text: //===- MCExpr.h - Assembly Level Expressions --------------------*- C++ -*-===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_MC_MCEXPR_H
  #define LLVM_MC_MCEXPR_H
  
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/Support/SMLoc.h"
  #include <cstdint>
  
  namespace llvm {
  
  class MCAsmInfo;
  class MCAsmLayout;
  class MCAssembler;
  class MCContext;
  class MCFixup;
  class MCFragment;
  class MCSection;
  class MCStreamer;
  class MCSymbol;
  class MCValue;
  class raw_ostream;
  class StringRef;
  
  using SectionAddrMap = DenseMap<const MCSection *, uint64_t>;
  
  /// Base class for the full range of assembler expressions which are
  /// needed for parsing.
  class MCExpr {
  public:
    enum ExprKind : uint8_t {
      Binary,    ///< Binary expressions.
      Constant,  ///< Constant expressions.
      SymbolRef, ///< References to labels and assigned expressions.
      Unary,     ///< Unary expressions.
      Target     ///< Target specific expression.
    };
  
  private:
    static const unsigned NumSubclassDataBits = 24;
    static_assert(
        NumSubclassDataBits == CHAR_BIT * (sizeof(unsigned) - sizeof(ExprKind)),
        "ExprKind and SubclassData together should take up one word");
  
    ExprKind Kind;
    /// Field reserved for use by MCExpr subclasses.
    unsigned SubclassData : NumSubclassDataBits;
    SMLoc Loc;
  
    bool evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm,
                            const MCAsmLayout *Layout,
                            const SectionAddrMap *Addrs, bool InSet) const;
  
  protected:
    explicit MCExpr(ExprKind Kind, SMLoc Loc, unsigned SubclassData = 0)
        : Kind(Kind), SubclassData(SubclassData), Loc(Loc) {
      assert(SubclassData < (1 << NumSubclassDataBits) &&
             "Subclass data too large");
    }
  
    bool evaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
                                   const MCAsmLayout *Layout,
                                   const MCFixup *Fixup,
                                   const SectionAddrMap *Addrs, bool InSet) const;
  
    unsigned getSubclassData() const { return SubclassData; }
  
  public:
    MCExpr(const MCExpr &) = delete;
    MCExpr &operator=(const MCExpr &) = delete;
  
    /// \name Accessors
    /// @{
  
    ExprKind getKind() const { return Kind; }
    SMLoc getLoc() const { return Loc; }
  
    /// @}
    /// \name Utility Methods
    /// @{
  
    void print(raw_ostream &OS, const MCAsmInfo *MAI,
               bool InParens = false) const;
    void dump() const;
  
    /// @}
    /// \name Expression Evaluation
    /// @{
  
    /// Try to evaluate the expression to an absolute value.
    ///
    /// \param Res - The absolute value, if evaluation succeeds.
    /// \param Layout - The assembler layout object to use for evaluating symbol
    /// values. If not given, then only non-symbolic expressions will be
    /// evaluated.
    /// \return - True on success.
    bool evaluateAsAbsolute(int64_t &Res, const MCAsmLayout &Layout,
                            const SectionAddrMap &Addrs) const;
    bool evaluateAsAbsolute(int64_t &Res) const;
    bool evaluateAsAbsolute(int64_t &Res, const MCAssembler &Asm) const;
    bool evaluateAsAbsolute(int64_t &Res, const MCAssembler *Asm) const;
    bool evaluateAsAbsolute(int64_t &Res, const MCAsmLayout &Layout) const;
  
    bool evaluateKnownAbsolute(int64_t &Res, const MCAsmLayout &Layout) const;
  
    /// Try to evaluate the expression to a relocatable value, i.e. an
    /// expression of the fixed form (a - b + constant).
    ///
    /// \param Res - The relocatable value, if evaluation succeeds.
    /// \param Layout - The assembler layout object to use for evaluating values.
    /// \param Fixup - The Fixup object if available.
    /// \return - True on success.
    bool evaluateAsRelocatable(MCValue &Res, const MCAsmLayout *Layout,
                               const MCFixup *Fixup) const;
  
