(); |
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341 | break; |
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342 | case BranchStmt::FallThrough: |
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343 | assert( ! targetEntry->useFallExit().empty() ); |
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344 | exitLabel = targetEntry->useFallExit(); |
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345 | break; |
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346 | case BranchStmt::FallThroughDefault: |
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347 | assert( ! targetEntry->useFallDefaultExit().empty() ); |
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348 | exitLabel = targetEntry->useFallDefaultExit(); |
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349 | // Check that fallthrough default comes before the default clause. |
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350 | if ( ! targetEntry->isFallDefaultValid() ) { |
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351 | SemanticError( stmt->location, "\"fallthrough default\" must precede the \"default\" clause" ); |
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352 | } |
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353 | break; |
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354 | default: |
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355 | assert(0); |
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356 | } |
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357 | assert( !exitLabel.empty() ); |
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358 | |
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359 | // Add unused attribute to silence warnings. |
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360 | targetEntry->stmt = addUnused( targetEntry->stmt, stmt->originalTarget ); |
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361 | |
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362 | // Replace with goto to make later passes more uniform. |
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363 | return new BranchStmt( stmt->location, BranchStmt::Goto, exitLabel ); |
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364 | } |
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365 | |
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366 | void MultiLevelExitCore::previsit( const WhileDoStmt * stmt ) { |
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367 | return prehandleLoopStmt( stmt ); |
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368 | } |
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369 | |
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370 | const WhileDoStmt * MultiLevelExitCore::postvisit( const WhileDoStmt * stmt ) { |
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371 | return posthandleLoopStmt( stmt ); |
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372 | } |
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373 | |
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374 | void MultiLevelExitCore::previsit( const ForStmt * stmt ) { |
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375 | return prehandleLoopStmt( stmt ); |
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376 | } |
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377 | |
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378 | const ForStmt * MultiLevelExitCore::postvisit( const ForStmt * stmt ) { |
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379 | return posthandleLoopStmt( stmt ); |
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380 | } |
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381 | |
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382 | // Mimic what the built-in push_front would do anyways. It is O(n). |
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383 | void push_front( vector<ptr<Stmt>> & vec, const Stmt * element ) { |
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384 | vec.emplace_back( nullptr ); |
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385 | for ( size_t i = vec.size() - 1 ; 0 < i ; --i ) { |
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386 | vec[ i ] = std::move( vec[ i - 1 ] ); |
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387 | } |
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388 | vec[ 0 ] = element; |
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389 | } |
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390 | |
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391 | const CaseClause * MultiLevelExitCore::previsit( const CaseClause * stmt ) { |
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392 | visit_children = false; |
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393 | |
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394 | // If default, mark seen. |
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395 | if ( stmt->isDefault() ) { |
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396 | assert( ! enclosing_control_structures.empty() ); |
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397 | enclosing_control_structures.back().seenDefault(); |
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398 | } |
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399 | |
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400 | // The cond may not exist, but if it does update it now. |
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401 | visitor->maybe_accept( stmt, &CaseClause::cond ); |
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402 | |
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403 | // Just save the mutated node for simplicity. |
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404 | CaseClause * mutStmt = mutate( stmt ); |
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405 | |
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406 | Label fallLabel = newLabel( "fallThrough", stmt->location ); |
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407 | if ( ! mutStmt->stmts.empty() ) { |
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408 | // These should already be in a block. |
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409 | auto first = mutStmt->stmts.front().get_and_mutate(); |
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410 | auto block = strict_dynamic_cast<CompoundStmt *>( first ); |
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411 | |
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412 | // Ensure that the stack isn't corrupted by exceptions in fixBlock. |
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413 | auto guard = makeFuncGuard( |
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414 | [&](){ enclosing_control_structures.emplace_back( mutStmt, block, fallLabel ); }, |
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415 | [this](){ enclosing_control_structures.pop_back(); } |
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416 | ); |
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417 | |
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418 | block->kids = fixBlock( block->kids, true ); |
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419 | |
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420 | // Add fallthrough label if necessary. |
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421 | assert( ! enclosing_control_structures.empty() ); |
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422 | Entry & entry = enclosing_control_structures.back(); |
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423 | if ( entry.isFallUsed() ) { |
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424 | mutStmt->stmts.push_back( labelledNullStmt( block->location, entry.useFallExit() ) ); |
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425 | } |
