text: //===- lib/MC/MCWasmStreamer.cpp - Wasm Object Output ---------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file assembles .s files and emits Wasm .o object files.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/MC/MCWasmStreamer.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/MC/MCAsmBackend.h"
  #include "llvm/MC/MCAsmLayout.h"
  #include "llvm/MC/MCAssembler.h"
  #include "llvm/MC/MCCodeEmitter.h"
  #include "llvm/MC/MCContext.h"
  #include "llvm/MC/MCExpr.h"
  #include "llvm/MC/MCInst.h"
  #include "llvm/MC/MCObjectStreamer.h"
  #include "llvm/MC/MCSection.h"
  #include "llvm/MC/MCSectionWasm.h"
  #include "llvm/MC/MCSymbol.h"
  #include "llvm/MC/MCSymbolWasm.h"
  #include "llvm/MC/MCValue.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/TargetRegistry.h"
  #include "llvm/Support/raw_ostream.h"
  
  using namespace llvm;
  
  MCWasmStreamer::~MCWasmStreamer() {}
  
  void MCWasmStreamer::mergeFragment(MCDataFragment *DF, MCDataFragment *EF) {
    flushPendingLabels(DF, DF->getContents().size());
  
    for (unsigned i = 0, e = EF->getFixups().size(); i != e; ++i) {
      EF->getFixups()[i].setOffset(EF->getFixups()[i].getOffset() +
                                   DF->getContents().size());
      DF->getFixups().push_back(EF->getFixups()[i]);
    }
    if (DF->getSubtargetInfo() == nullptr && EF->getSubtargetInfo())
      DF->setHasInstructions(*EF->getSubtargetInfo());
    DF->getContents().append(EF->getContents().begin(), EF->getContents().end());
  }
  
  void MCWasmStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
    // Let the target do whatever target specific stuff it needs to do.
    getAssembler().getBackend().handleAssemblerFlag(Flag);
  
    // Do any generic stuff we need to do.
    llvm_unreachable("invalid assembler flag!");
  }
  
  void MCWasmStreamer::ChangeSection(MCSection *Section,
                                     const MCExpr *Subsection) {
    MCAssembler &Asm = getAssembler();
    auto *SectionWasm = cast<MCSectionWasm>(Section);
    const MCSymbol *Grp = SectionWasm->getGroup();
    if (Grp)
      Asm.registerSymbol(*Grp);
  
    this->MCObjectStreamer::ChangeSection(Section, Subsection);
    Asm.registerSymbol(*Section->getBeginSymbol());
  }
  
  void MCWasmStreamer::EmitWeakReference(MCSymbol *Alias,
                                         const MCSymbol *Symbol) {
    getAssembler().registerSymbol(*Symbol);
    const MCExpr *Value = MCSymbolRefExpr::create(
        Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
    Alias->setVariableValue(Value);
  }
  
  bool MCWasmStreamer::EmitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
    assert(Attribute != MCSA_IndirectSymbol && "indirect symbols not supported");
  
    auto *Symbol = cast<MCSymbolWasm>(S);
  
    // Adding a symbol attribute always introduces the symbol; note that an
    // important side effect of calling registerSymbol here is to register the
    // symbol with the assembler.
    getAssembler().registerSymbol(*Symbol);
  
    switch (Attribute) {
    case MCSA_LazyReference:
    case MCSA_Reference:
    case MCSA_SymbolResolver:
    case MCSA_PrivateExtern:
    case MCSA_WeakDefinition:
    case MCSA_WeakDefAutoPrivate:
    case MCSA_Invalid:
    case MCSA_IndirectSymbol:
    case MCSA_Protected:
      return false;
  
    case MCSA_Hidden:
      Symbol->setHidden(true);
      break;
  
    case MCSA_Weak:
    case MCSA_WeakReference:
      Symbol->setWeak(true);
      Symbol->setExternal(true);
      break;
  
