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 <utility>
18 
19 namespace clang {
20 
21 /// Describes the different kinds of linkage
22 /// (C++ [basic.link], C99 6.2.2) that an entity may have.
23 enum Linkage : unsigned char {
24   /// No linkage, which means that the entity is unique and
25   /// can only be referred to from within its scope.
26   NoLinkage = 0,
27 
28   /// Internal linkage, which indicates that the entity can
29   /// be referred to from within the translation unit (but not other
30   /// translation units).
31   InternalLinkage,
32 
33   /// External linkage within a unique namespace.
34   ///
35   /// From the language perspective, these entities have external
36   /// linkage. However, since they reside in an anonymous namespace,
37   /// their names are unique to this translation unit, which is
38   /// equivalent to having internal linkage from the code-generation
39   /// point of view.
40   UniqueExternalLinkage,
41 
42   /// No linkage according to the standard, but is visible from other
43   /// translation units because of types defined in a inline function.
44   VisibleNoLinkage,
45 
46   /// Internal linkage according to the Modules TS, but can be referred
47   /// to from other translation units indirectly through inline functions and
48   /// templates in the module interface.
49   ModuleInternalLinkage,
50 
51   /// Module linkage, which indicates that the entity can be referred
52   /// to from other translation units within the same module, and indirectly
53   /// from arbitrary other translation units through inline functions and
54   /// templates in the module interface.
55   ModuleLinkage,
56 
57   /// External linkage, which indicates that the entity can
58   /// be referred to from other translation units.
59   ExternalLinkage
60 };
61 
62 /// Describes the different kinds of language linkage
63 /// (C++ [dcl.link]) that an entity may have.
64 enum LanguageLinkage {
65   CLanguageLinkage,
66   CXXLanguageLinkage,
67   NoLanguageLinkage
68 };
69 
70 /// A more specific kind of linkage than enum Linkage.
71 ///
72 /// This is relevant to CodeGen and AST file reading.
73 enum GVALinkage {
74   GVA_Internal,
75   GVA_AvailableExternally,
76   GVA_DiscardableODR,
77   GVA_StrongExternal,
78   GVA_StrongODR
79 };
80 
81 inline bool isDiscardableGVALinkage(GVALinkage L) {
82   return L <= GVA_DiscardableODR;
83 }
84 
85 /// Do we know that this will be the only definition of this symbol (excluding
86 /// inlining-only definitions)?
87 inline bool isUniqueGVALinkage(GVALinkage L) {
88   return L == GVA_Internal || L == GVA_StrongExternal;
89 }
90 
91 inline bool isExternallyVisible(Linkage L) {
92   return L >= VisibleNoLinkage;
93 }
94 
95 inline Linkage getFormalLinkage(Linkage L) {
96   switch (L) {
97   case UniqueExternalLinkage:
98     return ExternalLinkage;
99   case VisibleNoLinkage:
100     return NoLinkage;
101   case ModuleInternalLinkage:
102     return InternalLinkage;
103   default:
104     return L;
105   }
106 }
107 
108 inline bool isExternalFormalLinkage(Linkage L) {
109   return getFormalLinkage(L) == ExternalLinkage;
110 }
111 
112 /// Compute the minimum linkage given two linkages.
113 ///
114 /// The linkage can be interpreted as a pair formed by the formal linkage and
115 /// a boolean for external visibility. This is just what getFormalLinkage and
116 /// isExternallyVisible return. We want the minimum of both components. The
117 /// Linkage enum is defined in an order that makes this simple, we just need
118 /// special cases for when VisibleNoLinkage would lose the visible bit and
119 /// become NoLinkage.
120 inline Linkage minLinkage(Linkage L1, Linkage L2) {
121   if (L2 == VisibleNoLinkage)
122     std::swap(L1, L2);
123   if (L1 == VisibleNoLinkage) {
124     if (L2 == InternalLinkage)
125       return NoLinkage;
126     if (L2 == UniqueExternalLinkage)
127       return NoLinkage;
128   }
129   return L1 < L2 ? L1 : L2;
130 }
131 
132 } // namespace clang
133 
134 #endif // LLVM_CLANG_BASIC_LINKAGE_H
135