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      1 //===-- HexagonTargetObjectFile.cpp ---------------------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file contains the declarations of the HexagonTargetAsmInfo properties.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 #define DEBUG_TYPE "hexagon-sdata"
     14 
     15 #include "HexagonTargetMachine.h"
     16 #include "HexagonTargetObjectFile.h"
     17 #include "llvm/IR/DataLayout.h"
     18 #include "llvm/IR/DerivedTypes.h"
     19 #include "llvm/IR/Function.h"
     20 #include "llvm/IR/GlobalVariable.h"
     21 #include "llvm/MC/MCContext.h"
     22 #include "llvm/Support/CommandLine.h"
     23 #include "llvm/Support/ELF.h"
     24 
     25 using namespace llvm;
     26 
     27 static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold",
     28   cl::init(8), cl::Hidden,
     29   cl::desc("The maximum size of an object in the sdata section"));
     30 
     31 static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false),
     32   cl::Hidden, cl::desc("Disable small data sections sorting"));
     33 
     34 static cl::opt<bool> StaticsInSData("hexagon-statics-in-small-data",
     35   cl::init(false), cl::Hidden, cl::ZeroOrMore,
     36   cl::desc("Allow static variables in .sdata"));
     37 
     38 static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
     39   cl::Hidden, cl::init(false),
     40   cl::desc("Trace global value placement"));
     41 
     42 // TraceGVPlacement controls messages for all builds. For builds with assertions
     43 // (debug or release), messages are also controlled by the usual debug flags
     44 // (e.g. -debug and -debug-only=globallayout)
     45 #define TRACE_TO(s, X) s << X
     46 #ifdef NDEBUG
     47 #define TRACE(X) do { if (TraceGVPlacement) { TRACE_TO(errs(), X); } } while (0)
     48 #else
     49 #define TRACE(X) \
     50   do { \
     51     if (TraceGVPlacement) { TRACE_TO(errs(), X); } \
     52     else { DEBUG( TRACE_TO(dbgs(), X) ); } \
     53   } while (0)
     54 #endif
     55 
     56 // Returns true if the section name is such that the symbol will be put
     57 // in a small data section.
     58 // For instance, global variables with section attributes such as ".sdata"
     59 // ".sdata.*", ".sbss", and ".sbss.*" will go into small data.
     60 static bool isSmallDataSection(StringRef Sec) {
     61   // sectionName is either ".sdata" or ".sbss". Looking for an exact match
     62   // obviates the need for checks for section names such as ".sdatafoo".
     63   if (Sec.equals(".sdata") || Sec.equals(".sbss") || Sec.equals(".scommon"))
     64     return true;
     65   // If either ".sdata." or ".sbss." is a substring of the section name
     66   // then put the symbol in small data.
     67   return Sec.find(".sdata.") != StringRef::npos ||
     68          Sec.find(".sbss.") != StringRef::npos ||
     69          Sec.find(".scommon.") != StringRef::npos;
     70 }
     71 
     72 
     73 static const char *getSectionSuffixForSize(unsigned Size) {
     74   switch (Size) {
     75   default:
     76     return "";
     77   case 1:
     78     return ".1";
     79   case 2:
     80     return ".2";
     81   case 4:
     82     return ".4";
     83   case 8:
     84     return ".8";
     85   }
     86 }
     87 
     88 void HexagonTargetObjectFile::Initialize(MCContext &Ctx,
     89       const TargetMachine &TM) {
     90   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
     91   InitializeELF(TM.Options.UseInitArray);
     92 
     93   SmallDataSection =
     94     getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
     95                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
     96                                ELF::SHF_HEX_GPREL);
     97   SmallBSSSection =
     98     getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
     99                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
    100                                ELF::SHF_HEX_GPREL);
    101 }
    102 
    103 
    104 MCSection *HexagonTargetObjectFile::SelectSectionForGlobal(
    105       const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
    106       const TargetMachine &TM) const {
    107   TRACE("[SelectSectionForGlobal] GV(" << GV->getName() << ") ");
    108   TRACE("input section(" << GV->getSection() << ") ");
    109 
    110   TRACE((GV->hasPrivateLinkage() ? "private_linkage " : "")
    111          << (GV->hasLocalLinkage() ? "local_linkage " : "")
    112          << (GV->hasInternalLinkage() ? "internal " : "")
    113          << (GV->hasExternalLinkage() ? "external " : "")
    114          << (GV->hasCommonLinkage() ? "common_linkage " : "")
    115          << (GV->hasCommonLinkage() ? "common " : "" )
    116          << (Kind.isCommon() ? "kind_common " : "" )
    117          << (Kind.isBSS() ? "kind_bss " : "" )
    118          << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
    119 
    120   if (isGlobalInSmallSection(GV, TM))
    121     return selectSmallSectionForGlobal(GV, Kind, Mang, TM);
    122 
    123   if (Kind.isCommon()) {
    124     // This is purely for LTO+Linker Script because commons don't really have a
    125     // section. However, the BitcodeSectionWriter pass will query for the
    126     // sections of commons (and the linker expects us to know their section) so
    127     // we'll return one here.
