[GCC] Attribute ifunc support in llvm

[DmitryPolukhin]

Summary

This patch add support for GCC attribute((ifunc("resolver"))) for targets that use ELF as object file format. In general ifunc is a special kind of function alias with type @gnu_indirect_function. Patch for Clang http://reviews.llvm.org/D15524

[• rafael]

include/llvm/IR/GlobalAlias.h

90 ↗

(On Diff #42846)

Don't repeat name in comments.

[DmitryPolukhin]

Fixed comment.

[dexonsmith]

Since this modifies the IR, please start with an RFC on llvm-dev.
(I just did a search for "ifunc"... sorry if you already posted
one and I'm just incapable of using search correctly.)

I'd be interested, in particular, to hear whether you considered
adding a separate construct rather than piggy-backing on
GlobalAlias, and if so, why you rejected that alternative. It
seems like, semantically, ifuncs are very different from aliases.
A straw-man counter-proposal might be:

• Move the relevant guts of GlobalAlias into a base class, maybe called GlobalIndirectSymbol (bike shed that).
• Add a new subclass called GlobalIFunc.
• Use ifunc *instead* of alias in textual IR (making it a separate construct, rather than an attribute).

The main benefit? Current optimizations/etc. may assume that
isa<GlobalAlias>(GV) implies that GV is a global alias. It
seems clearer to use the type hierarchy to differentiate. It'll
probably be cleaner for new code, as well.

Regardless, please take it to an llvm-dev RFC so we can get more
eyes on it. (Although given the time of year, you may not get
the usual number of responses over the next couple of weeks...)

[echristo]

FWIW both I and John had the feedback on GlobalAlias on the cfe-commits
thread. :)

[DmitryPolukhin]

Thank you for pointing out the direction. I'll start working on RFC with different approaches how ifunc could be represented in IR.

Just for the sake of completeness, there is a way to avoid IR extension - it is possible to emit global asm statement like __asm__ (".type resolver_alias_name, @gnu_indirect_function") and avoid IR extension but I didn't seriously consider this path.

[DmitryPolukhin]

Work in progress patch that shows amount of changes required to introduce GloablIFunc and put it into separate list in module.

Clang part also needs to be update but it depends on LLVM part so it makes sense to reach at least some consensus on LLVM part first.

[• rafael]

include/llvm-c/Core.h

1890 ↗

(On Diff #43599)

I am not sure about adding a C api right away. Maybe wait a bit once the patch is in?

include/llvm/IR/GlobalIndirectSymbol.h

63

Is this meaningful for ifunc?

IMHO it is a design mistake for GlobalAlias to take an arbitrary expression. If ifunc can take just a GlobalValue that would be nice.

include/llvm/IR/Module.h

589

Is there real value in these @{}?

591

clang-format

lib/AsmParser/LLParser.cpp

757

Any type restrictions when it is not an alias?

lib/AsmParser/LLParser.h

274 ↗

(On Diff #43599)

Start functions with lowercase.

lib/Bitcode/Writer/BitcodeWriter.cpp

814

You are missing the address space in the comment.

[DmitryPolukhin]

Still work in progress, fixed most of comments.

[DmitryPolukhin]

New patch uploaded.

include/llvm-c/Core.h

1890 ↗

(On Diff #43599)

I added it just for completeness. I can remove it before commit if needed. I'm worry that it will be easy to forget if I remove it now.

include/llvm/IR/GlobalIndirectSymbol.h

63

It makes sense to me.

include/llvm/IR/Module.h

589

I don't see them in generated doxygen so it seems useless. I put them just to follow style of surrounding code. I'll remove them if there a consensus here.

591

Same here, such formatting is used in the whole file very consistent so I decided to follow local style. Please let me know if you really want to reformat only new block of code differently.

lib/AsmParser/LLParser.cpp

757

At least we could check that it is a function. Checking the function return type is trickier because GCC allows any type even void same as for the parameters of the function.

[DmitryPolukhin]

Clang part was updated to use new representation so I think now patch is ready for review, please take a look.

[DmitryPolukhin]

Friendly ping, please review this patch.

Clang part of ifunc support was approved for commit but llvm part needs to be committed first.

[vsk]

Please add a short test to test/Bitcode/compatibility.ll.

[DmitryPolukhin]

• added test case in test/Bitcode/compatibility.ll
• added test test/Assembler/ifunc-use-list-order.ll
• fixed ordering problem in bitcode writer
• fix for alias on ifunc
• fixed nit in LangRef

PTAL

[DmitryPolukhin]

Friendly ping, please take a look!

Please let me know if in general things look fine but this patch needs to be splatted into smaller parts to simplify review as Duncan suggested.

[DmitryPolukhin]

Friendly ping, please take a look!

[grooverdan]

Friendly ping. As a user I'm really looking forward to this feature. Thanks DmitryPolukhin for writing it.

[asl]

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

1072

Why alias? Shouldn't this be llvm_unreachable?

[echristo]

A couple of inline comments for the next patch, but a quick top level comment:

Since we agree that the GlobalIndirectFunc hierarchy is the right way to do this, can you split the patch in two and add that layer of indirection first and then we can add ifunc later to make it easier to see what each side of things is doing?

Also, thank you very much for all of your work and patience here. I really appreciate it.

Thanks!

-eric

include/llvm-c/Core.h

1790 ↗

(On Diff #44637)

We typically add them on demand. I'd rather leave it off for now and we can add it later if it's necessary.

include/llvm/IR/Module.h

591

No, consistency is fine here, thanks.

[DmitryPolukhin]

Eric, that you for looking to the code! I'll split the patch and send first part for review ASAP.

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

1072

Local linkage is possible here but I'll update text to reflect that ifunc could be here too.

[DmitryPolukhin]

Extracted GlobalIndirectSymbol creation to separate patch http://reviews.llvm.org/D18433

This patch will be rebased when D18433 is committed to continue ifunc specific review.

[DmitryPolukhin]

• rebease on top of GlobalIndirectSymbol committed to LLVM
• removed C interface for ifunc, it seems that it is not required for now

[echristo]

Highlighted a couple of things that could be pulled out into an incremental patch (and you can pull out similar Alias->IndirectSymbol changes).

Thanks!

-eric

include/llvm/CodeGen/AsmPrinter.h

550–552 ↗

(On Diff #52205)

This isn't part of the previous patch?

lib/AsmParser/LLParser.h

278–282 ↗

(On Diff #52205)

Ditto.

[DmitryPolukhin]

include/llvm/CodeGen/AsmPrinter.h

550–552 ↗

(On Diff #52205)

In previous patch I included things that have sense without ifunc and functions that won't be updated in ifunc patch. For printer and bitcode write the same functions will have to be updated twice so it won't reduce this patch so significantly. But OK, I'll extract as much as I can.

[echristo]

include/llvm/CodeGen/AsmPrinter.h

550–552 ↗

(On Diff #52205)

Awesome. Thank you very much :)

[DmitryPolukhin]

Rebased on top of D18754

Eric, thank you a lot for fast review previous parts and please take a look to the remaining changes.

[echristo]

LGTM. Since Duncan has been looking at these as well you might want to wait for an ACK from him as well.

Thanks a ton for doing all of this. :)

-eric

[dexonsmith]

I have a bunch of nitpicks inline below; once you resolve those, LGTM!

[DmitryPolukhin]

• fixed comments

docs/LangRef.rst

 
 * No alias in the expression can be weak as the possibility of the
   intermediate alias being overridden cannot be represented in an
   object file.
 
