text: //===- MCStreamer.h - High-level Streaming Machine Code Output --*- 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
  //
  //===----------------------------------------------------------------------===//
  //
  // This file declares the MCStreamer class.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_MC_MCSTREAMER_H
  #define LLVM_MC_MCSTREAMER_H
  
  #include "llvm/ADT/APInt.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/Optional.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/MC/MCDirectives.h"
  #include "llvm/MC/MCLinkerOptimizationHint.h"
  #include "llvm/MC/MCPseudoProbe.h"
  #include "llvm/MC/MCSymbol.h"
  #include "llvm/MC/MCWinEH.h"
  #include "llvm/Support/Error.h"
  #include "llvm/Support/MD5.h"
  #include "llvm/Support/SMLoc.h"
  #include "llvm/Support/TargetParser.h"
  #include "llvm/Support/VersionTuple.h"
  #include <cassert>
  #include <cstdint>
  #include <memory>
  #include <string>
  #include <utility>
  #include <vector>
  
  namespace llvm {
  
  class AssemblerConstantPools;
  class formatted_raw_ostream;
  class MCAsmBackend;
  class MCCodeEmitter;
  class MCContext;
  struct MCDwarfFrameInfo;
  class MCExpr;
  class MCInst;
  class MCInstPrinter;
  class MCRegister;
  class MCSection;
  class MCStreamer;
  class MCSymbolRefExpr;
  class MCSubtargetInfo;
  class raw_ostream;
  class Twine;
  
  namespace codeview {
  struct DefRangeRegisterRelHeader;
  struct DefRangeSubfieldRegisterHeader;
  struct DefRangeRegisterHeader;
  struct DefRangeFramePointerRelHeader;
  }
  
  using MCSectionSubPair = std::pair<MCSection *, const MCExpr *>;
  
  /// 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, uint64_t Address,
                                const MCInst &Inst, const MCSubtargetInfo &STI,
                                raw_ostream &OS);
  
    virtual void emitDwarfFileDirective(StringRef Directive);
  
    /// Update streamer for a new active section.
    ///
    /// This is called by PopSection and SwitchSection, if the current
    /// section changes.
    virtual void changeSection(const MCSection *CurSection, MCSection *Section,
                               const MCExpr *SubSection, raw_ostream &OS);
  
    virtual void emitValue(const MCExpr *Value);
  
    /// Emit the bytes in \p Data into the output.
    ///
    /// This is used to emit bytes in \p Data as sequence of .byte directives.
    virtual void emitRawBytes(StringRef Data);
  
    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(ARM::ArchKind Arch);
    virtual void emitArchExtension(uint64_t ArchExt);
    virtual void emitObjectArch(ARM::ArchKind Arch);
    void emitTargetAttributes(const MCSubtargetInfo &STI);
    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;
  };
  
  /// 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;
  
    std::vector<MCDwarfFrameInfo> DwarfFrameInfos;
    MCDwarfFrameInfo *getCurrentDwarfFrameInfo();
  
    /// Similar to DwarfFrameInfos, but for SEH unwind info. Chained frames may
    /// refer to each other, so use std::unique_ptr to provide pointer stability.
    std::vector<std::unique_ptr<WinEH::FrameInfo>> WinFrameInfos;
  
    WinEH::FrameInfo *CurrentWinFrameInfo;
    size_t CurrentProcWinFrameInfoStartIndex;
  
    /// 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;
  
    /// This is stack of current and previous section values saved by
    /// PushSection.
    SmallVector<std::pair<MCSectionSubPair, MCSectionSubPair>, 4> SectionStack;
  
    /// Pointer to the parser's SMLoc if available. This is used to provide
    /// locations for diagnostics.
    const SMLoc *StartTokLocPtr = nullptr;
  
    /// The next unique ID to use when creating a WinCFI-related section (.pdata
    /// or .xdata). This ID ensures that we have a one-to-one mapping from
    /// code section to unwind info section, which MSVC's incremental linker
    /// requires.
    unsigned NextWinCFIID = 0;
  
    bool UseAssemblerInfoForParsing;
  
