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  1. //===-- llvm/GlobalValue.h - Class to represent a global value --*- 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. // This file is a common base class of all globally definable objects.  As such,
  10. // it is subclassed by GlobalVariable, GlobalAlias and by Function.  This is
  11. // used because you can do certain things with these global objects that you
  12. // can't do to anything else.  For example, use the address of one as a
  13. // constant.
  14. //
  15. //===----------------------------------------------------------------------===//
  16.  
  17. #ifndef LLVM_IR_GLOBALVALUE_H
  18. #define LLVM_IR_GLOBALVALUE_H
  19.  
  20. #include "llvm/ADT/StringRef.h"
  21. #include "llvm/ADT/Twine.h"
  22. #include "llvm/IR/Constant.h"
  23. #include "llvm/IR/DerivedTypes.h"
  24. #include "llvm/IR/Value.h"
  25. #include "llvm/Support/Casting.h"
  26. #include "llvm/Support/ErrorHandling.h"
  27. #include "llvm/Support/MD5.h"
  28. #include <cassert>
  29. #include <cstdint>
  30. #include <string>
  31.  
  32. namespace llvm {
  33.  
  34. class Comdat;
  35. class ConstantRange;
  36. class Error;
  37. class GlobalObject;
  38. class Module;
  39.  
  40. namespace Intrinsic {
  41. typedef unsigned ID;
  42. } // end namespace Intrinsic
  43.  
  44. class GlobalValue : public Constant {
  45. public:
  46.   /// An enumeration for the kinds of linkage for global values.
  47.   enum LinkageTypes {
  48.     ExternalLinkage = 0,///< Externally visible function
  49.     AvailableExternallyLinkage, ///< Available for inspection, not emission.
  50.     LinkOnceAnyLinkage, ///< Keep one copy of function when linking (inline)
  51.     LinkOnceODRLinkage, ///< Same, but only replaced by something equivalent.
  52.     WeakAnyLinkage,     ///< Keep one copy of named function when linking (weak)
  53.     WeakODRLinkage,     ///< Same, but only replaced by something equivalent.
  54.     AppendingLinkage,   ///< Special purpose, only applies to global arrays
  55.     InternalLinkage,    ///< Rename collisions when linking (static functions).
  56.     PrivateLinkage,     ///< Like Internal, but omit from symbol table.
  57.     ExternalWeakLinkage,///< ExternalWeak linkage description.
  58.     CommonLinkage       ///< Tentative definitions.
  59.   };
  60.  
  61.   /// An enumeration for the kinds of visibility of global values.
  62.   enum VisibilityTypes {
  63.     DefaultVisibility = 0,  ///< The GV is visible
  64.     HiddenVisibility,       ///< The GV is hidden
  65.     ProtectedVisibility     ///< The GV is protected
  66.   };
  67.  
  68.   /// Storage classes of global values for PE targets.
  69.   enum DLLStorageClassTypes {
  70.     DefaultStorageClass   = 0,
  71.     DLLImportStorageClass = 1, ///< Function to be imported from DLL
  72.     DLLExportStorageClass = 2  ///< Function to be accessible from DLL.
  73.   };
  74.  
  75. protected:
  76.   GlobalValue(Type *Ty, ValueTy VTy, Use *Ops, unsigned NumOps,
  77.               LinkageTypes Linkage, const Twine &Name, unsigned AddressSpace)
  78.       : Constant(PointerType::get(Ty, AddressSpace), VTy, Ops, NumOps),
  79.         ValueType(Ty), Visibility(DefaultVisibility),
  80.         UnnamedAddrVal(unsigned(UnnamedAddr::None)),
  81.         DllStorageClass(DefaultStorageClass), ThreadLocal(NotThreadLocal),
  82.         HasLLVMReservedName(false), IsDSOLocal(false), HasPartition(false),
  83.         HasSanitizerMetadata(false) {
  84.     setLinkage(Linkage);
  85.     setName(Name);
  86.   }
  87.  
