llvm/lib/IR/Globals.cpp

   1 //===-- Globals.cpp - Implement the GlobalValue & GlobalVariable class ----===//
   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 implements the GlobalValue & GlobalVariable classes for the IR
  10 // library.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "LLVMContextImpl.h"
  15 #include "llvm/ADT/SmallPtrSet.h"
  16 #include "llvm/ADT/Triple.h"
  17 #include "llvm/IR/ConstantRange.h"
  18 #include "llvm/IR/Constants.h"
  19 #include "llvm/IR/DerivedTypes.h"
  20 #include "llvm/IR/GlobalAlias.h"
  21 #include "llvm/IR/GlobalValue.h"
  22 #include "llvm/IR/GlobalVariable.h"
  23 #include "llvm/IR/Module.h"
  24 #include "llvm/IR/Operator.h"
  25 #include "llvm/Support/Error.h"
  26 #include "llvm/Support/ErrorHandling.h"
  27 using namespace llvm;
  28
  29 //===----------------------------------------------------------------------===//
  30 //                            GlobalValue Class
  31 //===----------------------------------------------------------------------===//
  32
  33 // GlobalValue should be a Constant, plus a type, a module, some flags, and an
  34 // intrinsic ID. Add an assert to prevent people from accidentally growing
  35 // GlobalValue while adding flags.
  36 static_assert(sizeof(GlobalValue) ==
  37                   sizeof(Constant) + 2 * sizeof(void *) + 2 * sizeof(unsigned),
  38               "unexpected GlobalValue size growth");
  39
  40 // GlobalObject adds a comdat.
  41 static_assert(sizeof(GlobalObject) == sizeof(GlobalValue) + sizeof(void *),
  42               "unexpected GlobalObject size growth");
  43
  44 bool GlobalValue::isMaterializable() const {
  45   if (const Function *F = dyn_cast<Function>(this))
  46     return F->isMaterializable();
  47   return false;
  48 }
  49 Error GlobalValue::materialize() {
  50   return getParent()->materialize(this);
  51 }
  52
  53 /// Override destroyConstantImpl to make sure it doesn't get called on
  54 /// GlobalValue's because they shouldn't be treated like other constants.
  55 void GlobalValue::destroyConstantImpl() {
  56   llvm_unreachable("You can't GV->destroyConstantImpl()!");
  57 }
  58
  59 Value *GlobalValue::handleOperandChangeImpl(Value *From, Value *To) {
  60   llvm_unreachable("Unsupported class for handleOperandChange()!");
  61 }
  62
  63 /// copyAttributesFrom - copy all additional attributes (those not needed to
  64 /// create a GlobalValue) from the GlobalValue Src to this one.
  65 void GlobalValue::copyAttributesFrom(const GlobalValue *Src) {
  66   setVisibility(Src->getVisibility());
  67   setUnnamedAddr(Src->getUnnamedAddr());
  68   setThreadLocalMode(Src->getThreadLocalMode());
  69   setDLLStorageClass(Src->getDLLStorageClass());
  70   setDSOLocal(Src->isDSOLocal());
  71   setPartition(Src->getPartition());
  72 }
  73
  74 void GlobalValue::removeFromParent() {
  75   switch (getValueID()) {
  76 #define HANDLE_GLOBAL_VALUE(NAME)                                              \
  77   case Value::NAME##Val:                                                       \
  78     return static_cast<NAME *>(this)->removeFromParent();
  79 #include "llvm/IR/Value.def"
  80   default:
  81     break;
  82   }
  83   llvm_unreachable("not a global");
  84 }
  85
  86 void GlobalValue::eraseFromParent() {
  87   switch (getValueID()) {
  88 #define HANDLE_GLOBAL_VALUE(NAME)                                              \
  89   case Value::NAME##Val:                                                       \
  90     return static_cast<NAME *>(this)->eraseFromParent();
  91 #include "llvm/IR/Value.def"
  92   default:
  93     break;
  94   }
  95   llvm_unreachable("not a global");
  96 }
  97
  98 bool GlobalValue::isInterposable() const {
  99   if (isInterposableLinkage(getLinkage()))
 100     return true;
 101   return getParent() && getParent()->getSemanticInterposition() &&
 102          !isDSOLocal();
 103 }
 104
 105 bool GlobalValue::canBenefitFromLocalAlias() const {
 106   // See AsmPrinter::getSymbolPreferLocal().