    /// Is the assembler allowed to insert padding automatically?  For
    /// correctness reasons, we sometimes need to ensure instructions aren't
    /// seperated in unexpected ways.  At the moment, this feature is only
    /// useable from an integrated assembler, but assembly syntax is under
    /// discussion for future inclusion.
    bool AllowAutoPadding = false;
  
  protected:
    MCStreamer(MCContext &Ctx);
  
    virtual void emitCFIStartProcImpl(MCDwarfFrameInfo &Frame);
    virtual void emitCFIEndProcImpl(MCDwarfFrameInfo &CurFrame);
  
    WinEH::FrameInfo *getCurrentWinFrameInfo() {
      return CurrentWinFrameInfo;
    }
  
    virtual void EmitWindowsUnwindTables(WinEH::FrameInfo *Frame);
  
    virtual void EmitWindowsUnwindTables();
  
    virtual void emitRawTextImpl(StringRef String);
  
    /// Returns true if the the .cv_loc directive is in the right section.
    bool checkCVLocSection(unsigned FuncId, unsigned FileNo, SMLoc Loc);
  
  public:
    MCStreamer(const MCStreamer &) = delete;
    MCStreamer &operator=(const MCStreamer &) = delete;
    virtual ~MCStreamer();
  
    void visitUsedExpr(const MCExpr &Expr);
    virtual void visitUsedSymbol(const MCSymbol &Sym);
  
    void setTargetStreamer(MCTargetStreamer *TS) {
      TargetStreamer.reset(TS);
    }
  
    void setStartTokLocPtr(const SMLoc *Loc) { StartTokLocPtr = Loc; }
    SMLoc getStartTokLoc() const {
      return StartTokLocPtr ? *StartTokLocPtr : SMLoc();
    }
  
    /// State management
    ///
    virtual void reset();
  
    MCContext &getContext() const { return Context; }
  
    virtual MCAssembler *getAssemblerPtr() { return nullptr; }
  
    void setUseAssemblerInfoForParsing(bool v) { UseAssemblerInfoForParsing = v; }
    bool getUseAssemblerInfoForParsing() { return UseAssemblerInfoForParsing; }
  
    MCTargetStreamer *getTargetStreamer() {
      return TargetStreamer.get();
    }
  
    void setAllowAutoPadding(bool v) { AllowAutoPadding = v; }
    bool getAllowAutoPadding() const { return AllowAutoPadding; }
  
    /// When emitting an object file, create and emit a real label. When emitting
    /// textual assembly, this should do nothing to avoid polluting our output.
    virtual MCSymbol *emitCFILabel();
  
    /// Retreive the current frame info if one is available and it is not yet
    /// closed. Otherwise, issue an error and return null.
    WinEH::FrameInfo *EnsureValidWinFrameInfo(SMLoc Loc);
  
    unsigned getNumFrameInfos();
    ArrayRef<MCDwarfFrameInfo> getDwarfFrameInfos() const;
  
    bool hasUnfinishedDwarfFrameInfo();
  
    unsigned getNumWinFrameInfos() { return WinFrameInfos.size(); }
    ArrayRef<std::unique_ptr<WinEH::FrameInfo>> getWinFrameInfos() const {
      return WinFrameInfos;
    }
  
    void generateCompactUnwindEncodings(MCAsmBackend *MAB);
  
    /// \name Assembly File Formatting.
    /// @{
  
    /// Return true if this streamer supports verbose assembly and if it is
    /// enabled.
    virtual bool isVerboseAsm() const { return false; }
  
    /// Return true if this asm streamer supports emitting unformatted text
    /// to the .s file with EmitRawText.
    virtual bool hasRawTextSupport() const { return false; }
  
    /// Is the integrated assembler required for this streamer to function
    /// correctly?
    virtual bool isIntegratedAssemblerRequired() const { return false; }
  
    /// Add a textual comment.
    ///
    /// 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.
    /// By default, each comment is terminated with an end of line, i.e. the
    /// EOL param is set to true by default. If one prefers not to end the
    /// comment with a new line then the EOL param should be passed
    /// with a false value.
    virtual void AddComment(const Twine &T, bool EOL = true) {}
  
    /// 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();
  