  88.   Type *ValueType;
  89.  
  90.   static const unsigned GlobalValueSubClassDataBits = 15;
  91.  
  92.   // All bitfields use unsigned as the underlying type so that MSVC will pack
  93.   // them.
  94.   unsigned Linkage : 4;       // The linkage of this global
  95.   unsigned Visibility : 2;    // The visibility style of this global
  96.   unsigned UnnamedAddrVal : 2; // This value's address is not significant
  97.   unsigned DllStorageClass : 2; // DLL storage class
  98.  
  99.   unsigned ThreadLocal : 3; // Is this symbol "Thread Local", if so, what is
  100.                             // the desired model?
  101.  
  102.   /// True if the function's name starts with "llvm.".  This corresponds to the
  103.   /// value of Function::isIntrinsic(), which may be true even if
  104.   /// Function::intrinsicID() returns Intrinsic::not_intrinsic.
  105.   unsigned HasLLVMReservedName : 1;
  106.  
  107.   /// If true then there is a definition within the same linkage unit and that
  108.   /// definition cannot be runtime preempted.
  109.   unsigned IsDSOLocal : 1;
  110.  
  111.   /// True if this symbol has a partition name assigned (see
  112.   /// https://lld.llvm.org/Partitions.html).
  113.   unsigned HasPartition : 1;
  114.  
  115.   /// True if this symbol has sanitizer metadata available. Should only happen
  116.   /// if sanitizers were enabled when building the translation unit which
  117.   /// contains this GV.
  118.   unsigned HasSanitizerMetadata : 1;
  119.  
  120. private:
  121.   // Give subclasses access to what otherwise would be wasted padding.
  122.   // (15 + 4 + 2 + 2 + 2 + 3 + 1 + 1 + 1 + 1) == 32.
  123.   unsigned SubClassData : GlobalValueSubClassDataBits;
  124.  
  125.   friend class Constant;
  126.  
  127.   void destroyConstantImpl();
  128.   Value *handleOperandChangeImpl(Value *From, Value *To);
  129.  
  130.   /// Returns true if the definition of this global may be replaced by a
  131.   /// differently optimized variant of the same source level function at link
  132.   /// time.
  133.   bool mayBeDerefined() const {
  134.     switch (getLinkage()) {
  135.     case WeakODRLinkage:
  136.     case LinkOnceODRLinkage:
  137.     case AvailableExternallyLinkage:
  138.       return true;
  139.  
  140.     case WeakAnyLinkage:
  141.     case LinkOnceAnyLinkage:
  142.     case CommonLinkage:
  143.     case ExternalWeakLinkage:
  144.     case ExternalLinkage:
  145.     case AppendingLinkage:
  146.     case InternalLinkage:
  147.     case PrivateLinkage:
  148.       // Optimizations may assume builtin semantics for functions defined as
  149.       // nobuiltin due to attributes at call-sites. To avoid applying IPO based
  150.       // on nobuiltin semantics, treat such function definitions as maybe
  151.       // derefined.
  152.       return isInterposable() || isNobuiltinFnDef();
  153.     }
  154.  
  155.     llvm_unreachable("Fully covered switch above!");
  156.   }
  157.  
  158.   /// Returns true if the global is a function definition with the nobuiltin
  159.   /// attribute.
  160.   bool isNobuiltinFnDef() const;
  161.  
  162. protected:
  163.   /// The intrinsic ID for this subclass (which must be a Function).
  164.   ///
  165.   /// This member is defined by this class, but not used for anything.
  166.   /// Subclasses can use it to store their intrinsic ID, if they have one.
  167.   ///
  168.   /// This is stored here to save space in Function on 64-bit hosts.
  169.   Intrinsic::ID IntID = (Intrinsic::ID)0U;
  170.  
  171.   unsigned getGlobalValueSubClassData() const {
  172.     return SubClassData;
  173.   }
  174.   void setGlobalValueSubClassData(unsigned V) {
  175.     assert(V < (1 << GlobalValueSubClassDataBits) && "It will not fit");
  176.     SubClassData = V;
  177.   }
  178.  
