llvm-3.8-dev 1:3.8-2ubuntu1 / usr / include / llvm-3.8 / llvm / MC / MCStreamer.h

//===- MCStreamer.h - High-level Streaming Machine Code Output --*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file declares the MCStreamer class.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_MC_MCSTREAMER_H
#define LLVM_MC_MCSTREAMER_H

#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/MC/MCDirectives.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCLinkerOptimizationHint.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCWinEH.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/SMLoc.h"
#include <string>

namespace llvm {
class MCAsmBackend;
class MCCodeEmitter;
class MCContext;
class MCExpr;
class MCInst;
class MCInstPrinter;
class MCSection;
class MCStreamer;
class MCSymbolELF;
class MCSymbolRefExpr;
class MCSubtargetInfo;
class StringRef;
class Twine;
class raw_ostream;
class formatted_raw_ostream;
class AssemblerConstantPools;

typedef std::pair<MCSection *, const MCExpr *> MCSectionSubPair;

/// Target specific streamer interface. This is used so that targets can
/// implement support for target specific assembly directives.
///
/// If target foo wants to use this, it should implement 3 classes:
/// * FooTargetStreamer : public MCTargetStreamer
/// * FooTargetAsmStreamer : public FooTargetStreamer
/// * FooTargetELFStreamer : public FooTargetStreamer
///
/// FooTargetStreamer should have a pure virtual method for each directive. For
/// example, for a ".bar symbol_name" directive, it should have
/// virtual emitBar(const MCSymbol &Symbol) = 0;
///
/// The FooTargetAsmStreamer and FooTargetELFStreamer classes implement the
/// method. The assembly streamer just prints ".bar symbol_name". The object
/// streamer does whatever is needed to implement .bar in the object file.
///
/// In the assembly printer and parser the target streamer can be used by
/// calling getTargetStreamer and casting it to FooTargetStreamer:
///
/// MCTargetStreamer &TS = OutStreamer.getTargetStreamer();
/// FooTargetStreamer &ATS = static_cast<FooTargetStreamer &>(TS);
///
/// The base classes FooTargetAsmStreamer and FooTargetELFStreamer should
/// *never* be treated differently. Callers should always talk to a
/// FooTargetStreamer.
class MCTargetStreamer {
protected:
  MCStreamer &Streamer;

public:
  MCTargetStreamer(MCStreamer &S);
  virtual ~MCTargetStreamer();

  MCStreamer &getStreamer() { return Streamer; }

  // Allow a target to add behavior to the EmitLabel of MCStreamer.
  virtual void emitLabel(MCSymbol *Symbol);
  // Allow a target to add behavior to the emitAssignment of MCStreamer.
  virtual void emitAssignment(MCSymbol *Symbol, const MCExpr *Value);

  virtual void prettyPrintAsm(MCInstPrinter &InstPrinter, raw_ostream &OS,
                              const MCInst &Inst, const MCSubtargetInfo &STI);

  virtual void finish();
};

// FIXME: declared here because it is used from
// lib/CodeGen/AsmPrinter/ARMException.cpp.
class ARMTargetStreamer : public MCTargetStreamer {
public:
  ARMTargetStreamer(MCStreamer &S);
  ~ARMTargetStreamer() override;

  virtual void emitFnStart();
  virtual void emitFnEnd();
  virtual void emitCantUnwind();
  virtual void emitPersonality(const MCSymbol *Personality);
  virtual void emitPersonalityIndex(unsigned Index);
  virtual void emitHandlerData();
  virtual void emitSetFP(unsigned FpReg, unsigned SpReg,
                         int64_t Offset = 0);
  virtual void emitMovSP(unsigned Reg, int64_t Offset = 0);
  virtual void emitPad(int64_t Offset);
  virtual void emitRegSave(const SmallVectorImpl<unsigned> &RegList,
                           bool isVector);
  virtual void emitUnwindRaw(int64_t StackOffset,
                             const SmallVectorImpl<uint8_t> &Opcodes);

