lib/Target/Hexagon/HexagonTargetObjectFile.cpp

   1 //===-- HexagonTargetObjectFile.cpp ---------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file contains the declarations of the HexagonTargetAsmInfo properties.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #define DEBUG_TYPE "hexagon-sdata"
  14
  15 #include "HexagonTargetObjectFile.h"
  16 #include "llvm/ADT/SmallString.h"
  17 #include "llvm/ADT/StringRef.h"
  18 #include "llvm/ADT/Twine.h"
  19 #include "llvm/BinaryFormat/ELF.h"
  20 #include "llvm/IR/DataLayout.h"
  21 #include "llvm/IR/DerivedTypes.h"
  22 #include "llvm/IR/GlobalObject.h"
  23 #include "llvm/IR/GlobalValue.h"
  24 #include "llvm/IR/GlobalVariable.h"
  25 #include "llvm/IR/Type.h"
  26 #include "llvm/MC/MCContext.h"
  27 #include "llvm/MC/SectionKind.h"
  28 #include "llvm/Support/Casting.h"
  29 #include "llvm/Support/CommandLine.h"
  30 #include "llvm/Support/Debug.h"
  31 #include "llvm/Support/raw_ostream.h"
  32 #include "llvm/Target/TargetMachine.h"
  33
  34 using namespace llvm;
  35
  36 static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold",
  37   cl::init(8), cl::Hidden,
  38   cl::desc("The maximum size of an object in the sdata section"));
  39
  40 static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false),
  41   cl::Hidden, cl::desc("Disable small data sections sorting"));
  42
  43 static cl::opt<bool> StaticsInSData("hexagon-statics-in-small-data",
  44   cl::init(false), cl::Hidden, cl::ZeroOrMore,
  45   cl::desc("Allow static variables in .sdata"));
  46
  47 static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
  48   cl::Hidden, cl::init(false),
  49   cl::desc("Trace global value placement"));
  50
  51 static cl::opt<bool>
  52     EmitJtInText("hexagon-emit-jt-text", cl::Hidden, cl::init(false),
  53                  cl::desc("Emit hexagon jump tables in function section"));
  54
  55 static cl::opt<bool>
  56     EmitLutInText("hexagon-emit-lut-text", cl::Hidden, cl::init(false),
  57                  cl::desc("Emit hexagon lookup tables in function section"));
  58
  59 // TraceGVPlacement controls messages for all builds. For builds with assertions
  60 // (debug or release), messages are also controlled by the usual debug flags
  61 // (e.g. -debug and -debug-only=globallayout)
  62 #define TRACE_TO(s, X) s << X
  63 #ifdef NDEBUG
  64 #define TRACE(X)                                                               \
  65   do {                                                                         \
  66     if (TraceGVPlacement) {                                                    \
  67       TRACE_TO(errs(), X);                                                     \
  68     }                                                                          \
  69   } while (false)
  70 #else
  71 #define TRACE(X)                                                               \
  72   do {                                                                         \
  73     if (TraceGVPlacement) {                                                    \
  74       TRACE_TO(errs(), X);                                                     \
  75     } else {                                                                   \
  76       LLVM_DEBUG(TRACE_TO(dbgs(), X));                                         \
  77     }                                                                          \
  78   } while (false)
  79 #endif
  80
  81 // Returns true if the section name is such that the symbol will be put
  82 // in a small data section.
  83 // For instance, global variables with section attributes such as ".sdata"
  84 // ".sdata.*", ".sbss", and ".sbss.*" will go into small data.
  85 static bool isSmallDataSection(StringRef Sec) {
  86   // sectionName is either ".sdata" or ".sbss". Looking for an exact match
  87   // obviates the need for checks for section names such as ".sdatafoo".
  88   if (Sec.equals(".sdata") || Sec.equals(".sbss") || Sec.equals(".scommon"))
  89     return true;
  90   // If either ".sdata." or ".sbss." is a substring of the section name
  91   // then put the symbol in small data.