 107   return hasDefaultVisibility() &&
 108          GlobalObject::isExternalLinkage(getLinkage()) && !isDeclaration() &&
 109          !isa<GlobalIFunc>(this) && !hasComdat();
 110 }
 111
 112 unsigned GlobalValue::getAddressSpace() const {
 113   PointerType *PtrTy = getType();
 114   return PtrTy->getAddressSpace();
 115 }
 116
 117 void GlobalObject::setAlignment(MaybeAlign Align) {
 118   assert((!Align || *Align <= MaximumAlignment) &&
 119          "Alignment is greater than MaximumAlignment!");
 120   unsigned AlignmentData = encode(Align);
 121   unsigned OldData = getGlobalValueSubClassData();
 122   setGlobalValueSubClassData((OldData & ~AlignmentMask) | AlignmentData);
 123   assert(MaybeAlign(getAlignment()) == Align &&
 124          "Alignment representation error!");
 125 }
 126
 127 void GlobalObject::copyAttributesFrom(const GlobalObject *Src) {
 128   GlobalValue::copyAttributesFrom(Src);
 129   setAlignment(MaybeAlign(Src->getAlignment()));
 130   setSection(Src->getSection());
 131 }
 132
 133 std::string GlobalValue::getGlobalIdentifier(StringRef Name,
 134                                              GlobalValue::LinkageTypes Linkage,
 135                                              StringRef FileName) {
 136
 137   // Value names may be prefixed with a binary '1' to indicate
 138   // that the backend should not modify the symbols due to any platform
 139   // naming convention. Do not include that '1' in the PGO profile name.
 140   if (Name[0] == '\1')
 141     Name = Name.substr(1);
 142
 143   std::string NewName = std::string(Name);
 144   if (llvm::GlobalValue::isLocalLinkage(Linkage)) {
 145     // For local symbols, prepend the main file name to distinguish them.
 146     // Do not include the full path in the file name since there's no guarantee
 147     // that it will stay the same, e.g., if the files are checked out from
 148     // version control in different locations.
 149     if (FileName.empty())
 150       NewName = NewName.insert(0, "<unknown>:");
 151     else
 152       NewName = NewName.insert(0, FileName.str() + ":");
 153   }
 154   return NewName;
 155 }
 156
 157 std::string GlobalValue::getGlobalIdentifier() const {
 158   return getGlobalIdentifier(getName(), getLinkage(),
 159                              getParent()->getSourceFileName());
 160 }
 161
 162 StringRef GlobalValue::getSection() const {
 163   if (auto *GA = dyn_cast<GlobalAlias>(this)) {
 164     // In general we cannot compute this at the IR level, but we try.
 165     if (const GlobalObject *GO = GA->getBaseObject())
 166       return GO->getSection();
 167     return "";
 168   }
 169   return cast<GlobalObject>(this)->getSection();
 170 }
 171
 172 const Comdat *GlobalValue::getComdat() const {
 173   if (auto *GA = dyn_cast<GlobalAlias>(this)) {
 174     // In general we cannot compute this at the IR level, but we try.
 175     if (const GlobalObject *GO = GA->getBaseObject())
 176       return const_cast<GlobalObject *>(GO)->getComdat();
 177     return nullptr;
 178   }
 179   // ifunc and its resolver are separate things so don't use resolver comdat.