 * No global value in the expression can be a declaration, since that
   would require a relocation, which is not possible.
 
+.. _langref_ifunc:
+
+IFuncs
+-------
+
+IFuncs, like as aliases, don't create any new data or func. They are just a new
+symbol that dynamic linker resolves at runtime by calling a resolver function.
+
+IFuncs have a name and a resolver that is a function called by dynamic linker
+that returns address of another function associated with the name.
+
+IFunc may have an optional :ref:`linkage type <linkage>` and an optional
+:ref:`visibility style <visibility>`.
+
+Syntax::
+
+    @<Name> = [Linkage] [Visibility] ifunc <IFuncTy>, <ResolverTy>* @<Resolver>
+
+
 .. _langref_comdats:
 
 Comdats
 -------
 
 Comdat IR provides access to COFF and ELF object file COMDAT functionality.
 
 Comdats have a name which represents the COMDAT key. All global objects that

include/llvm/Bitcode/LLVMBitCodes.h

enum ModuleCodes {
 
   MODULE_CODE_METADATA_VALUES_UNUSED = 15,
 
   // SOURCE_FILENAME: [namechar x N]
   MODULE_CODE_SOURCE_FILENAME = 16,
 
   // HASH: [5*i32]
   MODULE_CODE_HASH = 17,
+
+  // IFUNC: [ifunc value type, addrspace, resolver val#, linkage, visibility]
+  MODULE_CODE_IFUNC = 18,
 };
 
 /// PARAMATTR blocks have code for defining a parameter attribute set.
 enum AttributeCodes {
   // FIXME: Remove `PARAMATTR_CODE_ENTRY_OLD' in 4.0
   PARAMATTR_CODE_ENTRY_OLD = 1, // ENTRY: [paramidx0, attr0,
                                 //         paramidx1, attr1...]
   PARAMATTR_CODE_ENTRY = 2,     // ENTRY: [paramidx0, attrgrp0,

include/llvm/IR/GlobalIFunc.h

+//===-------- llvm/GlobalIFunc.h - GlobalIFunc class ------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \brief
+/// This file contains the declaration of the GlobalIFunc class, which
+/// represents a single indirect function in the IR. Indirect function uses
+/// ELF symbol type extension to mark that the address of a declaration should
+/// be resolved at runtime by calling a resolver function.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_IR_GLOBALIFUNC_H
+#define LLVM_IR_GLOBALIFUNC_H
+
+#include "llvm/ADT/Twine.h"
+#include "llvm/ADT/ilist_node.h"
+#include "llvm/IR/GlobalIndirectSymbol.h"
+
+namespace llvm {
+
+class Module;
+template <typename ValueSubClass> class SymbolTableListTraits;
+
+class GlobalIFunc : public GlobalIndirectSymbol,
+                    public ilist_node<GlobalIFunc> {
+  friend class SymbolTableListTraits<GlobalIFunc>;
+  void operator=(const GlobalIFunc &) = delete;
+  GlobalIFunc(const GlobalIFunc &) = delete;
+
+  void setParent(Module *parent);
+
+  GlobalIFunc(Type *Ty, unsigned AddressSpace, LinkageTypes Linkage,
+              const Twine &Name, Constant *Resolver, Module *Parent);
+
+public:
+  /// If a parent module is specified, the ifunc is automatically inserted into
+  /// the end of the specified module's ifunc list.
+  static GlobalIFunc *create(Type *Ty, unsigned AddressSpace,
+                             LinkageTypes Linkage, const Twine &Name,
+                             Constant *Resolver, Module *Parent);
+
+  /// This method unlinks 'this' from the containing module, but does not
+  /// delete it.
+  void removeFromParent() override;
+
+  /// This method unlinks 'this' from the containing module and deletes it.
+  void eraseFromParent() override;
+
+  /// These methods retrieve and set ifunc resolver function.
+  void setResolver(Constant *Resolver) {
+    setIndirectSymbol(Resolver);
+  }
+  const Constant *getResolver() const {
+    return getIndirectSymbol();
+  }
+  Constant *getResolver() {
+    return getIndirectSymbol();
+  }
+
+  // Methods for support type inquiry through isa, cast, and dyn_cast:
+  static inline bool classof(const Value *V) {
+    return V->getValueID() == Value::GlobalIFuncVal;
+  }
+};
+
+} // End llvm namespace
+
+#endif

include/llvm/IR/GlobalIndirectSymbol.h

const Constant *getIndirectSymbol() const {
     return const_cast<GlobalIndirectSymbol *>(this)->getIndirectSymbol();
   }
   Constant *getIndirectSymbol() {
     return getOperand(0);
   }
 
   // Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const Value *V) {
-    return V->getValueID() == Value::GlobalAliasVal;
+    return V->getValueID() == Value::GlobalAliasVal ||
+           V->getValueID() == Value::GlobalIFuncVal;
   }
 };
 
 template <>
 struct OperandTraits<GlobalIndirectSymbol> :
   public FixedNumOperandTraits<GlobalIndirectSymbol, 1> {
 };
 
 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalIndirectSymbol, Constant)
 
 } // End llvm namespace
 
 #endif

include/llvm/IR/GlobalValue.h

/// @}
   /// 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::GlobalAliasVal ||
+           V->getValueID() == Value::GlobalIFuncVal;
   }
 };
 
 } // End llvm namespace
 
 #endif

include/llvm/IR/Module.h

 #define LLVM_IR_MODULE_H
 
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/IR/Comdat.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalAlias.h"
+#include "llvm/IR/GlobalIFunc.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/Support/CBindingWrapping.h"
 #include "llvm/Support/CodeGen.h"
 #include "llvm/Support/DataTypes.h"
 #include <system_error>
 
 namespace llvm {

 /// @{
 public:
   /// The type for the list of global variables.
   typedef SymbolTableList<GlobalVariable> GlobalListType;
   /// The type for the list of functions.
   typedef SymbolTableList<Function> FunctionListType;
   /// The type for the list of aliases.
   typedef SymbolTableList<GlobalAlias> AliasListType;
+  /// The type for the list of ifuncs.
+  typedef SymbolTableList<GlobalIFunc> IFuncListType;
   /// The type for the list of named metadata.
   typedef ilist<NamedMDNode> NamedMDListType;
   /// The type of the comdat "symbol" table.
   typedef StringMap<Comdat> ComdatSymTabType;
 
   /// The Global Variable iterator.
   typedef GlobalListType::iterator                      global_iterator;
   /// The Global Variable constant iterator.
public:
   /// The Function constant reverse iterator.
   typedef FunctionListType::const_reverse_iterator const_reverse_iterator;
 
   /// The Global Alias iterators.
   typedef AliasListType::iterator                        alias_iterator;
   /// The Global Alias constant iterator
   typedef AliasListType::const_iterator            const_alias_iterator;
 
+  /// The Global IFunc iterators.
+  typedef IFuncListType::iterator                        ifunc_iterator;
+  /// The Global IFunc constant iterator
+  typedef IFuncListType::const_iterator            const_ifunc_iterator;
+
   /// The named metadata iterators.
   typedef NamedMDListType::iterator             named_metadata_iterator;
   /// The named metadata constant iterators.
   typedef NamedMDListType::const_iterator const_named_metadata_iterator;
 
   /// This enumeration defines the supported behaviors of module flags.
   enum ModFlagBehavior {
     /// Emits an error if two values disagree, otherwise the resulting value is