    128     return BSSSection;
    129   }
    130 
    131   TRACE("default_ELF_section\n");
    132   // Otherwise, we work the same as ELF.
    133   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind,
    134               Mang, TM);
    135 }
    136 
    137 
    138 MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal(
    139       const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
    140       const TargetMachine &TM) const {
    141   TRACE("[getExplicitSectionGlobal] GV(" << GV->getName() << ") from("
    142         << GV->getSection() << ") ");
    143   TRACE((GV->hasPrivateLinkage() ? "private_linkage " : "")
    144          << (GV->hasLocalLinkage() ? "local_linkage " : "")
    145          << (GV->hasInternalLinkage() ? "internal " : "")
    146          << (GV->hasExternalLinkage() ? "external " : "")
    147          << (GV->hasCommonLinkage() ? "common_linkage " : "")
    148          << (GV->hasCommonLinkage() ? "common " : "" )
    149          << (Kind.isCommon() ? "kind_common " : "" )
    150          << (Kind.isBSS() ? "kind_bss " : "" )
    151          << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
    152 
    153   if (GV->hasSection()) {
    154     StringRef Section = GV->getSection();
    155     if (Section.find(".access.text.group") != StringRef::npos)
    156       return getContext().getELFSection(GV->getSection(), ELF::SHT_PROGBITS,
    157                                         ELF::SHF_ALLOC | ELF::SHF_EXECINSTR);
    158     if (Section.find(".access.data.group") != StringRef::npos)
    159       return getContext().getELFSection(GV->getSection(), ELF::SHT_PROGBITS,
    160                                         ELF::SHF_WRITE | ELF::SHF_ALLOC);
    161   }
    162 
    163   if (isGlobalInSmallSection(GV, TM))
    164     return selectSmallSectionForGlobal(GV, Kind, Mang, TM);
    165 
    166   // Otherwise, we work the same as ELF.
    167   TRACE("default_ELF_section\n");
    168   return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GV, Kind,
    169             Mang, TM);
    170 }
    171 
    172 
    173 /// Return true if this global value should be placed into small data/bss
    174 /// section.
    175 bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalValue *GV,
    176       const TargetMachine &TM) const {
    177   // Only global variables, not functions.
    178   DEBUG(dbgs() << "Checking if value is in small-data, -G"
    179                << SmallDataThreshold << ": \"" << GV->getName() << "\": ");
    180   const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
    181   if (!GVar) {
    182     DEBUG(dbgs() << "no, not a global variable\n");
    183     return false;
    184   }
    185 
    186   // Globals with external linkage that have an original section set must be
    187   // emitted to that section, regardless of whether we would put them into
    188   // small data or not. This is how we can support mixing -G0/-G8 in LTO.
    189   if (GVar->hasSection()) {
    190     bool IsSmall = isSmallDataSection(GVar->getSection());
    191     DEBUG(dbgs() << (IsSmall ? "yes" : "no") << ", has section: "
    192                  << GVar->getSection() << '\n');
    193     return IsSmall;
    194   }
    195 
    196   if (GVar->isConstant()) {
    197     DEBUG(dbgs() << "no, is a constant\n");
    198     return false;
    199   }
    200 
    201   bool IsLocal = GVar->hasLocalLinkage();
    202   if (!StaticsInSData && IsLocal) {
    203     DEBUG(dbgs() << "no, is static\n");
    204     return false;
    205   }
    206 
    207   Type *GType = GVar->getType();
    208   if (PointerType *PT = dyn_cast<PointerType>(GType))
    209     GType = PT->getElementType();
    210 
    211   if (isa<ArrayType>(GType)) {
    212     DEBUG(dbgs() << "no, is an array\n");
    213     return false;
    214   }
    215 
    216   // If the type is a struct with no body provided, treat is conservatively.
    217   // There cannot be actual definitions of object of such a type in this CU
    218   // (only references), so assuming that they are not in sdata is safe. If
    219   // these objects end up in the sdata, the references will still be valid.
    220   if (StructType *ST = dyn_cast<StructType>(GType)) {
    221     if (ST->isOpaque()) {
    222       DEBUG(dbgs() << "no, has opaque type\n");
    223       return false;
    224     }
    225   }
    226 
    227   unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType);
    228   if (Size == 0) {
    229     DEBUG(dbgs() << "no, has size 0\n");
    230     return false;
    231   }
    232   if (Size > SmallDataThreshold) {
    233     DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
    234     return false;
    235   }
    236 
    237   DEBUG(dbgs() << "yes\n");
    238   return true;
    239 }
    240 
    241 
    242 bool HexagonTargetObjectFile::isSmallDataEnabled() const {
    243   return SmallDataThreshold > 0;
    244 }
    245 
    246 
    247 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
    248   return SmallDataThreshold;
    249 }
    250 
    251 
    252 /// Descends any type down to "elementary" components,
    253 /// discovering the smallest addressable one.
    254 /// If zero is returned, declaration will not be modified.
