C++ Constant::getRelocationInfo方法代码示例

/// getKindForGlobal - This is a top-level target-independent classifier for
/// a global variable.  Given an global variable and information from TM, it
/// classifies the global in a variety of ways that make various target
/// implementations simpler.  The target implementation is free to ignore this
/// extra info of course.
SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
                                                       const TargetMachine &TM){
  assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
         "Can only be used for global definitions");

  Reloc::Model ReloModel = TM.getRelocationModel();

  // Early exit - functions should be always in text sections.
  const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
  if (GVar == 0)
    return SectionKind::getText();

  // Handle thread-local data first.
  if (GVar->isThreadLocal()) {
    if (isSuitableForBSS(GVar))
      return SectionKind::getThreadBSS();
    return SectionKind::getThreadData();
  }

  // Variables with common linkage always get classified as common.
  if (GVar->hasCommonLinkage())
    return SectionKind::getCommon();

  // Variable can be easily put to BSS section.
  if (isSuitableForBSS(GVar)) {
    if (GVar->hasLocalLinkage())
      return SectionKind::getBSSLocal();
    else if (GVar->hasExternalLinkage())
      return SectionKind::getBSSExtern();
    return SectionKind::getBSS();
  }

  Constant *C = GVar->getInitializer();

  // If the global is marked constant, we can put it into a mergable section,
  // a mergable string section, or general .data if it contains relocations.
  if (GVar->isConstant()) {
    // If the initializer for the global contains something that requires a
    // relocation, then we may have to drop this into a wriable data section
    // even though it is marked const.
    switch (C->getRelocationInfo()) {
    default: assert(0 && "unknown relocation info kind");
    case Constant::NoRelocation:
      // If initializer is a null-terminated string, put it in a "cstring"
      // section of the right width.
      if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
        if (const IntegerType *ITy =
              dyn_cast<IntegerType>(ATy->getElementType())) {
          if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
               ITy->getBitWidth() == 32) &&
              IsNullTerminatedString(C)) {
            if (ITy->getBitWidth() == 8)
              return SectionKind::getMergeable1ByteCString();
            if (ITy->getBitWidth() == 16)
              return SectionKind::getMergeable2ByteCString();

            assert(ITy->getBitWidth() == 32 && "Unknown width");
            return SectionKind::getMergeable4ByteCString();
          }
        }
      }

      // Otherwise, just drop it into a mergable constant section.  If we have
      // a section for this size, use it, otherwise use the arbitrary sized
      // mergable section.
      switch (TM.getTargetData()->getTypeAllocSize(C->getType())) {
      case 4:  return SectionKind::getMergeableConst4();
      case 8:  return SectionKind::getMergeableConst8();
      case 16: return SectionKind::getMergeableConst16();
      default: return SectionKind::getMergeableConst();
      }

    case Constant::LocalRelocation:
      // In static relocation model, the linker will resolve all addresses, so
      // the relocation entries will actually be constants by the time the app
      // starts up.  However, we can't put this into a mergable section, because
      // the linker doesn't take relocations into consideration when it tries to
      // merge entries in the section.
      if (ReloModel == Reloc::Static)
        return SectionKind::getReadOnly();

      // Otherwise, the dynamic linker needs to fix it up, put it in the
      // writable data.rel.local section.
      return SectionKind::getReadOnlyWithRelLocal();

    case Constant::GlobalRelocations:
      // In static relocation model, the linker will resolve all addresses, so
      // the relocation entries will actually be constants by the time the app
      // starts up.  However, we can't put this into a mergable section, because
      // the linker doesn't take relocations into consideration when it tries to
      // merge entries in the section.
      if (ReloModel == Reloc::Static)
        return SectionKind::getReadOnly();

      // Otherwise, the dynamic linker needs to fix it up, put it in the
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