text: //===-- HexagonTargetObjectFile.cpp ---------------------------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file contains the declarations of the HexagonTargetAsmInfo properties.
  //
  //===----------------------------------------------------------------------===//
  #define DEBUG_TYPE "hexagon-sdata"
  
  #include "HexagonTargetMachine.h"
  #include "HexagonTargetObjectFile.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/DerivedTypes.h"
  #include "llvm/IR/Function.h"
  #include "llvm/IR/GlobalVariable.h"
  #include "llvm/MC/MCContext.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/ELF.h"
  
  using namespace llvm;
  
  static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold",
    cl::init(8), cl::Hidden,
    cl::desc("The maximum size of an object in the sdata section"));
  
  static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false),
    cl::Hidden, cl::desc("Disable small data sections sorting"));
  
  static cl::opt<bool> StaticsInSData("hexagon-statics-in-small-data",
    cl::init(false), cl::Hidden, cl::ZeroOrMore,
    cl::desc("Allow static variables in .sdata"));
  
  static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
    cl::Hidden, cl::init(false),
    cl::desc("Trace global value placement"));
  
  // TraceGVPlacement controls messages for all builds. For builds with assertions
  // (debug or release), messages are also controlled by the usual debug flags
  // (e.g. -debug and -debug-only=globallayout)
  #define TRACE_TO(s, X) s << X
  #ifdef NDEBUG
  #define TRACE(X) do { if (TraceGVPlacement) { TRACE_TO(errs(), X); } } while (0)
  #else
  #define TRACE(X) \
    do { \
      if (TraceGVPlacement) { TRACE_TO(errs(), X); } \
      else { DEBUG( TRACE_TO(dbgs(), X) ); } \
    } while (0)
  #endif
  
  // Returns true if the section name is such that the symbol will be put
  // in a small data section.
  // For instance, global variables with section attributes such as ".sdata"
  // ".sdata.*", ".sbss", and ".sbss.*" will go into small data.
  static bool isSmallDataSection(StringRef Sec) {
    // sectionName is either ".sdata" or ".sbss". Looking for an exact match
    // obviates the need for checks for section names such as ".sdatafoo".
    if (Sec.equals(".sdata") || Sec.equals(".sbss") || Sec.equals(".scommon"))
      return true;
    // If either ".sdata." or ".sbss." is a substring of the section name
    // then put the symbol in small data.
    return Sec.find(".sdata.") != StringRef::npos ||
           Sec.find(".sbss.") != StringRef::npos ||
           Sec.find(".scommon.") != StringRef::npos;
  }
  
  
  static const char *getSectionSuffixForSize(unsigned Size) {
    switch (Size) {
    default:
      return "";
    case 1:
      return ".1";
    case 2:
      return ".2";
    case 4:
      return ".4";
    case 8:
      return ".8";
    }
  }
  
  void HexagonTargetObjectFile::Initialize(MCContext &Ctx,
        const TargetMachine &TM) {
    TargetLoweringObjectFileELF::Initialize(Ctx, TM);
    InitializeELF(TM.Options.UseInitArray);
  
    SmallDataSection =
      getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
                                 ELF::SHF_WRITE | ELF::SHF_ALLOC |
                                 ELF::SHF_HEX_GPREL);
    SmallBSSSection =
      getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
                                 ELF::SHF_WRITE | ELF::SHF_ALLOC |
                                 ELF::SHF_HEX_GPREL);
  }
  
  
  MCSection *HexagonTargetObjectFile::SelectSectionForGlobal(
        const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
        const TargetMachine &TM) const {
    TRACE("[SelectSectionForGlobal] GV(" << GV->getName() << ") ");
    TRACE("input section(" << GV->getSection() << ") ");
  
    TRACE((GV->hasPrivateLinkage() ? "private_linkage " : "")
           << (GV->hasLocalLinkage() ? "local_linkage " : "")
           << (GV->hasInternalLinkage() ? "internal " : "")
           << (GV->hasExternalLinkage() ? "external " : "")
           << (GV->hasCommonLinkage() ? "common_linkage " : "")
           << (GV->hasCommonLinkage() ? "common " : "" )
           << (Kind.isCommon() ? "kind_common " : "" )
           << (Kind.isBSS() ? "kind_bss " : "" )
           << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
  
    if (isGlobalInSmallSection(GV, TM))
      return selectSmallSectionForGlobal(GV, Kind, Mang, TM);
  
    if (Kind.isCommon()) {
      // This is purely for LTO+Linker Script because commons don't really have a
      // section. However, the BitcodeSectionWriter pass will query for the
      // sections of commons (and the linker expects us to know their section) so
      // we'll return one here.
      return BSSSection;
    }
  