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426 | } |
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427 | assert( ! enclosing_control_structures.empty() ); |
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428 | Entry & entry = enclosing_control_structures.back(); |
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429 | assertf( dynamic_cast< const SwitchStmt * >( entry.stmt ), |
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430 | "CFA internal error: control structure enclosing a case clause must be a switch, but is: %s", |
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431 | toString( entry.stmt ).c_str() ); |
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432 | if ( mutStmt->isDefault() ) { |
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433 | if ( entry.isFallDefaultUsed() ) { |
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434 | // Add fallthrough default label if necessary. |
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435 | push_front( mutStmt->stmts, labelledNullStmt( stmt->location, entry.useFallDefaultExit() ) ); |
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436 | } |
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437 | } |
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438 | return mutStmt; |
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439 | } |
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440 | |
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441 | void MultiLevelExitCore::previsit( const IfStmt * stmt ) { |
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442 | bool labeledBlock = ! stmt->labels.empty(); |
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443 | if ( labeledBlock ) { |
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444 | Label breakLabel = newLabel( "blockBreak", stmt ); |
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445 | enclosing_control_structures.emplace_back( stmt, breakLabel ); |
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446 | GuardAction( [this](){ enclosing_control_structures.pop_back(); } ); |
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447 | } |
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448 | } |
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449 | |
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450 | const IfStmt * MultiLevelExitCore::postvisit( const IfStmt * stmt ) { |
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451 | bool labeledBlock = ! stmt->labels.empty(); |
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452 | if ( labeledBlock ) { |
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453 | auto this_label = enclosing_control_structures.back().useBreakExit(); |
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454 | if ( ! this_label.empty() ) { |
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455 | break_label = this_label; |
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456 | } |
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457 | } |
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458 | return stmt; |
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459 | } |
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460 | |
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461 | static bool isDefaultCase( const ptr<CaseClause> & caseClause ) { |
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462 | return caseClause->isDefault(); |
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463 | } |
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464 | |
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465 | void MultiLevelExitCore::previsit( const SwitchStmt * stmt ) { |
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466 | Label label = newLabel( "switchBreak", stmt ); |
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467 | auto it = find_if( stmt->cases.rbegin(), stmt->cases.rend(), isDefaultCase ); |
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468 | |
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469 | const CaseClause * defaultCase = it != stmt->cases.rend() ? (*it) : nullptr; |
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470 | Label defaultLabel = defaultCase ? newLabel( "fallThroughDefault", defaultCase->location ) : Label( stmt->location, "" ); |
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471 | enclosing_control_structures.emplace_back( stmt, label, defaultLabel ); |
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472 | GuardAction( [this]() { enclosing_control_structures.pop_back(); } ); |
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473 | |
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474 | // Collect valid labels for fallthrough. It starts with all labels at this level, then remove as each is seen during |
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475 | // traversal. |
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476 | for ( const CaseClause * caseStmt : stmt->cases ) { |
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477 | if ( caseStmt->stmts.empty() ) continue; |
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478 | auto block = caseStmt->stmts.front().strict_as<CompoundStmt>(); |
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479 | for ( const Stmt * stmt : block->kids ) { |
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480 | for ( const Label & l : stmt->labels ) { |
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481 | fallthrough_labels.insert( l ); |
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482 | } |
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483 | } |
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484 | } |
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485 | } |
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486 | |
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487 | const SwitchStmt * MultiLevelExitCore::postvisit( const SwitchStmt * stmt ) { |
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488 | assert( ! enclosing_control_structures.empty() ); |
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489 | Entry & entry = enclosing_control_structures.back(); |
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490 | assert( entry.stmt == stmt ); |
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491 | |
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492 | // Only run to generate the break label. |
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493 | if ( entry.isBreakUsed() ) { |
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494 | // To keep the switch statements uniform (all direct children of a SwitchStmt should be CastStmts), append the |
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495 | // exit label and break to the last case, create a default case if no cases. |
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496 | SwitchStmt * mutStmt = mutate( stmt ); |
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497 | if ( mutStmt->cases.empty() ) { |
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498 | mutStmt->cases.push_back( new CaseClause( mutStmt->location, nullptr, {} ) ); |
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499 | } |
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500 | |
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501 | auto mutCase = mutStmt->cases.back().get_and_mutate(); |
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502 | |
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503 | Label label( mutCase->location, "breakLabel" ); |
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504 | auto branch = new BranchStmt( mutCase->location, BranchStmt::Break, label ); |
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505 | branch->labels.push_back( entry.useBreakExit() ); |
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506 | mutCase->stmts.push_back( branch ); |
