C++ MCSymbol::isUndefined方法代码示例

bool MachObjectWriter::doesSymbolRequireExternRelocation(const MCSymbol &S) {
  // Undefined symbols are always extern.
  if (S.isUndefined())
    return true;

  // References to weak definitions require external relocation entries; the
  // definition may not always be the one in the same object file.
  if (cast<MCSymbolMachO>(S).isWeakDefinition())
    return true;

  // Otherwise, we can use an internal relocation.
  return false;
}

void MCELFStreamer::ChangeSection(const MCSection *Section,
                                  const MCExpr *Subsection) {
  MCSectionData *CurSection = getCurrentSectionData();
  if (CurSection && CurSection->isBundleLocked())
    report_fatal_error("Unterminated .bundle_lock when changing a section");

  MCAssembler &Asm = getAssembler();
  auto *SectionELF = static_cast<const MCSectionELF *>(Section);
  const MCSymbol *Grp = SectionELF->getGroup();
  if (Grp)
    Asm.getOrCreateSymbolData(*Grp);

  this->MCObjectStreamer::ChangeSection(Section, Subsection);
  MCSymbol *SectionSymbol = getContext().getOrCreateSectionSymbol(*SectionELF);
  if (SectionSymbol->isUndefined()) {
    EmitLabel(SectionSymbol);
    MCELF::SetType(Asm.getSymbolData(*SectionSymbol), ELF::STT_SECTION);
  }
}

void PTXAsmPrinter::EmitVariableDeclaration(const GlobalVariable *gv) {
  // Check to see if this is a special global used by LLVM, if so, emit it.
  if (EmitSpecialLLVMGlobal(gv))
    return;

  MCSymbol *gvsym = Mang->getSymbol(gv);

  assert(gvsym->isUndefined() && "Cannot define a symbol twice!");

  std::string decl;

  // check if it is defined in some other translation unit
  if (gv->isDeclaration())
    decl += ".extern ";

  // state space: e.g., .global
  decl += ".";
  decl += getStateSpaceName(gv->getType()->getAddressSpace());
  decl += " ";

  // alignment (optional)
  unsigned alignment = gv->getAlignment();
  if (alignment != 0) {
    decl += ".align ";
    decl += utostr(Log2_32(gv->getAlignment()));
    decl += " ";
  }

  // TODO: add types
  decl += ".s32 ";

  decl += gvsym->getName();

  if (ArrayType::classof(gv->getType()) || PointerType::classof(gv->getType()))
    decl += "[]";

  decl += ";";

  OutStreamer.EmitRawText(Twine(decl));

  OutStreamer.AddBlankLine();
}

static MCSymbol *smallData(AsmPrinter &AP, const MachineInstr &MI,
                           MCStreamer &OutStreamer, const MCOperand &Imm,
                           int AlignSize) {
  MCSymbol *Sym;
  int64_t Value;
  if (Imm.getExpr()->evaluateAsAbsolute(Value)) {
    StringRef sectionPrefix;
    std::string ImmString;
    StringRef Name;
    if (AlignSize == 8) {
       Name = ".CONST_0000000000000000";
       sectionPrefix = ".gnu.linkonce.l8";
       ImmString = utohexstr(Value);
    } else {
       Name = ".CONST_00000000";
       sectionPrefix = ".gnu.linkonce.l4";
       ImmString = utohexstr(static_cast<uint32_t>(Value));
    }

    std::string symbolName =   // Yes, leading zeros are kept.
      Name.drop_back(ImmString.size()).str() + ImmString;
    std::string sectionName = sectionPrefix.str() + symbolName;

    MCSectionELF *Section = OutStreamer.getContext().getELFSection(
        sectionName, ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
    OutStreamer.SwitchSection(Section);

    Sym = AP.OutContext.getOrCreateSymbol(Twine(symbolName));
    if (Sym->isUndefined()) {
      OutStreamer.EmitLabel(Sym);
      OutStreamer.EmitSymbolAttribute(Sym, MCSA_Global);
      OutStreamer.EmitIntValue(Value, AlignSize);
      OutStreamer.EmitCodeAlignment(AlignSize);
    }
  } else {
    assert(Imm.isExpr() && "Expected expression and found none");
    const MachineOperand &MO = MI.getOperand(1);
    assert(MO.isGlobal() || MO.isCPI() || MO.isJTI());
    MCSymbol *MOSymbol = nullptr;
    if (MO.isGlobal())
      MOSymbol = AP.getSymbol(MO.getGlobal());
    else if (MO.isCPI())
      MOSymbol = AP.GetCPISymbol(MO.getIndex());
    else if (MO.isJTI())
      MOSymbol = AP.GetJTISymbol(MO.getIndex());
    else
      llvm_unreachable("Unknown operand type!");

    StringRef SymbolName = MOSymbol->getName();
    std::string LitaName = ".CONST_" + SymbolName.str();

    MCSectionELF *Section = OutStreamer.getContext().getELFSection(
        ".lita", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);

    OutStreamer.SwitchSection(Section);
    Sym = AP.OutContext.getOrCreateSymbol(Twine(LitaName));
    if (Sym->isUndefined()) {
      OutStreamer.EmitLabel(Sym);
      OutStreamer.EmitSymbolAttribute(Sym, MCSA_Local);
      OutStreamer.EmitValue(Imm.getExpr(), AlignSize);
      OutStreamer.EmitCodeAlignment(AlignSize);
    }
  }
  return Sym;
}

