llvm/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 #include "HexagonTargetObjectFile.h"
  14 #include "llvm/ADT/SmallString.h"
  15 #include "llvm/ADT/StringRef.h"
  16 #include "llvm/ADT/Twine.h"
  17 #include "llvm/BinaryFormat/ELF.h"
  18 #include "llvm/IR/DataLayout.h"
  19 #include "llvm/IR/DerivedTypes.h"
  20 #include "llvm/IR/GlobalObject.h"
  21 #include "llvm/IR/GlobalValue.h"
  22 #include "llvm/IR/GlobalVariable.h"
  23 #include "llvm/IR/Module.h"
  24 #include "llvm/IR/Type.h"
  25 #include "llvm/MC/MCContext.h"
  26 #include "llvm/MC/SectionKind.h"
  27 #include "llvm/Support/Casting.h"
  28 #include "llvm/Support/CommandLine.h"
  29 #include "llvm/Support/Debug.h"
  30 #include "llvm/Support/raw_ostream.h"
  31 #include "llvm/Target/TargetMachine.h"
  32
  33 #define DEBUG_TYPE "hexagon-sdata"
  34
  35 using namespace llvm;
  36
  37 static cl::opt<unsigned> SmallDataThreshold("hexagon-small-data-threshold",
  38   cl::init(8), cl::Hidden,
  39   cl::desc("The maximum size of an object in the sdata section"));
  40
  41 static cl::opt<bool> NoSmallDataSorting("mno-sort-sda", cl::init(false),
  42   cl::Hidden, cl::desc("Disable small data sections sorting"));
  43
  44 static cl::opt<bool>
  45     StaticsInSData("hexagon-statics-in-small-data", cl::Hidden,
  46                    cl::desc("Allow static variables in .sdata"));
  47
  48 static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
  49   cl::Hidden, cl::init(false),
  50   cl::desc("Trace global value placement"));
  51
  52 static cl::opt<bool>
  53     EmitJtInText("hexagon-emit-jt-text", cl::Hidden, cl::init(false),
  54                  cl::desc("Emit hexagon jump tables in function section"));
  55
  56 static cl::opt<bool>
  57     EmitLutInText("hexagon-emit-lut-text", cl::Hidden, cl::init(false),
  58                  cl::desc("Emit hexagon lookup tables in function section"));
  59
  60 // TraceGVPlacement controls messages for all builds. For builds with assertions
  61 // (debug or release), messages are also controlled by the usual debug flags
  62 // (e.g. -debug and -debug-only=globallayout)
  63 #define TRACE_TO(s, X) s << X
  64 #ifdef NDEBUG
  65 #define TRACE(X)                                                               \
  66   do {                                                                         \
  67     if (TraceGVPlacement) {                                                    \
  68       TRACE_TO(errs(), X);                                                     \
  69     }                                                                          \
  70   } while (false)
  71 #else
  72 #define TRACE(X)                                                               \
  73   do {                                                                         \
  74     if (TraceGVPlacement) {                                                    \
  75       TRACE_TO(errs(), X);                                                     \
  76     } else {                                                                   \
  77       LLVM_DEBUG(TRACE_TO(dbgs(), X));                                         \
  78     }                                                                          \
  79   } while (false)
  80 #endif
  81
  82 // Returns true if the section name is such that the symbol will be put
  83 // in a small data section.
  84 // For instance, global variables with section attributes such as ".sdata"
  85 // ".sdata.*", ".sbss", and ".sbss.*" will go into small data.
  86 static bool isSmallDataSection(StringRef Sec) {
  87   // sectionName is either ".sdata" or ".sbss". Looking for an exact match
  88   // obviates the need for checks for section names such as ".sdatafoo".
  89   if (Sec == ".sdata" || Sec == ".sbss" || Sec == ".scommon")
  90     return true;
  91   // If either ".sdata." or ".sbss." is a substring of the section name
  92   // then put the symbol in small data.
