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//===-- llvm/GlobalValue.h - Class to represent a global value --*- 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
// This file is a common base class of all globally definable objects. As such,
// it is subclassed by GlobalVariable, GlobalAlias and by Function. This is
// used because you can do certain things with these global objects that you
// can't do to anything else. For example, use the address of one as a
// constant.
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MD5.h"
#include <cassert>
#include <cstdint>
#include <string>
namespace llvm {
class Comdat;
class ConstantRange;
class Error;
class GlobalObject;
class Module;
namespace Intrinsic {
typedef unsigned ID;
} // end namespace Intrinsic
class GlobalValue : public Constant {
/// An enumeration for the kinds of linkage for global values.
enum LinkageTypes {
ExternalLinkage = 0,///< Externally visible function
AvailableExternallyLinkage, ///< Available for inspection, not emission.
LinkOnceAnyLinkage, ///< Keep one copy of function when linking (inline)
LinkOnceODRLinkage, ///< Same, but only replaced by something equivalent.
WeakAnyLinkage, ///< Keep one copy of named function when linking (weak)
WeakODRLinkage, ///< Same, but only replaced by something equivalent.
AppendingLinkage, ///< Special purpose, only applies to global arrays
InternalLinkage, ///< Rename collisions when linking (static functions).
PrivateLinkage, ///< Like Internal, but omit from symbol table.
ExternalWeakLinkage,///< ExternalWeak linkage description.
CommonLinkage ///< Tentative definitions.
/// An enumeration for the kinds of visibility of global values.
enum VisibilityTypes {
DefaultVisibility = 0, ///< The GV is visible
HiddenVisibility, ///< The GV is hidden
ProtectedVisibility ///< The GV is protected
/// Storage classes of global values for PE targets.
enum DLLStorageClassTypes {
DefaultStorageClass = 0,
DLLImportStorageClass = 1, ///< Function to be imported from DLL
DLLExportStorageClass = 2 ///< Function to be accessible from DLL.
GlobalValue(Type *Ty, ValueTy VTy, Use *Ops, unsigned NumOps,
LinkageTypes Linkage, const Twine &Name, unsigned AddressSpace)
: Constant(PointerType::get(Ty, AddressSpace), VTy, Ops, NumOps),
ValueType(Ty), Visibility(DefaultVisibility),
DllStorageClass(DefaultStorageClass), ThreadLocal(NotThreadLocal),
HasLLVMReservedName(false), IsDSOLocal(false), HasPartition(false),
IntID((Intrinsic::ID)0U), Parent(nullptr) {
Type *ValueType;
static const unsigned GlobalValueSubClassDataBits = 16;
// All bitfields use unsigned as the underlying type so that MSVC will pack
// them.
unsigned Linkage : 4; // The linkage of this global
unsigned Visibility : 2; // The visibility style of this global
unsigned UnnamedAddrVal : 2; // This value's address is not significant
unsigned DllStorageClass : 2; // DLL storage class
unsigned ThreadLocal : 3; // Is this symbol "Thread Local", if so, what is
// the desired model?
/// True if the function's name starts with "llvm.". This corresponds to the
/// value of Function::isIntrinsic(), which may be true even if
/// Function::intrinsicID() returns Intrinsic::not_intrinsic.
unsigned HasLLVMReservedName : 1;
/// If true then there is a definition within the same linkage unit and that
/// definition cannot be runtime preempted.
unsigned IsDSOLocal : 1;
/// True if this symbol has a partition name assigned (see
unsigned HasPartition : 1;
// Give subclasses access to what otherwise would be wasted padding.