    /// Try to evaluate the expression to the form (a - b + constant) where
    /// neither a nor b are variables.
    ///
    /// This is a more aggressive variant of evaluateAsRelocatable. The intended
    /// use is for when relocations are not available, like the .size directive.
    bool evaluateAsValue(MCValue &Res, const MCAsmLayout &Layout) const;
  
    /// Find the "associated section" for this expression, which is
    /// currently defined as the absolute section for constants, or
    /// otherwise the section associated with the first defined symbol in the
    /// expression.
    MCFragment *findAssociatedFragment() const;
  
    /// @}
  };
  
  inline raw_ostream &operator<<(raw_ostream &OS, const MCExpr &E) {
    E.print(OS, nullptr);
    return OS;
  }
  
  ////  Represent a constant integer expression.
  class MCConstantExpr : public MCExpr {
    int64_t Value;
  
    // Subclass data stores SizeInBytes in bits 0..7 and PrintInHex in bit 8.
    static const unsigned SizeInBytesBits = 8;
    static const unsigned SizeInBytesMask = (1 << SizeInBytesBits) - 1;
    static const unsigned PrintInHexBit = 1 << SizeInBytesBits;
  
    static unsigned encodeSubclassData(bool PrintInHex, unsigned SizeInBytes) {
      assert(SizeInBytes <= sizeof(int64_t) && "Excessive size");
      return SizeInBytes | (PrintInHex ? PrintInHexBit : 0);
    }
  
    MCConstantExpr(int64_t Value, bool PrintInHex, unsigned SizeInBytes)
        : MCExpr(MCExpr::Constant, SMLoc(),
                 encodeSubclassData(PrintInHex, SizeInBytes)), Value(Value) {}
  
  public:
    /// \name Construction
    /// @{
  
    static const MCConstantExpr *create(int64_t Value, MCContext &Ctx,
                                        bool PrintInHex = false,
                                        unsigned SizeInBytes = 0);
  
    /// @}
    /// \name Accessors
    /// @{
  
    int64_t getValue() const { return Value; }
    unsigned getSizeInBytes() const {
      return getSubclassData() & SizeInBytesMask;
    }
  
    bool useHexFormat() const { return (getSubclassData() & PrintInHexBit) != 0; }
  
    /// @}
  
    static bool classof(const MCExpr *E) {
      return E->getKind() == MCExpr::Constant;
    }
  };
  
  ///  Represent a reference to a symbol from inside an expression.
  ///
  /// A symbol reference in an expression may be a use of a label, a use of an
  /// assembler variable (defined constant), or constitute an implicit definition
  /// of the symbol as external.
  class MCSymbolRefExpr : public MCExpr {
  public:
    enum VariantKind : uint16_t {
      VK_None,
      VK_Invalid,
  
      VK_GOT,
      VK_GOTOFF,
      VK_GOTREL,
      VK_PCREL,
      VK_GOTPCREL,
      VK_GOTTPOFF,
      VK_INDNTPOFF,
      VK_NTPOFF,
      VK_GOTNTPOFF,
      VK_PLT,
      VK_TLSGD,
      VK_TLSLD,
      VK_TLSLDM,
      VK_TPOFF,
      VK_DTPOFF,
      VK_TLSCALL,   // symbol(tlscall)
      VK_TLSDESC,   // symbol(tlsdesc)
      VK_TLVP,      // Mach-O thread local variable relocations
      VK_TLVPPAGE,
      VK_TLVPPAGEOFF,
      VK_PAGE,
      VK_PAGEOFF,
      VK_GOTPAGE,
      VK_GOTPAGEOFF,
      VK_SECREL,
      VK_SIZE,      // symbol@SIZE
      VK_WEAKREF,   // The link between the symbols in .weakref foo, bar
  