  virtual void switchVendor(StringRef Vendor);
  virtual void emitAttribute(unsigned Attribute, unsigned Value);
  virtual void emitTextAttribute(unsigned Attribute, StringRef String);
  virtual void emitIntTextAttribute(unsigned Attribute, unsigned IntValue,
                                    StringRef StringValue = "");
  virtual void emitFPU(unsigned FPU);
  virtual void emitArch(unsigned Arch);
  virtual void emitArchExtension(unsigned ArchExt);
  virtual void emitObjectArch(unsigned Arch);
  virtual void finishAttributeSection();
  virtual void emitInst(uint32_t Inst, char Suffix = '\0');

  virtual void AnnotateTLSDescriptorSequence(const MCSymbolRefExpr *SRE);

  virtual void emitThumbSet(MCSymbol *Symbol, const MCExpr *Value);

  void finish() override;

  /// Reset any state between object emissions, i.e. the equivalent of
  /// MCStreamer's reset method.
  virtual void reset();

  /// Callback used to implement the ldr= pseudo.
  /// Add a new entry to the constant pool for the current section and return an
  /// MCExpr that can be used to refer to the constant pool location.
  const MCExpr *addConstantPoolEntry(const MCExpr *, SMLoc Loc);

  /// Callback used to implemnt the .ltorg directive.
  /// Emit contents of constant pool for the current section.
  void emitCurrentConstantPool();

private:
  std::unique_ptr<AssemblerConstantPools> ConstantPools;
};

/// \brief Streaming machine code generation interface.
///
/// This interface is intended to provide a programatic interface that is very
/// similar to the level that an assembler .s file provides.  It has callbacks
/// to emit bytes, handle directives, etc.  The implementation of this interface
/// retains state to know what the current section is etc.
///
/// There are multiple implementations of this interface: one for writing out
/// a .s file, and implementations that write out .o files of various formats.
///
class MCStreamer {
  MCContext &Context;
  std::unique_ptr<MCTargetStreamer> TargetStreamer;

  MCStreamer(const MCStreamer &) = delete;
  MCStreamer &operator=(const MCStreamer &) = delete;

  std::vector<MCDwarfFrameInfo> DwarfFrameInfos;
  MCDwarfFrameInfo *getCurrentDwarfFrameInfo();
  void EnsureValidDwarfFrame();

  MCSymbol *EmitCFICommon();

  std::vector<WinEH::FrameInfo *> WinFrameInfos;
  WinEH::FrameInfo *CurrentWinFrameInfo;
  void EnsureValidWinFrameInfo();

  /// \brief Tracks an index to represent the order a symbol was emitted in.
  /// Zero means we did not emit that symbol.
  DenseMap<const MCSymbol *, unsigned> SymbolOrdering;

  /// \brief This is stack of current and previous section values saved by
  /// PushSection.
  SmallVector<std::pair<MCSectionSubPair, MCSectionSubPair>, 4> SectionStack;

protected:
  MCStreamer(MCContext &Ctx);

  virtual void EmitCFIStartProcImpl(MCDwarfFrameInfo &Frame);
  virtual void EmitCFIEndProcImpl(MCDwarfFrameInfo &CurFrame);

  WinEH::FrameInfo *getCurrentWinFrameInfo() {
    return CurrentWinFrameInfo;
  }

  virtual void EmitWindowsUnwindTables();

  virtual void EmitRawTextImpl(StringRef String);

public:
  virtual ~MCStreamer();

  void visitUsedExpr(const MCExpr &Expr);
  virtual void visitUsedSymbol(const MCSymbol &Sym);

  void setTargetStreamer(MCTargetStreamer *TS) {
    TargetStreamer.reset(TS);
  }

  /// State management
  ///
  virtual void reset();

  MCContext &getContext() const { return Context; }

  MCTargetStreamer *getTargetStreamer() {
    return TargetStreamer.get();
  }

  unsigned getNumFrameInfos() { return DwarfFrameInfos.size(); }
  ArrayRef<MCDwarfFrameInfo> getDwarfFrameInfos() const {
    return DwarfFrameInfos;
  }

  unsigned getNumWinFrameInfos() { return WinFrameInfos.size(); }
  ArrayRef<WinEH::FrameInfo *> getWinFrameInfos() const {
    return WinFrameInfos;
  }

  void generateCompactUnwindEncodings(MCAsmBackend *MAB);