// (16 + 4 + 2 + 2 + 2 + 3 + 1 + 1 + 1) == 32.
unsigned SubClassData : GlobalValueSubClassDataBits;
friend class Constant;
void destroyConstantImpl();
Value *handleOperandChangeImpl(Value *From, Value *To);
/// Returns true if the definition of this global may be replaced by a
/// differently optimized variant of the same source level function at link
/// time.
bool mayBeDerefined() const {
switch (getLinkage()) {
case WeakODRLinkage:
case LinkOnceODRLinkage:
case AvailableExternallyLinkage:
return true;
case WeakAnyLinkage:
case LinkOnceAnyLinkage:
case CommonLinkage:
case ExternalWeakLinkage:
case ExternalLinkage:
case AppendingLinkage:
case InternalLinkage:
case PrivateLinkage:
return isInterposable();
llvm_unreachable("Fully covered switch above!");
void maybeSetDsoLocal() {
if (hasLocalLinkage() ||
(!hasDefaultVisibility() && !hasExternalWeakLinkage()))
/// The intrinsic ID for this subclass (which must be a Function).
/// This member is defined by this class, but not used for anything.
/// Subclasses can use it to store their intrinsic ID, if they have one.
/// This is stored here to save space in Function on 64-bit hosts.
Intrinsic::ID IntID;
unsigned getGlobalValueSubClassData() const {
return SubClassData;
void setGlobalValueSubClassData(unsigned V) {
assert(V < (1 << GlobalValueSubClassDataBits) && "It will not fit");
SubClassData = V;
Module *Parent; // The containing module.
// Used by SymbolTableListTraits.
void setParent(Module *parent) {
Parent = parent;
~GlobalValue() {
removeDeadConstantUsers(); // remove any dead constants using this.
enum ThreadLocalMode {
NotThreadLocal = 0,
GlobalValue(const GlobalValue &) = delete;
unsigned getAlignment() const;
unsigned getAddressSpace() const;
enum class UnnamedAddr {
bool hasGlobalUnnamedAddr() const {
return getUnnamedAddr() == UnnamedAddr::Global;
/// Returns true if this value's address is not significant in this module.
/// This attribute is intended to be used only by the code generator and LTO
/// to allow the linker to decide whether the global needs to be in the symbol
/// table. It should probably not be used in optimizations, as the value may
/// have uses outside the module; use hasGlobalUnnamedAddr() instead.
bool hasAtLeastLocalUnnamedAddr() const {
return getUnnamedAddr() != UnnamedAddr::None;
UnnamedAddr getUnnamedAddr() const {
return UnnamedAddr(UnnamedAddrVal);
void setUnnamedAddr(UnnamedAddr Val) { UnnamedAddrVal = unsigned(Val); }
static UnnamedAddr getMinUnnamedAddr(UnnamedAddr A, UnnamedAddr B) {
if (A == UnnamedAddr::None || B == UnnamedAddr::None)
return UnnamedAddr::None;
if (A == UnnamedAddr::Local || B == UnnamedAddr::Local)
return UnnamedAddr::Local;
return UnnamedAddr::Global;
bool hasComdat() const { return getComdat() != nullptr; }
const Comdat *getComdat() const;
Comdat *getComdat() {
return const_cast<Comdat *>(
static_cast<const GlobalValue *>(this)->getComdat());
VisibilityTypes getVisibility() const { return VisibilityTypes(Visibility); }
bool hasDefaultVisibility() const { return Visibility == DefaultVisibility; }
bool hasHiddenVisibility() const { return Visibility == HiddenVisibility; }
bool hasProtectedVisibility() const {
return Visibility == ProtectedVisibility;
void setVisibility(VisibilityTypes V) {
assert((!hasLocalLinkage() || V == DefaultVisibility) &&
"local linkage requires default visibility");
Visibility = V;
/// If the value is "Thread Local", its value isn't shared by the threads.
bool isThreadLocal() const { return getThreadLocalMode() != NotThreadLocal; }
void setThreadLocal(bool Val) {
setThreadLocalMode(Val ? GeneralDynamicTLSModel : NotThreadLocal);
void setThreadLocalMode(ThreadLocalMode Val) {
assert(Val == NotThreadLocal || getValueID() != Value::FunctionVal);
ThreadLocal = Val;
ThreadLocalMode getThreadLocalMode() const {
return static_cast<ThreadLocalMode>(ThreadLocal);
DLLStorageClassTypes getDLLStorageClass() const {
return DLLStorageClassTypes(DllStorageClass);
bool hasDLLImportStorageClass() const {
return DllStorageClass == DLLImportStorageClass;
bool hasDLLExportStorageClass() const {
return DllStorageClass == DLLExportStorageClass;
void setDLLStorageClass(DLLStorageClassTypes C) { DllStorageClass = C; }
bool hasSection() const { return !getSection().empty(); }
StringRef getSection() const;
/// Global values are always pointers.