  92   return Sec.find(".sdata.") != StringRef::npos ||
  93          Sec.find(".sbss.") != StringRef::npos ||
  94          Sec.find(".scommon.") != StringRef::npos;
  95 }
  96
  97 static const char *getSectionSuffixForSize(unsigned Size) {
  98   switch (Size) {
  99   default:
 100     return "";
 101   case 1:
 102     return ".1";
 103   case 2:
 104     return ".2";
 105   case 4:
 106     return ".4";
 107   case 8:
 108     return ".8";
 109   }
 110 }
 111
 112 void HexagonTargetObjectFile::Initialize(MCContext &Ctx,
 113       const TargetMachine &TM) {
 114   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
 115   InitializeELF(TM.Options.UseInitArray);
 116
 117   SmallDataSection =
 118     getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
 119                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
 120                                ELF::SHF_HEX_GPREL);
 121   SmallBSSSection =
 122     getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
 123                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
 124                                ELF::SHF_HEX_GPREL);
 125 }
 126
 127 MCSection *HexagonTargetObjectFile::SelectSectionForGlobal(
 128     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
 129   TRACE("[SelectSectionForGlobal] GO(" << GO->getName() << ") ");
 130   TRACE("input section(" << GO->getSection() << ") ");
 131
 132   TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
 133          << (GO->hasLocalLinkage() ? "local_linkage " : "")
 134          << (GO->hasInternalLinkage() ? "internal " : "")
 135          << (GO->hasExternalLinkage() ? "external " : "")
 136          << (GO->hasCommonLinkage() ? "common_linkage " : "")
 137          << (GO->hasCommonLinkage() ? "common " : "" )
 138          << (Kind.isCommon() ? "kind_common " : "" )
 139          << (Kind.isBSS() ? "kind_bss " : "" )
 140          << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
 141
 142   // If the lookup table is used by more than one function, do not place
 143   // it in text section.
 144   if (EmitLutInText && GO->getName().startswith("switch.table")) {
 145     if (const Function *Fn = getLutUsedFunction(GO))
 146       return selectSectionForLookupTable(GO, TM, Fn);
 147   }
 148
 149   if (isGlobalInSmallSection(GO, TM))
 150     return selectSmallSectionForGlobal(GO, Kind, TM);
 151
 152   if (Kind.isCommon()) {
 153     // This is purely for LTO+Linker Script because commons don't really have a
 154     // section. However, the BitcodeSectionWriter pass will query for the
 155     // sections of commons (and the linker expects us to know their section) so
 156     // we'll return one here.
 157     return BSSSection;
 158   }
 159
 160   TRACE("default_ELF_section\n");
 161   // Otherwise, we work the same as ELF.
 162   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
 163 }
 164
 165 MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal(
 166     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
 167   TRACE("[getExplicitSectionGlobal] GO(" << GO->getName() << ") from("
 168         << GO->getSection() << ") ");
 169   TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
 170          << (GO->hasLocalLinkage() ? "local_linkage " : "")
 171          << (GO->hasInternalLinkage() ? "internal " : "")
 172          << (GO->hasExternalLinkage() ? "external " : "")
 173          << (GO->hasCommonLinkage() ? "common_linkage " : "")
 174          << (GO->hasCommonLinkage() ? "common " : "" )
 175          << (Kind.isCommon() ? "kind_common " : "" )
 176          << (Kind.isBSS() ? "kind_bss " : "" )
 177          << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
 178
 179   if (GO->hasSection()) {
 180     StringRef Section = GO->getSection();
 181     if (Section.find(".access.text.group") != StringRef::npos)
 182       return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
 183                                         ELF::SHF_ALLOC | ELF::SHF_EXECINSTR);
 184     if (Section.find(".access.data.group") != StringRef::npos)
 185       return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
 186                                         ELF::SHF_WRITE | ELF::SHF_ALLOC);
 187   }
 188
 189   if (isGlobalInSmallSection(GO, TM))
 190     return selectSmallSectionForGlobal(GO, Kind, TM);
 191
 192   // Otherwise, we work the same as ELF.
 193   TRACE("default_ELF_section\n");
 194   return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, Kind, TM);
 195 }
 196
 197 /// Return true if this global value should be placed into small data/bss
 198 /// section.
 199 bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
 200       const TargetMachine &TM) const {
 201   bool HaveSData = isSmallDataEnabled(TM);
 202   if (!HaveSData)
 203     LLVM_DEBUG(dbgs() << "Small-data allocation is disabled, but symbols "
 204                          "may have explicit section assignments...\n");
 205   // Only global variables, not functions.
 206   LLVM_DEBUG(dbgs() << "Checking if value is in small-data, -G"
 207                     << SmallDataThreshold << ": \"" << GO->getName() << "\": ");
 208   const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
 209   if (!GVar) {
 210     LLVM_DEBUG(dbgs() << "no, not a global variable\n");
 211     return false;
 212   }
 213
 214   // Globals with external linkage that have an original section set must be
 215   // emitted to that section, regardless of whether we would put them into
 216   // small data or not. This is how we can support mixing -G0/-G8 in LTO.