      VK_X86_ABS8,
  
      VK_ARM_NONE,
      VK_ARM_GOT_PREL,
      VK_ARM_TARGET1,
      VK_ARM_TARGET2,
      VK_ARM_PREL31,
      VK_ARM_SBREL,          // symbol(sbrel)
      VK_ARM_TLSLDO,         // symbol(tlsldo)
      VK_ARM_TLSDESCSEQ,
  
      VK_AVR_NONE,
      VK_AVR_LO8,
      VK_AVR_HI8,
      VK_AVR_HLO8,
      VK_AVR_DIFF8,
      VK_AVR_DIFF16,
      VK_AVR_DIFF32,
  
      VK_PPC_LO,             // symbol@l
      VK_PPC_HI,             // symbol@h
      VK_PPC_HA,             // symbol@ha
      VK_PPC_HIGH,           // symbol@high
      VK_PPC_HIGHA,          // symbol@higha
      VK_PPC_HIGHER,         // symbol@higher
      VK_PPC_HIGHERA,        // symbol@highera
      VK_PPC_HIGHEST,        // symbol@highest
      VK_PPC_HIGHESTA,       // symbol@highesta
      VK_PPC_GOT_LO,         // symbol@got@l
      VK_PPC_GOT_HI,         // symbol@got@h
      VK_PPC_GOT_HA,         // symbol@got@ha
      VK_PPC_TOCBASE,        // symbol@tocbase
      VK_PPC_TOC,            // symbol@toc
      VK_PPC_TOC_LO,         // symbol@toc@l
      VK_PPC_TOC_HI,         // symbol@toc@h
      VK_PPC_TOC_HA,         // symbol@toc@ha
      VK_PPC_U,              // symbol@u
      VK_PPC_L,              // symbol@l
      VK_PPC_DTPMOD,         // symbol@dtpmod
      VK_PPC_TPREL_LO,       // symbol@tprel@l
      VK_PPC_TPREL_HI,       // symbol@tprel@h
      VK_PPC_TPREL_HA,       // symbol@tprel@ha
      VK_PPC_TPREL_HIGH,     // symbol@tprel@high
      VK_PPC_TPREL_HIGHA,    // symbol@tprel@higha
      VK_PPC_TPREL_HIGHER,   // symbol@tprel@higher
      VK_PPC_TPREL_HIGHERA,  // symbol@tprel@highera
      VK_PPC_TPREL_HIGHEST,  // symbol@tprel@highest
      VK_PPC_TPREL_HIGHESTA, // symbol@tprel@highesta
      VK_PPC_DTPREL_LO,      // symbol@dtprel@l
      VK_PPC_DTPREL_HI,      // symbol@dtprel@h
      VK_PPC_DTPREL_HA,      // symbol@dtprel@ha
      VK_PPC_DTPREL_HIGH,    // symbol@dtprel@high
      VK_PPC_DTPREL_HIGHA,   // symbol@dtprel@higha
      VK_PPC_DTPREL_HIGHER,  // symbol@dtprel@higher
      VK_PPC_DTPREL_HIGHERA, // symbol@dtprel@highera
      VK_PPC_DTPREL_HIGHEST, // symbol@dtprel@highest
      VK_PPC_DTPREL_HIGHESTA,// symbol@dtprel@highesta
      VK_PPC_GOT_TPREL,      // symbol@got@tprel
      VK_PPC_GOT_TPREL_LO,   // symbol@got@tprel@l
      VK_PPC_GOT_TPREL_HI,   // symbol@got@tprel@h
      VK_PPC_GOT_TPREL_HA,   // symbol@got@tprel@ha
      VK_PPC_GOT_DTPREL,     // symbol@got@dtprel
      VK_PPC_GOT_DTPREL_LO,  // symbol@got@dtprel@l
      VK_PPC_GOT_DTPREL_HI,  // symbol@got@dtprel@h
      VK_PPC_GOT_DTPREL_HA,  // symbol@got@dtprel@ha
      VK_PPC_TLS,            // symbol@tls
      VK_PPC_GOT_TLSGD,      // symbol@got@tlsgd
      VK_PPC_GOT_TLSGD_LO,   // symbol@got@tlsgd@l
      VK_PPC_GOT_TLSGD_HI,   // symbol@got@tlsgd@h
      VK_PPC_GOT_TLSGD_HA,   // symbol@got@tlsgd@ha
      VK_PPC_TLSGD,          // symbol@tlsgd
      VK_PPC_GOT_TLSLD,      // symbol@got@tlsld
      VK_PPC_GOT_TLSLD_LO,   // symbol@got@tlsld@l
      VK_PPC_GOT_TLSLD_HI,   // symbol@got@tlsld@h
      VK_PPC_GOT_TLSLD_HA,   // symbol@got@tlsld@ha
      VK_PPC_TLSLD,          // symbol@tlsld
      VK_PPC_LOCAL,          // symbol@local
      VK_PPC_NOTOC,          // symbol@notoc
  