PointerType *getType() const { return cast<PointerType>(User::getType()); }
Type *getValueType() const { return ValueType; }
void setDSOLocal(bool Local) { IsDSOLocal = Local; }
bool isDSOLocal() const {
return IsDSOLocal;
bool hasPartition() const {
return HasPartition;
StringRef getPartition() const;
void setPartition(StringRef Part);
static LinkageTypes getLinkOnceLinkage(bool ODR) {
return ODR ? LinkOnceODRLinkage : LinkOnceAnyLinkage;
static LinkageTypes getWeakLinkage(bool ODR) {
return ODR ? WeakODRLinkage : WeakAnyLinkage;
static bool isExternalLinkage(LinkageTypes Linkage) {
return Linkage == ExternalLinkage;
static bool isAvailableExternallyLinkage(LinkageTypes Linkage) {
return Linkage == AvailableExternallyLinkage;
static bool isLinkOnceODRLinkage(LinkageTypes Linkage) {
return Linkage == LinkOnceODRLinkage;
static bool isLinkOnceLinkage(LinkageTypes Linkage) {
return Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage;
static bool isWeakAnyLinkage(LinkageTypes Linkage) {
return Linkage == WeakAnyLinkage;
static bool isWeakODRLinkage(LinkageTypes Linkage) {
return Linkage == WeakODRLinkage;
static bool isWeakLinkage(LinkageTypes Linkage) {
return isWeakAnyLinkage(Linkage) || isWeakODRLinkage(Linkage);
static bool isAppendingLinkage(LinkageTypes Linkage) {
return Linkage == AppendingLinkage;
static bool isInternalLinkage(LinkageTypes Linkage) {
return Linkage == InternalLinkage;
static bool isPrivateLinkage(LinkageTypes Linkage) {
return Linkage == PrivateLinkage;
static bool isLocalLinkage(LinkageTypes Linkage) {
return isInternalLinkage(Linkage) || isPrivateLinkage(Linkage);
static bool isExternalWeakLinkage(LinkageTypes Linkage) {
return Linkage == ExternalWeakLinkage;
static bool isCommonLinkage(LinkageTypes Linkage) {
return Linkage == CommonLinkage;
static bool isValidDeclarationLinkage(LinkageTypes Linkage) {
return isExternalWeakLinkage(Linkage) || isExternalLinkage(Linkage);
/// Whether the definition of this global may be replaced by something
/// non-equivalent at link time. For example, if a function has weak linkage
/// then the code defining it may be replaced by different code.
static bool isInterposableLinkage(LinkageTypes Linkage) {
switch (Linkage) {
case WeakAnyLinkage:
case LinkOnceAnyLinkage:
case CommonLinkage:
case ExternalWeakLinkage:
return true;
case AvailableExternallyLinkage:
case LinkOnceODRLinkage:
case WeakODRLinkage:
// The above three cannot be overridden but can be de-refined.
case ExternalLinkage:
case AppendingLinkage:
case InternalLinkage:
case PrivateLinkage:
return false;
llvm_unreachable("Fully covered switch above!");
/// Whether the definition of this global may be discarded if it is not used
/// in its compilation unit.
static bool isDiscardableIfUnused(LinkageTypes Linkage) {
return isLinkOnceLinkage(Linkage) || isLocalLinkage(Linkage) ||
/// Whether the definition of this global may be replaced at link time. NB:
/// Using this method outside of the code generators is almost always a
/// mistake: when working at the IR level use isInterposable instead as it
/// knows about ODR semantics.
static bool isWeakForLinker(LinkageTypes Linkage) {
return Linkage == WeakAnyLinkage || Linkage == WeakODRLinkage ||
Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage ||
Linkage == CommonLinkage || Linkage == ExternalWeakLinkage;
/// Return true if the currently visible definition of this global (if any) is
/// exactly the definition we will see at runtime.