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507 | |
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508 | return mutStmt; |
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509 | } |
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510 | return stmt; |
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511 | } |
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512 | |
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513 | void MultiLevelExitCore::previsit( const ReturnStmt * stmt ) { |
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514 | char const * context; |
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515 | switch ( ret_context ) { |
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516 | case ReturnContext::MayReturn: |
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517 | return; |
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518 | case ReturnContext::InTryWithHandler: |
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519 | context = "try statement with a catch clause"; |
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520 | break; |
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521 | case ReturnContext::InResumeHandler: |
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522 | context = "catchResume clause"; |
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523 | break; |
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524 | case ReturnContext::InFinally: |
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525 | context = "finally clause"; |
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526 | break; |
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527 | default: |
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528 | assert(0); |
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529 | } |
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530 | SemanticError( stmt->location, "\"return\" may not appear in a %s", context ); |
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531 | } |
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532 | |
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533 | bool hasTerminate( const TryStmt * stmt ) { |
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534 | for ( auto clause : stmt->handlers ) { |
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535 | if ( ast::Terminate == clause->kind ) return true; |
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536 | } |
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537 | return false; |
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538 | } |
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539 | |
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540 | void MultiLevelExitCore::previsit( const TryStmt * stmt ) { |
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541 | visit_children = false; |
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542 | |
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543 | bool isLabeled = ! stmt->labels.empty(); |
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544 | if ( isLabeled ) { |
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545 | Label breakLabel = newLabel( "blockBreak", stmt ); |
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546 | enclosing_control_structures.emplace_back( stmt, breakLabel ); |
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547 | GuardAction([this](){ enclosing_control_structures.pop_back(); } ); |
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548 | } |
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549 | |
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550 | // Try statements/try blocks are only sealed with a termination handler. |
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551 | if ( hasTerminate( stmt ) ) { |
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552 | // This is just enterSealedContext except scoped to the block. |
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553 | // And that is because the state must change for a single field. |
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554 | ValueGuard< ReturnContext > guard0( ret_context ); |
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555 | ret_context = ReturnContext::InTryWithHandler; |
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556 | auto guard = makeFuncGuard( [](){}, [this, old = std::move(enclosing_control_structures)](){ enclosing_control_structures = std::move(old); }); |
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557 | enclosing_control_structures = vector<Entry>(); |
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558 | visitor->maybe_accept( stmt, &TryStmt::body ); |
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559 | } else { |
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560 | visitor->maybe_accept( stmt, &TryStmt::body ); |
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561 | } |
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562 | |
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563 | visitor->maybe_accept( stmt, &TryStmt::handlers ); |
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564 | visitor->maybe_accept( stmt, &TryStmt::finally ); |
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565 | } |
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566 | |
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567 | void MultiLevelExitCore::postvisit( const TryStmt * stmt ) { |
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568 | bool isLabeled = ! stmt->labels.empty(); |
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569 | if ( isLabeled ) { |
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570 | auto this_label = enclosing_control_structures.back().useBreakExit(); |
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571 | if ( ! this_label.empty() ) { |
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572 | break_label = this_label; |
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573 | } |
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574 | } |
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575 | } |
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576 | |
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577 | void MultiLevelExitCore::previsit( const CatchClause * clause ) { |
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578 | if ( ast::Resume == clause->kind ) { |
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579 | enterSealedContext( ReturnContext::InResumeHandler ); |
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580 | } |
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581 | } |
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582 | |
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583 | void MultiLevelExitCore::previsit( const FinallyClause * ) { |
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584 | enterSealedContext( ReturnContext::InFinally ); |
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585 | } |
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586 | |
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587 | const Stmt * MultiLevelExitCore::mutateLoop( |
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588 | const Stmt * body, Entry & entry ) { |
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589 | if ( entry.isBreakUsed() ) { |
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590 | break_label = entry.useBreakExit(); |
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591 | } |
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592 | |
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593 | // if continue is used insert a continue label into the back of the body of the loop |
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594 | if ( entry.isContUsed() ) { |