 /// @name Member Variables
 /// @{
 private:
   LLVMContext &Context;           ///< The LLVMContext from which types and
                                   ///< constants are allocated.
   GlobalListType GlobalList;      ///< The Global Variables in the module
   FunctionListType FunctionList;  ///< The Functions in the module
   AliasListType AliasList;        ///< The Aliases in the module
+  IFuncListType IFuncList;        ///< The IFuncs in the module
   NamedMDListType NamedMDList;    ///< The named metadata in the module
   std::string GlobalScopeAsm;     ///< Inline Asm at global scope.
   ValueSymbolTable *ValSymTab;    ///< Symbol table for values
   ComdatSymTabType ComdatSymTab;  ///< Symbol table for COMDATs
   std::unique_ptr<GVMaterializer>
   Materializer;                   ///< Used to materialize GlobalValues
   std::string ModuleID;           ///< Human readable identifier for the module
   std::string SourceFileName;     ///< Original source file name for module,

 /// @{
 
   /// Return the global alias in the module with the specified name, of
   /// arbitrary type. This method returns null if a global with the specified
   /// name is not found.
   GlobalAlias *getNamedAlias(StringRef Name) const;
 
 /// @}
+/// @name Global IFunc Accessors
+/// @{
+
+  /// Return the global alias in the module with the specified name, of
+  /// arbitrary type. This method returns null if a global with the specified
+  /// name is not found.
+  GlobalIFunc *getNamedIFunc(StringRef Name) const;
+
+/// @}
 /// @name Named Metadata Accessors
 /// @{
 
   /// Return the first NamedMDNode in the module with the specified name. This
   /// method returns null if a NamedMDNode with the specified name is not found.
   NamedMDNode *getNamedMetadata(const Twine &Name) const;
 
   /// Return the named MDNode in the module with the specified name. This method
/// @{
   }
   /// Get the Module's list of aliases (constant).
   const AliasListType    &getAliasList() const        { return AliasList; }
   /// Get the Module's list of aliases.
   AliasListType          &getAliasList()              { return AliasList; }
   static AliasListType Module::*getSublistAccess(GlobalAlias*) {
     return &Module::AliasList;
   }
+  /// Get the Module's list of ifuncs (constant).
+  const IFuncListType    &getIFuncList() const        { return IFuncList; }
+  /// Get the Module's list of ifuncs.
+  IFuncListType          &getIFuncList()              { return IFuncList; }
+  static IFuncListType Module::*getSublistAccess(GlobalIFunc*) {
+    return &Module::IFuncList;
+  }
   /// Get the Module's list of named metadata (constant).
   const NamedMDListType  &getNamedMDList() const      { return NamedMDList; }
   /// Get the Module's list of named metadata.
   NamedMDListType        &getNamedMDList()            { return NamedMDList; }
   static NamedMDListType Module::*getSublistAccess(NamedMDNode*) {
     return &Module::NamedMDList;
   }
   /// Get the symbol table of global variable and function identifiers
/// @{
   iterator_range<alias_iterator> aliases() {
     return make_range(alias_begin(), alias_end());
   }
   iterator_range<const_alias_iterator> aliases() const {
     return make_range(alias_begin(), alias_end());
   }
 
 /// @}
+/// @name IFunc Iteration
+/// @{
+
+  ifunc_iterator       ifunc_begin()            { return IFuncList.begin(); }
+  const_ifunc_iterator ifunc_begin() const      { return IFuncList.begin(); }
+  ifunc_iterator       ifunc_end  ()            { return IFuncList.end();   }
+  const_ifunc_iterator ifunc_end  () const      { return IFuncList.end();   }
+  size_t               ifunc_size () const      { return IFuncList.size();  }
+  bool                 ifunc_empty() const      { return IFuncList.empty(); }
+
+  iterator_range<ifunc_iterator> ifuncs() {
+    return make_range(ifunc_begin(), ifunc_end());
+  }
+  iterator_range<const_ifunc_iterator> ifuncs() const {
+    return make_range(ifunc_begin(), ifunc_end());
+  }
+
+/// @}
 /// @name Named Metadata Iteration
 /// @{
 
   named_metadata_iterator named_metadata_begin() { return NamedMDList.begin(); }
   const_named_metadata_iterator named_metadata_begin() const {
     return NamedMDList.begin();
   }
 

include/llvm/IR/SymbolTableListTraits.h

 /// single template parameter for the list and traits.
 template <typename NodeTy> struct SymbolTableListParentType {};
 class Argument;
 class BasicBlock;
 class Function;
 class Instruction;
 class GlobalVariable;
 class GlobalAlias;
+class GlobalIFunc;
 class Module;
 #define DEFINE_SYMBOL_TABLE_PARENT_TYPE(NODE, PARENT)                          \
   template <> struct SymbolTableListParentType<NODE> { typedef PARENT type; };
 DEFINE_SYMBOL_TABLE_PARENT_TYPE(Instruction, BasicBlock)
 DEFINE_SYMBOL_TABLE_PARENT_TYPE(BasicBlock, Function)
 DEFINE_SYMBOL_TABLE_PARENT_TYPE(Argument, Function)
 DEFINE_SYMBOL_TABLE_PARENT_TYPE(Function, Module)
 DEFINE_SYMBOL_TABLE_PARENT_TYPE(GlobalVariable, Module)
 DEFINE_SYMBOL_TABLE_PARENT_TYPE(GlobalAlias, Module)
+DEFINE_SYMBOL_TABLE_PARENT_TYPE(GlobalIFunc, Module)
 #undef DEFINE_SYMBOL_TABLE_PARENT_TYPE
 
 template <typename NodeTy> class SymbolTableList;
 
 // ValueSubClass   - The type of objects that I hold, e.g. Instruction.
 // ItemParentClass - The type of object that owns the list, e.g. BasicBlock.
 //
 template <typename ValueSubClass>

include/llvm/IR/Value.h

 class Argument;
 class AssemblyAnnotationWriter;
 class BasicBlock;
 class Constant;
 class ConstantData;
 class DataLayout;
 class Function;
 class GlobalAlias;
+class GlobalIFunc;
 class GlobalIndirectSymbol;
 class GlobalObject;
 class GlobalValue;
 class GlobalVariable;
 class InlineAsm;
 class Instruction;
 class LLVMContext;
 class Module;

 };
 
 template <> struct isa_impl<GlobalAlias, Value> {
   static inline bool doit(const Value &Val) {
     return Val.getValueID() == Value::GlobalAliasVal;
   }
 };
 
+template <> struct isa_impl<GlobalIFunc, Value> {
+  static inline bool doit(const Value &Val) {
+    return Val.getValueID() == Value::GlobalIFuncVal;
+  }
+};
+
 template <> struct isa_impl<GlobalIndirectSymbol, Value> {
   static inline bool doit(const Value &Val) {
-    return isa<GlobalAlias>(Val);
+    return isa<GlobalAlias>(Val) || isa<GlobalIFunc>(Val);
   }
 };
 
 template <> struct isa_impl<GlobalValue, Value> {
   static inline bool doit(const Value &Val) {
     return isa<GlobalObject>(Val) || isa<GlobalIndirectSymbol>(Val);
   }
 };

include/llvm/IR/Value.def

 HANDLE_VALUE(Argument)
 HANDLE_VALUE(BasicBlock)
 HANDLE_VALUE(MemoryUse)
 HANDLE_VALUE(MemoryDef)
 HANDLE_VALUE(MemoryPhi)
 
