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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT COMPILER COMPONENTS --
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4 -- --
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5 -- S E M _ C A S E --
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6 -- --
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7 -- S p e c --
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8 -- --
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9 -- Copyright (C) 1996-2018, Free Software Foundation, Inc. --
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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17 -- for more details. You should have received a copy of the GNU General --
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18 -- Public License distributed with GNAT; see file COPYING3. If not, go to --
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19 -- http://www.gnu.org/licenses for a complete copy of the license. --
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20 -- --
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21 -- GNAT was originally developed by the GNAT team at New York University. --
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22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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23 -- --
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24 ------------------------------------------------------------------------------
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25
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26 -- Package containing the routines to process a list of discrete choices.
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27 -- Such lists can occur in two different constructs: case statements and
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28 -- record variants. We have factorized what used to be two very similar
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29 -- sets of routines in one place. These are not currently used for the
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30 -- aggregate case, since issues with nested aggregates make that case
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31 -- substantially different.
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32
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33 -- The following processing is required for such cases:
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34
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35 -- 1. Analysis of names of subtypes, constants, expressions appearing within
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36 -- the choices. This must be done when the construct is encountered to get
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37 -- proper visibility of names.
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38
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39 -- 2. Checking for semantic correctness of the choices. A lot of this could
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40 -- be done at the time when the construct is encountered, but not all, since
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41 -- in the case of variants, statically predicated subtypes won't be frozen
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42 -- (and the choice sets known) till the enclosing record type is frozen. So
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43 -- at least the check for no overlaps and covering the range must be delayed
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44 -- till the freeze point in this case.
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45
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46 -- 3. Set the Others_Discrete_Choices list for an others choice. This is
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47 -- used in various ways, e.g. to construct the disriminant checking function
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48 -- for the case of a variant with an others choice.
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49
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50 -- 4. In the case of static predicates, we need to expand out choices that
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51 -- correspond to the predicate for the back end. This expansion destroys
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52 -- the list of choices, so it should be delayed to expansion time. We do
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53 -- not want to mess up the -gnatct ASIS tree, which needs to be able to
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54
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55 -- Step 1 is performed by the generic procedure Analyze_Choices, which is
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56 -- called when the variant record or case statement/expression is first
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57 -- encountered.
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58
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59 -- Step 2 is performed by the generic procedure Check_Choices. We decide to
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60 -- do all semantic checking in that step, since as noted above some of this
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61 -- has to be deferred to the freeze point in any case for variants. For case
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62 -- statements and expressions, this procedure can be called at the time the
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63 -- case construct is encountered (after calling Analyze_Choices).
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64
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65 -- Step 3 is also performed by Check_Choices, since we need the static ranges
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66 -- for predicated subtypes to accurately construct this.
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67
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68 -- Step 4 is performed by the procedure Expand_Static_Predicates_In_Choices.
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69 -- For case statements, this call only happens during expansion, so the tree
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70 -- generated for ASIS does not have this expansion. For the Variant case, the
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71 -- expansion is done in the ASIS -gnatct case, but with a proper Rewrite call
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72 -- on the N_Variant node, so ASIS can retrieve the original. The reason we do
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73 -- the expansion unconditionally for variants is that other processing, for
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74 -- example for aggregates, relies on having a complete list of choices.
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75
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76 -- Historical note: We used to perform all four of these functions at once in
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77 -- a single procedure called Analyze_Choices. This routine was called at the
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78 -- time the construct was first encountered. That seemed to work OK up to Ada
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79 -- 2005, but the introduction of statically predicated subtypes with delayed
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80 -- evaluation of the static ranges made this completely wrong, both because
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81 -- the ASIS tree got destroyed by step 4, and steps 2 and 3 were too early
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82 -- in the variant record case.
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83
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84 with Types; use Types;
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85
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86 package Sem_Case is
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87
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88 procedure No_OP (C : Node_Id);
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89 -- The no-operation routine. Does mostly nothing. Can be used
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90 -- in the following generics for the parameters Process_Empty_Choice,
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91 -- or Process_Associated_Node. In the case of an empty range choice,
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92 -- routine emits a warning when Warn_On_Redundant_Constructs is enabled.
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93
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94 generic
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95 with procedure Process_Associated_Node (A : Node_Id);
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96 -- Associated with each case alternative or record variant A there is
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97 -- a node or list of nodes that need additional processing. This routine
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98 -- implements that processing.
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99
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100 package Generic_Analyze_Choices is
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101
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102 procedure Analyze_Choices
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103 (Alternatives : List_Id;
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104 Subtyp : Entity_Id);
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105 -- From a case expression, case statement, or record variant, this
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106 -- routine analyzes the corresponding list of discrete choices which
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107 -- appear in each element of the list Alternatives (for the variant
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108 -- part case, this is the variants, for a case expression or statement,
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109 -- this is the Alternatives).
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110 --
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111 -- Subtyp is the subtype of the discrete choices. The type against which
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112 -- the discrete choices must be resolved is its base type.
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113
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114 end Generic_Analyze_Choices;
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115
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116 generic
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117 with procedure Process_Empty_Choice (Choice : Node_Id);
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118 -- Processing to carry out for an empty Choice. Set to No_Op (declared
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119 -- above) if no such processing is required.
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120
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121 with procedure Process_Non_Static_Choice (Choice : Node_Id);
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122 -- Processing to carry out for a non static Choice (gives an error msg)
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123
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124 with procedure Process_Associated_Node (A : Node_Id);
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125 -- Associated with each case alternative or record variant A there is
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126 -- a node or list of nodes that need semantic processing. This routine
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127 -- implements that processing.
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128
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129 package Generic_Check_Choices is
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130
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131 procedure Check_Choices
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132 (N : Node_Id;
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133 Alternatives : List_Id;
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134 Subtyp : Entity_Id;
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135 Others_Present : out Boolean);
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136 -- From a case expression, case statement, or record variant N, this
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137 -- routine analyzes the corresponding list of discrete choices which
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138 -- appear in each element of the list Alternatives (for the variant
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139 -- part case, this is the variants, for a case expression or statement,
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140 -- this is the Alternatives).
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141 --
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142 -- Subtyp is the subtype of the discrete choices. The type against which
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143 -- the discrete choices must be resolved is its base type.
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144 --
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145 -- Others_Present is set to True if an Others choice is present in the
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146 -- list of choices, and in this case Others_Discrete_Choices is set in
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147 -- the N_Others_Choice node.
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148 --
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149 -- If a Discrete_Choice list contains at least one instance of a subtype
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150 -- with a static predicate, then the Has_SP_Choice flag is set true in
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151 -- the parent node (N_Variant, N_Case_Expression/Statement_Alternative).
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152
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153 end Generic_Check_Choices;
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154 end Sem_Case;
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