    /// 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);
  
    /// Add explicit comment T. T is required to be a valid
    /// comment in the output and does not need to be escaped.
    virtual void addExplicitComment(const Twine &T);
  
    /// Emit added explicit comments.
    virtual void emitExplicitComments();
  
    /// AddBlankLine - Emit a blank line to a .s file to pretty it up.
    virtual void AddBlankLine() {}
  
    /// @}
  
    /// \name Symbol & Section Management
    /// @{
  
    /// 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; }
  
    /// Return the previous section that the streamer is emitting code to.
    MCSectionSubPair getPreviousSection() const {
      if (!SectionStack.empty())
        return SectionStack.back().second;
      return MCSectionSubPair();
    }
  
    /// 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);
    }
  
    /// 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 *);
  
    /// Save the current and previous section on the section stack.
    void PushSection() {
      SectionStack.push_back(
          std::make_pair(getCurrentSection(), getPreviousSection()));
    }
  
    /// 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 (NewSection.first && 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);
  
    /// 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);
    }
  
    /// Create the default sections and set the initial one.
    virtual void InitSections(bool NoExecStack);
  
    MCSymbol *endSection(MCSection *Section);
  
    /// 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);
  
    /// Returns the mnemonic for \p MI, if the streamer has access to a
    /// instruction printer and returns an empty string otherwise.
    virtual StringRef getMnemonic(MCInst &MI) { return ""; }
  
    /// 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, SMLoc Loc = SMLoc());
  
    virtual void emitEHSymAttributes(const MCSymbol *Symbol, MCSymbol *EHSymbol);
  
    /// Note in the output the specified \p Flag.
    virtual void emitAssemblerFlag(MCAssemblerFlag Flag);
  
    /// Emit the given list \p Options of strings as linker
    /// options into the output.
    virtual void emitLinkerOptions(ArrayRef<std::string> Kind) {}
  
    /// Note in the output the specified region \p Kind.
    virtual void emitDataRegion(MCDataRegionType Kind) {}
  
    /// Specify the Mach-O minimum deployment target version.
    virtual void emitVersionMin(MCVersionMinType Type, unsigned Major,
                                unsigned Minor, unsigned Update,
                                VersionTuple SDKVersion) {}
  
    /// Emit/Specify Mach-O build version command.
    /// \p Platform should be one of MachO::PlatformType.
    virtual void emitBuildVersion(unsigned Platform, unsigned Major,
                                  unsigned Minor, unsigned Update,
                                  VersionTuple SDKVersion) {}
  
    void emitVersionForTarget(const Triple &Target,
                              const VersionTuple &SDKVersion);
  
    /// Note in the output that the specified \p Func is a Thumb mode
    /// function (ARM target only).
    virtual void emitThumbFunc(MCSymbol *Func);
  
    /// 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);
  
    /// 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);
  
    /// Add the given \p Attribute to \p Symbol.
    virtual bool emitSymbolAttribute(MCSymbol *Symbol,
                                     MCSymbolAttr Attribute) = 0;
  
    /// 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);
  
    /// Start emitting COFF symbol definition
    ///
    /// \param Symbol - The symbol to have its External & Type fields set.
    virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol);
  
    /// Emit the storage class of the symbol.
    ///
    /// \param StorageClass - The storage class the symbol should have.
    virtual void EmitCOFFSymbolStorageClass(int StorageClass);
  
    /// Emit the type of the symbol.
    ///
    /// \param Type - A COFF type identifier (see COFF::SymbolType in X86COFF.h)
    virtual void EmitCOFFSymbolType(int Type);
  
    /// Marks the end of the symbol definition.
    virtual void EndCOFFSymbolDef();
  
    virtual void EmitCOFFSafeSEH(MCSymbol const *Symbol);
  
    /// Emits the symbol table index of a Symbol into the current section.
    virtual void EmitCOFFSymbolIndex(MCSymbol const *Symbol);
  
    /// Emits a COFF section index.
    ///
    /// \param Symbol - Symbol the section number relocation should point to.
    virtual void EmitCOFFSectionIndex(MCSymbol const *Symbol);
  
