1 //===- Linkage.h - Linkage enumeration and utilities ------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 /// \file
10 /// Defines the Linkage enumeration and various utility functions.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #ifndef LLVM_CLANG_BASIC_LINKAGE_H
15 #define LLVM_CLANG_BASIC_LINKAGE_H
16
17 #include "llvm/Support/ErrorHandling.h"
18 #include <utility>
19
20 namespace clang {
21
22 /// Describes the different kinds of linkage
23 /// (C++ [basic.link], C99 6.2.2) that an entity may have.
24 enum class Linkage : unsigned char {
25 // Linkage hasn't been computed.
26 Invalid = 0,
27
28 /// No linkage, which means that the entity is unique and
29 /// can only be referred to from within its scope.
30 None,
31
32 /// Internal linkage, which indicates that the entity can
33 /// be referred to from within the translation unit (but not other
34 /// translation units).
35 Internal,
36
37 /// External linkage within a unique namespace.
38 ///
39 /// From the language perspective, these entities have external
40 /// linkage. However, since they reside in an anonymous namespace,
41 /// their names are unique to this translation unit, which is
42 /// equivalent to having internal linkage from the code-generation
43 /// point of view.
44 UniqueExternal,
45
46 /// No linkage according to the standard, but is visible from other
47 /// translation units because of types defined in a inline function.
48 VisibleNone,
49
50 /// Module linkage, which indicates that the entity can be referred
51 /// to from other translation units within the same module, and indirectly
52 /// from arbitrary other translation units through inline functions and
53 /// templates in the module interface.
54 Module,
55
56 /// External linkage, which indicates that the entity can
57 /// be referred to from other translation units.
58 External
59 };
60
61 /// Describes the different kinds of language linkage
62 /// (C++ [dcl.link]) that an entity may have.
63 enum LanguageLinkage {
64 CLanguageLinkage,
65 CXXLanguageLinkage,
66 NoLanguageLinkage
67 };
68
69 /// A more specific kind of linkage than enum Linkage.
70 ///
71 /// This is relevant to CodeGen and AST file reading.
72 enum GVALinkage {
73 GVA_Internal,
74 GVA_AvailableExternally,
75 GVA_DiscardableODR,
76 GVA_StrongExternal,
77 GVA_StrongODR
78 };
79
isDiscardableGVALinkage(GVALinkage L)80 inline bool isDiscardableGVALinkage(GVALinkage L) {
81 return L <= GVA_DiscardableODR;
82 }
83
84 /// Do we know that this will be the only definition of this symbol (excluding
85 /// inlining-only definitions)?
isUniqueGVALinkage(GVALinkage L)86 inline bool isUniqueGVALinkage(GVALinkage L) {
87 return L == GVA_Internal || L == GVA_StrongExternal;
88 }
89
isExternallyVisible(Linkage L)90 inline bool isExternallyVisible(Linkage L) {
91 switch (L) {
92 case Linkage::Invalid:
93 llvm_unreachable("Linkage hasn't been computed!");
94 case Linkage::None:
95 case Linkage::Internal:
96 case Linkage::UniqueExternal:
97 return false;
98 case Linkage::VisibleNone:
99 case Linkage::Module:
100 case Linkage::External:
101 return true;
102 }
103 llvm_unreachable("Unhandled Linkage enum");
104 }
105
getFormalLinkage(Linkage L)106 inline Linkage getFormalLinkage(Linkage L) {
107 switch (L) {
108 case Linkage::UniqueExternal:
109 return Linkage::External;
110 case Linkage::VisibleNone:
111 return Linkage::None;
112 default:
113 return L;
114 }
115 }
116
isExternalFormalLinkage(Linkage L)117 inline bool isExternalFormalLinkage(Linkage L) {
118 return getFormalLinkage(L) == Linkage::External;
119 }
120
121 /// Compute the minimum linkage given two linkages.
122 ///
123 /// The linkage can be interpreted as a pair formed by the formal linkage and
124 /// a boolean for external visibility. This is just what getFormalLinkage and
125 /// isExternallyVisible return. We want the minimum of both components. The
126 /// Linkage enum is defined in an order that makes this simple, we just need
127 /// special cases for when VisibleNoLinkage would lose the visible bit and
128 /// become NoLinkage.
minLinkage(Linkage L1,Linkage L2)129 inline Linkage minLinkage(Linkage L1, Linkage L2) {
130 if (L2 == Linkage::VisibleNone)
131 std::swap(L1, L2);
132 if (L1 == Linkage::VisibleNone) {
133 if (L2 == Linkage::Internal)
134 return Linkage::None;
135 if (L2 == Linkage::UniqueExternal)
136 return Linkage::None;
137 }
138 return L1 < L2 ? L1 : L2;
139 }
140
141 } // namespace clang
142
143 #endif // LLVM_CLANG_BASIC_LINKAGE_H
144