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author kono
date Fri, 27 Oct 2017 22:46:09 +0900
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1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- S E M _ C A S E --
6 -- --
7 -- S p e c --
8 -- --
9 -- Copyright (C) 1996-2016, Free Software Foundation, Inc. --
10 -- --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 3, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING3. If not, go to --
19 -- http://www.gnu.org/licenses for a complete copy of the license. --
20 -- --
21 -- GNAT was originally developed by the GNAT team at New York University. --
22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
23 -- --
24 ------------------------------------------------------------------------------
25
26 -- Package containing the routines to process a list of discrete choices.
27 -- Such lists can occur in two different constructs: case statements and
28 -- record variants. We have factorized what used to be two very similar
29 -- sets of routines in one place. These are not currently used for the
30 -- aggregate case, since issues with nested aggregates make that case
31 -- substantially different.
32
33 -- The following processing is required for such cases:
34
35 -- 1. Analysis of names of subtypes, constants, expressions appearing within
36 -- the choices. This must be done when the construct is encountered to get
37 -- proper visibility of names.
38
39 -- 2. Checking for semantic correctness of the choices. A lot of this could
40 -- be done at the time when the construct is encountered, but not all, since
41 -- in the case of variants, statically predicated subtypes won't be frozen
42 -- (and the choice sets known) till the enclosing record type is frozen. So
43 -- at least the check for no overlaps and covering the range must be delayed
44 -- till the freeze point in this case.
45
46 -- 3. Set the Others_Discrete_Choices list for an others choice. This is
47 -- used in various ways, e.g. to construct the disriminant checking function
48 -- for the case of a variant with an others choice.
49
50 -- 4. In the case of static predicates, we need to expand out choices that
51 -- correspond to the predicate for the back end. This expansion destroys
52 -- the list of choices, so it should be delayed to expansion time. We do
53 -- not want to mess up the -gnatct ASIS tree, which needs to be able to
54
55 -- Step 1 is performed by the generic procedure Analyze_Choices, which is
56 -- called when the variant record or case statement/expression is first
57 -- encountered.
58
59 -- Step 2 is performed by the generic procedure Check_Choices. We decide to
60 -- do all semantic checking in that step, since as noted above some of this
61 -- has to be deferred to the freeze point in any case for variants. For case
62 -- statements and expressions, this procedure can be called at the time the
63 -- case construct is encountered (after calling Analyze_Choices).
64
65 -- Step 3 is also performed by Check_Choices, since we need the static ranges
66 -- for predicated subtypes to accurately construct this.
67
68 -- Step 4 is performed by the procedure Expand_Static_Predicates_In_Choices.
69 -- For case statements, this call only happens during expansion, so the tree
70 -- generated for ASIS does not have this expansion. For the Variant case, the
71 -- expansion is done in the ASIS -gnatct case, but with a proper Rewrite call
72 -- on the N_Variant node, so ASIS can retrieve the original. The reason we do
73 -- the expansion unconditionally for variants is that other processing, for
74 -- example for aggregates, relies on having a complete list of choices.
75
76 -- Historical note: We used to perform all four of these functions at once in
77 -- a single procedure called Analyze_Choices. This routine was called at the
78 -- time the construct was first encountered. That seemed to work OK up to Ada
79 -- 2005, but the introduction of statically predicated subtypes with delayed
80 -- evaluation of the static ranges made this completely wrong, both because
81 -- the ASIS tree got destroyed by step 4, and steps 2 and 3 were too early
82 -- in the variant record case.
83
84 with Types; use Types;
85
86 package Sem_Case is
87
88 procedure No_OP (C : Node_Id);
89 -- The no-operation routine. Does mostly nothing. Can be used
90 -- in the following generics for the parameters Process_Empty_Choice,
91 -- or Process_Associated_Node. In the case of an empty range choice,
92 -- routine emits a warning when Warn_On_Redundant_Constructs is enabled.
93
94 generic
95 with procedure Process_Associated_Node (A : Node_Id);
96 -- Associated with each case alternative or record variant A there is
97 -- a node or list of nodes that need additional processing. This routine
98 -- implements that processing.
99
100 package Generic_Analyze_Choices is
101
102 procedure Analyze_Choices
103 (Alternatives : List_Id;
104 Subtyp : Entity_Id);
105 -- From a case expression, case statement, or record variant, this
106 -- routine analyzes the corresponding list of discrete choices which
107 -- appear in each element of the list Alternatives (for the variant
108 -- part case, this is the variants, for a case expression or statement,
109 -- this is the Alternatives).
110 --
111 -- Subtyp is the subtype of the discrete choices. The type against which
112 -- the discrete choices must be resolved is its base type.
113
114 end Generic_Analyze_Choices;
115
116 generic
117 with procedure Process_Empty_Choice (Choice : Node_Id);
118 -- Processing to carry out for an empty Choice. Set to No_Op (declared
119 -- above) if no such processing is required.
120
121 with procedure Process_Non_Static_Choice (Choice : Node_Id);
122 -- Processing to carry out for a non static Choice (gives an error msg)
123
124 with procedure Process_Associated_Node (A : Node_Id);
125 -- Associated with each case alternative or record variant A there is
126 -- a node or list of nodes that need semantic processing. This routine
127 -- implements that processing.
128
129 package Generic_Check_Choices is
130
131 procedure Check_Choices
132 (N : Node_Id;
133 Alternatives : List_Id;
134 Subtyp : Entity_Id;
135 Others_Present : out Boolean);
136 -- From a case expression, case statement, or record variant N, this
137 -- routine analyzes the corresponding list of discrete choices which
138 -- appear in each element of the list Alternatives (for the variant
139 -- part case, this is the variants, for a case expression or statement,
140 -- this is the Alternatives).
141 --
142 -- Subtyp is the subtype of the discrete choices. The type against which
143 -- the discrete choices must be resolved is its base type.
144 --
145 -- Others_Present is set to True if an Others choice is present in the
146 -- list of choices, and in this case Others_Discrete_Choices is set in
147 -- the N_Others_Choice node.
148 --
149 -- If a Discrete_Choice list contains at least one instance of a subtype
150 -- with a static predicate, then the Has_SP_Choice flag is set true in
151 -- the parent node (N_Variant, N_Case_Expression/Statement_Alternative).
152
153 end Generic_Check_Choices;
154 end Sem_Case;