  93   return Sec.contains(".sdata.") || Sec.contains(".sbss.") ||
  94          Sec.contains(".scommon.");
  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
 116   SmallDataSection =
 117     getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
 118                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
 119                                ELF::SHF_HEX_GPREL);
 120   SmallBSSSection =
 121     getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
 122                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
 123                                ELF::SHF_HEX_GPREL);
 124 }
 125
 126 MCSection *HexagonTargetObjectFile::SelectSectionForGlobal(
 127     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
 128   TRACE("[SelectSectionForGlobal] GO(" << GO->getName() << ") ");
 129   TRACE("input section(" << GO->getSection() << ") ");
 130
 131   TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
 132          << (GO->hasLocalLinkage() ? "local_linkage " : "")
 133          << (GO->hasInternalLinkage() ? "internal " : "")
 134          << (GO->hasExternalLinkage() ? "external " : "")
 135          << (GO->hasCommonLinkage() ? "common_linkage " : "")
 136          << (GO->hasCommonLinkage() ? "common " : "" )
 137          << (Kind.isCommon() ? "kind_common " : "" )
 138          << (Kind.isBSS() ? "kind_bss " : "" )
 139          << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
 140
 141   // If the lookup table is used by more than one function, do not place
 142   // it in text section.
 143   if (EmitLutInText && GO->getName().starts_with("switch.table")) {
 144     if (const Function *Fn = getLutUsedFunction(GO))
 145       return selectSectionForLookupTable(GO, TM, Fn);
 146   }
 147
 148   if (isGlobalInSmallSection(GO, TM))
 149     return selectSmallSectionForGlobal(GO, Kind, TM);
 150
 151   if (Kind.isCommon()) {
 152     // This is purely for LTO+Linker Script because commons don't really have a
 153     // section. However, the BitcodeSectionWriter pass will query for the
 154     // sections of commons (and the linker expects us to know their section) so
 155     // we'll return one here.
 156     return BSSSection;
 157   }
 158
 159   TRACE("default_ELF_section\n");
 160   // Otherwise, we work the same as ELF.
 161   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
 162 }
 163
 164 MCSection *HexagonTargetObjectFile::getExplicitSectionGlobal(
 165     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
 166   TRACE("[getExplicitSectionGlobal] GO(" << GO->getName() << ") from("
 167         << GO->getSection() << ") ");
 168   TRACE((GO->hasPrivateLinkage() ? "private_linkage " : "")
 169          << (GO->hasLocalLinkage() ? "local_linkage " : "")
 170          << (GO->hasInternalLinkage() ? "internal " : "")
 171          << (GO->hasExternalLinkage() ? "external " : "")
 172          << (GO->hasCommonLinkage() ? "common_linkage " : "")
 173          << (GO->hasCommonLinkage() ? "common " : "" )
 174          << (Kind.isCommon() ? "kind_common " : "" )
 175          << (Kind.isBSS() ? "kind_bss " : "" )
 176          << (Kind.isBSSLocal() ? "kind_bss_local " : "" ));
 177
 178   if (GO->hasSection()) {
 179     StringRef Section = GO->getSection();
 180     if (Section.contains(".access.text.group"))
 181       return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
 182                                         ELF::SHF_ALLOC | ELF::SHF_EXECINSTR);
 183     if (Section.contains(".access.data.group"))
 184       return getContext().getELFSection(GO->getSection(), ELF::SHT_PROGBITS,
 185                                         ELF::SHF_WRITE | ELF::SHF_ALLOC);
 186   }
 187
 188   if (isGlobalInSmallSection(GO, TM))
 189     return selectSmallSectionForGlobal(GO, Kind, TM);
 190
 191   // Otherwise, we work the same as ELF.
 192   TRACE("default_ELF_section\n");
 193   return TargetLoweringObjectFileELF::getExplicitSectionGlobal(GO, Kind, TM);
 194 }
 195
 196 /// Return true if this global value should be placed into small data/bss
 197 /// section.
 198 bool HexagonTargetObjectFile::isGlobalInSmallSection(const GlobalObject *GO,
 199       const TargetMachine &TM) const {
 200   bool HaveSData = isSmallDataEnabled(TM);
 201   if (!HaveSData)
 202     LLVM_DEBUG(dbgs() << "Small-data allocation is disabled, but symbols "
 203                          "may have explicit section assignments...\n");
 204   // Only global variables, not functions.
 205   LLVM_DEBUG(dbgs() << "Checking if value is in small-data, -G"
 206                     << SmallDataThreshold << ": \"" << GO->getName() << "\": ");
 207   const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
 208   if (!GVar) {
 209     LLVM_DEBUG(dbgs() << "no, not a global variable\n");
 210     return false;
 211   }
 212
 213   // Globals with external linkage that have an original section set must be
 214   // emitted to that section, regardless of whether we would put them into
 215   // small data or not. This is how we can support mixing -G0/-G8 in LTO.
 216   if (GVar->hasSection()) {
 217     bool IsSmall = isSmallDataSection(GVar->getSection());
 218     LLVM_DEBUG(dbgs() << (IsSmall ? "yes" : "no")
 219                       << ", has section: " << GVar->getSection() << '\n');
 220     return IsSmall;
 221   }
 222
 223   // If sdata is disabled, stop the checks here.