    /// Emits a COFF section relative relocation.
    ///
    /// \param Symbol - Symbol the section relative relocation should point to.
    virtual void EmitCOFFSecRel32(MCSymbol const *Symbol, uint64_t Offset);
  
    /// Emits a COFF image relative relocation.
    ///
    /// \param Symbol - Symbol the image relative relocation should point to.
    virtual void EmitCOFFImgRel32(MCSymbol const *Symbol, int64_t Offset);
  
    /// Emits an lcomm directive with XCOFF csect information.
    ///
    /// \param LabelSym - Label on the block of storage.
    /// \param Size - The size of the block of storage.
    /// \param CsectSym - Csect name for the block of storage.
    /// \param ByteAlignment - The alignment of the symbol in bytes. Must be a
    /// power of 2.
    virtual void emitXCOFFLocalCommonSymbol(MCSymbol *LabelSym, uint64_t Size,
                                            MCSymbol *CsectSym,
                                            unsigned ByteAlignment);
  
    /// Emit a symbol's linkage and visibilty with a linkage directive for XCOFF.
    ///
    /// \param Symbol - The symbol to emit.
    /// \param Linkage - The linkage of the symbol to emit.
    /// \param Visibility - The visibility of the symbol to emit or MCSA_Invalid
    /// if the symbol does not have an explicit visibility.
    virtual void emitXCOFFSymbolLinkageWithVisibility(MCSymbol *Symbol,
                                                      MCSymbolAttr Linkage,
                                                      MCSymbolAttr Visibility);
  
    /// Emit a XCOFF .rename directive which creates a synonym for an illegal or
    /// undesirable name.
    ///
    /// \param Name - The name used internally in the assembly for references to
    /// the symbol.
    /// \param Rename - The value to which the Name parameter is
    /// changed at the end of assembly.
    virtual void emitXCOFFRenameDirective(const MCSymbol *Name, StringRef Rename);
  
    /// Emit an ELF .size directive.
    ///
    /// This corresponds to an assembler statement such as:
    ///  .size symbol, expression
    virtual void emitELFSize(MCSymbol *Symbol, const MCExpr *Value);
  
    /// Emit an ELF .symver directive.
    ///
    /// This corresponds to an assembler statement such as:
    ///  .symver _start, foo@@SOME_VERSION
    /// \param AliasName - The versioned alias (i.e. "foo@@SOME_VERSION")
    /// \param Aliasee - The aliased symbol (i.e. "_start")
    virtual void emitELFSymverDirective(StringRef AliasName,
                                        const MCSymbol *Aliasee);
  
    /// Emit a Linker Optimization Hint (LOH) directive.
    /// \param Args - Arguments of the LOH.
    virtual void emitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) {}
  
    /// 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;
  
    /// 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);
  
    /// 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,
                              SMLoc Loc = SMLoc()) = 0;
  
    /// 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
    /// @{
  
    /// 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);
  
    /// Functionally identical to EmitBytes. When emitting textual assembly, this
    /// method uses .byte directives instead of .ascii or .asciz for readability.
    virtual void emitBinaryData(StringRef Data);
  
    /// 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());
  
    /// 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 emitIntValue(APInt Value);
  
    /// Special case of EmitValue that avoids the client having to pass
    /// in a MCExpr for constant integers & prints in Hex format for certain
    /// modes.
    virtual void emitIntValueInHex(uint64_t Value, unsigned Size) {
      emitIntValue(Value, Size);
    }
  
    void emitInt8(uint64_t Value) { emitIntValue(Value, 1); }
    void emitInt16(uint64_t Value) { emitIntValue(Value, 2); }
    void emitInt32(uint64_t Value) { emitIntValue(Value, 4); }
    void emitInt64(uint64_t Value) { emitIntValue(Value, 8); }
  
    /// Special case of EmitValue that avoids the client having to pass
    /// in a MCExpr for constant integers & prints in Hex format for certain
    /// modes, pads the field with leading zeros to Size width
    virtual void emitIntValueInHexWithPadding(uint64_t Value, unsigned Size) {
      emitIntValue(Value, Size);
    }
  
    virtual void emitULEB128Value(const MCExpr *Value);
  
    virtual void emitSLEB128Value(const MCExpr *Value);
  
