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comparison gcc/ada/expander.ads @ 111:04ced10e8804
gcc 7
author | kono |
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date | Fri, 27 Oct 2017 22:46:09 +0900 |
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children | 84e7813d76e9 |
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1 ------------------------------------------------------------------------------ | |
2 -- -- | |
3 -- GNAT COMPILER COMPONENTS -- | |
4 -- -- | |
5 -- E X P A N D E R -- | |
6 -- -- | |
7 -- S p e c -- | |
8 -- -- | |
9 -- Copyright (C) 1992-2016, 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 -- This procedure performs any required expansion for the specified node. | |
27 -- The argument is the node that is a candidate for possible expansion. | |
28 -- If no expansion is required, then Expand returns without doing anything. | |
29 | |
30 -- If the node does need expansion, then the subtree is replaced by the | |
31 -- tree corresponding to the required rewriting. This tree is a syntactic | |
32 -- tree, except that all Entity fields must be correctly set on all | |
33 -- direct names, since the expander presumably knows what it wants, and in | |
34 -- any case it doesn't work to have the semantic analyzer perform visibility | |
35 -- analysis on these trees (they may have references to non-visible runtime | |
36 -- routines etc.) There are a few exceptions to this rule in special cases, | |
37 -- but they must be documented clearly. | |
38 | |
39 -- Expand is called in two different situations: | |
40 | |
41 -- Nodes that are not subexpressions (Nkind not in N_Subexpr) | |
42 | |
43 -- In this case, Expand is called from the body of Sem, immediately | |
44 -- after completing semantic analysis by calling the corresponding | |
45 -- Analyze_N_xxx procedure. If expansion occurs, the given node must | |
46 -- be replaced with another node that is also not a subexpression. | |
47 -- This seems naturally to be the case, since it is hard to imagine any | |
48 -- situation in which it would make sense to replace a non-expression | |
49 -- subtree with an expression. Once the substitution is completed, the | |
50 -- Expand routine must call Analyze on the resulting node to do any | |
51 -- required semantic analysis. Note that references to children copied | |
52 -- from the old tree won't be reanalyzed, since their Analyzed flag | |
53 -- is set. | |
54 | |
55 -- Nodes that are subexpressions (Nkind in N_Subexpr) | |
56 | |
57 -- In this case, Expand is called from Sem_Res.Resolve after completing | |
58 -- the resolution of the subexpression (this means that the expander sees | |
59 -- the fully typed subtree). If expansion occurs, the given node must be | |
60 -- replaced by a node that is also a subexpression. Again it is hard | |
61 -- to see how this restriction could possibly be violated. Once the | |
62 -- substitution is completed, the Expand routine must first call Analyze | |
63 -- on the resulting node to do any required semantic analysis, and then | |
64 -- call Resolve on the node to set the type (typically the type will be | |
65 -- the same as the original type of the input node, but this is not | |
66 -- always the case). | |
67 | |
68 -- In both these cases, Replace or Rewrite must be used to achieve the | |
69 -- expansion of the node, since the Expander routine is only passed the | |
70 -- Node_Id of the node to be expanded, and the resulting expanded Node_Id | |
71 -- must be the same (the parameter to Expand is mode in, not mode in-out). | |
72 | |
73 -- For nodes other than subexpressions, it is not necessary to preserve the | |
74 -- original tree in the Expand routines, unlike the case for modifications | |
75 -- to the tree made in the semantic analyzer. This is because anyone who is | |
76 -- interested in working with the original tree (like ASIS) is required to | |
77 -- compile in semantics checks only mode. Thus Replace may be freely used | |
78 -- in such instances. | |
79 | |
80 -- For subexpressions, preservation of the original tree is required because | |
81 -- of the need for conformance checking of default expressions, which occurs | |
82 -- on expanded trees. This means that Replace should not ever be used on | |
83 -- on subexpression nodes. Instead use Rewrite. | |
84 | |
85 -- Note: the front end avoids calls to any of the expand routines if code | |
86 -- is not being generated. This is done for three reasons: | |
87 | |