  179.   Module *Parent = nullptr; // The containing module.
  180.  
  181.   // Used by SymbolTableListTraits.
  182.   void setParent(Module *parent) {
  183.     Parent = parent;
  184.   }
  185.  
  186.   ~GlobalValue() {
  187.     removeDeadConstantUsers();   // remove any dead constants using this.
  188.   }
  189.  
  190. public:
  191.   enum ThreadLocalMode {
  192.     NotThreadLocal = 0,
  193.     GeneralDynamicTLSModel,
  194.     LocalDynamicTLSModel,
  195.     InitialExecTLSModel,
  196.     LocalExecTLSModel
  197.   };
  198.  
  199.   GlobalValue(const GlobalValue &) = delete;
  200.  
  201.   unsigned getAddressSpace() const {
  202.     return getType()->getAddressSpace();
  203.   }
  204.  
  205.   enum class UnnamedAddr {
  206.     None,
  207.     Local,
  208.     Global,
  209.   };
  210.  
  211.   bool hasGlobalUnnamedAddr() const {
  212.     return getUnnamedAddr() == UnnamedAddr::Global;
  213.   }
  214.  
  215.   /// Returns true if this value's address is not significant in this module.
  216.   /// This attribute is intended to be used only by the code generator and LTO
  217.   /// to allow the linker to decide whether the global needs to be in the symbol
  218.   /// table. It should probably not be used in optimizations, as the value may
  219.   /// have uses outside the module; use hasGlobalUnnamedAddr() instead.
  220.   bool hasAtLeastLocalUnnamedAddr() const {
  221.     return getUnnamedAddr() != UnnamedAddr::None;
  222.   }
  223.  
  224.   UnnamedAddr getUnnamedAddr() const {
  225.     return UnnamedAddr(UnnamedAddrVal);
  226.   }
  227.   void setUnnamedAddr(UnnamedAddr Val) { UnnamedAddrVal = unsigned(Val); }
  228.  
  229.   static UnnamedAddr getMinUnnamedAddr(UnnamedAddr A, UnnamedAddr B) {
  230.     if (A == UnnamedAddr::None || B == UnnamedAddr::None)
  231.       return UnnamedAddr::None;
  232.     if (A == UnnamedAddr::Local || B == UnnamedAddr::Local)
  233.       return UnnamedAddr::Local;
  234.     return UnnamedAddr::Global;
  235.   }
  236.  
  237.   bool hasComdat() const { return getComdat() != nullptr; }
  238.   const Comdat *getComdat() const;
  239.   Comdat *getComdat() {
  240.     return const_cast<Comdat *>(
  241.                            static_cast<const GlobalValue *>(this)->getComdat());
  242.   }
  243.  
  244.   VisibilityTypes getVisibility() const { return VisibilityTypes(Visibility); }
  245.   bool hasDefaultVisibility() const { return Visibility == DefaultVisibility; }
  246.   bool hasHiddenVisibility() const { return Visibility == HiddenVisibility; }
  247.   bool hasProtectedVisibility() const {
  248.     return Visibility == ProtectedVisibility;
  249.   }
  250.   void setVisibility(VisibilityTypes V) {
  251.     assert((!hasLocalLinkage() || V == DefaultVisibility) &&
  252.            "local linkage requires default visibility");
  253.     Visibility = V;
  254.     if (isImplicitDSOLocal())
  255.       setDSOLocal(true);
  256.   }
  257.  
  258.   /// If the value is "Thread Local", its value isn't shared by the threads.
  259.   bool isThreadLocal() const { return getThreadLocalMode() != NotThreadLocal; }
  260.   void setThreadLocal(bool Val) {
  261.     setThreadLocalMode(Val ? GeneralDynamicTLSModel : NotThreadLocal);
  262.   }
  263.   void setThreadLocalMode(ThreadLocalMode Val) {
  264.     assert(Val == NotThreadLocal || getValueID() != Value::FunctionVal);
  265.     ThreadLocal = Val;
  266.   }
  267.   ThreadLocalMode getThreadLocalMode() const {
  268.     return static_cast<ThreadLocalMode>(ThreadLocal);
  269.   }
  270.  