    /// Special case of EmitULEB128Value that avoids the client having to
    /// pass in a MCExpr for constant integers.
    void emitULEB128IntValue(uint64_t Value, unsigned PadTo = 0);
  
    /// Special case of EmitSLEB128Value that avoids the client having to
    /// pass in a MCExpr for constant integers.
    void emitSLEB128IntValue(int64_t Value);
  
    /// 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);
  
    /// Emit the expression \p Value into the output as a dtprel
    /// (64-bit DTP relative) value.
    ///
    /// This is used to implement assembler directives such as .dtpreldword on
    /// targets that support them.
    virtual void emitDTPRel64Value(const MCExpr *Value);
  
    /// Emit the expression \p Value into the output as a dtprel
    /// (32-bit DTP relative) value.
    ///
    /// This is used to implement assembler directives such as .dtprelword on
    /// targets that support them.
    virtual void emitDTPRel32Value(const MCExpr *Value);
  
    /// Emit the expression \p Value into the output as a tprel
    /// (64-bit TP relative) value.
    ///
    /// This is used to implement assembler directives such as .tpreldword on
    /// targets that support them.
    virtual void emitTPRel64Value(const MCExpr *Value);
  
    /// Emit the expression \p Value into the output as a tprel
    /// (32-bit TP relative) value.
    ///
    /// This is used to implement assembler directives such as .tprelword on
    /// targets that support them.
    virtual void emitTPRel32Value(const MCExpr *Value);
  
    /// 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);
  
    /// 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);
  
    /// Emit NumBytes bytes worth of the value specified by FillValue.
    /// This implements directives such as '.space'.
    void emitFill(uint64_t NumBytes, uint8_t FillValue);
  
    /// Emit \p Size bytes worth of the value specified by \p FillValue.
    ///
    /// This is used to implement assembler directives such as .space or .skip.
    ///
    /// \param NumBytes - The number of bytes to emit.
    /// \param FillValue - The value to use when filling bytes.
    /// \param Loc - The location of the expression for error reporting.
    virtual void emitFill(const MCExpr &NumBytes, uint64_t FillValue,
                          SMLoc Loc = SMLoc());
  
    /// Emit \p NumValues copies of \p Size bytes. Each \p Size bytes is
    /// taken from the lowest order 4 bytes of \p Expr expression.
    ///
    /// This is used to implement assembler directives such as .fill.
    ///
    /// \param NumValues - The number of copies of \p Size bytes to emit.
    /// \param Size - The size (in bytes) of each repeated value.
    /// \param Expr - The expression from which \p Size bytes are used.
    virtual void emitFill(const MCExpr &NumValues, int64_t Size, int64_t Expr,
                          SMLoc Loc = SMLoc());
  
    virtual void emitNops(int64_t NumBytes, int64_t ControlledNopLength,
                          SMLoc Loc);
  
    /// Emit NumBytes worth of zeros.
    /// This function properly handles data in virtual sections.
    void emitZeros(uint64_t NumBytes);
  
    /// 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);
  
    /// 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);
  
    /// 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,
                                   SMLoc Loc);
  
    /// @}
  
    /// Switch to a new logical file.  This is used to implement the '.file
    /// "foo.c"' assembler directive.
    virtual void emitFileDirective(StringRef Filename);
  
    /// Emit the "identifiers" directive.  This implements the
    /// '.ident "version foo"' assembler directive.
    virtual void emitIdent(StringRef IdentString) {}
  
    /// Associate a filename with a specified logical file number.  This
    /// implements the DWARF2 '.file 4 "foo.c"' assembler directive.
    unsigned emitDwarfFileDirective(unsigned FileNo, StringRef Directory,
                                    StringRef Filename,
                                    Optional<MD5::MD5Result> Checksum = None,
                                    Optional<StringRef> Source = None,
                                    unsigned CUID = 0) {
      return cantFail(
          tryEmitDwarfFileDirective(FileNo, Directory, Filename, Checksum,
                                    Source, CUID));
    }
  