  /// \name Assembly File Formatting.
  /// @{

  /// \brief Return true if this streamer supports verbose assembly and if it is
  /// enabled.
  virtual bool isVerboseAsm() const { return false; }

  /// \brief Return true if this asm streamer supports emitting unformatted text
  /// to the .s file with EmitRawText.
  virtual bool hasRawTextSupport() const { return false; }

  /// \brief Is the integrated assembler required for this streamer to function
  /// correctly?
  virtual bool isIntegratedAssemblerRequired() const { return false; }

  /// \brief Add a textual command.
  ///
  /// Typically for comments that can be emitted to the generated .s
  /// file if applicable as a QoI issue to make the output of the compiler
  /// more readable.  This only affects the MCAsmStreamer, and only when
  /// verbose assembly output is enabled.
  ///
  /// If the comment includes embedded \n's, they will each get the comment
  /// prefix as appropriate.  The added comment should not end with a \n.
  virtual void AddComment(const Twine &T) {}

  /// \brief Return a raw_ostream that comments can be written to. Unlike
  /// AddComment, you are required to terminate comments with \n if you use this
  /// method.
  virtual raw_ostream &GetCommentOS();

  /// \brief Print T and prefix it with the comment string (normally #) and
  /// optionally a tab. This prints the comment immediately, not at the end of
  /// the current line. It is basically a safe version of EmitRawText: since it
  /// only prints comments, the object streamer ignores it instead of asserting.
  virtual void emitRawComment(const Twine &T, bool TabPrefix = true);

  /// AddBlankLine - Emit a blank line to a .s file to pretty it up.
  virtual void AddBlankLine() {}

  /// @}

  /// \name Symbol & Section Management
  /// @{

  /// \brief Return the current section that the streamer is emitting code to.
  MCSectionSubPair getCurrentSection() const {
    if (!SectionStack.empty())
      return SectionStack.back().first;
    return MCSectionSubPair();
  }
  MCSection *getCurrentSectionOnly() const { return getCurrentSection().first; }

  /// \brief Return the previous section that the streamer is emitting code to.
  MCSectionSubPair getPreviousSection() const {
    if (!SectionStack.empty())
      return SectionStack.back().second;
    return MCSectionSubPair();
  }

  /// \brief Returns an index to represent the order a symbol was emitted in.
  /// (zero if we did not emit that symbol)
  unsigned GetSymbolOrder(const MCSymbol *Sym) const {
    return SymbolOrdering.lookup(Sym);
  }

  /// \brief Update streamer for a new active section.
  ///
  /// This is called by PopSection and SwitchSection, if the current
  /// section changes.
  virtual void ChangeSection(MCSection *, const MCExpr *);

  /// \brief Save the current and previous section on the section stack.
  void PushSection() {
    SectionStack.push_back(
        std::make_pair(getCurrentSection(), getPreviousSection()));
  }

  /// \brief Restore the current and previous section from the section stack.
  /// Calls ChangeSection as needed.
  ///
  /// Returns false if the stack was empty.
  bool PopSection() {
    if (SectionStack.size() <= 1)
      return false;
    auto I = SectionStack.end();
    --I;
    MCSectionSubPair OldSection = I->first;
    --I;
    MCSectionSubPair NewSection = I->first;

    if (OldSection != NewSection)
      ChangeSection(NewSection.first, NewSection.second);
    SectionStack.pop_back();
    return true;
  }

  bool SubSection(const MCExpr *Subsection) {
    if (SectionStack.empty())
      return false;

    SwitchSection(SectionStack.back().first.first, Subsection);
    return true;
  }

  /// Set the current section where code is being emitted to \p Section.  This
  /// is required to update CurSection.
  ///
  /// This corresponds to assembler directives like .section, .text, etc.
  virtual void SwitchSection(MCSection *Section,
                             const MCExpr *Subsection = nullptr);

  /// \brief Set the current section where code is being emitted to \p Section.
  /// This is required to update CurSection. This version does not call
  /// ChangeSection.
  void SwitchSectionNoChange(MCSection *Section,
                             const MCExpr *Subsection = nullptr) {
    assert(Section && "Cannot switch to a null section!");
    MCSectionSubPair curSection = SectionStack.back().first;
    SectionStack.back().second = curSection;
    if (MCSectionSubPair(Section, Subsection) != curSection)
      SectionStack.back().first = MCSectionSubPair(Section, Subsection);
  }