 HANDLE_GLOBAL_VALUE(Function)
 HANDLE_GLOBAL_VALUE(GlobalAlias)
+HANDLE_GLOBAL_VALUE(GlobalIFunc)
 HANDLE_GLOBAL_VALUE(GlobalVariable)
 HANDLE_CONSTANT(BlockAddress)
 HANDLE_CONSTANT(ConstantExpr)
 HANDLE_CONSTANT(ConstantArray)
 HANDLE_CONSTANT(ConstantStruct)
 HANDLE_CONSTANT(ConstantVector)
 
 // ConstantData.

include/llvm/IR/ValueSymbolTable.h

 class ValueSymbolTable {
   friend class Value;
   friend class SymbolTableListTraits<Argument>;
   friend class SymbolTableListTraits<BasicBlock>;
   friend class SymbolTableListTraits<Instruction>;
   friend class SymbolTableListTraits<Function>;
   friend class SymbolTableListTraits<GlobalVariable>;
   friend class SymbolTableListTraits<GlobalAlias>;
+  friend class SymbolTableListTraits<GlobalIFunc>;
 /// @name Types
 /// @{
 public:
   /// @brief A mapping of names to values.
   typedef StringMap<Value*> ValueMap;
 
   /// @brief An iterator over a ValueMap.
   typedef ValueMap::iterator iterator;

lib/AsmParser/LLLexer.cpp

#define KEYWORD(STR)                                                           \
   KEYWORD(nuw);
   KEYWORD(nsw);
   KEYWORD(exact);
   KEYWORD(inbounds);
   KEYWORD(align);
   KEYWORD(addrspace);
   KEYWORD(section);
   KEYWORD(alias);
+  KEYWORD(ifunc);
   KEYWORD(module);
   KEYWORD(asm);
   KEYWORD(sideeffect);
   KEYWORD(alignstack);
   KEYWORD(inteldialect);
   KEYWORD(gc);
   KEYWORD(prefix);
   KEYWORD(prologue);

lib/AsmParser/LLParser.cpp

else {
     IsConstant = false;
     return TokError("expected 'global' or 'constant'");
   }
   Lex.Lex();
   return false;
 }
 
 /// ParseUnnamedGlobal:
-///   OptionalVisibility ALIAS ...
+///   OptionalVisibility (ALIAS | IFUNC) ...
 ///   OptionalLinkage OptionalVisibility OptionalDLLStorageClass
 ///                                                     ...   -> global variable
-///   GlobalID '=' OptionalVisibility ALIAS ...
+///   GlobalID '=' OptionalVisibility (ALIAS | IFUNC) ...
 ///   GlobalID '=' OptionalLinkage OptionalVisibility OptionalDLLStorageClass
 ///                                                     ...   -> global variable
 bool LLParser::ParseUnnamedGlobal() {
   unsigned VarID = NumberedVals.size();
   std::string Name;
   LocTy NameLoc = Lex.getLoc();
 
   // Handle the GlobalID form.
bool LLParser::ParseUnnamedGlobal() {
   bool UnnamedAddr;
   if (ParseOptionalLinkage(Linkage, HasLinkage) ||
       ParseOptionalVisibility(Visibility) ||
       ParseOptionalDLLStorageClass(DLLStorageClass) ||
       ParseOptionalThreadLocal(TLM) ||
       parseOptionalUnnamedAddr(UnnamedAddr))
     return true;
 
-  if (Lex.getKind() != lltok::kw_alias)
+  if (Lex.getKind() != lltok::kw_alias && Lex.getKind() != lltok::kw_ifunc)
     return ParseGlobal(Name, NameLoc, Linkage, HasLinkage, Visibility,
                        DLLStorageClass, TLM, UnnamedAddr);
 
   return parseIndirectSymbol(Name, NameLoc, Linkage, Visibility,
                              DLLStorageClass, TLM, UnnamedAddr);
 }
 
 /// ParseNamedGlobal:
-///   GlobalVar '=' OptionalVisibility ALIAS ...
+///   GlobalVar '=' OptionalVisibility (ALIAS | IFUNC) ...
 ///   GlobalVar '=' OptionalLinkage OptionalVisibility OptionalDLLStorageClass
 ///                                                     ...   -> global variable
 bool LLParser::ParseNamedGlobal() {
   assert(Lex.getKind() == lltok::GlobalVar);
   LocTy NameLoc = Lex.getLoc();
   std::string Name = Lex.getStrVal();
   Lex.Lex();
 
   bool HasLinkage;
   unsigned Linkage, Visibility, DLLStorageClass;
   GlobalVariable::ThreadLocalMode TLM;
   bool UnnamedAddr;
   if (ParseToken(lltok::equal, "expected '=' in global variable") ||
       ParseOptionalLinkage(Linkage, HasLinkage) ||
       ParseOptionalVisibility(Visibility) ||
       ParseOptionalDLLStorageClass(DLLStorageClass) ||
       ParseOptionalThreadLocal(TLM) ||
       parseOptionalUnnamedAddr(UnnamedAddr))
     return true;
 
-  if (Lex.getKind() != lltok::kw_alias)
+  if (Lex.getKind() != lltok::kw_alias && Lex.getKind() != lltok::kw_ifunc)
     return ParseGlobal(Name, NameLoc, Linkage, HasLinkage, Visibility,
                        DLLStorageClass, TLM, UnnamedAddr);
 
   return parseIndirectSymbol(Name, NameLoc, Linkage, Visibility,
                              DLLStorageClass, TLM, UnnamedAddr);
 }
 
 bool LLParser::parseComdat() {

 static bool isValidVisibilityForLinkage(unsigned V, unsigned L) {
   return !GlobalValue::isLocalLinkage((GlobalValue::LinkageTypes)L) ||
          (GlobalValue::VisibilityTypes)V == GlobalValue::DefaultVisibility;
 }
 
 /// parseIndirectSymbol:
 ///   ::= GlobalVar '=' OptionalLinkage OptionalVisibility
 ///                     OptionalDLLStorageClass OptionalThreadLocal
-///                     OptionalUnnamedAddr 'alias' IndirectSymbol
+///                     OptionalUnnamedAddr 'alias|ifunc' IndirectSymbol
 ///
 /// IndirectSymbol
 ///   ::= TypeAndValue
 ///
 /// Everything through OptionalUnnamedAddr has already been parsed.
 ///
 bool LLParser::parseIndirectSymbol(const std::string &Name, LocTy NameLoc,
                                    unsigned L, unsigned Visibility,
                                    unsigned DLLStorageClass,
                                    GlobalVariable::ThreadLocalMode TLM,
                                    bool UnnamedAddr) {
   bool IsAlias;
   if (Lex.getKind() == lltok::kw_alias)
     IsAlias = true;
+  else if (Lex.getKind() == lltok::kw_ifunc)
+    IsAlias = false;
   else
-    llvm_unreachable("Not an alias!");
+    llvm_unreachable("Not an alias or ifunc!");
   Lex.Lex();
 
   GlobalValue::LinkageTypes Linkage = (GlobalValue::LinkageTypes) L;
 
   if(IsAlias && !GlobalAlias::isValidLinkage(Linkage))
     return Error(NameLoc, "invalid linkage type for alias");
 
   if (!isValidVisibilityForLinkage(Visibility, L))
     return Error(NameLoc,
                  "symbol with local linkage must have default visibility");
 
   Type *Ty;
   LocTy ExplicitTypeLoc = Lex.getLoc();
   if (ParseType(Ty) ||
-      ParseToken(lltok::comma, "expected comma after alias's type"))
+      ParseToken(lltok::comma, "expected comma after alias or ifunc's type"))
     return true;
 