  271.   DLLStorageClassTypes getDLLStorageClass() const {
  272.     return DLLStorageClassTypes(DllStorageClass);
  273.   }
  274.   bool hasDLLImportStorageClass() const {
  275.     return DllStorageClass == DLLImportStorageClass;
  276.   }
  277.   bool hasDLLExportStorageClass() const {
  278.     return DllStorageClass == DLLExportStorageClass;
  279.   }
  280.   void setDLLStorageClass(DLLStorageClassTypes C) {
  281.     assert((!hasLocalLinkage() || C == DefaultStorageClass) &&
  282.            "local linkage requires DefaultStorageClass");
  283.     DllStorageClass = C;
  284.   }
  285.  
  286.   bool hasSection() const { return !getSection().empty(); }
  287.   StringRef getSection() const;
  288.  
  289.   /// Global values are always pointers.
  290.   PointerType *getType() const { return cast<PointerType>(User::getType()); }
  291.  
  292.   Type *getValueType() const { return ValueType; }
  293.  
  294.   bool isImplicitDSOLocal() const {
  295.     return hasLocalLinkage() ||
  296.            (!hasDefaultVisibility() && !hasExternalWeakLinkage());
  297.   }
  298.  
  299.   void setDSOLocal(bool Local) { IsDSOLocal = Local; }
  300.  
  301.   bool isDSOLocal() const {
  302.     return IsDSOLocal;
  303.   }
  304.  
  305.   bool hasPartition() const {
  306.     return HasPartition;
  307.   }
  308.   StringRef getPartition() const;
  309.   void setPartition(StringRef Part);
  310.  
  311.   // ASan, HWASan and Memtag sanitizers have some instrumentation that applies
  312.   // specifically to global variables.
  313.   struct SanitizerMetadata {
  314.     SanitizerMetadata()
  315.         : NoAddress(false), NoHWAddress(false),
  316.           Memtag(false), IsDynInit(false) {}
  317.     // For ASan and HWASan, this instrumentation is implicitly applied to all
  318.     // global variables when built with -fsanitize=*. What we need is a way to
  319.     // persist the information that a certain global variable should *not* have
  320.     // sanitizers applied, which occurs if:
  321.     //   1. The global variable is in the sanitizer ignore list, or
  322.     //   2. The global variable is created by the sanitizers itself for internal
  323.     //      usage, or
  324.     //   3. The global variable has __attribute__((no_sanitize("..."))) or
  325.     //      __attribute__((disable_sanitizer_instrumentation)).
  326.     //
  327.     // This is important, a some IR passes like GlobalMerge can delete global
  328.     // variables and replace them with new ones. If the old variables were
  329.     // marked to be unsanitized, then the new ones should also be.
  330.     unsigned NoAddress : 1;
  331.     unsigned NoHWAddress : 1;
  332.  
  333.     // Memtag sanitization works differently: sanitization is requested by clang
  334.     // when `-fsanitize=memtag-globals` is provided, and the request can be
  335.     // denied (and the attribute removed) by the AArch64 global tagging pass if
  336.     // it can't be fulfilled (e.g. the global variable is a TLS variable).
  337.     // Memtag sanitization has to interact with other parts of LLVM (like
  338.     // supressing certain optimisations, emitting assembly directives, or
  339.     // creating special relocation sections).
  340.     //
  341.     // Use `GlobalValue::isTagged()` to check whether tagging should be enabled
  342.     // for a global variable.
  343.     unsigned Memtag : 1;
  344.  
  345.     // ASan-specific metadata. Is this global variable dynamically initialized
  346.     // (from a C++ language perspective), and should therefore be checked for
  347.     // ODR violations.