 217   if (GVar->hasSection()) {
 218     bool IsSmall = isSmallDataSection(GVar->getSection());
 219     LLVM_DEBUG(dbgs() << (IsSmall ? "yes" : "no")
 220                       << ", has section: " << GVar->getSection() << '\n');
 221     return IsSmall;
 222   }
 223
 224   // If sdata is disabled, stop the checks here.
 225   if (!HaveSData) {
 226     LLVM_DEBUG(dbgs() << "no, small-data allocation is disabled\n");
 227     return false;
 228   }
 229
 230   if (GVar->isConstant()) {
 231     LLVM_DEBUG(dbgs() << "no, is a constant\n");
 232     return false;
 233   }
 234
 235   bool IsLocal = GVar->hasLocalLinkage();
 236   if (!StaticsInSData && IsLocal) {
 237     LLVM_DEBUG(dbgs() << "no, is static\n");
 238     return false;
 239   }
 240
 241   Type *GType = GVar->getValueType();
 242   if (isa<ArrayType>(GType)) {
 243     LLVM_DEBUG(dbgs() << "no, is an array\n");
 244     return false;
 245   }
 246
 247   // If the type is a struct with no body provided, treat is conservatively.
 248   // There cannot be actual definitions of object of such a type in this CU
 249   // (only references), so assuming that they are not in sdata is safe. If
 250   // these objects end up in the sdata, the references will still be valid.
 251   if (StructType *ST = dyn_cast<StructType>(GType)) {
 252     if (ST->isOpaque()) {
 253       LLVM_DEBUG(dbgs() << "no, has opaque type\n");
 254       return false;
 255     }
 256   }
 257
 258   unsigned Size = GVar->getParent()->getDataLayout().getTypeAllocSize(GType);
 259   if (Size == 0) {
 260     LLVM_DEBUG(dbgs() << "no, has size 0\n");
 261     return false;
 262   }
 263   if (Size > SmallDataThreshold) {
 264     LLVM_DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
 265     return false;
 266   }
 267
 268   LLVM_DEBUG(dbgs() << "yes\n");
 269   return true;
 270 }
 271
 272 bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
 273     const {
 274   return SmallDataThreshold > 0 && !TM.isPositionIndependent();
 275 }
 276
 277 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
 278   return SmallDataThreshold;
 279 }
 280
 281 bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection(
 282     bool UsesLabelDifference, const Function &F) const {
 283   return EmitJtInText;
 284 }
 285
 286 /// Descends any type down to "elementary" components,
 287 /// discovering the smallest addressable one.
 288 /// If zero is returned, declaration will not be modified.
 289 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
 290       const GlobalValue *GV, const TargetMachine &TM) const {
 291   // Assign the smallest element access size to the highest
 292   // value which assembler can handle.
 293   unsigned SmallestElement = 8;
 294
 295   if (!Ty)
 296     return 0;
 297   switch (Ty->getTypeID()) {
 298   case Type::StructTyID: {
 299     const StructType *STy = cast<const StructType>(Ty);
 300     for (auto &E : STy->elements()) {
 301       unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
 302       if (AtomicSize < SmallestElement)
 303         SmallestElement = AtomicSize;
 304     }
 305     return (STy->getNumElements() == 0) ? 0 : SmallestElement;
 306   }
 307   case Type::ArrayTyID: {
 308     const ArrayType *ATy = cast<const ArrayType>(Ty);
 309     return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
 310   }
 311   case Type::VectorTyID: {
 312     const VectorType *PTy = cast<const VectorType>(Ty);
 313     return getSmallestAddressableSize(PTy->getElementType(), GV, TM);
 314   }
 315   case Type::PointerTyID:
 316   case Type::HalfTyID:
 317   case Type::FloatTyID:
 318   case Type::DoubleTyID:
 319   case Type::IntegerTyID: {
 320     const DataLayout &DL = GV->getParent()->getDataLayout();
 321     // It is unfortunate that DL's function take non-const Type*.