    255 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
    256       const GlobalValue *GV, const TargetMachine &TM) const {
    257   // Assign the smallest element access size to the highest
    258   // value which assembler can handle.
    259   unsigned SmallestElement = 8;
    260 
    261   if (!Ty)
    262     return 0;
    263   switch (Ty->getTypeID()) {
    264   case Type::StructTyID: {
    265     const StructType *STy = cast<const StructType>(Ty);
    266     for (auto &E : STy->elements()) {
    267       unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
    268       if (AtomicSize < SmallestElement)
    269         SmallestElement = AtomicSize;
    270     }
    271     return (STy->getNumElements() == 0) ? 0 : SmallestElement;
    272   }
    273   case Type::ArrayTyID: {
    274     const ArrayType *ATy = cast<const ArrayType>(Ty);
    275     return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
    276   }
    277   case Type::VectorTyID: {
    278     const VectorType *PTy = cast<const VectorType>(Ty);
    279     return getSmallestAddressableSize(PTy->getElementType(), GV, TM);
    280   }
    281   case Type::PointerTyID:
    282   case Type::HalfTyID:
    283   case Type::FloatTyID:
    284   case Type::DoubleTyID:
    285   case Type::IntegerTyID: {
    286     const DataLayout &DL = GV->getParent()->getDataLayout();
    287     // It is unfortunate that DL's function take non-const Type*.
    288     return DL.getTypeAllocSize(const_cast<Type*>(Ty));
    289   }
    290   case Type::FunctionTyID:
    291   case Type::VoidTyID:
    292   case Type::X86_FP80TyID:
    293   case Type::FP128TyID:
    294   case Type::PPC_FP128TyID:
    295   case Type::LabelTyID:
    296   case Type::MetadataTyID:
    297   case Type::X86_MMXTyID:
    298   case Type::TokenTyID:
    299     return 0;
    300   }
    301 
    302   return 0;
    303 }
    304 
    305 
    306 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
    307       const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
    308       const TargetMachine &TM) const {
    309   const Type *GTy = GV->getType()->getElementType();
    310   unsigned Size = getSmallestAddressableSize(GTy, GV, TM);
    311 
    312   // If we have -ffunction-section or -fdata-section then we should emit the
    313   // global value to a unique section specifically for it... even for sdata.
    314   bool EmitUniquedSection = TM.getDataSections();
    315 
    316   TRACE("Small data. Size(" << Size << ")");
    317   // Handle Small Section classification here.
    318   if (Kind.isBSS() || Kind.isBSSLocal()) {
    319     // If -mno-sort-sda is not set, find out smallest accessible entity in
    320     // declaration and add it to the section name string.
    321     // Note. It does not track the actual usage of the value, only its de-
    322     // claration. Also, compiler adds explicit pad fields to some struct
    323     // declarations - they are currently counted towards smallest addres-
    324     // sable entity.
    325     if (NoSmallDataSorting) {
    326       TRACE(" default sbss\n");
    327       return SmallBSSSection;
    328     }
    329 
    330     StringRef Prefix(".sbss");
    331     SmallString<128> Name(Prefix);
    332     Name.append(getSectionSuffixForSize(Size));
    333 
    334     if (EmitUniquedSection) {
    335       Name.append(".");
    336       Name.append(GV->getName());
    337     }
    338     TRACE(" unique sbss(" << Name << ")\n");
    339     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
    340                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
    341   }
    342 
    343   if (Kind.isCommon()) {
    344     // This is purely for LTO+Linker Script because commons don't really have a
    345     // section. However, the BitcodeSectionWriter pass will query for the
    346     // sections of commons (and the linker expects us to know their section) so
    347     // we'll return one here.
    348     if (NoSmallDataSorting)
    349       return BSSSection;
    350 
    351     Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
    352     TRACE(" small COMMON (" << Name << ")\n");
    353 
    354     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
    355                                       ELF::SHF_WRITE | ELF::SHF_ALLOC |
    356                                       ELF::SHF_HEX_GPREL);
    357   }
    358 
    359   // We could have changed sdata object to a constant... in this
    360   // case the Kind could be wrong for it.
    361   if (Kind.isMergeableConst()) {
    362     TRACE(" const_object_as_data ");
    363     const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
    364     if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
    365       Kind = SectionKind::getData();
    366   }
    367 
    368   if (Kind.isData()) {
    369     if (NoSmallDataSorting) {
    370       TRACE(" default sdata\n");
    371       return SmallDataSection;
    372     }
    373 
    374     StringRef Prefix(".sdata");
    375     SmallString<128> Name(Prefix);
    376     Name.append(getSectionSuffixForSize(Size));
    377 
    378     if (EmitUniquedSection) {
    379       Name.append(".");
    380       Name.append(GV->getName());
    381     }
    382     TRACE(" unique sdata(" << Name << ")\n");
    383     return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
    384                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
    385   }
    386 
    387   TRACE("default ELF section\n");
    388   // Otherwise, we work the same as ELF.
    389   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind,
    390               Mang, TM);
    391 }
    392