  348.     unsigned IsDynInit : 1;
  349.   };
  350.  
  351.   bool hasSanitizerMetadata() const { return HasSanitizerMetadata; }
  352.   const SanitizerMetadata &getSanitizerMetadata() const;
  353.   // Note: Not byref as it's a POD and otherwise it's too easy to call
  354.   // G.setSanitizerMetadata(G2.getSanitizerMetadata()), and the argument becomes
  355.   // dangling when the backing storage allocates the metadata for `G`, as the
  356.   // storage is shared between `G1` and `G2`.
  357.   void setSanitizerMetadata(SanitizerMetadata Meta);
  358.   void removeSanitizerMetadata();
  359.  
  360.   bool isTagged() const {
  361.     return hasSanitizerMetadata() && getSanitizerMetadata().Memtag;
  362.   }
  363.  
  364.   static LinkageTypes getLinkOnceLinkage(bool ODR) {
  365.     return ODR ? LinkOnceODRLinkage : LinkOnceAnyLinkage;
  366.   }
  367.   static LinkageTypes getWeakLinkage(bool ODR) {
  368.     return ODR ? WeakODRLinkage : WeakAnyLinkage;
  369.   }
  370.  
  371.   static bool isExternalLinkage(LinkageTypes Linkage) {
  372.     return Linkage == ExternalLinkage;
  373.   }
  374.   static bool isAvailableExternallyLinkage(LinkageTypes Linkage) {
  375.     return Linkage == AvailableExternallyLinkage;
  376.   }
  377.   static bool isLinkOnceAnyLinkage(LinkageTypes Linkage) {
  378.     return Linkage == LinkOnceAnyLinkage;
  379.   }
  380.   static bool isLinkOnceODRLinkage(LinkageTypes Linkage) {
  381.     return Linkage == LinkOnceODRLinkage;
  382.   }
  383.   static bool isLinkOnceLinkage(LinkageTypes Linkage) {
  384.     return isLinkOnceAnyLinkage(Linkage) || isLinkOnceODRLinkage(Linkage);
  385.   }
  386.   static bool isWeakAnyLinkage(LinkageTypes Linkage) {
  387.     return Linkage == WeakAnyLinkage;
  388.   }
  389.   static bool isWeakODRLinkage(LinkageTypes Linkage) {
  390.     return Linkage == WeakODRLinkage;
  391.   }
  392.   static bool isWeakLinkage(LinkageTypes Linkage) {
  393.     return isWeakAnyLinkage(Linkage) || isWeakODRLinkage(Linkage);
  394.   }
  395.   static bool isAppendingLinkage(LinkageTypes Linkage) {
  396.     return Linkage == AppendingLinkage;
  397.   }
  398.   static bool isInternalLinkage(LinkageTypes Linkage) {
  399.     return Linkage == InternalLinkage;
  400.   }
  401.   static bool isPrivateLinkage(LinkageTypes Linkage) {
  402.     return Linkage == PrivateLinkage;
  403.   }
  404.   static bool isLocalLinkage(LinkageTypes Linkage) {
  405.     return isInternalLinkage(Linkage) || isPrivateLinkage(Linkage);
  406.   }
  407.   static bool isExternalWeakLinkage(LinkageTypes Linkage) {
  408.     return Linkage == ExternalWeakLinkage;
  409.   }
  410.   static bool isCommonLinkage(LinkageTypes Linkage) {
  411.     return Linkage == CommonLinkage;
  412.   }
  413.   static bool isValidDeclarationLinkage(LinkageTypes Linkage) {
  414.     return isExternalWeakLinkage(Linkage) || isExternalLinkage(Linkage);
  415.   }
  416.  
  417.   /// Whether the definition of this global may be replaced by something
  418.   /// non-equivalent at link time. For example, if a function has weak linkage
  419.   /// then the code defining it may be replaced by different code.
