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//===--- Linkage.h - Linkage enumeration and utilities ----------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
/// \file
/// \brief Defines the Linkage enumeration and various utility functions.
namespace clang {
/// \brief Describes the different kinds of linkage
/// (C++ [], C99 6.2.2) that an entity may have.
enum Linkage {
/// \brief No linkage, which means that the entity is unique and
/// can only be referred to from within its scope.
NoLinkage = 0,
/// \brief Internal linkage, which indicates that the entity can
/// be referred to from within the translation unit (but not other
/// translation units).
/// \brief External linkage within a unique namespace.
/// From the language perspective, these entities have external
/// linkage. However, since they reside in an anonymous namespace,
/// their names are unique to this translation unit, which is
/// equivalent to having internal linkage from the code-generation
/// point of view.
/// \brief No linkage according to the standard, but is visible from other
/// translation units because of types defined in a inline function.
/// \brief External linkage, which indicates that the entity can
/// be referred to from other translation units.
/// \brief Describes the different kinds of language linkage
/// (C++ []) that an entity may have.
enum LanguageLinkage {
/// \brief A more specific kind of linkage than enum Linkage.
/// This is relevant to CodeGen and AST file reading.
enum GVALinkage {
inline bool isExternallyVisible(Linkage L) {
return L == ExternalLinkage || L == VisibleNoLinkage;
inline Linkage getFormalLinkage(Linkage L) {
if (L == UniqueExternalLinkage)
return ExternalLinkage;
if (L == VisibleNoLinkage)
return NoLinkage;
return L;
inline bool isExternalFormalLinkage(Linkage L) {
return getFormalLinkage(L) == ExternalLinkage;
/// \brief Compute the minimum linkage given two linkages.
/// The linkage can be interpreted as a pair formed by the formal linkage and
/// a boolean for external visibility. This is just what getFormalLinkage and
/// isExternallyVisible return. We want the minimum of both components. The
/// Linkage enum is defined in an order that makes this simple, we just need
/// special cases for when VisibleNoLinkage would lose the visible bit and
/// become NoLinkage.
inline Linkage minLinkage(Linkage L1, Linkage L2) {
if (L2 == VisibleNoLinkage)
std::swap(L1, L2);
if (L1 == VisibleNoLinkage) {
if (L2 == InternalLinkage)
return NoLinkage;
if (L2 == UniqueExternalLinkage)
return NoLinkage;
return L1 < L2 ? L1 : L2;
} // end namespace clang