 224   if (!HaveSData) {
 225     LLVM_DEBUG(dbgs() << "no, small-data allocation is disabled\n");
 226     return false;
 227   }
 228
 229   if (GVar->isConstant()) {
 230     LLVM_DEBUG(dbgs() << "no, is a constant\n");
 231     return false;
 232   }
 233
 234   bool IsLocal = GVar->hasLocalLinkage();
 235   if (!StaticsInSData && IsLocal) {
 236     LLVM_DEBUG(dbgs() << "no, is static\n");
 237     return false;
 238   }
 239
 240   Type *GType = GVar->getValueType();
 241   if (isa<ArrayType>(GType)) {
 242     LLVM_DEBUG(dbgs() << "no, is an array\n");
 243     return false;
 244   }
 245
 246   // If the type is a struct with no body provided, treat is conservatively.
 247   // There cannot be actual definitions of object of such a type in this CU
 248   // (only references), so assuming that they are not in sdata is safe. If
 249   // these objects end up in the sdata, the references will still be valid.
 250   if (StructType *ST = dyn_cast<StructType>(GType)) {
 251     if (ST->isOpaque()) {
 252       LLVM_DEBUG(dbgs() << "no, has opaque type\n");
 253       return false;
 254     }
 255   }
 256
 257   unsigned Size = GVar->getDataLayout().getTypeAllocSize(GType);
 258   if (Size == 0) {
 259     LLVM_DEBUG(dbgs() << "no, has size 0\n");
 260     return false;
 261   }
 262   if (Size > SmallDataThreshold) {
 263     LLVM_DEBUG(dbgs() << "no, size exceeds sdata threshold: " << Size << '\n');
 264     return false;
 265   }
 266
 267   LLVM_DEBUG(dbgs() << "yes\n");
 268   return true;
 269 }
 270
 271 bool HexagonTargetObjectFile::isSmallDataEnabled(const TargetMachine &TM)
 272     const {
 273   return SmallDataThreshold > 0 && !TM.isPositionIndependent();
 274 }
 275
 276 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
 277   return SmallDataThreshold;
 278 }
 279
 280 bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection(
 281     bool UsesLabelDifference, const Function &F) const {
 282   return EmitJtInText;
 283 }
 284
 285 /// Descends any type down to "elementary" components,
 286 /// discovering the smallest addressable one.
 287 /// If zero is returned, declaration will not be modified.
 288 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
 289       const GlobalValue *GV, const TargetMachine &TM) const {
 290   // Assign the smallest element access size to the highest
 291   // value which assembler can handle.
 292   unsigned SmallestElement = 8;
 293
 294   if (!Ty)
 295     return 0;
 296   switch (Ty->getTypeID()) {
 297   case Type::StructTyID: {
 298     const StructType *STy = cast<const StructType>(Ty);
 299     for (auto &E : STy->elements()) {
 300       unsigned AtomicSize = getSmallestAddressableSize(E, GV, TM);
 301       if (AtomicSize < SmallestElement)
 302         SmallestElement = AtomicSize;
 303     }
 304     return (STy->getNumElements() == 0) ? 0 : SmallestElement;
 305   }
 306   case Type::ArrayTyID: {
 307     const ArrayType *ATy = cast<const ArrayType>(Ty);
 308     return getSmallestAddressableSize(ATy->getElementType(), GV, TM);
 309   }
 310   case Type::FixedVectorTyID:
 311   case Type::ScalableVectorTyID: {
 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->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::BFloatTyID:
 327   case Type::X86_FP80TyID:
 328   case Type::FP128TyID:
 329   case Type::PPC_FP128TyID:
 330   case Type::LabelTyID:
 331   case Type::MetadataTyID:
 332   case Type::X86_MMXTyID:
 333   case Type::X86_AMXTyID:
 334   case Type::TokenTyID:
 335   case Type::TypedPointerTyID:
 336   case Type::TargetExtTyID:
 337     return 0;
 338   }
 339
 340   return 0;
 341 }
 342
 343 MCSection *HexagonTargetObjectFile::selectSmallSectionForGlobal(
 344     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
 345   const Type *GTy = GO->getValueType();
 346   unsigned Size = getSmallestAddressableSize(GTy, GO, TM);
 347
 348   // If we have -ffunction-section or -fdata-section then we should emit the
 349   // global value to a unique section specifically for it... even for sdata.
