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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 | -- -- | |
1d005acc | 9 | -- Copyright (C) 1992-2019, Free Software Foundation, Inc. -- |
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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- -- | |
b5c84c3c | 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- -- |
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 -- | |
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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. -- | |
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20 | -- -- |
21 | -- GNAT was originally developed by the GNAT team at New York University. -- | |
71ff80dc | 22 | -- Extensive contributions were provided by Ada Core Technologies Inc. -- |
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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 | |
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52 | -- from the old tree won't be reanalyzed, since their Analyzed flag |
53 | -- is set. | |
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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 | |
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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). | |
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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 | -- | |
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138 | -- (b) when starting/completing the preanalysis of an expression |
139 | -- (see the spec of package Sem for more info on preanalysis.) | |
70482933 | 140 | -- |
efde9617 | 141 | -- Note that when processing a spec expression (In_Spec_Expression |
70482933 | 142 | -- is True) or performing semantic analysis of a generic spec or body |
812e6118 | 143 | -- (Inside_A_Generic) or when performing preanalysis (Full_Analysis is |
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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. | |
fbf5a39b | 152 | -- |
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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. | |
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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 | |
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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). | |
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168 | |
169 | end Expander; |