    TRACE("default_ELF_section\n");
    // Otherwise, we work the same as ELF.
    return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind,
                Mang, TM);
  }
  
  
  MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal(
        const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
        const TargetMachine &TM) const {
    TRACE("[getExplicitSectionGlobal] GV(" << GV->getName() << ") from("
          << GV->getSection() << ") ");
    TRACE((GV->hasPrivateLinkage() ? "private_linkage " : "")
           << (GV->hasLocalLinkage() ? "local_linkage " : "")
           << (GV->hasInternalLinkage() ? "internal " : "")
           << (GV->hasExternalLinkage() ? "external " : "")
           << (GV->hasCommonLinkage() ? "common_linkage " : "")
           << (GV->hasCommonLinkage() ? "common " : "" )
           << (Kind.isCommon() ? "kind_common " : "" )
           << (Kind.isBSS() ? "kind_bss " : "" )
           << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
  
    if (GV->hasSection()) {
      StringRef Section = GV->getSection();
      if (Section.find(".access.text.group") != StringRef::npos)
        return getContext().getELFSection(GV->getSection(), ELF::SHT_PROGBITS,
                                          ELF::SHF_ALLOC | ELF::SHF_EXECINSTR);
      if (Section.find(".access.data.group") != StringRef::npos)
        return getContext().getELFSection(GV->getSection(), ELF::SHT_PROGBITS,
                                          ELF::SHF_WRITE | ELF::SHF_ALLOC);
    }
  
    if (isGlobalInSmallSection(GV, TM))
      return selectSmallSectionForGlobal(GV, Kind, Mang, TM);
  
    // Otherwise, we work the same as ELF.
    TRACE("default_ELF_section\n");
    return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GV, Kind,
              Mang, TM);
  }
  
  
  /// Return true if this global value should be placed into small data/bss
  /// section.
  bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalValue *GV,
        const TargetMachine &TM) const {
    // Only global variables, not functions.
    DEBUG(dbgs() << "Checking if value is in small-data, -G"
                 << SmallDataThreshold << ": \"" << GV->getName() << "\": ");
    const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
    if (!GVar) {
      DEBUG(dbgs() << "no, not a global variable\n");
      return false;
    }
  
    // Globals with external linkage that have an original section set must be
    // emitted to that section, regardless of whether we would put them into
    // small data or not. This is how we can support mixing -G0/-G8 in LTO.
    if (GVar->hasSection()) {
      bool IsSmall = isSmallDataSection(GVar->getSection());
      DEBUG(dbgs() << (IsSmall ? "yes" : "no") << ", has section: "
                   << GVar->getSection() << '\n');
      return IsSmall;
    }
  
    if (GVar->isConstant()) {
      DEBUG(dbgs() << "no, is a constant\n");
      return false;
    }
  
    bool IsLocal = GVar->hasLocalLinkage();
    if (!StaticsInSData && IsLocal) {
      DEBUG(dbgs() << "no, is static\n");
      return false;
    }
  
    Type *GType = GVar->getType();
    if (PointerType *PT = dyn_cast<PointerType>(GType))
      GType = PT->getElementType();
  
    if (isa<ArrayType>(GType)) {
      DEBUG(dbgs() << "no, is an array\n");
      return false;
    }
  
    // If the type is a struct with no body provided, treat is conservatively.
    // There cannot be actual definitions of object of such a type in this CU
    // (only references), so assuming that they are not in sdata is safe. If
    // these objects end up in the sdata, the references will still be valid.
    if (StructType *ST = dyn_cast<StructType>(GType)) {
      if (ST->isOpaque()) {
        DEBUG(dbgs() << "no, has opaque type\n");
        return false;
      }
    }
  
    unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType);
    if (Size == 0) {
      DEBUG(dbgs() << "no, has size 0\n");
      return false;
    }
    if (Size > SmallDataThreshold) {
      DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
      return false;
    }
  
    DEBUG(dbgs() << "yes\n");
    return true;
  }
  
  
  bool HexagonTargetObjectFile::isSmallDataEnabled() const {
    return SmallDataThreshold > 0;
  }
  
  
  unsigned HexagonTargetObjectFile::getSmallDataSize() const {
    return SmallDataThreshold;
  }
  