  420.   static bool isInterposableLinkage(LinkageTypes Linkage) {
  421.     switch (Linkage) {
  422.     case WeakAnyLinkage:
  423.     case LinkOnceAnyLinkage:
  424.     case CommonLinkage:
  425.     case ExternalWeakLinkage:
  426.       return true;
  427.  
  428.     case AvailableExternallyLinkage:
  429.     case LinkOnceODRLinkage:
  430.     case WeakODRLinkage:
  431.     // The above three cannot be overridden but can be de-refined.
  432.  
  433.     case ExternalLinkage:
  434.     case AppendingLinkage:
  435.     case InternalLinkage:
  436.     case PrivateLinkage:
  437.       return false;
  438.     }
  439.     llvm_unreachable("Fully covered switch above!");
  440.   }
  441.  
  442.   /// Whether the definition of this global may be discarded if it is not used
  443.   /// in its compilation unit.
  444.   static bool isDiscardableIfUnused(LinkageTypes Linkage) {
  445.     return isLinkOnceLinkage(Linkage) || isLocalLinkage(Linkage) ||
  446.            isAvailableExternallyLinkage(Linkage);
  447.   }
  448.  
  449.   /// Whether the definition of this global may be replaced at link time.  NB:
  450.   /// Using this method outside of the code generators is almost always a
  451.   /// mistake: when working at the IR level use isInterposable instead as it
  452.   /// knows about ODR semantics.
  453.   static bool isWeakForLinker(LinkageTypes Linkage)  {
  454.     return Linkage == WeakAnyLinkage || Linkage == WeakODRLinkage ||
  455.            Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage ||
  456.            Linkage == CommonLinkage || Linkage == ExternalWeakLinkage;
  457.   }
  458.  
  459.   /// Return true if the currently visible definition of this global (if any) is
  460.   /// exactly the definition we will see at runtime.
  461.   ///
  462.   /// Non-exact linkage types inhibits most non-inlining IPO, since a
  463.   /// differently optimized variant of the same function can have different
  464.   /// observable or undefined behavior than in the variant currently visible.
  465.   /// For instance, we could have started with
  466.   ///
  467.   ///   void foo(int *v) {
  468.   ///     int t = 5 / v[0];
  469.   ///     (void) t;
  470.   ///   }
  471.   ///
  472.   /// and "refined" it to
  473.   ///
  474.   ///   void foo(int *v) { }
  475.   ///
  476.   /// However, we cannot infer readnone for `foo`, since that would justify
  477.   /// DSE'ing a store to `v[0]` across a call to `foo`, which can cause
  478.   /// undefined behavior if the linker replaces the actual call destination with
  479.   /// the unoptimized `foo`.
  480.   ///
  481.   /// Inlining is okay across non-exact linkage types as long as they're not
  482.   /// interposable (see \c isInterposable), since in such cases the currently
  483.   /// visible variant is *a* correct implementation of the original source
  484.   /// function; it just isn't the *only* correct implementation.
  485.   bool isDefinitionExact() const {
  486.     return !mayBeDerefined();
  487.   }
  488.  
  489.   /// Return true if this global has an exact defintion.
  490.   bool hasExactDefinition() const {
  491.     // While this computes exactly the same thing as
  492.     // isStrongDefinitionForLinker, the intended uses are different.  This
  493.     // function is intended to help decide if specific inter-procedural
  494.     // transforms are correct, while isStrongDefinitionForLinker's intended use
  495.     // is in low level code generation.
  496.     return !isDeclaration() && isDefinitionExact();
  497.   }
  498.  
  499.   /// Return true if this global's definition can be substituted with an
  500.   /// *arbitrary* definition at link time or load time. We cannot do any IPO or
  501.   /// inlining across interposable call edges, since the callee can be
  502.   /// replaced with something arbitrary.
  503.   bool isInterposable() const;
  504.   bool canBenefitFromLocalAlias() const;
  505.  