/// Non-exact linkage types inhibits most non-inlining IPO, since a
/// differently optimized variant of the same function can have different
/// observable or undefined behavior than in the variant currently visible.
/// For instance, we could have started with
/// void foo(int *v) {
/// int t = 5 / v[0];
/// (void) t;
/// }
/// and "refined" it to
/// void foo(int *v) { }
/// However, we cannot infer readnone for `foo`, since that would justify
/// DSE'ing a store to `v[0]` across a call to `foo`, which can cause
/// undefined behavior if the linker replaces the actual call destination with
/// the unoptimized `foo`.
/// Inlining is okay across non-exact linkage types as long as they're not
/// interposable (see \c isInterposable), since in such cases the currently
/// visible variant is *a* correct implementation of the original source
/// function; it just isn't the *only* correct implementation.
bool isDefinitionExact() const {
return !mayBeDerefined();
/// Return true if this global has an exact defintion.
bool hasExactDefinition() const {
// While this computes exactly the same thing as
// isStrongDefinitionForLinker, the intended uses are different. This
// function is intended to help decide if specific inter-procedural
// transforms are correct, while isStrongDefinitionForLinker's intended use
// is in low level code generation.
return !isDeclaration() && isDefinitionExact();
/// Return true if this global's definition can be substituted with an
/// *arbitrary* definition at link time. We cannot do any IPO or inlinining
/// across interposable call edges, since the callee can be replaced with
/// something arbitrary at link time.
bool isInterposable() const { return isInterposableLinkage(getLinkage()); }
bool hasExternalLinkage() const { return isExternalLinkage(getLinkage()); }
bool hasAvailableExternallyLinkage() const {
return isAvailableExternallyLinkage(getLinkage());
bool hasLinkOnceLinkage() const { return isLinkOnceLinkage(getLinkage()); }
bool hasLinkOnceODRLinkage() const {
return isLinkOnceODRLinkage(getLinkage());
bool hasWeakLinkage() const { return isWeakLinkage(getLinkage()); }
bool hasWeakAnyLinkage() const { return isWeakAnyLinkage(getLinkage()); }
bool hasWeakODRLinkage() const { return isWeakODRLinkage(getLinkage()); }
bool hasAppendingLinkage() const { return isAppendingLinkage(getLinkage()); }
bool hasInternalLinkage() const { return isInternalLinkage(getLinkage()); }
bool hasPrivateLinkage() const { return isPrivateLinkage(getLinkage()); }
bool hasLocalLinkage() const { return isLocalLinkage(getLinkage()); }
bool hasExternalWeakLinkage() const {
return isExternalWeakLinkage(getLinkage());
bool hasCommonLinkage() const { return isCommonLinkage(getLinkage()); }
bool hasValidDeclarationLinkage() const {
return isValidDeclarationLinkage(getLinkage());
void setLinkage(LinkageTypes LT) {
if (isLocalLinkage(LT))
Visibility = DefaultVisibility;
Linkage = LT;
LinkageTypes getLinkage() const { return LinkageTypes(Linkage); }
bool isDiscardableIfUnused() const {
return isDiscardableIfUnused(getLinkage());
bool isWeakForLinker() const { return isWeakForLinker(getLinkage()); }
/// Copy all additional attributes (those not needed to create a GlobalValue)
/// from the GlobalValue Src to this one.
void copyAttributesFrom(const GlobalValue *Src);
/// If the given string begins with the GlobalValue name mangling escape
/// character '\1', drop it.