   Constant *Aliasee;
   LocTy AliaseeLoc = Lex.getLoc();
   if (Lex.getKind() != lltok::kw_bitcast &&
       Lex.getKind() != lltok::kw_getelementptr &&
       Lex.getKind() != lltok::kw_addrspacecast &&
       Lex.getKind() != lltok::kw_inttoptr) {
     if (ParseGlobalTypeAndValue(Aliasee))
       return true;
   } else {
     // The bitcast dest type is not present, it is implied by the dest type.
     ValID ID;
     if (ParseValID(ID))
       return true;
     if (ID.Kind != ValID::t_Constant)
       return Error(AliaseeLoc, "invalid aliasee");
     Aliasee = ID.ConstantVal;
   }
 
   Type *AliaseeType = Aliasee->getType();
   auto *PTy = dyn_cast<PointerType>(AliaseeType);
   if (!PTy)
-    return Error(AliaseeLoc, "An alias must have pointer type");
+    return Error(AliaseeLoc, "An alias or ifunc must have pointer type");
   unsigned AddrSpace = PTy->getAddressSpace();
 
   if (IsAlias && Ty != PTy->getElementType())
     return Error(
         ExplicitTypeLoc,
         "explicit pointee type doesn't match operand's pointee type");
 
   if (!IsAlias && !PTy->getElementType()->isFunctionTy())
     return Error(
         ExplicitTypeLoc,
         "explicit pointee type should be a function type");
bool LLParser::parseIndirectSymbol(const std::string &Name, LocTy NameLoc,
 
   // Okay, create the alias but do not insert it into the module yet.
   std::unique_ptr<GlobalIndirectSymbol> GA;
   if (IsAlias)
     GA.reset(GlobalAlias::create(Ty, AddrSpace,
                                  (GlobalValue::LinkageTypes)Linkage, Name,
                                  Aliasee, /*Parent*/ nullptr));
   else
-    llvm_unreachable("Not an alias!");
+    GA.reset(GlobalIFunc::create(Ty, AddrSpace,
+                                 (GlobalValue::LinkageTypes)Linkage, Name,
+                                 Aliasee, /*Parent*/ nullptr));
   GA->setThreadLocalMode(TLM);
   GA->setVisibility((GlobalValue::VisibilityTypes)Visibility);
   GA->setDLLStorageClass((GlobalValue::DLLStorageClassTypes)DLLStorageClass);
   GA->setUnnamedAddr(UnnamedAddr);
 
   if (Name.empty())
     NumberedVals.push_back(GA.get());
 
if (GVal) {
     GVal->replaceAllUsesWith(GA.get());
     GVal->eraseFromParent();
   }
 
   // Insert into the module, we know its name won't collide now.
   if (IsAlias)
     M->getAliasList().push_back(cast<GlobalAlias>(GA.get()));
   else
-    llvm_unreachable("Not an alias!");
+    M->getIFuncList().push_back(cast<GlobalIFunc>(GA.get()));
   assert(GA->getName() == Name && "Should not be a name conflict!");
 
   // The module owns this now
   GA.release();
 
   return false;
 }
 

lib/AsmParser/LLToken.h

enum Kind {
     kw_nuw,
     kw_nsw,
     kw_exact,
     kw_inbounds,
     kw_align,
     kw_addrspace,
     kw_section,
     kw_alias,
+    kw_ifunc,
     kw_module,
     kw_asm,
     kw_sideeffect,
     kw_alignstack,
     kw_inteldialect,
     kw_gc,
     kw_prefix,
     kw_prologue,

lib/Bitcode/Reader/BitcodeReader.cpp

case bitc::MODULE_CODE_FUNCTION: {
         Func->setIsMaterializable(true);
         FunctionsWithBodies.push_back(Func);
         DeferredFunctionInfo[Func] = 0;
       }
       break;
     }
     // ALIAS: [alias type, addrspace, aliasee val#, linkage]
     // ALIAS: [alias type, addrspace, aliasee val#, linkage, visibility, dllstorageclass]
+    // IFUNC: [alias type, addrspace, aliasee val#, linkage, visibility, dllstorageclass]
     case bitc::MODULE_CODE_ALIAS:
-    case bitc::MODULE_CODE_ALIAS_OLD: {
+    case bitc::MODULE_CODE_ALIAS_OLD:
+    case bitc::MODULE_CODE_IFUNC: {
       bool NewRecord = BitCode != bitc::MODULE_CODE_ALIAS_OLD;
       if (Record.size() < (3 + (unsigned)NewRecord))
         return error("Invalid record");
       unsigned OpNum = 0;
       Type *Ty = getTypeByID(Record[OpNum++]);
       if (!Ty)
         return error("Invalid record");
 
case bitc::MODULE_CODE_IFUNC: {
       auto Val = Record[OpNum++];
       auto Linkage = Record[OpNum++];
       GlobalIndirectSymbol *NewGA;
       if (BitCode == bitc::MODULE_CODE_ALIAS ||
           BitCode == bitc::MODULE_CODE_ALIAS_OLD)
         NewGA = GlobalAlias::create(
           Ty, AddrSpace, getDecodedLinkage(Linkage), "", TheModule);
       else
-        llvm_unreachable("Not an alias!");
+        NewGA = GlobalIFunc::create(
+          Ty, AddrSpace, getDecodedLinkage(Linkage), "", nullptr, TheModule);
       // Old bitcode files didn't have visibility field.
       // Local linkage must have default visibility.
       if (OpNum != Record.size()) {
         auto VisInd = OpNum++;
         if (!NewGA->hasLocalLinkage())
           // FIXME: Change to an error if non-default in 4.0.
           NewGA->setVisibility(getDecodedVisibility(Record[VisInd]));
       }

lib/Bitcode/Writer/BitcodeWriter.cpp

for (const GlobalAlias &A : M->aliases()) {
     Vals.push_back(getEncodedDLLStorageClass(A));
     Vals.push_back(getEncodedThreadLocalMode(A));
     Vals.push_back(A.hasUnnamedAddr());
     unsigned AbbrevToUse = 0;
     Stream.EmitRecord(bitc::MODULE_CODE_ALIAS, Vals, AbbrevToUse);
     Vals.clear();
   }
 
+  // Emit the ifunc information.
+  for (const GlobalIFunc &I : M->ifuncs()) {
+    // IFUNC: [ifunc type, address space, resolver val#, linkage, visibility]
+    Vals.push_back(VE.getTypeID(I.getValueType()));
+    Vals.push_back(I.getType()->getAddressSpace());
+    Vals.push_back(VE.getValueID(I.getResolver()));
+    Vals.push_back(getEncodedLinkage(I));
+    Vals.push_back(getEncodedVisibility(I));
+    unsigned AbbrevToUse = 0;
+    Stream.EmitRecord(bitc::MODULE_CODE_IFUNC, Vals, AbbrevToUse);
+    Vals.clear();
+  }
+
   // Emit the module's source file name.
   {
     StringEncoding Bits = getStringEncoding(M->getSourceFileName().data(),
                                             M->getSourceFileName().size());
     BitCodeAbbrevOp AbbrevOpToUse = BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8);
     if (Bits == SE_Char6)
       AbbrevOpToUse = BitCodeAbbrevOp(BitCodeAbbrevOp::Char6);
     else if (Bits == SE_Fixed7)

lib/Bitcode/Writer/ValueEnumerator.cpp

static OrderMap orderModule(const Module &M) {
   // implicitly.
   for (const GlobalVariable &G : M.globals())
     if (G.hasInitializer())
       if (!isa<GlobalValue>(G.getInitializer()))
         orderValue(G.getInitializer(), OM);
   for (const GlobalAlias &A : M.aliases())
     if (!isa<GlobalValue>(A.getAliasee()))
       orderValue(A.getAliasee(), OM);
+  for (const GlobalIFunc &I : M.ifuncs())
+    if (!isa<GlobalValue>(I.getResolver()))
+      orderValue(I.getResolver(), OM);
   for (const Function &F : M) {
     for (const Use &U : F.operands())
       if (!isa<GlobalValue>(U.get()))
         orderValue(U.get(), OM);
   }
   OM.LastGlobalConstantID = OM.size();
 