      VK_COFF_IMGREL32, // symbol@imgrel (image-relative)
  
      VK_Hexagon_LO16,
      VK_Hexagon_HI16,
      VK_Hexagon_GPREL,
      VK_Hexagon_GD_GOT,
      VK_Hexagon_LD_GOT,
      VK_Hexagon_GD_PLT,
      VK_Hexagon_LD_PLT,
      VK_Hexagon_IE,
      VK_Hexagon_IE_GOT,
  
      VK_WASM_TYPEINDEX, // Reference to a symbol's type (signature)
      VK_WASM_MBREL,     // Memory address relative to memory base
      VK_WASM_TBREL,     // Table index relative to table bare
  
      VK_AMDGPU_GOTPCREL32_LO, // symbol@gotpcrel32@lo
      VK_AMDGPU_GOTPCREL32_HI, // symbol@gotpcrel32@hi
      VK_AMDGPU_REL32_LO,      // symbol@rel32@lo
      VK_AMDGPU_REL32_HI,      // symbol@rel32@hi
      VK_AMDGPU_REL64,         // symbol@rel64
      VK_AMDGPU_ABS32_LO,      // symbol@abs32@lo
      VK_AMDGPU_ABS32_HI,      // symbol@abs32@hi
  
      VK_TPREL,
      VK_DTPREL
    };
  
  private:
    /// The symbol being referenced.
    const MCSymbol *Symbol;
  
    // Subclass data stores VariantKind in bits 0..15, UseParensForSymbolVariant
    // in bit 16 and HasSubsectionsViaSymbols in bit 17.
    static const unsigned VariantKindBits = 16;
    static const unsigned VariantKindMask = (1 << VariantKindBits) - 1;
  
    /// Specifies how the variant kind should be printed.
    static const unsigned UseParensForSymbolVariantBit = 1 << VariantKindBits;
  
    // FIXME: Remove this bit.
    static const unsigned HasSubsectionsViaSymbolsBit =
        1 << (VariantKindBits + 1);
  
    static unsigned encodeSubclassData(VariantKind Kind,
                                bool UseParensForSymbolVariant,
                                bool HasSubsectionsViaSymbols) {
      return (unsigned)Kind |
             (UseParensForSymbolVariant ? UseParensForSymbolVariantBit : 0) |
             (HasSubsectionsViaSymbols ? HasSubsectionsViaSymbolsBit : 0);
    }
  
    bool useParensForSymbolVariant() const {
      return (getSubclassData() & UseParensForSymbolVariantBit) != 0;
    }
  
    explicit MCSymbolRefExpr(const MCSymbol *Symbol, VariantKind Kind,
                             const MCAsmInfo *MAI, SMLoc Loc = SMLoc());
  
  public:
    /// \name Construction
    /// @{
  
    static const MCSymbolRefExpr *create(const MCSymbol *Symbol, MCContext &Ctx) {
      return MCSymbolRefExpr::create(Symbol, VK_None, Ctx);
    }
  
    static const MCSymbolRefExpr *create(const MCSymbol *Symbol, VariantKind Kind,
                                         MCContext &Ctx, SMLoc Loc = SMLoc());
    static const MCSymbolRefExpr *create(StringRef Name, VariantKind Kind,
                                         MCContext &Ctx);
  
