LLVM IR to Asm Part 4

/// LLVM Value Representation
/// This is a very important LLVM class. It is the base class of all values
/// computed by a program that may be used as operands to other values. Value is
/// the super class of other important classes such as Instruction and Function.
/// All Values have a Type. Type is not a subclass of Value. Some values can
/// have a name and they belong to some Module.  Setting the name on the Value
/// automatically updates the module's symbol table.
/// Every value has a "use list" that keeps track of which other Values are
/// using this Value.  A Value can also have an arbitrary number of ValueHandle
/// objects that watch it and listen to RAUW and Destroy events.  See
/// llvm/IR/ValueHandle.h for details.
class Value {
  Type *VTy;
  Use *UseList;
  const unsigned char SubclassID;   // Subclass identifier (for isa/dyn_cast)
  unsigned char HasValueHandle : 1; // Has a ValueHandle pointing to this?
protected:
  /// Hold subclass data that can be dropped.
  /// This member is similar to SubclassData, however it is for holding
  /// information which may be used to aid optimization, but which may be
  /// cleared to zero without affecting conservative interpretation.
  unsigned char SubclassOptionalData : 7;
private:
  /// Hold arbitrary subclass data.
  /// This member is defined by this class, but is not used for anything.
  /// Subclasses can use it to hold whatever state they find useful.  This
  /// field is initialized to zero by the ctor.
  unsigned short SubclassData;
protected:
  /// The number of operands in the subclass.
  /// This member is defined by this class, but not used for anything.
  /// Subclasses can use it to store their number of operands, if they have
  /// any.
  /// This is stored here to save space in User on 64-bit hosts.  Since most
  /// instances of Value have operands, 32-bit hosts aren't significantly
  /// affected.
  /// Note, this should *NOT* be used directly by any class other than User.
  /// User uses this value to find the Use list.
  enum : unsigned { NumUserOperandsBits = 28 };
  unsigned NumUserOperands : NumUserOperandsBits;
  // Use the same type as the bitfield above so that MSVC will pack them.
  unsigned IsUsedByMD : 1;
  unsigned HasName : 1;
  unsigned HasHungOffUses : 1;
  unsigned HasDescriptor : 1;
};

/// A Use represents the edge between a Value definition and its users.
/// This is notionally a two-dimensional linked list. It supports traversing
/// all of the uses for a particular value definition. It also supports jumping
/// directly to the used value when we arrive from the User's operands, and
/// jumping directly to the User when we arrive from the Value's uses.
class Use {
  Value *Val = nullptr;
  Use *Next = nullptr;
  Use **Prev = nullptr;
  User *Parent = nullptr;
};

class User : public Value {};

/// A Module instance is used to store all the information related to an
/// LLVM module. Modules are the top level container of all other LLVM
/// Intermediate Representation (IR) objects. Each module directly contains a
/// list of globals variables, a list of functions, a list of libraries (or
/// other modules) this module depends on, a symbol table, and various data
/// about the target's characteristics.
/// A module maintains a GlobalValRefMap object that is used to hold all
/// constant references to global variables in the module.  When a global
/// variable is destroyed, it should have no entries in the GlobalValueRefMap.
/// The main container class for the LLVM Intermediate Representation.
class Module {
  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.
  std::unique_ptr<ValueSymbolTable> ValSymTab; ///< Symbol table for values
  ComdatSymTabType ComdatSymTab;  ///< Symbol table for COMDATs
  std::unique_ptr<MemoryBuffer>
  OwnedMemoryBuffer;              ///< Memory buffer directly owned by this
                                  ///< module, for legacy clients only.
  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,
                                  ///< recorded in bitcode.
  std::string TargetTriple;       ///< Platform target triple Module compiled on
                                  ///< Format: (arch)(sub)-(vendor)-(sys0-(abi)
  NamedMDSymTabType NamedMDSymTab;  ///< NamedMDNode names.
  DataLayout DL;                  ///< DataLayout associated with the module
};

/// This class provides a symbol table of name/value pairs. It is essentially
/// a std::map<std::string,Value*> but has a controlled interface provided by
/// LLVM as well as ensuring uniqueness of names.
///
class ValueSymbolTable {
  ValueMap vmap;                    ///< The map that holds the symbol table.
  mutable uint32_t LastUnique = 0;  ///< Counter for tracking unique names
};

class Function : public GlobalObject, public ilist_node<Function> {
  // Important things that make up a function!
  BasicBlockListType BasicBlocks;         ///< The basic blocks
  mutable Argument *Arguments = nullptr;  ///< The formal arguments
  size_t NumArgs;
  std::unique_ptr<ValueSymbolTable>
  SymTab;                             ///< Symbol table of args/instructions
  AttributeList AttributeSets;            ///< Parameter attributes
};

/// This class represents an incoming formal argument to a Function. A formal
/// argument, since it is ``formal'', does not contain an actual value but
/// instead represents the type, argument number, and attributes of an argument
/// for a specific function. When used in the body of said function, the
/// argument of course represents the value of the actual argument that the
/// function was called with.
class Argument final : public Value {
  Function *Parent;
  unsigned ArgNo;
};

/// LLVM Basic Block Representation
///
/// This represents a single basic block in LLVM. A basic block is simply a
/// container of instructions that execute sequentially. Basic blocks are Values
/// because they are referenced by instructions such as branches and switch
/// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
/// represents a label to which a branch can jump.
///
/// A well formed basic block is formed of a list of non-terminating
/// instructions followed by a single terminator instruction. Terminator
/// instructions may not occur in the middle of basic blocks, and must terminate
/// the blocks. The BasicBlock class allows malformed basic blocks to occur
/// because it may be useful in the intermediate stage of constructing or
/// modifying a program. However, the verifier will ensure that basic blocks are
/// "well formed".
class BasicBlock final : public Value, // Basic blocks are data objects also
                         public ilist_node_with_parent<BasicBlock, Function> {
  InstListType InstList;
  Function *Parent;
};

class Instruction : public User,
                    public ilist_node_with_parent<Instruction, BasicBlock> {
  BasicBlock *Parent;
  DebugLoc DbgLoc;                         // 'dbg' Metadata cache.
  /// Relative order of this instruction in its parent basic block. Used for
  /// O(1) local dominance checks between instructions.
  mutable unsigned Order = 0;
};

class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> {
  AttributeSet Attrs;
  bool isConstantGlobal : 1;                   // Is this a global constant?
  bool isExternallyInitializedConstant : 1;    // Is this a global whose value
                                               // can change from its initial
                                               // value before global
                                               // initializers are run?
};

class GlobalAlias : public GlobalIndirectSymbol,
                    public ilist_node<GlobalAlias> {};

class GlobalIFunc final : public GlobalIndirectSymbol,
                          public ilist_node<GlobalIFunc> {};

//===----------------------------------------------------------------------===//
/// A tuple of MDNodes.
///
/// Despite its name, a NamedMDNode isn't itself an MDNode.
///
/// NamedMDNodes are named module-level entities that contain lists of MDNodes.
///
/// It is illegal for a NamedMDNode to appear as an operand of an MDNode.
class NamedMDNode : public ilist_node<NamedMDNode> {
  std::string Name;
  Module *Parent = nullptr;
  void *Operands; // SmallVector<TrackingMDRef, 4>
};