 322     return DL.getTypeAllocSize(const_cast<Type*>(Ty));
 323   }
 324   case Type::FunctionTyID:
 325   case Type::VoidTyID:
 326   case Type::X86_FP80TyID:
 327   case Type::FP128TyID:
 328   case Type::PPC_FP128TyID:
 329   case Type::LabelTyID:
 330   case Type::MetadataTyID:
 331   case Type::X86_MMXTyID:
 332   case Type::TokenTyID:
 333     return 0;
 334   }
 335
 336   return 0;
 337 }
 338
 339 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
 340     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
 341   const Type *GTy = GO->getValueType();
 342   unsigned Size = getSmallestAddressableSize(GTy, GO, TM);
 343
 344   // If we have -ffunction-section or -fdata-section then we should emit the
 345   // global value to a unique section specifically for it... even for sdata.
 346   bool EmitUniquedSection = TM.getDataSections();
 347
 348   TRACE("Small data. Size(" << Size << ")");
 349   // Handle Small Section classification here.
 350   if (Kind.isBSS() || Kind.isBSSLocal()) {
 351     // If -mno-sort-sda is not set, find out smallest accessible entity in
 352     // declaration and add it to the section name string.
 353     // Note. It does not track the actual usage of the value, only its de-
 354     // claration. Also, compiler adds explicit pad fields to some struct
 355     // declarations - they are currently counted towards smallest addres-
 356     // sable entity.
 357     if (NoSmallDataSorting) {
 358       TRACE(" default sbss\n");
 359       return SmallBSSSection;
 360     }
 361
 362     StringRef Prefix(".sbss");
 363     SmallString<128> Name(Prefix);
 364     Name.append(getSectionSuffixForSize(Size));
 365
 366     if (EmitUniquedSection) {
 367       Name.append(".");
 368       Name.append(GO->getName());
 369     }
 370     TRACE(" unique sbss(" << Name << ")\n");
 371     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
 372                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
 373   }
 374
 375   if (Kind.isCommon()) {
 376     // This is purely for LTO+Linker Script because commons don't really have a
 377     // section. However, the BitcodeSectionWriter pass will query for the
 378     // sections of commons (and the linker expects us to know their section) so
 379     // we'll return one here.
 380     if (NoSmallDataSorting)
 381       return BSSSection;
 382
 383     Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
 384     TRACE(" small COMMON (" << Name << ")\n");
 385
 386     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
 387                                       ELF::SHF_WRITE | ELF::SHF_ALLOC |
 388                                       ELF::SHF_HEX_GPREL);
 389   }
 390
 391   // We could have changed sdata object to a constant... in this
 392   // case the Kind could be wrong for it.
 393   if (Kind.isMergeableConst()) {
 394     TRACE(" const_object_as_data ");
 395     const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
 396     if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
 397       Kind = SectionKind::getData();
 398   }
 399
 400   if (Kind.isData()) {
 401     if (NoSmallDataSorting) {
 402       TRACE(" default sdata\n");
 403       return SmallDataSection;
 404     }
 405
 406     StringRef Prefix(".sdata");
 407     SmallString<128> Name(Prefix);
 408     Name.append(getSectionSuffixForSize(Size));
 409
 410     if (EmitUniquedSection) {
 411       Name.append(".");
 412       Name.append(GO->getName());
 413     }
 414     TRACE(" unique sdata(" << Name << ")\n");
 415     return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
 416                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
 417   }
 418
 419   TRACE("default ELF section\n");
 420   // Otherwise, we work the same as ELF.
 421   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
 422 }
 423
 424 // Return the function that uses the lookup table. If there are more
 425 // than one live function that uses this look table, bail out and place
 426 // the lookup table in default section.
 427 const Function *
 428 HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const {
 429   const Function *ReturnFn = nullptr;
 430   for (auto U : GO->users()) {
 431     // validate each instance of user to be a live function.
 432     auto *I = dyn_cast<Instruction>(U);
 433     if (!I)
 434       continue;
 435     auto *Bb = I->getParent();
 436     if (!Bb)
 437       continue;
 438     auto *UserFn = Bb->getParent();
 439     if (!ReturnFn)
 440       ReturnFn = UserFn;
 441     else if (ReturnFn != UserFn)
 442       return nullptr;
 443   }
 444   return ReturnFn;
 445 }
 446
 447 MCSection *HexagonTargetObjectFile::selectSectionForLookupTable(
 448     const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const {
 449
 450   SectionKind Kind = SectionKind::getText();
 451   // If the function has explicit section, place the lookup table in this
 452   // explicit section.
 453   if (Fn->hasSection())
 454     return getExplicitSectionGlobal(Fn, Kind, TM);
 455
 456   const auto *FuncObj = dyn_cast<GlobalObject>(Fn);
 457   return SelectSectionForGlobal(FuncObj, Kind, TM);
 458 }