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
20namespace clang {
21
22/// Describes the different kinds of linkage
23/// (C++ [basic.link], C99 6.2.2) that an entity may have.
24enum 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.
63enum 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.
72enum GVALinkage {
73 GVA_Internal,
74 GVA_AvailableExternally,
75 GVA_DiscardableODR,
76 GVA_StrongExternal,
77 GVA_StrongODR
78};
79
80inline 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)?
86inline bool isUniqueGVALinkage(GVALinkage L) {
87 return L == GVA_Internal || L == GVA_StrongExternal;
88}
89
90inline 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
106inline 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
117inline 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.
129inline Linkage minLinkage(Linkage L1, Linkage L2) {
130 if (L2 == Linkage::VisibleNone)
131 std::swap(a&: L1, b&: 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