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595 | // { |
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596 | // body |
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597 | // ContinueLabel: ; |
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598 | // } |
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599 | return new CompoundStmt( body->location, { |
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600 | body, |
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601 | labelledNullStmt( body->location, entry.useContExit() ), |
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602 | } ); |
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603 | } |
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604 | |
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605 | return body; |
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606 | } |
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607 | |
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608 | template<typename LoopNode> |
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609 | void MultiLevelExitCore::prehandleLoopStmt( const LoopNode * loopStmt ) { |
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610 | // Create temporary labels and mark the enclosing loop before traversal. |
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611 | // The labels will be folded in if they are used. |
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612 | Label breakLabel = newLabel( "loopBreak", loopStmt ); |
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613 | Label contLabel = newLabel( "loopContinue", loopStmt ); |
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614 | enclosing_control_structures.emplace_back( loopStmt, breakLabel, contLabel ); |
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615 | |
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616 | GuardAction( [this](){ enclosing_control_structures.pop_back(); } ); |
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617 | |
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618 | // Because of fixBlock, this should be empty now (and must be). |
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619 | assert( nullptr == loopStmt->else_ ); |
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620 | } |
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621 | |
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622 | template<typename LoopNode> |
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623 | const LoopNode * MultiLevelExitCore::posthandleLoopStmt( const LoopNode * loopStmt ) { |
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624 | assert( ! enclosing_control_structures.empty() ); |
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625 | Entry & entry = enclosing_control_structures.back(); |
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626 | assert( entry.stmt == loopStmt ); |
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627 | |
---|
628 | // Now check if the labels are used and add them if so. |
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629 | return mutate_field( loopStmt, &LoopNode::body, mutateLoop( loopStmt->body, entry ) ); |
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630 | } |
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631 | |
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632 | list<ptr<Stmt>> MultiLevelExitCore::fixBlock( |
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633 | const list<ptr<Stmt>> & kids, bool is_case_clause ) { |
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634 | // Unfortunately cannot use automatic error collection. |
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635 | SemanticErrorException errors; |
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636 | |
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637 | list<ptr<Stmt>> ret; |
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638 | |
---|
639 | // Manually visit each child. |
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640 | for ( const ptr<Stmt> & kid : kids ) { |
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641 | if ( is_case_clause ) { |
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642 | // Once a label is seen, it's no longer a valid for fallthrough. |
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643 | for ( const Label & l : kid->labels ) { |
---|
644 | fallthrough_labels.erase( l ); |
---|
645 | } |
---|
646 | } |
---|
647 | |
---|
648 | ptr<Stmt> else_stmt = nullptr; |
---|
649 | const Stmt * to_visit; |
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650 | // check if loop node and if so add else clause if it exists |
---|
651 | if ( auto ptr = kid.as<WhileDoStmt>() ; ptr && ptr->else_ ) { |
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652 | else_stmt = ptr->else_; |
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653 | to_visit = mutate_field( ptr, &WhileDoStmt::else_, nullptr ); |
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654 | } else if ( auto ptr = kid.as<ForStmt>() ; ptr && ptr->else_ ) { |
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655 | else_stmt = ptr->else_; |
---|
656 | to_visit = mutate_field( ptr, &ForStmt::else_, nullptr ); |
---|
657 | } else { |
---|
658 | to_visit = kid.get(); |
---|
659 | } |
---|
660 | |
---|
661 | // This is the main (safe) visit of the child node. |
---|
662 | try { |
---|
663 | ret.push_back( to_visit->accept( *visitor ) ); |
---|
664 | } catch ( SemanticErrorException & e ) { |
---|
665 | errors.append( e ); |
---|
666 | } |
---|
667 | |
---|
668 | // The following sections handle visiting loop else clause and makes |
---|
669 | // sure breaking from a loop body does not execute that clause. |
---|
670 | Label local_break_label = std::move( break_label ); |
---|
671 | break_label = Label( CodeLocation(), "" ); |
---|
672 | |
---|
673 | if ( else_stmt ) try { |
---|
674 | ret.push_back( else_stmt->accept( *visitor ) ); |
---|
675 | } catch ( SemanticErrorException & e ) { |
---|
676 | errors.append( e ); |
---|
677 | } |
---|
678 | |
---|
679 | if ( !break_label.empty() ) { |
---|
680 | ret.push_back( labelledNullStmt( ret.back()->location, break_label ) ); |
---|
681 | break_label = Label( CodeLocation(), "" ); |
---|
682 | } |
---|
683 | |
---|
684 | // This handles a break from the body or non-loop statement. |
---|
685 | if ( !local_break_label.empty() ) { |
---|
686 | ret.push_back( labelledNullStmt( ret.back()->location, local_break_label ) ); |
---|
687 | } |
---|
688 | } |
---|
689 | |
---|
690 | if ( !errors.isEmpty() ) { |
---|
691 | throw errors; |
---|
692 | } |
---|
693 | return ret; |
---|
694 | } |
---|
695 | |
---|
696 | void MultiLevelExitCore::enterSealedContext( ReturnContext enter_context ) { |
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697 | GuardAction([this, old = std::move(enclosing_control_structures)](){ enclosing_control_structures = std::move(old); }); |
---|
698 | enclosing_control_structures = vector<Entry>(); |
---|
699 | GuardValue( ret_context ) = enter_context; |
---|
700 | } |
---|
701 | |
---|
702 | } // namespace |
---|
703 | |
---|
704 | const CompoundStmt * multiLevelExitUpdate( |
---|
705 | const CompoundStmt * stmt, const LabelToStmt & labelTable ) { |
---|
706 | // Must start in the body, so FunctionDecls can be a stopping point. |
---|
707 | Pass<MultiLevelExitCore> visitor( labelTable ); |
---|
708 | return stmt->accept( visitor ); |
---|
709 | } |
---|
710 | |
---|
711 | } // namespace ControlStruct |
---|
712 | |
---|
713 | // Local Variables: // |
---|
714 | // tab-width: 4 // |
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715 | // mode: c++ // |
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716 | // compile-command: "make install" // |
---|
717 | // End: // |
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