   // Initializers of GlobalValues are processed in
   // BitcodeReader::ResolveGlobalAndAliasInits().  Match the order there rather
   // than ValueEnumerator, and match the code in predictValueUseListOrderImpl()
   // by giving IDs in reverse order.
   //
   // Since GlobalValues never reference each other directly (just through
   // initializers), their relative IDs only matter for determining order of
   // uses in their initializers.
   for (const Function &F : M)
     orderValue(&F, OM);
   for (const GlobalAlias &A : M.aliases())
     orderValue(&A, OM);
+  for (const GlobalIFunc &I : M.ifuncs())
+    orderValue(&I, OM);
   for (const GlobalVariable &G : M.globals())
     orderValue(&G, OM);
   OM.LastGlobalValueID = OM.size();
 
   for (const Function &F : M) {
     if (F.isDeclaration())
       continue;
     // Here we need to match the union of ValueEnumerator::incorporateFunction()
static UseListOrderStack predictUseListOrder(const Module &M) {
   // Visit globals last, since the module-level use-list block will be seen
   // before the function bodies are processed.
   for (const GlobalVariable &G : M.globals())
     predictValueUseListOrder(&G, nullptr, OM, Stack);
   for (const Function &F : M)
     predictValueUseListOrder(&F, nullptr, OM, Stack);
   for (const GlobalAlias &A : M.aliases())
     predictValueUseListOrder(&A, nullptr, OM, Stack);
+  for (const GlobalIFunc &I : M.ifuncs())
+    predictValueUseListOrder(&I, nullptr, OM, Stack);
   for (const GlobalVariable &G : M.globals())
     if (G.hasInitializer())
       predictValueUseListOrder(G.getInitializer(), nullptr, OM, Stack);
   for (const GlobalAlias &A : M.aliases())
     predictValueUseListOrder(A.getAliasee(), nullptr, OM, Stack);
+  for (const GlobalIFunc &I : M.ifuncs())
+    predictValueUseListOrder(I.getResolver(), nullptr, OM, Stack);
   for (const Function &F : M) {
     for (const Use &U : F.operands())
       predictValueUseListOrder(U.get(), nullptr, OM, Stack);
   }
 
   return Stack;
 }
 
for (const Function & F : M) {
     EnumerateValue(&F);
     EnumerateAttributes(F.getAttributes());
   }
 
   // Enumerate the aliases.
   for (const GlobalAlias &GA : M.aliases())
     EnumerateValue(&GA);
 
+  // Enumerate the ifuncs.
+  for (const GlobalIFunc &GIF : M.ifuncs())
+    EnumerateValue(&GIF);
+
   // Remember what is the cutoff between globalvalue's and other constants.
   unsigned FirstConstant = Values.size();
 
   // Enumerate the global variable initializers.
   for (const GlobalVariable &GV : M.globals())
     if (GV.hasInitializer())
       EnumerateValue(GV.getInitializer());
 
   // Enumerate the aliasees.
   for (const GlobalAlias &GA : M.aliases())
     EnumerateValue(GA.getAliasee());
 
+  // Enumerate the ifunc resolvers.
+  for (const GlobalIFunc &GIF : M.ifuncs())
+    EnumerateValue(GIF.getResolver());
+
   // Enumerate any optional Function data.
   for (const Function &F : M)
     for (const Use &U : F.operands())
       EnumerateValue(U.get());
 
   // Enumerate the metadata type.
   //
   // TODO: Move this to ValueEnumerator::EnumerateOperandType() once bitcode

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

void AsmPrinter::emitGlobalIndirectSymbol(Module &M,
                                           const GlobalIndirectSymbol& GIS) {
   MCSymbol *Name = getSymbol(&GIS);
 
   if (GIS.hasExternalLinkage() || !MAI->getWeakRefDirective())
     OutStreamer->EmitSymbolAttribute(Name, MCSA_Global);
   else if (GIS.hasWeakLinkage() || GIS.hasLinkOnceLinkage())
     OutStreamer->EmitSymbolAttribute(Name, MCSA_WeakReference);
   else
-    assert(GIS.hasLocalLinkage() && "Invalid alias linkage");
+    assert(GIS.hasLocalLinkage() && "Invalid alias or ifunc linkage");
 
   // Set the symbol type to function if the alias has a function type.
   // This affects codegen when the aliasee is not a function.
-  if (GIS.getType()->getPointerElementType()->isFunctionTy())
+  if (GIS.getType()->getPointerElementType()->isFunctionTy()) {
     OutStreamer->EmitSymbolAttribute(Name, MCSA_ELF_TypeFunction);
+    if (isa<GlobalIFunc>(GIS))
+      OutStreamer->EmitSymbolAttribute(Name, MCSA_ELF_TypeIndFunction);
+  }
 
   EmitVisibility(Name, GIS.getVisibility());
 
   const MCExpr *Expr = lowerConstant(GIS.getIndirectSymbol());
 
   if (isa<GlobalAlias>(&GIS) && MAI->hasAltEntry() && isa<MCBinaryExpr>(Expr))
     OutStreamer->EmitSymbolAttribute(Name, MCSA_AltEntry);
 
for (const GlobalAlias *Cur = &Alias; Cur;
       if (!AliasVisited.insert(Cur).second)
         break;
       AliasStack.push_back(Cur);
     }
     for (const GlobalAlias *AncestorAlias : reverse(AliasStack))
       emitGlobalIndirectSymbol(M, *AncestorAlias);
     AliasStack.clear();
   }
+  for (const auto &IFunc : M.ifuncs())
+    emitGlobalIndirectSymbol(M, IFunc);
 
   GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
   assert(MI && "AsmPrinter didn't require GCModuleInfo?");
   for (GCModuleInfo::iterator I = MI->end(), E = MI->begin(); I != E; )
     if (GCMetadataPrinter *MP = GetOrCreateGCPrinter(**--I))
       MP->finishAssembly(M, *MI, *this);
 
   // Emit llvm.ident metadata in an '.ident' directive.

lib/IR/AsmWriter.cpp

if (G.hasInitializer())
         orderValue(G.getInitializer(), OM);
     orderValue(&G, OM);
   }
   for (const GlobalAlias &A : M->aliases()) {
     if (!isa<GlobalValue>(A.getAliasee()))
       orderValue(A.getAliasee(), OM);
     orderValue(&A, OM);
   }
+  for (const GlobalIFunc &I : M->ifuncs()) {
+    if (!isa<GlobalValue>(I.getResolver()))
+      orderValue(I.getResolver(), OM);
+    orderValue(&I, OM);
+  }
   for (const Function &F : *M) {
     for (const Use &U : F.operands())
       if (!isa<GlobalValue>(U.get()))
         orderValue(U.get(), OM);
 
     orderValue(&F, OM);
 
     if (F.isDeclaration())
static UseListOrderStack predictUseListOrder(const Module *M) {
 