88 -- 1. Make sure tree does not get mucked up by the expander if no | |
89 -- code is being generated, and is thus usable by ASIS etc. | |
90 | |
91 -- 2. Save time, since expansion is not needed if a compilation is | |
92 -- being done only to check the semantics, or if code generation | |
93 -- has been canceled due to previously detected errors. | |
94 | |
95 -- 3. Allow the expand routines to assume that the tree is error free. | |
96 -- This results from the fact that code generation mode is always | |
97 -- cancelled when any error occurs. | |
98 | |
99 -- If we ever decide to implement a feature allowing object modules to be | |
100 -- generated even if errors have been detected, then point 3 will no longer | |
101 -- hold, and the expand routines will have to be modified to operate properly | |
102 -- in the presence of errors (for many reasons this is not currently true). | |
103 | |
104 -- Note: a consequence of this approach is that error messages must never | |
105 -- be generated in the expander, since this would mean that such error | |
106 -- messages are not generated when the expander is not being called. | |
107 | |
108 -- Expansion is the last stage of analyzing a node, so Expand sets the | |
109 -- Analyzed flag of the node being analyzed as its last action. This is | |
110 -- done even if expansion is off (in this case, the only effect of the | |
111 -- call to Expand is to set the Analyzed flag to True). | |
112 | |
113 with Types; use Types; | |
114 | |
115 package Expander is | |
116 | |
117 -- The flag Opt.Expander_Active controls whether expansion is active | |
118 -- (True) or deactivated (False). When expansion is deactivated all | |
119 -- calls to expander routines have no effect. To temporarily disable | |
120 -- expansion, always call the routines defined below, do NOT change | |
121 -- Expander_Active directly. | |
122 -- | |
123 -- You should not use this flag to test if you are currently processing | |
124 -- a generic spec or body. Use the flag Inside_A_Generic instead (see | |
125 -- the spec of package Sem). | |
126 -- | |
127 -- There is no good reason for permanently changing the value of this flag | |
128 -- except after detecting a syntactic or semantic error. In this event | |
129 -- this flag is set to False to disable all subsequent expansion activity. | |
130 -- | |
131 -- In general this flag should be used as a read only value. The only | |
132 -- exceptions where it makes sense to temporarily change its value are: | |
133 -- | |
134 -- (a) when starting/completing the processing of a generic definition | |
135 -- or declaration (see routines Start_Generic_Processing and | |
136 -- End_Generic_Processing in Sem_Ch12) | |
137 -- | |
138 -- (b) when starting/completing the pre-analysis of an expression | |
139 -- (see the spec of package Sem for more info on pre-analysis.) | |
140 -- | |
141 -- Note that when processing a spec expression (In_Spec_Expression | |
142 -- is True) or performing semantic analysis of a generic spec or body | |
143 -- (Inside_A_Generic) or when performing pre-analysis (Full_Analysis is | |
144 -- False) the Expander_Active flag is False. | |
145 | |
146 procedure Expand (N : Node_Id); | |
147 -- Expand node N, as described above | |
148 | |
149 procedure Expander_Mode_Save_And_Set (Status : Boolean); | |
150 -- Saves the current setting of the Expander_Active flag on an internal | |
151 -- stack and then sets the flag to the given value. | |
152 -- | |
153 -- Note: this routine has no effect in ASIS and GNATprove modes. In ASIS | |
154 -- mode, all expansion activity is always off, since we want the original | |
155 -- semantic tree for ASIS purposes without any expansion. In GNATprove | |
156 -- mode, a very light expansion is performed on specific nodes. Both are | |
157 -- achieved by setting Expander_Active False in ASIS and GNATprove modes. | |
158 -- In situations such as the call to Instantiate_Bodies in Frontend, | |
159 -- Expander_Mode_Save_And_Set may be called to temporarily turn the | |
160 -- expander on, but this will have no effect in ASIS and GNATprove modes. | |
161 | |
162 procedure Expander_Mode_Restore; | |
163 -- Restores the setting of the Expander_Active flag using the top entry | |
164 -- pushed onto the stack by Expander_Mode_Save_And_Reset, popping the | |
165 -- stack, except that if any errors have been detected, then the state of | |
166 -- the flag is left set to False. Disabled for ASIS and GNATprove modes | |
167 -- (see above). | |
168 | |
169 end Expander; |