    /// @}
    /// \name Accessors
    /// @{
  
    const MCSymbol &getSymbol() const { return *Symbol; }
  
    VariantKind getKind() const {
      return (VariantKind)(getSubclassData() & VariantKindMask);
    }
  
    void printVariantKind(raw_ostream &OS) const;
  
    bool hasSubsectionsViaSymbols() const {
      return (getSubclassData() & HasSubsectionsViaSymbolsBit) != 0;
    }
  
    /// @}
    /// \name Static Utility Functions
    /// @{
  
    static StringRef getVariantKindName(VariantKind Kind);
  
    static VariantKind getVariantKindForName(StringRef Name);
  
    /// @}
  
    static bool classof(const MCExpr *E) {
      return E->getKind() == MCExpr::SymbolRef;
    }
  };
  
  /// Unary assembler expressions.
  class MCUnaryExpr : public MCExpr {
  public:
    enum Opcode {
      LNot,  ///< Logical negation.
      Minus, ///< Unary minus.
      Not,   ///< Bitwise negation.
      Plus   ///< Unary plus.
    };
  
  private:
    const MCExpr *Expr;
  
    MCUnaryExpr(Opcode Op, const MCExpr *Expr, SMLoc Loc)
        : MCExpr(MCExpr::Unary, Loc, Op), Expr(Expr) {}
  
  public:
    /// \name Construction
    /// @{
  
    static const MCUnaryExpr *create(Opcode Op, const MCExpr *Expr,
                                     MCContext &Ctx, SMLoc Loc = SMLoc());
  
    static const MCUnaryExpr *createLNot(const MCExpr *Expr, MCContext &Ctx, SMLoc Loc = SMLoc()) {
      return create(LNot, Expr, Ctx, Loc);
    }
  
    static const MCUnaryExpr *createMinus(const MCExpr *Expr, MCContext &Ctx, SMLoc Loc = SMLoc()) {
      return create(Minus, Expr, Ctx, Loc);
    }
  
    static const MCUnaryExpr *createNot(const MCExpr *Expr, MCContext &Ctx, SMLoc Loc = SMLoc()) {
      return create(Not, Expr, Ctx, Loc);
    }
  
    static const MCUnaryExpr *createPlus(const MCExpr *Expr, MCContext &Ctx, SMLoc Loc = SMLoc()) {
      return create(Plus, Expr, Ctx, Loc);
    }
  
    /// @}
    /// \name Accessors
    /// @{
  
    /// Get the kind of this unary expression.
    Opcode getOpcode() const { return (Opcode)getSubclassData(); }
  
    /// Get the child of this unary expression.
    const MCExpr *getSubExpr() const { return Expr; }
  
    /// @}
  
    static bool classof(const MCExpr *E) {
      return E->getKind() == MCExpr::Unary;
    }
  };
  
  /// Binary assembler expressions.
  class MCBinaryExpr : public MCExpr {
  public:
    enum Opcode {
      Add,  ///< Addition.
      And,  ///< Bitwise and.
      Div,  ///< Signed division.
      EQ,   ///< Equality comparison.
      GT,   ///< Signed greater than comparison (result is either 0 or some
            ///< target-specific non-zero value)
      GTE,  ///< Signed greater than or equal comparison (result is either 0 or
            ///< some target-specific non-zero value).
      LAnd, ///< Logical and.
      LOr,  ///< Logical or.
      LT,   ///< Signed less than comparison (result is either 0 or
            ///< some target-specific non-zero value).
      LTE,  ///< Signed less than or equal comparison (result is either 0 or
            ///< some target-specific non-zero value).
      Mod,  ///< Signed remainder.
      Mul,  ///< Multiplication.
      NE,   ///< Inequality comparison.
      Or,   ///< Bitwise or.
      Shl,  ///< Shift left.
      AShr, ///< Arithmetic shift right.
      LShr, ///< Logical shift right.
      Sub,  ///< Subtraction.
      Xor   ///< Bitwise exclusive or.
    };
  
  private:
    const MCExpr *LHS, *RHS;
  