 180   if (isa<GlobalIFunc>(this))
 181     return nullptr;
 182   return cast<GlobalObject>(this)->getComdat();
 183 }
 184
 185 StringRef GlobalValue::getPartition() const {
 186   if (!hasPartition())
 187     return "";
 188   return getContext().pImpl->GlobalValuePartitions[this];
 189 }
 190
 191 void GlobalValue::setPartition(StringRef S) {
 192   // Do nothing if we're clearing the partition and it is already empty.
 193   if (!hasPartition() && S.empty())
 194     return;
 195
 196   // Get or create a stable partition name string and put it in the table in the
 197   // context.
 198   if (!S.empty())
 199     S = getContext().pImpl->Saver.save(S);
 200   getContext().pImpl->GlobalValuePartitions[this] = S;
 201
 202   // Update the HasPartition field. Setting the partition to the empty string
 203   // means this global no longer has a partition.
 204   HasPartition = !S.empty();
 205 }
 206
 207 StringRef GlobalObject::getSectionImpl() const {
 208   assert(hasSection());
 209   return getContext().pImpl->GlobalObjectSections[this];
 210 }
 211
 212 void GlobalObject::setSection(StringRef S) {
 213   // Do nothing if we're clearing the section and it is already empty.
 214   if (!hasSection() && S.empty())
 215     return;
 216
 217   // Get or create a stable section name string and put it in the table in the
 218   // context.
 219   if (!S.empty())
 220     S = getContext().pImpl->Saver.save(S);
 221   getContext().pImpl->GlobalObjectSections[this] = S;
 222
 223   // Update the HasSectionHashEntryBit. Setting the section to the empty string
 224   // means this global no longer has a section.
 225   setGlobalObjectFlag(HasSectionHashEntryBit, !S.empty());
 226 }
 227
 228 bool GlobalValue::isDeclaration() const {
 229   // Globals are definitions if they have an initializer.
 230   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(this))
 231     return GV->getNumOperands() == 0;
 232
 233   // Functions are definitions if they have a body.
 234   if (const Function *F = dyn_cast<Function>(this))
 235     return F->empty() && !F->isMaterializable();
 236
 237   // Aliases and ifuncs are always definitions.
 238   assert(isa<GlobalIndirectSymbol>(this));
 239   return false;
 240 }
 241
 242 bool GlobalObject::canIncreaseAlignment() const {
 243   // Firstly, can only increase the alignment of a global if it
 244   // is a strong definition.
 245   if (!isStrongDefinitionForLinker())
 246     return false;
 247
 248   // It also has to either not have a section defined, or, not have
 249   // alignment specified. (If it is assigned a section, the global
 250   // could be densely packed with other objects in the section, and
 251   // increasing the alignment could cause padding issues.)
 252   if (hasSection() && getAlignment() > 0)
 253     return false;
 254
 255   // On ELF platforms, we're further restricted in that we can't
 256   // increase the alignment of any variable which might be emitted
 257   // into a shared library, and which is exported. If the main
 258   // executable accesses a variable found in a shared-lib, the main
 259   // exe actually allocates memory for and exports the symbol ITSELF,
 260   // overriding the symbol found in the library. That is, at link
 261   // time, the observed alignment of the variable is copied into the
 262   // executable binary. (A COPY relocation is also generated, to copy
 263   // the initial data from the shadowed variable in the shared-lib
 264   // into the location in the main binary, before running code.)
 265   //
 266   // And thus, even though you might think you are defining the
 267   // global, and allocating the memory for the global in your object
 268   // file, and thus should be able to set the alignment arbitrarily,
 269   // that's not actually true. Doing so can cause an ABI breakage; an
 270   // executable might have already been built with the previous
 271   // alignment of the variable, and then assuming an increased
 272   // alignment will be incorrect.
 273
 274   // Conservatively assume ELF if there's no parent pointer.