/// ParseDirectiveComm
///  ::= ( .comm | .lcomm ) identifier , size_expression [ , align_expression ]
bool MachOAsmParser::ParseDirectiveComm(bool IsLocal) {
  SMLoc IDLoc = Lexer.getLoc();
  StringRef Name;
  if (ParseIdentifier(Name))
    return TokError("expected identifier in directive");

  // Handle the identifier as the key symbol.
  MCSymbol *Sym = CreateSymbol(Name);

  if (Lexer.isNot(AsmToken::Comma))
    return TokError("unexpected token in directive");
  Lex();

  int64_t Size;
  SMLoc SizeLoc = Lexer.getLoc();
  if (ParseAbsoluteExpression(Size))
    return true;

  int64_t Pow2Alignment = 0;
  SMLoc Pow2AlignmentLoc;
  if (Lexer.is(AsmToken::Comma)) {
    Lex();
    Pow2AlignmentLoc = Lexer.getLoc();
    if (ParseAbsoluteExpression(Pow2Alignment))
      return true;

    // If this target takes alignments in bytes (not log) validate and convert.
    if (Lexer.getMAI().getAlignmentIsInBytes()) {
      if (!isPowerOf2_64(Pow2Alignment))
        return Error(Pow2AlignmentLoc, "alignment must be a power of 2");
      Pow2Alignment = Log2_64(Pow2Alignment);
    }
  }

  if (Lexer.isNot(AsmToken::EndOfStatement))
    return TokError("unexpected token in '.comm' or '.lcomm' directive");

  Lex();

  // NOTE: a size of zero for a .comm should create a undefined symbol
  // but a size of .lcomm creates a bss symbol of size zero.
  if (Size < 0)
    return Error(SizeLoc, "invalid '.comm' or '.lcomm' directive size, can't "
                 "be less than zero");

  // NOTE: The alignment in the directive is a power of 2 value, the assembler
  // may internally end up wanting an alignment in bytes.
  // FIXME: Diagnose overflow.
  if (Pow2Alignment < 0)
    return Error(Pow2AlignmentLoc, "invalid '.comm' or '.lcomm' directive "
                 "alignment, can't be less than zero");

  if (!Sym->isUndefined())
    return Error(IDLoc, "invalid symbol redefinition");

  // '.lcomm' is equivalent to '.zerofill'.
  // Create the Symbol as a common or local common with Size and Pow2Alignment
  if (IsLocal) {
    Out.EmitZerofill(Ctx.getMachOSection("__DATA", "__bss",
                                         MCSectionMachO::S_ZEROFILL, 0,
                                         SectionKind::getBSS()),
                     Sym, Size, 1 << Pow2Alignment);
    return false;
  }

  Out.EmitCommonSymbol(Sym, Size, 1 << Pow2Alignment);
  return false;
}

void PTXAsmPrinter::EmitVariableDeclaration(const GlobalVariable *gv) {
  // Check to see if this is a special global used by LLVM, if so, emit it.
  if (EmitSpecialLLVMGlobal(gv))
    return;

  MCSymbol *gvsym = Mang->getSymbol(gv);

  assert(gvsym->isUndefined() && "Cannot define a symbol twice!");

  SmallString<128> decl;
  raw_svector_ostream os(decl);

  // check if it is defined in some other translation unit
  if (gv->isDeclaration())
    os << ".extern ";

  // state space: e.g., .global
  os << '.' << getStateSpaceName(gv->getType()->getAddressSpace()) << ' ';

  // alignment (optional)
  unsigned alignment = gv->getAlignment();
  if (alignment != 0)
    os << ".align " << gv->getAlignment() << ' ';


  if (PointerType::classof(gv->getType())) {
    PointerType* pointerTy = dyn_cast<PointerType>(gv->getType());
    Type* elementTy = pointerTy->getElementType();

    if (elementTy->isArrayTy()) {
      assert(elementTy->isArrayTy() && "Only pointers to arrays are supported");

      ArrayType* arrayTy = dyn_cast<ArrayType>(elementTy);
      elementTy = arrayTy->getElementType();

      unsigned numElements = arrayTy->getNumElements();

      while (elementTy->isArrayTy()) {
        arrayTy = dyn_cast<ArrayType>(elementTy);
        elementTy = arrayTy->getElementType();

        numElements *= arrayTy->getNumElements();
      }

      // FIXME: isPrimitiveType() == false for i16?
      assert(elementTy->isSingleValueType() &&
             "Non-primitive types are not handled");

      // Find the size of the element in bits
      unsigned elementSize = elementTy->getPrimitiveSizeInBits();

      os << ".b" << elementSize << ' ' << gvsym->getName()
         << '[' << numElements << ']';
    } else {
      os << ".b8" << gvsym->getName() << "[]";
    }

    // handle string constants (assume ConstantArray means string)
    if (gv->hasInitializer()) {
      const Constant *C = gv->getInitializer();
      if (const ConstantArray *CA = dyn_cast<ConstantArray>(C)) {
        os << " = {";

        for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
          if (i > 0)
            os << ',';

          os << "0x";
          os.write_hex(cast<ConstantInt>(CA->getOperand(i))->getZExtValue());
        }

        os << '}';
      }
    }
  } else {
    // Note: this is currently the fall-through case and most likely generates
    //       incorrect code.
    os << getTypeName(gv->getType()) << ' ' << gvsym->getName();

    if (isa<ArrayType>(gv->getType()) || isa<PointerType>(gv->getType()))
      os << "[]";
  }

  os << ';';

  OutStreamer.EmitRawText(os.str());
  OutStreamer.AddBlankLine();
}