  /// \brief Create the default sections and set the initial one.
  virtual void InitSections(bool NoExecStack);

  MCSymbol *endSection(MCSection *Section);

  /// \brief Sets the symbol's section.
  ///
  /// Each emitted symbol will be tracked in the ordering table,
  /// so we can sort on them later.
  void AssignFragment(MCSymbol *Symbol, MCFragment *Fragment);

  /// \brief Emit a label for \p Symbol into the current section.
  ///
  /// This corresponds to an assembler statement such as:
  ///   foo:
  ///
  /// \param Symbol - The symbol to emit. A given symbol should only be
  /// emitted as a label once, and symbols emitted as a label should never be
  /// used in an assignment.
  // FIXME: These emission are non-const because we mutate the symbol to
  // add the section we're emitting it to later.
  virtual void EmitLabel(MCSymbol *Symbol);

  virtual void EmitEHSymAttributes(const MCSymbol *Symbol, MCSymbol *EHSymbol);

  /// \brief Note in the output the specified \p Flag.
  virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);

  /// \brief Emit the given list \p Options of strings as linker
  /// options into the output.
  virtual void EmitLinkerOptions(ArrayRef<std::string> Kind) {}

  /// \brief Note in the output the specified region \p Kind.
  virtual void EmitDataRegion(MCDataRegionType Kind) {}

  /// \brief Specify the MachO minimum deployment target version.
  virtual void EmitVersionMin(MCVersionMinType, unsigned Major, unsigned Minor,
                              unsigned Update) {}

  /// \brief Note in the output that the specified \p Func is a Thumb mode
  /// function (ARM target only).
  virtual void EmitThumbFunc(MCSymbol *Func);

  /// \brief Emit an assignment of \p Value to \p Symbol.
  ///
  /// This corresponds to an assembler statement such as:
  ///  symbol = value
  ///
  /// The assignment generates no code, but has the side effect of binding the
  /// value in the current context. For the assembly streamer, this prints the
  /// binding into the .s file.
  ///
  /// \param Symbol - The symbol being assigned to.
  /// \param Value - The value for the symbol.
  virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);

  /// \brief Emit an weak reference from \p Alias to \p Symbol.
  ///
  /// This corresponds to an assembler statement such as:
  ///  .weakref alias, symbol
  ///
  /// \param Alias - The alias that is being created.
  /// \param Symbol - The symbol being aliased.
  virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);

  /// \brief Add the given \p Attribute to \p Symbol.
  virtual bool EmitSymbolAttribute(MCSymbol *Symbol,
                                   MCSymbolAttr Attribute) = 0;

  /// \brief Set the \p DescValue for the \p Symbol.
  ///
  /// \param Symbol - The symbol to have its n_desc field set.
  /// \param DescValue - The value to set into the n_desc field.
  virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);

  /// \brief Start emitting COFF symbol definition
  ///
  /// \param Symbol - The symbol to have its External & Type fields set.
  virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol);

  /// \brief Emit the storage class of the symbol.
  ///
  /// \param StorageClass - The storage class the symbol should have.
  virtual void EmitCOFFSymbolStorageClass(int StorageClass);

  /// \brief Emit the type of the symbol.
  ///
  /// \param Type - A COFF type identifier (see COFF::SymbolType in X86COFF.h)
  virtual void EmitCOFFSymbolType(int Type);

  /// \brief Marks the end of the symbol definition.
  virtual void EndCOFFSymbolDef();

  virtual void EmitCOFFSafeSEH(MCSymbol const *Symbol);

  /// \brief Emits a COFF section index.
  ///
  /// \param Symbol - Symbol the section number relocation should point to.
  virtual void EmitCOFFSectionIndex(MCSymbol const *Symbol);

  /// \brief Emits a COFF section relative relocation.
  ///
  /// \param Symbol - Symbol the section relative relocation should point to.
  virtual void EmitCOFFSecRel32(MCSymbol const *Symbol);