/// This function applies a specific mangling that is used in PGO profiles,
/// among other things. If you're trying to get a symbol name for an
/// arbitrary GlobalValue, this is not the function you're looking for; see
/// Mangler.h.
static StringRef dropLLVMManglingEscape(StringRef Name) {
if (!Name.empty() && Name[0] == '\1')
return Name.substr(1);
return Name;
/// Return the modified name for a global value suitable to be
/// used as the key for a global lookup (e.g. profile or ThinLTO).
/// The value's original name is \c Name and has linkage of type
/// \c Linkage. The value is defined in module \c FileName.
static std::string getGlobalIdentifier(StringRef Name,
GlobalValue::LinkageTypes Linkage,
StringRef FileName);
/// Return the modified name for this global value suitable to be
/// used as the key for a global lookup (e.g. profile or ThinLTO).
std::string getGlobalIdentifier() const;
/// Declare a type to represent a global unique identifier for a global value.
/// This is a 64 bits hash that is used by PGO and ThinLTO to have a compact
/// unique way to identify a symbol.
using GUID = uint64_t;
/// Return a 64-bit global unique ID constructed from global value name
/// (i.e. returned by getGlobalIdentifier()).
static GUID getGUID(StringRef GlobalName) { return MD5Hash(GlobalName); }
/// Return a 64-bit global unique ID constructed from global value name
/// (i.e. returned by getGlobalIdentifier()).
GUID getGUID() const { return getGUID(getGlobalIdentifier()); }
/// @name Materialization
/// Materialization is used to construct functions only as they're needed.
/// This
/// is useful to reduce memory usage in LLVM or parsing work done by the
/// BitcodeReader to load the Module.
/// @{
/// If this function's Module is being lazily streamed in functions from disk
/// or some other source, this method can be used to check to see if the
/// function has been read in yet or not.
bool isMaterializable() const;
/// Make sure this GlobalValue is fully read.
Error materialize();
/// @}
/// Return true if the primary definition of this global value is outside of
/// the current translation unit.
bool isDeclaration() const;
bool isDeclarationForLinker() const {
if (hasAvailableExternallyLinkage())
return true;
return isDeclaration();
/// Returns true if this global's definition will be the one chosen by the
/// linker.
/// NB! Ideally this should not be used at the IR level at all. If you're
/// interested in optimization constraints implied by the linker's ability to
/// choose an implementation, prefer using \c hasExactDefinition.
bool isStrongDefinitionForLinker() const {
return !(isDeclarationForLinker() || isWeakForLinker());
// Returns true if the alignment of the value can be unilaterally
// increased.
bool canIncreaseAlignment() const;
const GlobalObject *getBaseObject() const;
GlobalObject *getBaseObject() {
return const_cast<GlobalObject *>(
static_cast<const GlobalValue *>(this)->getBaseObject());
/// Returns whether this is a reference to an absolute symbol.
bool isAbsoluteSymbolRef() const;
/// If this is an absolute symbol reference, returns the range of the symbol,
/// otherwise returns None.
Optional<ConstantRange> getAbsoluteSymbolRange() const;
/// This method unlinks 'this' from the containing module, but does not delete
/// it.
void removeFromParent();
/// This method unlinks 'this' from the containing module and deletes it.
void eraseFromParent();
/// Get the module that this global value is contained inside of...
Module *getParent() { return Parent; }
const Module *getParent() const { return Parent; }
// Methods for support type inquiry through isa, cast, and dyn_cast:
static bool classof(const Value *V) {
return V->getValueID() == Value::FunctionVal ||
V->getValueID() == Value::GlobalVariableVal ||
V->getValueID() == Value::GlobalAliasVal ||
V->getValueID() == Value::GlobalIFuncVal;
/// True if GV can be left out of the object symbol table. This is the case
/// for linkonce_odr values whose address is not significant. While legal, it
/// is not normally profitable to omit them from the .o symbol table. Using
/// this analysis makes sense when the information can be passed down to the
/// linker or we are in LTO.
bool canBeOmittedFromSymbolTable() const;
} // end namespace llvm