   // Visit globals last.
   for (const GlobalVariable &G : M->globals())
     predictValueUseListOrder(&G, nullptr, OM, Stack);
   for (const Function &F : *M)
     predictValueUseListOrder(&F, nullptr, OM, Stack);
   for (const GlobalAlias &A : M->aliases())
     predictValueUseListOrder(&A, nullptr, OM, Stack);
+  for (const GlobalIFunc &I : M->ifuncs())
+    predictValueUseListOrder(&I, nullptr, OM, Stack);
   for (const GlobalVariable &G : M->globals())
     if (G.hasInitializer())
       predictValueUseListOrder(G.getInitializer(), nullptr, OM, Stack);
   for (const GlobalAlias &A : M->aliases())
     predictValueUseListOrder(A.getAliasee(), nullptr, OM, Stack);
+  for (const GlobalIFunc &I : M->ifuncs())
+    predictValueUseListOrder(I.getResolver(), nullptr, OM, Stack);
   for (const Function &F : *M)
     for (const Use &U : F.operands())
       predictValueUseListOrder(U.get(), nullptr, OM, Stack);
 
   return Stack;
 }
 
 static const Module *getModuleFromVal(const Value *V) {
if (const BasicBlock *BB = dyn_cast<BasicBlock>(V))
     return new SlotTracker(BB->getParent());
 
   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
     return new SlotTracker(GV->getParent());
 
   if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V))
     return new SlotTracker(GA->getParent());
 
+  if (const GlobalIFunc *GIF = dyn_cast<GlobalIFunc>(V))
+    return new SlotTracker(GIF->getParent());
+
   if (const Function *Func = dyn_cast<Function>(V))
     return new SlotTracker(Func);
 
   return nullptr;
 }
 
 #if 0
 #define ST_DEBUG(X) dbgs() << X
if (!Var.hasName())
       CreateModuleSlot(&Var);
   }
 
   for (const GlobalAlias &A : TheModule->aliases()) {
     if (!A.hasName())
       CreateModuleSlot(&A);
   }
 
+  for (const GlobalIFunc &I : TheModule->ifuncs()) {
+    if (!I.hasName())
+      CreateModuleSlot(&I);
+  }
+
   // Add metadata used by named metadata.
   for (const NamedMDNode &NMD : TheModule->named_metadata()) {
     for (unsigned i = 0, e = NMD.getNumOperands(); i != e; ++i)
       CreateMetadataSlot(NMD.getOperand(i));
   }
 
   for (const Function &F : *TheModule) {
     if (!F.hasName())
void SlotTracker::CreateModuleSlot(const GlobalValue *V) {
   assert(!V->getType()->isVoidTy() && "Doesn't need a slot!");
   assert(!V->hasName() && "Doesn't need a slot!");
 
   unsigned DestSlot = mNext++;
   mMap[V] = DestSlot;
 
   ST_DEBUG("  Inserting value [" << V->getType() << "] = " << V << " slot=" <<
            DestSlot << " [");
-  // G = Global, F = Function, A = Alias, o = other
+  // G = Global, F = Function, A = Alias, I = IFunc, o = other
   ST_DEBUG((isa<GlobalVariable>(V) ? 'G' :
             (isa<Function>(V) ? 'F' :
-             (isa<GlobalAlias>(V) ? 'A' : 'o'))) << "]\n");
+             (isa<GlobalAlias>(V) ? 'A' :
+              (isa<GlobalIFunc>(V) ? 'I' : 'o')))) << "]\n");
 }
 
 /// CreateSlot - Create a new slot for the specified value if it has no name.
 void SlotTracker::CreateFunctionSlot(const Value *V) {
   assert(!V->getType()->isVoidTy() && !V->hasName() && "Doesn't need a slot!");
 
   unsigned DestSlot = fNext++;
   fMap[V] = DestSlot;
for (const GlobalVariable &GV : M->globals()) {
     printGlobal(&GV); Out << '\n';
   }
 
   // Output all aliases.
   if (!M->alias_empty()) Out << "\n";
   for (const GlobalAlias &GA : M->aliases())
     printIndirectSymbol(&GA);
 
+  // Output all ifuncs.
+  if (!M->ifunc_empty()) Out << "\n";
+  for (const GlobalIFunc &GI : M->ifuncs())
+    printIndirectSymbol(&GI);
+
   // Output global use-lists.
   printUseLists(nullptr);
 
   // Output all of the functions.
   for (const Function &F : *M)
     printFunction(&F);
   assert(UseListOrders.empty() && "All use-lists should have been consumed");
 
void AssemblyWriter::printIndirectSymbol(const GlobalIndirectSymbol *GIS) {
   PrintVisibility(GIS->getVisibility(), Out);
   PrintDLLStorageClass(GIS->getDLLStorageClass(), Out);
   PrintThreadLocalModel(GIS->getThreadLocalMode(), Out);
   if (GIS->hasUnnamedAddr())
     Out << "unnamed_addr ";
 
   if (isa<GlobalAlias>(GIS))
     Out << "alias ";
+  else if (isa<GlobalIFunc>(GIS))
+    Out << "ifunc ";
   else
-    llvm_unreachable("Not an alias!");
+    llvm_unreachable("Not an alias or ifunc!");
 
   TypePrinter.print(GIS->getValueType(), Out);
 
   Out << ", ";
 
   const Constant *IS = GIS->getIndirectSymbol();
 
   if (!IS) {

lib/IR/Globals.cpp

 
 Comdat *GlobalValue::getComdat() {
   if (auto *GA = dyn_cast<GlobalAlias>(this)) {
     // In general we cannot compute this at the IR level, but we try.
     if (const GlobalObject *GO = GA->getBaseObject())
       return const_cast<GlobalObject *>(GO)->getComdat();
     return nullptr;
   }
+  if (isa<GlobalIFunc>(this))
+    return nullptr;
   return cast<GlobalObject>(this)->getComdat();
 }
 
 void GlobalObject::setSection(StringRef S) { Section = S; }
 
 bool GlobalValue::isDeclaration() const {
   // Globals are definitions if they have an initializer.
   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(this))
void GlobalAlias::eraseFromParent() {
   getParent()->getAliasList().erase(getIterator());
 }
 
 void GlobalAlias::setAliasee(Constant *Aliasee) {
   assert((!Aliasee || Aliasee->getType() == getType()) &&
          "Alias and aliasee types should match!");
   setIndirectSymbol(Aliasee);
 }
+
+//===----------------------------------------------------------------------===//
+// GlobalIFunc Implementation
+//===----------------------------------------------------------------------===//
+
+GlobalIFunc::GlobalIFunc(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
+                         const Twine &Name, Constant *Resolver,
+                         Module *ParentModule)
+    : GlobalIndirectSymbol(Ty, Value::GlobalIFuncVal, AddressSpace, Link, Name,
+                           Resolver) {
+  if (ParentModule)
+    ParentModule->getIFuncList().push_back(this);
+}
+
+GlobalIFunc *GlobalIFunc::create(Type *Ty, unsigned AddressSpace,
+                                 LinkageTypes Link, const Twine &Name,
+                                 Constant *Resolver, Module *ParentModule) {
+  return new GlobalIFunc(Ty, AddressSpace, Link, Name, Resolver, ParentModule);
+}
+
+void GlobalIFunc::setParent(Module *parent) {
+  Parent = parent;
+}
+
+void GlobalIFunc::removeFromParent() {
+  getParent()->getIFuncList().remove(getIterator());
+}
+
+void GlobalIFunc::eraseFromParent() {
+  getParent()->getIFuncList().erase(getIterator());
+}

lib/IR/Module.cpp

 // Methods to implement the globals and functions lists.
 //
 
 // Explicit instantiations of SymbolTableListTraits since some of the methods
 // are not in the public header file.
 template class llvm::SymbolTableListTraits<Function>;
 template class llvm::SymbolTableListTraits<GlobalVariable>;
 template class llvm::SymbolTableListTraits<GlobalAlias>;
+template class llvm::SymbolTableListTraits<GlobalIFunc>;
 