 275   bool isELF =
 276       (!Parent || Triple(Parent->getTargetTriple()).isOSBinFormatELF());
 277   if (isELF && !isDSOLocal())
 278     return false;
 279
 280   return true;
 281 }
 282
 283 const GlobalObject *GlobalValue::getBaseObject() const {
 284   if (auto *GO = dyn_cast<GlobalObject>(this))
 285     return GO;
 286   if (auto *GA = dyn_cast<GlobalIndirectSymbol>(this))
 287     return GA->getBaseObject();
 288   return nullptr;
 289 }
 290
 291 bool GlobalValue::isAbsoluteSymbolRef() const {
 292   auto *GO = dyn_cast<GlobalObject>(this);
 293   if (!GO)
 294     return false;
 295
 296   return GO->getMetadata(LLVMContext::MD_absolute_symbol);
 297 }
 298
 299 Optional<ConstantRange> GlobalValue::getAbsoluteSymbolRange() const {
 300   auto *GO = dyn_cast<GlobalObject>(this);
 301   if (!GO)
 302     return None;
 303
 304   MDNode *MD = GO->getMetadata(LLVMContext::MD_absolute_symbol);
 305   if (!MD)
 306     return None;
 307
 308   return getConstantRangeFromMetadata(*MD);
 309 }
 310
 311 bool GlobalValue::canBeOmittedFromSymbolTable() const {
 312   if (!hasLinkOnceODRLinkage())
 313     return false;
 314
 315   // We assume that anyone who sets global unnamed_addr on a non-constant
 316   // knows what they're doing.
 317   if (hasGlobalUnnamedAddr())
 318     return true;
 319
 320   // If it is a non constant variable, it needs to be uniqued across shared
 321   // objects.
 322   if (auto *Var = dyn_cast<GlobalVariable>(this))
 323     if (!Var->isConstant())
 324       return false;
 325
 326   return hasAtLeastLocalUnnamedAddr();
 327 }
 328
 329 //===----------------------------------------------------------------------===//
 330 // GlobalVariable Implementation
 331 //===----------------------------------------------------------------------===//
 332
 333 GlobalVariable::GlobalVariable(Type *Ty, bool constant, LinkageTypes Link,
 334                                Constant *InitVal, const Twine &Name,
 335                                ThreadLocalMode TLMode, unsigned AddressSpace,
 336                                bool isExternallyInitialized)
 337     : GlobalObject(Ty, Value::GlobalVariableVal,
 338                    OperandTraits<GlobalVariable>::op_begin(this),
 339                    InitVal != nullptr, Link, Name, AddressSpace),
 340       isConstantGlobal(constant),
 341       isExternallyInitializedConstant(isExternallyInitialized) {
 342   assert(!Ty->isFunctionTy() && PointerType::isValidElementType(Ty) &&
 343          "invalid type for global variable");
 344   setThreadLocalMode(TLMode);
 345   if (InitVal) {
 346     assert(InitVal->getType() == Ty &&
 347            "Initializer should be the same type as the GlobalVariable!");
 348     Op<0>() = InitVal;
 349   }
 350 }
 351
 352 GlobalVariable::GlobalVariable(Module &M, Type *Ty, bool constant,
 353                                LinkageTypes Link, Constant *InitVal,
 354                                const Twine &Name, GlobalVariable *Before,
 355                                ThreadLocalMode TLMode,
 356                                Optional<unsigned> AddressSpace,
 357                                bool isExternallyInitialized)
 358     : GlobalObject(Ty, Value::GlobalVariableVal,
 359                    OperandTraits<GlobalVariable>::op_begin(this),
 360                    InitVal != nullptr, Link, Name,
 361                    AddressSpace
 362                        ? *AddressSpace
 363                        : M.getDataLayout().getDefaultGlobalsAddressSpace()),
 364       isConstantGlobal(constant),
 365       isExternallyInitializedConstant(isExternallyInitialized) {
 366   assert(!Ty->isFunctionTy() && PointerType::isValidElementType(Ty) &&
 367          "invalid type for global variable");
 368   setThreadLocalMode(TLMode);
 369   if (InitVal) {
 370     assert(InitVal->getType() == Ty &&
 371            "Initializer should be the same type as the GlobalVariable!");
 372     Op<0>() = InitVal;
 373   }
 374
 375   if (Before)
 376     Before->getParent()->getGlobalList().insert(Before->getIterator(), this);
 377   else
 378     M.getGlobalList().push_back(this);
 379 }
 380
 381 void GlobalVariable::removeFromParent() {
 382   getParent()->getGlobalList().remove(getIterator());
 383 }
 384
 385 void GlobalVariable::eraseFromParent() {
 386   getParent()->getGlobalList().erase(getIterator());
 387 }
 388
 389 void GlobalVariable::setInitializer(Constant *InitVal) {
 390   if (!InitVal) {
 391     if (hasInitializer()) {
 392       // Note, the num operands is used to compute the offset of the operand, so
 393       // the order here matters.  Clearing the operand then clearing the num
 394       // operands ensures we have the correct offset to the operand.
