Mercurial > hg > CbC > CbC_gcc
comparison gcc/ada/sem_mech.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 -- S E M _ M E C H -- | |
6 -- -- | |
7 -- S p e c -- | |
8 -- -- | |
9 -- Copyright (C) 1996-2014, 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 package contains the routine used to establish calling mechanisms | |
27 -- The reason we separate this off into its own package is that it is | |
28 -- entirely possible that it may need some target specific specialization. | |
29 | |
30 with Types; use Types; | |
31 | |
32 package Sem_Mech is | |
33 | |
34 ------------------------------------------------- | |
35 -- Definitions for Parameter Mechanism Control -- | |
36 ------------------------------------------------- | |
37 | |
38 -- For parameters passed to subprograms, and for function return values, | |
39 -- a passing mechanism is defined. The entity attribute Mechanism returns | |
40 -- an indication of the mechanism, and Set_Mechanism can be used to set | |
41 -- the mechanism. At the program level, there are three ways to explicitly | |
42 -- set the mechanism: | |
43 | |
44 -- An Import_xxx or Export_xxx pragma (where xxx is Function, Procedure, | |
45 -- or Valued_Procedure) can explicitly set the mechanism for either a | |
46 -- parameter or a function return value. A mechanism explicitly set by | |
47 -- such a pragma overrides the effect of C_Pass_By_Copy described below. | |
48 | |
49 -- If convention C_Pass_By_Copy is set for a record, and the record type | |
50 -- is used as the formal type of a subprogram with a foreign convention, | |
51 -- then the mechanism is set to By_Copy. | |
52 | |
53 -- If a pragma C_Pass_By_Copy applies, and a record type has Convention | |
54 -- C, and the record type is used as the formal type of a subprogram | |
55 -- with a foreign convention, then the mechanism is set to use By_Copy | |
56 -- if the size of the record is sufficiently small (as determined by | |
57 -- the value of the parameter to pragma C_Pass_By_Copy). | |
58 | |
59 -- The subtype Mechanism_Type (declared in Types) is used to describe | |
60 -- the mechanism to be used. The following special values of this type | |
61 -- specify the mechanism, as follows. | |
62 | |
63 Default_Mechanism : constant Mechanism_Type := 0; | |
64 -- The default setting indicates that the backend will choose the proper | |
65 -- default mechanism. This depends on the convention of the subprogram | |
66 -- involved, and is generally target dependent. In the compiler, the | |
67 -- backend chooses the mechanism in this case in accordance with any | |
68 -- requirements imposed by the ABI. Note that Default is never used for | |
69 -- record types on foreign convention subprograms, since By_Reference | |
70 -- is forced for such types unless one of the above described approaches | |
71 -- is used to explicitly force By_Copy. | |
72 | |
73 By_Copy : constant Mechanism_Type := -1; | |
74 -- Passing by copy is forced. The exact meaning of By_Copy (e.g. whether | |
75 -- at a low level the value is passed in registers, or the value is copied | |
76 -- and a pointer is passed), is determined by the backend in accordance | |
77 -- with requirements imposed by the ABI. Note that in the extended import | |
78 -- and export pragma mechanisms, this is called Value, rather than Copy. | |
79 | |
80 By_Reference : constant Mechanism_Type := -2; | |
81 -- Passing by reference is forced. This is always equivalent to passing | |
82 -- a simple pointer in the case of subprograms with a foreign convention. | |
83 -- For unconstrained arrays passed to foreign convention subprograms, the | |
84 -- address of the first element of the array is passed. For convention | |
85 -- Ada, the result is logically to pass a reference, but the precise | |
86 -- mechanism (e.g. to pass bounds of unconstrained types and other needed | |
87 -- special information) is determined by the backend in accordance with | |
88 -- requirements imposed by the ABI as interpreted for Ada. | |
89 | |
90 pragma Assert (Mechanism_Type'First = -2); | |
91 -- Check definition in types is right! | |
92 | |
93 -- All the above special values are non-positive. Positive values for | |
94 -- Mechanism_Type values have a special meaning. They are used only in | |
95 -- the case of records, as a result of the use of the C_Pass_By_Copy | |
96 -- pragma, and the meaning is that if the size of the record is known | |
97 -- at compile time and does not exceed the mechanism type value, then | |
98 -- By_Copy passing is forced, otherwise By_Reference is forced. | |
99 | |
100 ---------------------- | |
101 -- Global Variables -- | |
102 ---------------------- | |
103 | |
104 Default_C_Record_Mechanism : Mechanism_Type := By_Reference; | |
105 -- This value is the default mechanism used for C convention records | |
106 -- in foreign-convention subprograms if no mechanism is otherwise | |
107 -- specified. This value is modified appropriately by the occurrence | |
108 -- of a C_Pass_By_Copy configuration pragma. | |
109 | |
110 ----------------- | |
111 -- Subprograms -- | |
112 ----------------- | |
113 | |
114 procedure Set_Mechanisms (E : Entity_Id); | |
115 -- E is a subprogram or subprogram type that has been frozen, so the | |
116 -- convention of the subprogram and all its formal types and result | |
117 -- type in the case of a function are established. The function of | |
118 -- this call is to set mechanism values for formals and for the | |
119 -- function return if they have not already been explicitly set by | |
120 -- a use of an extended Import or Export pragma. The idea is to set | |
121 -- mechanism values wherever the semantics is dictated by either | |
122 -- requirements or implementation advice in the RM, and to leave | |
123 -- the mechanism set to Default if there is no requirement, so that | |
124 -- the back-end is free to choose the most efficient method. | |
125 | |
126 procedure Set_Mechanism_Value (Ent : Entity_Id; Mech_Name : Node_Id); | |
127 -- Mech is a parameter passing mechanism (see Import_Function syntax | |
128 -- for MECHANISM_NAME). This routine checks that the mechanism argument | |
129 -- has the right form, and if not issues an error message. If the | |
130 -- argument has the right form then the Mechanism field of Ent is | |
131 -- set appropriately. It also performs some error checks. Note that | |
132 -- the mechanism name has not been analyzed (and cannot indeed be | |
133 -- analyzed, since it is semantic nonsense), so we get it in the | |
134 -- exact form created by the parser. | |
135 | |
136 procedure Set_Mechanism_With_Checks | |
137 (Ent : Entity_Id; | |
138 Mech : Mechanism_Type; | |
139 Enod : Node_Id); | |
140 -- Sets the mechanism of Ent to the given Mech value, after first checking | |
141 -- that the request makes sense. If it does not make sense, a warning is | |
142 -- posted on node Enod, and the Mechanism of Ent is unchanged. | |
143 | |
144 end Sem_Mech; |