    /// Associate a filename with a specified logical file number.
    /// Also associate a directory, optional checksum, and optional source
    /// text with the logical file.  This implements the DWARF2
    /// '.file 4 "dir/foo.c"' assembler directive, and the DWARF5
    /// '.file 4 "dir/foo.c" md5 "..." source "..."' assembler directive.
    virtual Expected<unsigned> tryEmitDwarfFileDirective(
        unsigned FileNo, StringRef Directory, StringRef Filename,
        Optional<MD5::MD5Result> Checksum = None, Optional<StringRef> Source = None,
        unsigned CUID = 0);
  
    /// Specify the "root" file of the compilation, using the ".file 0" extension.
    virtual void emitDwarfFile0Directive(StringRef Directory, StringRef Filename,
                                         Optional<MD5::MD5Result> Checksum,
                                         Optional<StringRef> Source,
                                         unsigned CUID = 0);
  
    virtual void emitCFIBKeyFrame();
  
    /// 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);
  
    /// Associate a filename with a specified logical file number, and also
    /// specify that file's checksum information.  This implements the '.cv_file 4
    /// "foo.c"' assembler directive. Returns true on success.
    virtual bool EmitCVFileDirective(unsigned FileNo, StringRef Filename,
                                     ArrayRef<uint8_t> Checksum,
                                     unsigned ChecksumKind);
  
    /// Introduces a function id for use with .cv_loc.
    virtual bool EmitCVFuncIdDirective(unsigned FunctionId);
  
    /// Introduces an inline call site id for use with .cv_loc. Includes
    /// extra information for inline line table generation.
    virtual bool EmitCVInlineSiteIdDirective(unsigned FunctionId, unsigned IAFunc,
                                             unsigned IAFile, unsigned IALine,
                                             unsigned IACol, SMLoc Loc);
  
    /// This implements the CodeView '.cv_loc' assembler directive.
    virtual void emitCVLocDirective(unsigned FunctionId, unsigned FileNo,
                                    unsigned Line, unsigned Column,
                                    bool PrologueEnd, bool IsStmt,
                                    StringRef FileName, SMLoc Loc);
  
    /// This implements the CodeView '.cv_linetable' assembler directive.
    virtual void emitCVLinetableDirective(unsigned FunctionId,
                                          const MCSymbol *FnStart,
                                          const MCSymbol *FnEnd);
  
    /// This implements the CodeView '.cv_inline_linetable' assembler
    /// directive.
    virtual void emitCVInlineLinetableDirective(unsigned PrimaryFunctionId,
                                                unsigned SourceFileId,
                                                unsigned SourceLineNum,
                                                const MCSymbol *FnStartSym,
                                                const MCSymbol *FnEndSym);
  
    /// This implements the CodeView '.cv_def_range' assembler
    /// directive.
    virtual void emitCVDefRangeDirective(
        ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges,
        StringRef FixedSizePortion);
  
    virtual void emitCVDefRangeDirective(
        ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges,
        codeview::DefRangeRegisterRelHeader DRHdr);
  
    virtual void emitCVDefRangeDirective(
        ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges,
        codeview::DefRangeSubfieldRegisterHeader DRHdr);
  
    virtual void emitCVDefRangeDirective(
        ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges,
        codeview::DefRangeRegisterHeader DRHdr);
  
    virtual void emitCVDefRangeDirective(
        ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges,
        codeview::DefRangeFramePointerRelHeader DRHdr);
  
    /// This implements the CodeView '.cv_stringtable' assembler directive.
    virtual void emitCVStringTableDirective() {}
  
    /// This implements the CodeView '.cv_filechecksums' assembler directive.
    virtual void emitCVFileChecksumsDirective() {}
  
    /// This implements the CodeView '.cv_filechecksumoffset' assembler
    /// directive.
    virtual void emitCVFileChecksumOffsetDirective(unsigned FileNo) {}
  
    /// This implements the CodeView '.cv_fpo_data' assembler directive.
    virtual void EmitCVFPOData(const MCSymbol *ProcSym, SMLoc Loc = {}) {}
  
    /// 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);
  