 395       Op<0>().set(nullptr);
 396       setGlobalVariableNumOperands(0);
 397     }
 398   } else {
 399     assert(InitVal->getType() == getValueType() &&
 400            "Initializer type must match GlobalVariable type");
 401     // Note, the num operands is used to compute the offset of the operand, so
 402     // the order here matters.  We need to set num operands to 1 first so that
 403     // we get the correct offset to the first operand when we set it.
 404     if (!hasInitializer())
 405       setGlobalVariableNumOperands(1);
 406     Op<0>().set(InitVal);
 407   }
 408 }
 409
 410 /// Copy all additional attributes (those not needed to create a GlobalVariable)
 411 /// from the GlobalVariable Src to this one.
 412 void GlobalVariable::copyAttributesFrom(const GlobalVariable *Src) {
 413   GlobalObject::copyAttributesFrom(Src);
 414   setExternallyInitialized(Src->isExternallyInitialized());
 415   setAttributes(Src->getAttributes());
 416 }
 417
 418 void GlobalVariable::dropAllReferences() {
 419   User::dropAllReferences();
 420   clearMetadata();
 421 }
 422
 423 //===----------------------------------------------------------------------===//
 424 // GlobalIndirectSymbol Implementation
 425 //===----------------------------------------------------------------------===//
 426
 427 GlobalIndirectSymbol::GlobalIndirectSymbol(Type *Ty, ValueTy VTy,
 428     unsigned AddressSpace, LinkageTypes Linkage, const Twine &Name,
 429     Constant *Symbol)
 430     : GlobalValue(Ty, VTy, &Op<0>(), 1, Linkage, Name, AddressSpace) {
 431     Op<0>() = Symbol;
 432 }
 433
 434 static const GlobalObject *
 435 findBaseObject(const Constant *C, DenseSet<const GlobalAlias *> &Aliases) {
 436   if (auto *GO = dyn_cast<GlobalObject>(C))
 437     return GO;
 438   if (auto *GA = dyn_cast<GlobalAlias>(C))
 439     if (Aliases.insert(GA).second)
 440       return findBaseObject(GA->getOperand(0), Aliases);
 441   if (auto *CE = dyn_cast<ConstantExpr>(C)) {
 442     switch (CE->getOpcode()) {
 443     case Instruction::Add: {
 444       auto *LHS = findBaseObject(CE->getOperand(0), Aliases);
 445       auto *RHS = findBaseObject(CE->getOperand(1), Aliases);
 446       if (LHS && RHS)
 447         return nullptr;
 448       return LHS ? LHS : RHS;
 449     }
 450     case Instruction::Sub: {
 451       if (findBaseObject(CE->getOperand(1), Aliases))
 452         return nullptr;
 453       return findBaseObject(CE->getOperand(0), Aliases);
 454     }
 455     case Instruction::IntToPtr:
 456     case Instruction::PtrToInt:
 457     case Instruction::BitCast:
 458     case Instruction::GetElementPtr:
 459       return findBaseObject(CE->getOperand(0), Aliases);
 460     default:
 461       break;
 462     }
 463   }
 464   return nullptr;
 465 }
 466
 467 const GlobalObject *GlobalIndirectSymbol::getBaseObject() const {
 468   DenseSet<const GlobalAlias *> Aliases;
 469   return findBaseObject(getOperand(0), Aliases);
 470 }
 471
 472 //===----------------------------------------------------------------------===//
 473 // GlobalAlias Implementation
 474 //===----------------------------------------------------------------------===//
 475
 476 GlobalAlias::GlobalAlias(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