  /// \brief Emit an ELF .size directive.
  ///
  /// This corresponds to an assembler statement such as:
  ///  .size symbol, expression
  virtual void emitELFSize(MCSymbolELF *Symbol, const MCExpr *Value);

  /// \brief Emit a Linker Optimization Hint (LOH) directive.
  /// \param Args - Arguments of the LOH.
  virtual void EmitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) {}

  /// \brief Emit a common symbol.
  ///
  /// \param Symbol - The common symbol to emit.
  /// \param Size - The size of the common symbol.
  /// \param ByteAlignment - The alignment of the symbol if
  /// non-zero. This must be a power of 2.
  virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                unsigned ByteAlignment) = 0;

  /// \brief Emit a local common (.lcomm) symbol.
  ///
  /// \param Symbol - The common symbol to emit.
  /// \param Size - The size of the common symbol.
  /// \param ByteAlignment - The alignment of the common symbol in bytes.
  virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                     unsigned ByteAlignment);

  /// \brief Emit the zerofill section and an optional symbol.
  ///
  /// \param Section - The zerofill section to create and or to put the symbol
  /// \param Symbol - The zerofill symbol to emit, if non-NULL.
  /// \param Size - The size of the zerofill symbol.
  /// \param ByteAlignment - The alignment of the zerofill symbol if
  /// non-zero. This must be a power of 2 on some targets.
  virtual void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
                            uint64_t Size = 0, unsigned ByteAlignment = 0) = 0;

  /// \brief Emit a thread local bss (.tbss) symbol.
  ///
  /// \param Section - The thread local common section.
  /// \param Symbol - The thread local common symbol to emit.
  /// \param Size - The size of the symbol.
  /// \param ByteAlignment - The alignment of the thread local common symbol
  /// if non-zero.  This must be a power of 2 on some targets.
  virtual void EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
                              uint64_t Size, unsigned ByteAlignment = 0);

  /// @}
  /// \name Generating Data
  /// @{

  /// \brief Emit the bytes in \p Data into the output.
  ///
  /// This is used to implement assembler directives such as .byte, .ascii,
  /// etc.
  virtual void EmitBytes(StringRef Data);

  /// \brief Emit the expression \p Value into the output as a native
  /// integer of the given \p Size bytes.
  ///
  /// This is used to implement assembler directives such as .word, .quad,
  /// etc.
  ///
  /// \param Value - The value to emit.
  /// \param Size - The size of the integer (in bytes) to emit. This must
  /// match a native machine width.
  /// \param Loc - The location of the expression for error reporting.
  virtual void EmitValueImpl(const MCExpr *Value, unsigned Size,
                             SMLoc Loc = SMLoc());

  void EmitValue(const MCExpr *Value, unsigned Size, SMLoc Loc = SMLoc());

  /// \brief Special case of EmitValue that avoids the client having
  /// to pass in a MCExpr for constant integers.
  virtual void EmitIntValue(uint64_t Value, unsigned Size);

  virtual void EmitULEB128Value(const MCExpr *Value);

  virtual void EmitSLEB128Value(const MCExpr *Value);

  /// \brief Special case of EmitULEB128Value that avoids the client having to
  /// pass in a MCExpr for constant integers.
  void EmitULEB128IntValue(uint64_t Value, unsigned Padding = 0);

  /// \brief Special case of EmitSLEB128Value that avoids the client having to
  /// pass in a MCExpr for constant integers.
  void EmitSLEB128IntValue(int64_t Value);

  /// \brief Special case of EmitValue that avoids the client having to pass in
  /// a MCExpr for MCSymbols.
  void EmitSymbolValue(const MCSymbol *Sym, unsigned Size,
                       bool IsSectionRelative = false);

  /// \brief Emit the expression \p Value into the output as a gprel64 (64-bit
  /// GP relative) value.
  ///
  /// This is used to implement assembler directives such as .gpdword on
  /// targets that support them.
  virtual void EmitGPRel64Value(const MCExpr *Value);

  /// \brief Emit the expression \p Value into the output as a gprel32 (32-bit
  /// GP relative) value.
  ///
  /// This is used to implement assembler directives such as .gprel32 on
  /// targets that support them.
  virtual void EmitGPRel32Value(const MCExpr *Value);

