llvm-mirror/include/llvm/MC/MCSymbol.h

//===- MCSymbol.h - Machine Code Symbols ------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the declaration of the MCSymbol class.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_MC_MCSYMBOL_H
#define LLVM_MC_MCSYMBOL_H

#include "llvm/ADT/StringRef.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/Support/Compiler.h"

namespace llvm {
class MCExpr;
class MCSection;
class MCContext;
class raw_ostream;

/// MCSymbol - Instances of this class represent a symbol name in the MC file,
/// and MCSymbols are created and uniqued by the MCContext class.  MCSymbols
/// should only be constructed with valid names for the object file.
///
/// If the symbol is defined/emitted into the current translation unit, the
/// Section member is set to indicate what section it lives in.  Otherwise, if
/// it is a reference to an external entity, it has a null section.
class MCSymbol {
  // Special sentinal value for the absolute pseudo section.
  //
  // FIXME: Use a PointerInt wrapper for this?
  static const MCSection *AbsolutePseudoSection;

  /// Name - The name of the symbol.  The referred-to string data is actually
  /// held by the StringMap that lives in MCContext.
  StringRef Name;

  /// Section - The section the symbol is defined in. This is null for
  /// undefined symbols, and the special AbsolutePseudoSection value for
  /// absolute symbols. If this is a variable symbol, this caches the
  /// variable value's section.
  mutable const MCSection *Section;

  /// Value - If non-null, the value for a variable symbol.
  const MCExpr *Value;

  /// IsTemporary - True if this is an assembler temporary label, which
  /// typically does not survive in the .o file's symbol table.  Usually
  /// "Lfoo" or ".foo".
  unsigned IsTemporary : 1;

  /// \brief True if this symbol can be redefined.
  unsigned IsRedefinable : 1;

  /// IsUsed - True if this symbol has been used.
  mutable unsigned IsUsed : 1;

private: // MCContext creates and uniques these.
  friend class MCExpr;
  friend class MCContext;
  MCSymbol(StringRef name, bool isTemporary)
      : Name(name), Section(nullptr), Value(nullptr), IsTemporary(isTemporary),
        IsRedefinable(false), IsUsed(false) {}

  MCSymbol(const MCSymbol &) = delete;
  void operator=(const MCSymbol &) = delete;
  const MCSection *getSectionPtr() const {
    if (Section || !Value)
      return Section;
    return Section = Value->FindAssociatedSection();
  }

public:
  /// getName - Get the symbol name.
  StringRef getName() const { return Name; }

  /// \name Accessors
  /// @{

  /// isTemporary - Check if this is an assembler temporary symbol.
  bool isTemporary() const { return IsTemporary; }

  /// isUsed - Check if this is used.
  bool isUsed() const { return IsUsed; }
  void setUsed(bool Value) const { IsUsed = Value; }

  /// \brief Check if this symbol is redefinable.
  bool isRedefinable() const { return IsRedefinable; }
  /// \brief Mark this symbol as redefinable.
  void setRedefinable(bool Value) { IsRedefinable = Value; }
  /// \brief Prepare this symbol to be redefined.
  void redefineIfPossible() {
    if (IsRedefinable) {
      Value = nullptr;
      Section = nullptr;
      IsRedefinable = false;
    }
  }

  /// @}
  /// \name Associated Sections
  /// @{

  /// isDefined - Check if this symbol is defined (i.e., it has an address).
  ///
  /// Defined symbols are either absolute or in some section.
  bool isDefined() const { return getSectionPtr() != nullptr; }

  /// isInSection - Check if this symbol is defined in some section (i.e., it
  /// is defined but not absolute).
  bool isInSection() const { return isDefined() && !isAbsolute(); }

  /// isUndefined - Check if this symbol undefined (i.e., implicitly defined).
  bool isUndefined() const { return !isDefined(); }

  /// isAbsolute - Check if this is an absolute symbol.
  bool isAbsolute() const { return getSectionPtr() == AbsolutePseudoSection; }

  /// getSection - Get the section associated with a defined, non-absolute
  /// symbol.
  const MCSection &getSection() const {
    assert(isInSection() && "Invalid accessor!");
    return *getSectionPtr();
  }

  /// setSection - Mark the symbol as defined in the section \p S.
  void setSection(const MCSection &S) {
    assert(!isVariable() && "Cannot set section of variable");
    Section = &S;
  }

  /// setUndefined - Mark the symbol as undefined.
  void setUndefined() { Section = nullptr; }

  /// @}
  /// \name Variable Symbols
  /// @{

  /// isVariable - Check if this is a variable symbol.
  bool isVariable() const { return Value != nullptr; }

  /// getVariableValue() - Get the value for variable symbols.
  const MCExpr *getVariableValue() const {
    assert(isVariable() && "Invalid accessor!");
    IsUsed = true;
    return Value;
  }

  void setVariableValue(const MCExpr *Value);

  /// @}

  /// print - Print the value to the stream \p OS.
  void print(raw_ostream &OS) const;

  /// dump - Print the value to stderr.
  void dump() const;
};

inline raw_ostream &operator<<(raw_ostream &OS, const MCSymbol &Sym) {
  Sym.print(OS);
  return OS;
}
} // end namespace llvm

#endif