  
  /// Descends any type down to "elementary" components,
  /// discovering the smallest addressable one.
  /// If zero is returned, declaration will not be modified.
  unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
        const GlobalValue *GV, const TargetMachine &TM) const {
    // Assign the smallest element access size to the highest
    // value which assembler can handle.
    unsigned SmallestElement = 8;
  
    if (!Ty)
      return 0;
    switch (Ty->getTypeID()) {
    case Type::StructTyID: {
      const StructType *STy = cast<const StructType>(Ty);
      for (auto &E : STy->elements()) {
        unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
        if (AtomicSize < SmallestElement)
          SmallestElement = AtomicSize;
      }
      return (STy->getNumElements() == 0) ? 0 : SmallestElement;
    }
    case Type::ArrayTyID: {
      const ArrayType *ATy = cast<const ArrayType>(Ty);
      return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
    }
    case Type::VectorTyID: {
      const VectorType *PTy = cast<const VectorType>(Ty);
      return getSmallestAddressableSize(PTy->getElementType(), GV, TM);
    }
    case Type::PointerTyID:
    case Type::HalfTyID:
    case Type::FloatTyID:
    case Type::DoubleTyID:
    case Type::IntegerTyID: {
      const DataLayout &DL = GV->getParent()->getDataLayout();
      // It is unfortunate that DL's function take non-const Type*.
      return DL.getTypeAllocSize(const_cast<Type*>(Ty));
    }
    case Type::FunctionTyID:
    case Type::VoidTyID:
    case Type::X86_FP80TyID:
    case Type::FP128TyID:
    case Type::PPC_FP128TyID:
    case Type::LabelTyID:
    case Type::MetadataTyID:
    case Type::X86_MMXTyID:
    case Type::TokenTyID:
      return 0;
    }
  
    return 0;
  }
  
  
  MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
        const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
        const TargetMachine &TM) const {
    const Type *GTy = GV->getType()->getElementType();
    unsigned Size = getSmallestAddressableSize(GTy, GV, TM);
  
    // If we have -ffunction-section or -fdata-section then we should emit the
    // global value to a unique section specifically for it... even for sdata.
    bool EmitUniquedSection = TM.getDataSections();
  
    TRACE("Small data. Size(" << Size << ")");
    // Handle Small Section classification here.
    if (Kind.isBSS() || Kind.isBSSLocal()) {
      // If -mno-sort-sda is not set, find out smallest accessible entity in
      // declaration and add it to the section name string.
      // Note. It does not track the actual usage of the value, only its de-
      // claration. Also, compiler adds explicit pad fields to some struct
      // declarations - they are currently counted towards smallest addres-
      // sable entity.
      if (NoSmallDataSorting) {
        TRACE(" default sbss\n");
        return SmallBSSSection;
      }
  
      StringRef Prefix(".sbss");
      SmallString<128> Name(Prefix);
      Name.append(getSectionSuffixForSize(Size));
  
      if (EmitUniquedSection) {
        Name.append(".");
        Name.append(GV->getName());
      }
      TRACE(" unique sbss(" << Name << ")\n");
      return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
                  ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
    }
  
    if (Kind.isCommon()) {
      // This is purely for LTO+Linker Script because commons don't really have a
      // section. However, the BitcodeSectionWriter pass will query for the
      // sections of commons (and the linker expects us to know their section) so
      // we'll return one here.
      if (NoSmallDataSorting)
        return BSSSection;
  
      Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
      TRACE(" small COMMON (" << Name << ")\n");
  
      return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
                                        ELF::SHF_WRITE | ELF::SHF_ALLOC |
                                        ELF::SHF_HEX_GPREL);
    }
  
    // We could have changed sdata object to a constant... in this
    // case the Kind could be wrong for it.
    if (Kind.isMergeableConst()) {
      TRACE(" const_object_as_data ");
      const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
      if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
        Kind = SectionKind::getData();
    }
  
    if (Kind.isData()) {
      if (NoSmallDataSorting) {
        TRACE(" default sdata\n");
        return SmallDataSection;
      }
  
      StringRef Prefix(".sdata");
      SmallString<128> Name(Prefix);
      Name.append(getSectionSuffixForSize(Size));
  
      if (EmitUniquedSection) {
        Name.append(".");
        Name.append(GV->getName());
      }
      TRACE(" unique sdata(" << Name << ")\n");
      return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
                  ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
    }
  
    TRACE("default ELF section\n");
    // Otherwise, we work the same as ELF.
    return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind,
                Mang, TM);
  }
  