  /// \brief Emit NumBytes bytes worth of the value specified by FillValue.
  /// This implements directives such as '.space'.
  virtual void EmitFill(uint64_t NumBytes, uint8_t FillValue);

  /// \brief Emit NumBytes worth of zeros.
  /// This function properly handles data in virtual sections.
  void EmitZeros(uint64_t NumBytes);

  /// \brief Emit some number of copies of \p Value until the byte alignment \p
  /// ByteAlignment is reached.
  ///
  /// If the number of bytes need to emit for the alignment is not a multiple
  /// of \p ValueSize, then the contents of the emitted fill bytes is
  /// undefined.
  ///
  /// This used to implement the .align assembler directive.
  ///
  /// \param ByteAlignment - The alignment to reach. This must be a power of
  /// two on some targets.
  /// \param Value - The value to use when filling bytes.
  /// \param ValueSize - The size of the integer (in bytes) to emit for
  /// \p Value. This must match a native machine width.
  /// \param MaxBytesToEmit - The maximum numbers of bytes to emit, or 0. If
  /// the alignment cannot be reached in this many bytes, no bytes are
  /// emitted.
  virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
                                    unsigned ValueSize = 1,
                                    unsigned MaxBytesToEmit = 0);

  /// \brief Emit nops until the byte alignment \p ByteAlignment is reached.
  ///
  /// This used to align code where the alignment bytes may be executed.  This
  /// can emit different bytes for different sizes to optimize execution.
  ///
  /// \param ByteAlignment - The alignment to reach. This must be a power of
  /// two on some targets.
  /// \param MaxBytesToEmit - The maximum numbers of bytes to emit, or 0. If
  /// the alignment cannot be reached in this many bytes, no bytes are
  /// emitted.
  virtual void EmitCodeAlignment(unsigned ByteAlignment,
                                 unsigned MaxBytesToEmit = 0);

  /// \brief Emit some number of copies of \p Value until the byte offset \p
  /// Offset is reached.
  ///
  /// This is used to implement assembler directives such as .org.
  ///
  /// \param Offset - The offset to reach. This may be an expression, but the
  /// expression must be associated with the current section.
  /// \param Value - The value to use when filling bytes.
  virtual void emitValueToOffset(const MCExpr *Offset, unsigned char Value = 0);

  /// @}

  /// \brief Switch to a new logical file.  This is used to implement the '.file
  /// "foo.c"' assembler directive.
  virtual void EmitFileDirective(StringRef Filename);

  /// \brief Emit the "identifiers" directive.  This implements the
  /// '.ident "version foo"' assembler directive.
  virtual void EmitIdent(StringRef IdentString) {}

  /// \brief Associate a filename with a specified logical file number.  This
  /// implements the DWARF2 '.file 4 "foo.c"' assembler directive.
  virtual unsigned EmitDwarfFileDirective(unsigned FileNo, StringRef Directory,
                                          StringRef Filename,
                                          unsigned CUID = 0);

  /// \brief This implements the DWARF2 '.loc fileno lineno ...' assembler
  /// directive.
  virtual void EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                                     unsigned Column, unsigned Flags,
                                     unsigned Isa, unsigned Discriminator,
                                     StringRef FileName);

  /// Emit the absolute difference between two symbols.
  ///
  /// \pre Offset of \c Hi is greater than the offset \c Lo.
  virtual void emitAbsoluteSymbolDiff(const MCSymbol *Hi, const MCSymbol *Lo,
                                      unsigned Size);

  virtual MCSymbol *getDwarfLineTableSymbol(unsigned CUID);
  virtual void EmitCFISections(bool EH, bool Debug);
  void EmitCFIStartProc(bool IsSimple);
  void EmitCFIEndProc();
  virtual void EmitCFIDefCfa(int64_t Register, int64_t Offset);
  virtual void EmitCFIDefCfaOffset(int64_t Offset);
  virtual void EmitCFIDefCfaRegister(int64_t Register);
  virtual void EmitCFIOffset(int64_t Register, int64_t Offset);
  virtual void EmitCFIPersonality(const MCSymbol *Sym, unsigned Encoding);
  virtual void EmitCFILsda(const MCSymbol *Sym, unsigned Encoding);
  virtual void EmitCFIRememberState();
  virtual void EmitCFIRestoreState();
  virtual void EmitCFISameValue(int64_t Register);
  virtual void EmitCFIRestore(int64_t Register);
  virtual void EmitCFIRelOffset(int64_t Register, int64_t Offset);
  virtual void EmitCFIAdjustCfaOffset(int64_t Adjustment);
  virtual void EmitCFIEscape(StringRef Values);
  virtual void EmitCFIGnuArgsSize(int64_t Size);
  virtual void EmitCFISignalFrame();
  virtual void EmitCFIUndefined(int64_t Register);
  virtual void EmitCFIRegister(int64_t Register1, int64_t Register2);
  virtual void EmitCFIWindowSave();

