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//===- Core/Atom.h - A node in linking graph --------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "lld/Common/LLVM.h"
#include "llvm/ADT/StringRef.h"
namespace lld {
class File;
template<typename T>
class OwningAtomPtr;
/// The linker has a Graph Theory model of linking. An object file is seen
/// as a set of Atoms with References to other Atoms. Each Atom is a node
/// and each Reference is an edge. An Atom can be a DefinedAtom which has
/// content or a UndefinedAtom which is a placeholder and represents an
/// undefined symbol (extern declaration).
class Atom {
template<typename T> friend class OwningAtomPtr;
/// Whether this atom is defined or a proxy for an undefined symbol
enum Definition {
definitionRegular, ///< Normal C/C++ function or global variable.
definitionAbsolute, ///< Asm-only (foo = 10). Not tied to any content.
definitionUndefined, ///< Only in .o files to model reference to undef.
definitionSharedLibrary ///< Only in shared libraries to model export.
/// The scope in which this atom is accessible to other atoms.
enum Scope {
scopeTranslationUnit, ///< Accessible only to atoms in the same translation
/// unit (e.g. a C static).
scopeLinkageUnit, ///< Accessible to atoms being linked but not visible
/// to runtime loader (e.g. visibility=hidden).
scopeGlobal ///< Accessible to all atoms and visible to runtime
/// loader (e.g. visibility=default).
/// file - returns the File that produced/owns this Atom
virtual const File& file() const = 0;
/// name - The name of the atom. For a function atom, it is the (mangled)
/// name of the function.
virtual StringRef name() const = 0;
/// definition - Whether this atom is a definition or represents an undefined
/// symbol.
Definition definition() const { return _definition; }
static bool classof(const Atom *a) { return true; }
/// Atom is an abstract base class. Only subclasses can access constructor.
explicit Atom(Definition def) : _definition(def) {}
/// The memory for Atom objects is always managed by the owning File
/// object. Therefore, no one but the owning File object should call
/// delete on an Atom. In fact, some File objects may bulk allocate
/// an array of Atoms, so they cannot be individually deleted by anyone.
virtual ~Atom() = default;
Definition _definition;
/// Class which owns an atom pointer and runs the atom destructor when the
/// owning pointer goes out of scope.
template<typename T>
class OwningAtomPtr {
OwningAtomPtr(const OwningAtomPtr &) = delete;
void operator=(const OwningAtomPtr &) = delete;
OwningAtomPtr() = default;
OwningAtomPtr(T *atom) : atom(atom) { }
~OwningAtomPtr() {
if (atom)
void runDestructor(Atom *atom) {
OwningAtomPtr(OwningAtomPtr &&ptr) : atom(ptr.atom) {
ptr.atom = nullptr;
void operator=(OwningAtomPtr&& ptr) {
if (atom)
atom = ptr.atom;
ptr.atom = nullptr;
T *const &get() const {
return atom;
T *&get() {
return atom;
T *release() {
auto *v = atom;
atom = nullptr;
return v;
T *atom = nullptr;
} // end namespace lld
#endif // LLD_CORE_ATOM_H