    case MCSA_Global:
      Symbol->setExternal(true);
      break;
  
    case MCSA_ELF_TypeFunction:
      Symbol->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
      break;
  
    case MCSA_ELF_TypeObject:
      break;
  
    default:
      // unrecognized directive
      llvm_unreachable("unexpected MCSymbolAttr");
      return false;
    }
  
    return true;
  }
  
  void MCWasmStreamer::EmitCommonSymbol(MCSymbol *S, uint64_t Size,
                                        unsigned ByteAlignment) {
    llvm_unreachable("Common symbols are not yet implemented for Wasm");
  }
  
  void MCWasmStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
    cast<MCSymbolWasm>(Symbol)->setSize(Value);
  }
  
  void MCWasmStreamer::EmitLocalCommonSymbol(MCSymbol *S, uint64_t Size,
                                             unsigned ByteAlignment) {
    llvm_unreachable("Local common symbols are not yet implemented for Wasm");
  }
  
  void MCWasmStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
                                     SMLoc Loc) {
    MCObjectStreamer::EmitValueImpl(Value, Size, Loc);
  }
  
  void MCWasmStreamer::EmitValueToAlignment(unsigned ByteAlignment, int64_t Value,
                                            unsigned ValueSize,
                                            unsigned MaxBytesToEmit) {
    MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value, ValueSize,
                                           MaxBytesToEmit);
  }
  
  void MCWasmStreamer::EmitIdent(StringRef IdentString) {
    // TODO(sbc): Add the ident section once we support mergable strings
    // sections in the object format
  }
  
  void MCWasmStreamer::EmitInstToFragment(const MCInst &Inst,
                                          const MCSubtargetInfo &STI) {
    this->MCObjectStreamer::EmitInstToFragment(Inst, STI);
  }
  
  void MCWasmStreamer::EmitInstToData(const MCInst &Inst,
                                      const MCSubtargetInfo &STI) {
    MCAssembler &Assembler = getAssembler();
    SmallVector<MCFixup, 4> Fixups;
    SmallString<256> Code;
    raw_svector_ostream VecOS(Code);
    Assembler.getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
  
    // Append the encoded instruction to the current data fragment (or create a
    // new such fragment if the current fragment is not a data fragment).
    MCDataFragment *DF = getOrCreateDataFragment();
  
    // Add the fixups and data.
    for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
      Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
      DF->getFixups().push_back(Fixups[i]);
    }
    DF->setHasInstructions(STI);
    DF->getContents().append(Code.begin(), Code.end());
  }
  
  void MCWasmStreamer::FinishImpl() {
    EmitFrames(nullptr);
  
    this->MCObjectStreamer::FinishImpl();
  }
  
  MCStreamer *llvm::createWasmStreamer(MCContext &Context,
                                       std::unique_ptr<MCAsmBackend> &&MAB,
                                       std::unique_ptr<MCObjectWriter> &&OW,
                                       std::unique_ptr<MCCodeEmitter> &&CE,
                                       bool RelaxAll) {
    MCWasmStreamer *S =
        new MCWasmStreamer(Context, std::move(MAB), std::move(OW), std::move(CE));
    if (RelaxAll)
      S->getAssembler().setRelaxAll(true);
    return S;
  }
  
  void MCWasmStreamer::EmitThumbFunc(MCSymbol *Func) {
    llvm_unreachable("Generic Wasm doesn't support this directive");
  }
  
  void MCWasmStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
    llvm_unreachable("Wasm doesn't support this directive");
  }
  
  void MCWasmStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
                                    uint64_t Size, unsigned ByteAlignment,
                                    SMLoc Loc) {
    llvm_unreachable("Wasm doesn't support this directive");
  }
  
  void MCWasmStreamer::EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
                                      uint64_t Size, unsigned ByteAlignment) {
    llvm_unreachable("Wasm doesn't support this directive");
  }
  