  506.   bool hasExternalLinkage() const { return isExternalLinkage(getLinkage()); }
  507.   bool hasAvailableExternallyLinkage() const {
  508.     return isAvailableExternallyLinkage(getLinkage());
  509.   }
  510.   bool hasLinkOnceLinkage() const { return isLinkOnceLinkage(getLinkage()); }
  511.   bool hasLinkOnceAnyLinkage() const {
  512.     return isLinkOnceAnyLinkage(getLinkage());
  513.   }
  514.   bool hasLinkOnceODRLinkage() const {
  515.     return isLinkOnceODRLinkage(getLinkage());
  516.   }
  517.   bool hasWeakLinkage() const { return isWeakLinkage(getLinkage()); }
  518.   bool hasWeakAnyLinkage() const { return isWeakAnyLinkage(getLinkage()); }
  519.   bool hasWeakODRLinkage() const { return isWeakODRLinkage(getLinkage()); }
  520.   bool hasAppendingLinkage() const { return isAppendingLinkage(getLinkage()); }
  521.   bool hasInternalLinkage() const { return isInternalLinkage(getLinkage()); }
  522.   bool hasPrivateLinkage() const { return isPrivateLinkage(getLinkage()); }
  523.   bool hasLocalLinkage() const { return isLocalLinkage(getLinkage()); }
  524.   bool hasExternalWeakLinkage() const {
  525.     return isExternalWeakLinkage(getLinkage());
  526.   }
  527.   bool hasCommonLinkage() const { return isCommonLinkage(getLinkage()); }
  528.   bool hasValidDeclarationLinkage() const {
  529.     return isValidDeclarationLinkage(getLinkage());
  530.   }
  531.  
  532.   void setLinkage(LinkageTypes LT) {
  533.     if (isLocalLinkage(LT)) {
  534.       Visibility = DefaultVisibility;
  535.       DllStorageClass = DefaultStorageClass;
  536.     }
  537.     Linkage = LT;
  538.     if (isImplicitDSOLocal())
  539.       setDSOLocal(true);
  540.   }
  541.   LinkageTypes getLinkage() const { return LinkageTypes(Linkage); }
  542.  
  543.   bool isDiscardableIfUnused() const {
  544.     return isDiscardableIfUnused(getLinkage());
  545.   }
  546.  
  547.   bool isWeakForLinker() const { return isWeakForLinker(getLinkage()); }
  548.  
  549. protected:
  550.   /// Copy all additional attributes (those not needed to create a GlobalValue)
  551.   /// from the GlobalValue Src to this one.
  552.   void copyAttributesFrom(const GlobalValue *Src);
  553.  
  554. public:
  555.   /// If the given string begins with the GlobalValue name mangling escape
  556.   /// character '\1', drop it.
  557.   ///
  558.   /// This function applies a specific mangling that is used in PGO profiles,
  559.   /// among other things. If you're trying to get a symbol name for an
  560.   /// arbitrary GlobalValue, this is not the function you're looking for; see
  561.   /// Mangler.h.
  562.   static StringRef dropLLVMManglingEscape(StringRef Name) {
  563.     if (!Name.empty() && Name[0] == '\1')
  564.       return Name.substr(1);
  565.     return Name;
  566.   }
  567.  
  568.   /// Return the modified name for a global value suitable to be
  569.   /// used as the key for a global lookup (e.g. profile or ThinLTO).
  570.   /// The value's original name is \c Name and has linkage of type
  571.   /// \c Linkage. The value is defined in module \c FileName.
  572.   static std::string getGlobalIdentifier(StringRef Name,
  573.                                          GlobalValue::LinkageTypes Linkage,
  574.                                          StringRef FileName);
  575.  
  576.   /// Return the modified name for this global value suitable to be
  577.   /// used as the key for a global lookup (e.g. profile or ThinLTO).
  578.   std::string getGlobalIdentifier() const;
  579.  
  580.   /// Declare a type to represent a global unique identifier for a global value.
  581.   /// This is a 64 bits hash that is used by PGO and ThinLTO to have a compact
  582.   /// unique way to identify a symbol.
  583.   using GUID = uint64_t;
  584.  