    /// Emit the absolute difference between two symbols encoded with ULEB128.
    virtual void emitAbsoluteSymbolDiffAsULEB128(const MCSymbol *Hi,
                                                 const MCSymbol *Lo);
  
    virtual MCSymbol *getDwarfLineTableSymbol(unsigned CUID);
    virtual void emitCFISections(bool EH, bool Debug);
    void emitCFIStartProc(bool IsSimple, SMLoc Loc = SMLoc());
    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 emitCFIReturnColumn(int64_t Register);
    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 emitCFINegateRAState();
  
    virtual void EmitWinCFIStartProc(const MCSymbol *Symbol, SMLoc Loc = SMLoc());
    virtual void EmitWinCFIEndProc(SMLoc Loc = SMLoc());
    /// This is used on platforms, such as Windows on ARM64, that require function
    /// or funclet sizes to be emitted in .xdata before the End marker is emitted
    /// for the frame.  We cannot use the End marker, as it is not set at the
    /// point of emitting .xdata, in order to indicate that the frame is active.
    virtual void EmitWinCFIFuncletOrFuncEnd(SMLoc Loc = SMLoc());
    virtual void EmitWinCFIStartChained(SMLoc Loc = SMLoc());
    virtual void EmitWinCFIEndChained(SMLoc Loc = SMLoc());
    virtual void EmitWinCFIPushReg(MCRegister Register, SMLoc Loc = SMLoc());
    virtual void EmitWinCFISetFrame(MCRegister Register, unsigned Offset,
                                    SMLoc Loc = SMLoc());
    virtual void EmitWinCFIAllocStack(unsigned Size, SMLoc Loc = SMLoc());
    virtual void EmitWinCFISaveReg(MCRegister Register, unsigned Offset,
                                   SMLoc Loc = SMLoc());
    virtual void EmitWinCFISaveXMM(MCRegister Register, unsigned Offset,
                                   SMLoc Loc = SMLoc());
    virtual void EmitWinCFIPushFrame(bool Code, SMLoc Loc = SMLoc());
    virtual void EmitWinCFIEndProlog(SMLoc Loc = SMLoc());
    virtual void EmitWinEHHandler(const MCSymbol *Sym, bool Unwind, bool Except,
                                  SMLoc Loc = SMLoc());
    virtual void EmitWinEHHandlerData(SMLoc Loc = SMLoc());
  
    virtual void emitCGProfileEntry(const MCSymbolRefExpr *From,
                                    const MCSymbolRefExpr *To, uint64_t Count);
  
    /// Get the .pdata section used for the given section. Typically the given
    /// section is either the main .text section or some other COMDAT .text
    /// section, but it may be any section containing code.
    MCSection *getAssociatedPDataSection(const MCSection *TextSec);
  
    /// Get the .xdata section used for the given section.
    MCSection *getAssociatedXDataSection(const MCSection *TextSec);
  
    virtual void emitSyntaxDirective();
  
    /// Record a relocation described by the .reloc directive. Return None if
    /// succeeded. Otherwise, return a pair (Name is invalid, error message).
    virtual Optional<std::pair<bool, std::string>>
    emitRelocDirective(const MCExpr &Offset, StringRef Name, const MCExpr *Expr,
                       SMLoc Loc, const MCSubtargetInfo &STI) {
      return None;
    }
  
    virtual void emitAddrsig() {}
    virtual void emitAddrsigSym(const MCSymbol *Sym) {}
  
    /// Emit the given \p Instruction into the current section.
    virtual void emitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI);
  
    /// Emit the a pseudo probe into the current section.
    virtual void emitPseudoProbe(uint64_t Guid, uint64_t Index, uint64_t Type,
                                 uint64_t Attr,
                                 const MCPseudoProbeInlineStack &InlineStack);
  
    /// 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);
  
    /// 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);
  
    /// Ends a bundle-locked group.
    virtual void emitBundleUnlock();
  
    /// 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);
  
    /// Streamer specific finalization.
    virtual void finishImpl();
    /// Finish emission of machine code.
    void Finish(SMLoc EndLoc = SMLoc());
  
    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);
  
  } // end namespace llvm
  
  #endif // LLVM_MC_MCSTREAMER_H
  