 350   bool EmitUniquedSection = TM.getDataSections();
 351
 352   TRACE("Small data. Size(" << Size << ")");
 353   // Handle Small Section classification here.
 354   if (Kind.isBSS() || Kind.isBSSLocal()) {
 355     // If -mno-sort-sda is not set, find out smallest accessible entity in
 356     // declaration and add it to the section name string.
 357     // Note. It does not track the actual usage of the value, only its de-
 358     // claration. Also, compiler adds explicit pad fields to some struct
 359     // declarations - they are currently counted towards smallest addres-
 360     // sable entity.
 361     if (NoSmallDataSorting) {
 362       TRACE(" default sbss\n");
 363       return SmallBSSSection;
 364     }
 365
 366     StringRef Prefix(".sbss");
 367     SmallString<128> Name(Prefix);
 368     Name.append(getSectionSuffixForSize(Size));
 369
 370     if (EmitUniquedSection) {
 371       Name.append(".");
 372       Name.append(GO->getName());
 373     }
 374     TRACE(" unique sbss(" << Name << ")\n");
 375     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
 376                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
 377   }
 378
 379   if (Kind.isCommon()) {
 380     // This is purely for LTO+Linker Script because commons don't really have a
 381     // section. However, the BitcodeSectionWriter pass will query for the
 382     // sections of commons (and the linker expects us to know their section) so
 383     // we'll return one here.
 384     if (NoSmallDataSorting)
 385       return BSSSection;
 386
 387     Twine Name = Twine(".scommon") + getSectionSuffixForSize(Size);
 388     TRACE(" small COMMON (" << Name << ")\n");
 389
 390     return getContext().getELFSection(Name.str(), ELF::SHT_NOBITS,
 391                                       ELF::SHF_WRITE | ELF::SHF_ALLOC |
 392                                       ELF::SHF_HEX_GPREL);
 393   }
 394
 395   // We could have changed sdata object to a constant... in this
 396   // case the Kind could be wrong for it.
 397   if (Kind.isMergeableConst()) {
 398     TRACE(" const_object_as_data ");
 399     const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO);
 400     if (GVar->hasSection() && isSmallDataSection(GVar->getSection()))
 401       Kind = SectionKind::getData();
 402   }
 403
 404   if (Kind.isData()) {
 405     if (NoSmallDataSorting) {
 406       TRACE(" default sdata\n");
 407       return SmallDataSection;
 408     }
 409
 410     StringRef Prefix(".sdata");
 411     SmallString<128> Name(Prefix);
 412     Name.append(getSectionSuffixForSize(Size));
 413
 414     if (EmitUniquedSection) {
 415       Name.append(".");
 416       Name.append(GO->getName());
 417     }
 418     TRACE(" unique sdata(" << Name << ")\n");
 419     return getContext().getELFSection(Name.str(), ELF::SHT_PROGBITS,
 420                 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_HEX_GPREL);
 421   }
 422
 423   TRACE("default ELF section\n");
 424   // Otherwise, we work the same as ELF.
 425   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
 426 }
 427
 428 // Return the function that uses the lookup table. If there are more
 429 // than one live function that uses this look table, bail out and place
 430 // the lookup table in default section.
 431 const Function *
 432 HexagonTargetObjectFile::getLutUsedFunction(const GlobalObject *GO) const {
 433   const Function *ReturnFn = nullptr;
 434   for (const auto *U : GO->users()) {
 435     // validate each instance of user to be a live function.
 436     auto *I = dyn_cast<Instruction>(U);
 437     if (!I)
 438       continue;
 439     auto *Bb = I->getParent();
 440     if (!Bb)
 441       continue;
 442     auto *UserFn = Bb->getParent();
 443     if (!ReturnFn)
 444       ReturnFn = UserFn;
 445     else if (ReturnFn != UserFn)
 446       return nullptr;
 447   }
 448   return ReturnFn;
 449 }
 450
 451 MCSection *HexagonTargetObjectFile::selectSectionForLookupTable(
 452     const GlobalObject *GO, const TargetMachine &TM, const Function *Fn) const {
 453
 454   SectionKind Kind = SectionKind::getText();
 455   // If the function has explicit section, place the lookup table in this
 456   // explicit section.
 457   if (Fn->hasSection())
 458     return getExplicitSectionGlobal(Fn, Kind, TM);
 459
 460   const auto *FuncObj = dyn_cast<GlobalObject>(Fn);
 461   return SelectSectionForGlobal(FuncObj, Kind, TM);
 462 }