 //===----------------------------------------------------------------------===//
 // Primitive Module methods.
 //
 
 Module::Module(StringRef MID, LLVMContext &C)
     : Context(C), Materializer(), ModuleID(MID), SourceFileName(MID), DL("") {
   ValSymTab = new ValueSymbolTable();
   NamedMDSymTab = new StringMap<NamedMDNode *>();
   Context.addModule(this);
 }
 
 Module::~Module() {
   Context.removeModule(this);
   dropAllReferences();
   GlobalList.clear();
   FunctionList.clear();
   AliasList.clear();
+  IFuncList.clear();
   NamedMDList.clear();
   delete ValSymTab;
   delete static_cast<StringMap<NamedMDNode *> *>(NamedMDSymTab);
 }
 
 RandomNumberGenerator *Module::createRNG(const Pass* P) const {
   SmallString<32> Salt(P->getPassName());
 

 
 // getNamedAlias - Look up the specified global in the module symbol table.
 // If it does not exist, return null.
 //
 GlobalAlias *Module::getNamedAlias(StringRef Name) const {
   return dyn_cast_or_null<GlobalAlias>(getNamedValue(Name));
 }
 
+// getNamedIFunc - Look up the specified global in the module symbol table.
+// If it does not exist, return null.
+//
+GlobalIFunc *Module::getNamedIFunc(StringRef Name) const {
+  return dyn_cast_or_null<GlobalIFunc>(getNamedValue(Name));
+}
+
 /// getNamedMetadata - Return the first NamedMDNode in the module with the
 /// specified name. This method returns null if a NamedMDNode with the
 /// specified name is not found.
 NamedMDNode *Module::getNamedMetadata(const Twine &Name) const {
   SmallString<256> NameData;
   StringRef NameRef = Name.toStringRef(NameData);
   return static_cast<StringMap<NamedMDNode*> *>(NamedMDSymTab)->lookup(NameRef);
 }
void Module::dropAllReferences() {
   for (Function &F : *this)
     F.dropAllReferences();
 
   for (GlobalVariable &GV : globals())
     GV.dropAllReferences();
 
   for (GlobalAlias &GA : aliases())
     GA.dropAllReferences();
+
+  for (GlobalIFunc &GIF : ifuncs())
+    GIF.dropAllReferences();
 }
 
 unsigned Module::getDwarfVersion() const {
   auto *Val = cast_or_null<ConstantAsMetadata>(getModuleFlag("Dwarf Version"));
   if (!Val)
     return 0;
   return cast<ConstantInt>(Val->getValue())->getZExtValue();
 }

test/Assembler/ifunc-asm.ll

+; RUN: llvm-as < %s | llvm-dis | FileCheck %s --check-prefix=CHECK-LLVM
+; RUN: llvm-as < %s -o - | llc -filetype=asm | FileCheck %s --check-prefix=CHECK-ASM
+
+target triple = "x86_64-unknown-linux-gnu"
+
+@foo = ifunc i32 (i32), i64 ()* @foo_ifunc
+; CHECK-LLVM: @foo = ifunc i32 (i32), i64 ()* @foo_ifunc
+; CHECK-ASM: .type   foo,@gnu_indirect_function
+
+define internal i64 @foo_ifunc() {
+entry:
+  ret i64 0
+}
+; CHECK-LLVM: define internal i64 @foo_ifunc()

test/Assembler/ifunc-use-list-order.ll

+; RUN: verify-uselistorder < %s
+
+; Global referencing ifunc.
+@ptr_foo = global void ()* @foo_ifunc
+
+; Alias for ifunc.
+@alias_foo = alias void (), void ()* @foo_ifunc
+
+@foo_ifunc = ifunc void (), i8* ()* @foo_resolver
+
+define i8* @foo_resolver() {
+entry:
+  ret i8* null
+}
+
+; Function referencing ifunc.
+define void @bar() {
+entry:
+  call void @foo_ifunc()
+  ret void
+}
+
+; Global referencing function.
+@ptr_bar = global void ()* @bar
+
+; Alias for function.
+@alias_bar = alias void (), void ()* @bar
+
+@bar_ifunc = ifunc void (), i8* ()* @bar2_ifunc
+@bar2_ifunc = ifunc i8* (), i8* ()* @bar_resolver
+
+define i8* @bar_resolver() {
+entry:
+  ret i8* null
+}
+
+; Function referencing bar.
+define void @bar2() {
+entry:
+  call void @bar()
+  ret void
+}

test/Bitcode/compatibility.ll

 ; CHECK: @a.initialexec = thread_local(initialexec) alias i32, i32* @g.initialexec
 @a.localexec = thread_local(localexec) alias i32, i32* @g.localexec
 ; CHECK: @a.localexec = thread_local(localexec) alias i32, i32* @g.localexec
 
 ; Aliases -- unnamed_addr
 @a.unnamed_addr = unnamed_addr alias i32, i32* @g.unnamed_addr
 ; CHECK: @a.unnamed_addr = unnamed_addr alias i32, i32* @g.unnamed_addr
 
+;; IFunc
+; Format @<Name> = [Linkage] [Visibility] ifunc <IFuncTy>,
+;                  <ResolverTy>* @<Resolver>
+
+; IFunc -- Linkage
[e-mail] = external ifunc void (), i8* ()* @ifunc_resolver
+; CHECK: @ifunc.external = ifunc void (), i8* ()* @ifunc_resolver
[e-mail] = private ifunc void (), i8* ()* @ifunc_resolver
+; CHECK: @ifunc.private = private ifunc void (), i8* ()* @ifunc_resolver
[e-mail] = internal ifunc void (), i8* ()* @ifunc_resolver
+; CHECK: @ifunc.internal = internal ifunc void (), i8* ()* @ifunc_resolver
+
+; IFunc -- Visibility
[e-mail] = default ifunc void (), i8* ()* @ifunc_resolver
+; CHECK: @ifunc.default = ifunc void (), i8* ()* @ifunc_resolver
[e-mail] = hidden ifunc void (), i8* ()* @ifunc_resolver
+; CHECK: @ifunc.hidden = hidden ifunc void (), i8* ()* @ifunc_resolver
[e-mail] = protected ifunc void (), i8* ()* @ifunc_resolver
+; CHECK: @ifunc.protected = protected ifunc void (), i8* ()* @ifunc_resolver
+
+define i8* @ifunc_resolver() {
+entry:
+  ret i8* null
+}
+
 ;; Functions
 ; Format: define [linkage] [visibility] [DLLStorageClass]
 ;         [cconv] [ret attrs]
 ;         <ResultType> @<FunctionName> ([argument list])
 ;         [unnamed_addr] [fn Attrs] [section "name"] [comdat [($name)]]
 ;         [align N] [gc] [prefix Constant] [prologue Constant]
 ;         [personality Constant] { ... }