 477                          const Twine &Name, Constant *Aliasee,
 478                          Module *ParentModule)
 479     : GlobalIndirectSymbol(Ty, Value::GlobalAliasVal, AddressSpace, Link, Name,
 480                            Aliasee) {
 481   if (ParentModule)
 482     ParentModule->getAliasList().push_back(this);
 483 }
 484
 485 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 486                                  LinkageTypes Link, const Twine &Name,
 487                                  Constant *Aliasee, Module *ParentModule) {
 488   return new GlobalAlias(Ty, AddressSpace, Link, Name, Aliasee, ParentModule);
 489 }
 490
 491 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 492                                  LinkageTypes Linkage, const Twine &Name,
 493                                  Module *Parent) {
 494   return create(Ty, AddressSpace, Linkage, Name, nullptr, Parent);
 495 }
 496
 497 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 498                                  LinkageTypes Linkage, const Twine &Name,
 499                                  GlobalValue *Aliasee) {
 500   return create(Ty, AddressSpace, Linkage, Name, Aliasee, Aliasee->getParent());
 501 }
 502
 503 GlobalAlias *GlobalAlias::create(LinkageTypes Link, const Twine &Name,
 504                                  GlobalValue *Aliasee) {
 505   return create(Aliasee->getValueType(), Aliasee->getAddressSpace(), Link, Name,
 506                 Aliasee);
 507 }
 508
 509 GlobalAlias *GlobalAlias::create(const Twine &Name, GlobalValue *Aliasee) {
 510   return create(Aliasee->getLinkage(), Name, Aliasee);
 511 }
 512
 513 void GlobalAlias::removeFromParent() {
 514   getParent()->getAliasList().remove(getIterator());
 515 }
 516
 517 void GlobalAlias::eraseFromParent() {
 518   getParent()->getAliasList().erase(getIterator());
 519 }
 520
 521 void GlobalAlias::setAliasee(Constant *Aliasee) {
 522   assert((!Aliasee || Aliasee->getType() == getType()) &&
 523          "Alias and aliasee types should match!");
 524   setIndirectSymbol(Aliasee);
 525 }
 526
 527 //===----------------------------------------------------------------------===//
 528 // GlobalIFunc Implementation
 529 //===----------------------------------------------------------------------===//
 530
 531 GlobalIFunc::GlobalIFunc(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
 532                          const Twine &Name, Constant *Resolver,
 533                          Module *ParentModule)
 534     : GlobalIndirectSymbol(Ty, Value::GlobalIFuncVal, AddressSpace, Link, Name,
 535                            Resolver) {
 536   if (ParentModule)
 537     ParentModule->getIFuncList().push_back(this);
 538 }
 539
 540 GlobalIFunc *GlobalIFunc::create(Type *Ty, unsigned AddressSpace,
 541                                  LinkageTypes Link, const Twine &Name,
 542                                  Constant *Resolver, Module *ParentModule) {
 543   return new GlobalIFunc(Ty, AddressSpace, Link, Name, Resolver, ParentModule);
 544 }
 545
 546 void GlobalIFunc::removeFromParent() {
 547   getParent()->getIFuncList().remove(getIterator());
 548 }
 549
 550 void GlobalIFunc::eraseFromParent() {
 551   getParent()->getIFuncList().erase(getIterator());
 552 }