  585.   /// Return a 64-bit global unique ID constructed from global value name
  586.   /// (i.e. returned by getGlobalIdentifier()).
  587.   static GUID getGUID(StringRef GlobalName) { return MD5Hash(GlobalName); }
  588.  
  589.   /// Return a 64-bit global unique ID constructed from global value name
  590.   /// (i.e. returned by getGlobalIdentifier()).
  591.   GUID getGUID() const { return getGUID(getGlobalIdentifier()); }
  592.  
  593.   /// @name Materialization
  594.   /// Materialization is used to construct functions only as they're needed.
  595.   /// This
  596.   /// is useful to reduce memory usage in LLVM or parsing work done by the
  597.   /// BitcodeReader to load the Module.
  598.   /// @{
  599.  
  600.   /// If this function's Module is being lazily streamed in functions from disk
  601.   /// or some other source, this method can be used to check to see if the
  602.   /// function has been read in yet or not.
  603.   bool isMaterializable() const;
  604.  
  605.   /// Make sure this GlobalValue is fully read.
  606.   Error materialize();
  607.  
  608. /// @}
  609.  
  610.   /// Return true if the primary definition of this global value is outside of
  611.   /// the current translation unit.
  612.   bool isDeclaration() const;
  613.  
  614.   bool isDeclarationForLinker() const {
  615.     if (hasAvailableExternallyLinkage())
  616.       return true;
  617.  
  618.     return isDeclaration();
  619.   }
  620.  
  621.   /// Returns true if this global's definition will be the one chosen by the
  622.   /// linker.
  623.   ///
  624.   /// NB! Ideally this should not be used at the IR level at all.  If you're
  625.   /// interested in optimization constraints implied by the linker's ability to
  626.   /// choose an implementation, prefer using \c hasExactDefinition.
  627.   bool isStrongDefinitionForLinker() const {
  628.     return !(isDeclarationForLinker() || isWeakForLinker());
  629.   }
  630.  
  631.   const GlobalObject *getAliaseeObject() const;
  632.   GlobalObject *getAliaseeObject() {
  633.     return const_cast<GlobalObject *>(
  634.         static_cast<const GlobalValue *>(this)->getAliaseeObject());
  635.   }
  636.  
  637.   /// Returns whether this is a reference to an absolute symbol.
  638.   bool isAbsoluteSymbolRef() const;
  639.  
  640.   /// If this is an absolute symbol reference, returns the range of the symbol,
  641.   /// otherwise returns std::nullopt.
  642.   std::optional<ConstantRange> getAbsoluteSymbolRange() const;
  643.  
  644.   /// This method unlinks 'this' from the containing module, but does not delete
  645.   /// it.
  646.   void removeFromParent();
  647.  
  648.   /// This method unlinks 'this' from the containing module and deletes it.
  649.   void eraseFromParent();
  650.  
  651.   /// Get the module that this global value is contained inside of...
  652.   Module *getParent() { return Parent; }
  653.   const Module *getParent() const { return Parent; }
  654.  
  655.   // Methods for support type inquiry through isa, cast, and dyn_cast:
  656.   static bool classof(const Value *V) {
  657.     return V->getValueID() == Value::FunctionVal ||
  658.            V->getValueID() == Value::GlobalVariableVal ||
  659.            V->getValueID() == Value::GlobalAliasVal ||
  660.            V->getValueID() == Value::GlobalIFuncVal;
  661.   }
  662.  
  663.   /// True if GV can be left out of the object symbol table. This is the case
  664.   /// for linkonce_odr values whose address is not significant. While legal, it
  665.   /// is not normally profitable to omit them from the .o symbol table. Using
  666.   /// this analysis makes sense when the information can be passed down to the
  667.   /// linker or we are in LTO.
  668.   bool canBeOmittedFromSymbolTable() const;
  669. };
  670.  
  671. } // end namespace llvm
  672.  
  673. #endif // LLVM_IR_GLOBALVALUE_H
  674.