  virtual void EmitWinCFIStartProc(const MCSymbol *Symbol);
  virtual void EmitWinCFIEndProc();
  virtual void EmitWinCFIStartChained();
  virtual void EmitWinCFIEndChained();
  virtual void EmitWinCFIPushReg(unsigned Register);
  virtual void EmitWinCFISetFrame(unsigned Register, unsigned Offset);
  virtual void EmitWinCFIAllocStack(unsigned Size);
  virtual void EmitWinCFISaveReg(unsigned Register, unsigned Offset);
  virtual void EmitWinCFISaveXMM(unsigned Register, unsigned Offset);
  virtual void EmitWinCFIPushFrame(bool Code);
  virtual void EmitWinCFIEndProlog();

  virtual void EmitWinEHHandler(const MCSymbol *Sym, bool Unwind, bool Except);
  virtual void EmitWinEHHandlerData();

  virtual void EmitSyntaxDirective();

  /// \brief Emit a .reloc directive.
  /// Returns true if the relocation could not be emitted because Name is not
  /// known.
  virtual bool EmitRelocDirective(const MCExpr &Offset, StringRef Name,
                                  const MCExpr *Expr, SMLoc Loc) {
    return true;
  }

  /// \brief Emit the given \p Instruction into the current section.
  virtual void EmitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI);

  /// \brief Set the bundle alignment mode from now on in the section.
  /// The argument is the power of 2 to which the alignment is set. The
  /// value 0 means turn the bundle alignment off.
  virtual void EmitBundleAlignMode(unsigned AlignPow2);

  /// \brief The following instructions are a bundle-locked group.
  ///
  /// \param AlignToEnd - If true, the bundle-locked group will be aligned to
  ///                     the end of a bundle.
  virtual void EmitBundleLock(bool AlignToEnd);

  /// \brief Ends a bundle-locked group.
  virtual void EmitBundleUnlock();

  /// \brief If this file is backed by a assembly streamer, this dumps the
  /// specified string in the output .s file.  This capability is indicated by
  /// the hasRawTextSupport() predicate.  By default this aborts.
  void EmitRawText(const Twine &String);

  /// \brief Streamer specific finalization.
  virtual void FinishImpl();
  /// \brief Finish emission of machine code.
  void Finish();

  virtual bool mayHaveInstructions(MCSection &Sec) const { return true; }
};

/// Create a dummy machine code streamer, which does nothing. This is useful for
/// timing the assembler front end.
MCStreamer *createNullStreamer(MCContext &Ctx);

/// Create a machine code streamer which will print out assembly for the native
/// target, suitable for compiling with a native assembler.
///
/// \param InstPrint - If given, the instruction printer to use. If not given
/// the MCInst representation will be printed.  This method takes ownership of
/// InstPrint.
///
/// \param CE - If given, a code emitter to use to show the instruction
/// encoding inline with the assembly. This method takes ownership of \p CE.
///
/// \param TAB - If given, a target asm backend to use to show the fixup
/// information in conjunction with encoding information. This method takes
/// ownership of \p TAB.
///
/// \param ShowInst - Whether to show the MCInst representation inline with
/// the assembly.
MCStreamer *createAsmStreamer(MCContext &Ctx,
                              std::unique_ptr<formatted_raw_ostream> OS,
                              bool isVerboseAsm, bool useDwarfDirectory,
                              MCInstPrinter *InstPrint, MCCodeEmitter *CE,
                              MCAsmBackend *TAB, bool ShowInst);
} // end namespace llvm

#endif