    MCBinaryExpr(Opcode Op, const MCExpr *LHS, const MCExpr *RHS,
                 SMLoc Loc = SMLoc())
        : MCExpr(MCExpr::Binary, Loc, Op), LHS(LHS), RHS(RHS) {}
  
  public:
    /// \name Construction
    /// @{
  
    static const MCBinaryExpr *create(Opcode Op, const MCExpr *LHS,
                                      const MCExpr *RHS, MCContext &Ctx,
                                      SMLoc Loc = SMLoc());
  
    static const MCBinaryExpr *createAdd(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(Add, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createAnd(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(And, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createDiv(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(Div, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createEQ(const MCExpr *LHS, const MCExpr *RHS,
                                        MCContext &Ctx) {
      return create(EQ, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createGT(const MCExpr *LHS, const MCExpr *RHS,
                                        MCContext &Ctx) {
      return create(GT, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createGTE(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(GTE, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createLAnd(const MCExpr *LHS, const MCExpr *RHS,
                                          MCContext &Ctx) {
      return create(LAnd, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createLOr(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(LOr, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createLT(const MCExpr *LHS, const MCExpr *RHS,
                                        MCContext &Ctx) {
      return create(LT, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createLTE(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(LTE, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createMod(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(Mod, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createMul(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(Mul, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createNE(const MCExpr *LHS, const MCExpr *RHS,
                                        MCContext &Ctx) {
      return create(NE, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createOr(const MCExpr *LHS, const MCExpr *RHS,
                                        MCContext &Ctx) {
      return create(Or, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createShl(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(Shl, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createAShr(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(AShr, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createLShr(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(LShr, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createSub(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(Sub, LHS, RHS, Ctx);
    }
  
    static const MCBinaryExpr *createXor(const MCExpr *LHS, const MCExpr *RHS,
                                         MCContext &Ctx) {
      return create(Xor, LHS, RHS, Ctx);
    }
  
    /// @}
    /// \name Accessors
    /// @{
  
    /// Get the kind of this binary expression.
    Opcode getOpcode() const { return (Opcode)getSubclassData(); }
  
    /// Get the left-hand side expression of the binary operator.
    const MCExpr *getLHS() const { return LHS; }
  
    /// Get the right-hand side expression of the binary operator.
    const MCExpr *getRHS() const { return RHS; }
  
    /// @}
  
    static bool classof(const MCExpr *E) {
      return E->getKind() == MCExpr::Binary;
    }
  };
  
  /// This is an extension point for target-specific MCExpr subclasses to
  /// implement.
  ///
  /// NOTE: All subclasses are required to have trivial destructors because
  /// MCExprs are bump pointer allocated and not destructed.
  class MCTargetExpr : public MCExpr {
    virtual void anchor();
  
  protected:
    MCTargetExpr() : MCExpr(Target, SMLoc()) {}
    virtual ~MCTargetExpr() = default;
  
  public:
    virtual void printImpl(raw_ostream &OS, const MCAsmInfo *MAI) const = 0;
    virtual bool evaluateAsRelocatableImpl(MCValue &Res,
                                           const MCAsmLayout *Layout,
                                           const MCFixup *Fixup) const = 0;
    // allow Target Expressions to be checked for equality
    virtual bool isEqualTo(const MCExpr *x) const { return false; }
    // This should be set when assigned expressions are not valid ".set"
    // expressions, e.g. registers, and must be inlined.
    virtual bool inlineAssignedExpr() const { return false; }
    virtual void visitUsedExpr(MCStreamer& Streamer) const = 0;
    virtual MCFragment *findAssociatedFragment() const = 0;
  
    virtual void fixELFSymbolsInTLSFixups(MCAssembler &) const = 0;
  
    static bool classof(const MCExpr *E) {
      return E->getKind() == MCExpr::Target;
    }
  };
  
  } // end namespace llvm
  
  #endif // LLVM_MC_MCEXPR_H
  