lib/IR/Globals.cpp

   1 //===-- Globals.cpp - Implement the GlobalValue & GlobalVariable class ----===//
   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 implements the GlobalValue & GlobalVariable classes for the IR
  11 // library.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "LLVMContextImpl.h"
  16 #include "llvm/ADT/SmallPtrSet.h"
  17 #include "llvm/ADT/Triple.h"
  18 #include "llvm/IR/ConstantRange.h"
  19 #include "llvm/IR/Constants.h"
  20 #include "llvm/IR/DerivedTypes.h"
  21 #include "llvm/IR/GlobalAlias.h"
  22 #include "llvm/IR/GlobalValue.h"
  23 #include "llvm/IR/GlobalVariable.h"
  24 #include "llvm/IR/Module.h"
  25 #include "llvm/IR/Operator.h"
  26 #include "llvm/Support/Error.h"
  27 #include "llvm/Support/ErrorHandling.h"
  28 using namespace llvm;
  29
  30 //===----------------------------------------------------------------------===//
  31 //                            GlobalValue Class
  32 //===----------------------------------------------------------------------===//
  33
  34 // GlobalValue should be a Constant, plus a type, a module, some flags, and an
  35 // intrinsic ID. Add an assert to prevent people from accidentally growing
  36 // GlobalValue while adding flags.
  37 static_assert(sizeof(GlobalValue) ==
  38                   sizeof(Constant) + 2 * sizeof(void *) + 2 * sizeof(unsigned),
  39               "unexpected GlobalValue size growth");
  40
  41 // GlobalObject adds a comdat.
  42 static_assert(sizeof(GlobalObject) == sizeof(GlobalValue) + sizeof(void *),
  43               "unexpected GlobalObject size growth");
  44
  45 bool GlobalValue::isMaterializable() const {
  46   if (const Function *F = dyn_cast<Function>(this))
  47     return F->isMaterializable();
  48   return false;
  49 }
  50 Error GlobalValue::materialize() {
  51   return getParent()->materialize(this);
  52 }
  53
  54 /// Override destroyConstantImpl to make sure it doesn't get called on
  55 /// GlobalValue's because they shouldn't be treated like other constants.
  56 void GlobalValue::destroyConstantImpl() {
  57   llvm_unreachable("You can't GV->destroyConstantImpl()!");
  58 }
  59
  60 Value *GlobalValue::handleOperandChangeImpl(Value *From, Value *To) {
  61   llvm_unreachable("Unsupported class for handleOperandChange()!");
  62 }
  63
  64 /// copyAttributesFrom - copy all additional attributes (those not needed to
  65 /// create a GlobalValue) from the GlobalValue Src to this one.
  66 void GlobalValue::copyAttributesFrom(const GlobalValue *Src) {
  67   setVisibility(Src->getVisibility());
  68   setUnnamedAddr(Src->getUnnamedAddr());
  69   setDLLStorageClass(Src->getDLLStorageClass());
  70   setDSOLocal(Src->isDSOLocal());
  71 }
  72
  73 void GlobalValue::removeFromParent() {
  74   switch (getValueID()) {
  75 #define HANDLE_GLOBAL_VALUE(NAME)                                              \
  76   case Value::NAME##Val:                                                       \
  77     return static_cast<NAME *>(this)->removeFromParent();
  78 #include "llvm/IR/Value.def"
  79   default:
  80     break;
  81   }
  82   llvm_unreachable("not a global");
  83 }
  84
  85 void GlobalValue::eraseFromParent() {
  86   switch (getValueID()) {
  87 #define HANDLE_GLOBAL_VALUE(NAME)                                              \
  88   case Value::NAME##Val:                                                       \
  89     return static_cast<NAME *>(this)->eraseFromParent();
  90 #include "llvm/IR/Value.def"
  91   default:
  92     break;
  93   }
  94   llvm_unreachable("not a global");
  95 }
  96
  97 unsigned GlobalValue::getAlignment() const {
  98   if (auto *GA = dyn_cast<GlobalAlias>(this)) {
  99     // In general we cannot compute this at the IR level, but we try.
 100     if (const GlobalObject *GO = GA->getBaseObject())
 101       return GO->getAlignment();
 102
 103     // FIXME: we should also be able to handle:
 104     // Alias = Global + Offset
 105     // Alias = Absolute
 106     return 0;
 107   }
 108   return cast<GlobalObject>(this)->getAlignment();
 109 }
 110
 111 unsigned GlobalValue::getAddressSpace() const {
 112   PointerType *PtrTy = getType();
 113   return PtrTy->getAddressSpace();
 114 }
 115
 116 void GlobalObject::setAlignment(unsigned Align) {
 117   assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
 118   assert(Align <= MaximumAlignment &&
 119          "Alignment is greater than MaximumAlignment!");
 120   unsigned AlignmentData = Log2_32(Align) + 1;
 121   unsigned OldData = getGlobalValueSubClassData();
 122   setGlobalValueSubClassData((OldData & ~AlignmentMask) | AlignmentData);
 123   assert(getAlignment() == Align && "Alignment representation error!");
 124 }
 125
 126 void GlobalObject::copyAttributesFrom(const GlobalObject *Src) {
 127   GlobalValue::copyAttributesFrom(Src);
 128   setAlignment(Src->getAlignment());
 129   setSection(Src->getSection());
 130 }
 131
 132 std::string GlobalValue::getGlobalIdentifier(StringRef Name,
 133                                              GlobalValue::LinkageTypes Linkage,
 134                                              StringRef FileName) {
 135
 136   // Value names may be prefixed with a binary '1' to indicate
 137   // that the backend should not modify the symbols due to any platform
 138   // naming convention. Do not include that '1' in the PGO profile name.
 139   if (Name[0] == '\1')
 140     Name = Name.substr(1);
 141
 142   std::string NewName = Name;
 143   if (llvm::GlobalValue::isLocalLinkage(Linkage)) {
 144     // For local symbols, prepend the main file name to distinguish them.
 145     // Do not include the full path in the file name since there's no guarantee
 146     // that it will stay the same, e.g., if the files are checked out from
 147     // version control in different locations.
 148     if (FileName.empty())
 149       NewName = NewName.insert(0, "<unknown>:");
 150     else
 151       NewName = NewName.insert(0, FileName.str() + ":");
 152   }
 153   return NewName;
 154 }
 155
 156 std::string GlobalValue::getGlobalIdentifier() const {
 157   return getGlobalIdentifier(getName(), getLinkage(),
 158                              getParent()->getSourceFileName());
 159 }
 160
 161 StringRef GlobalValue::getSection() const {
 162   if (auto *GA = dyn_cast<GlobalAlias>(this)) {
 163     // In general we cannot compute this at the IR level, but we try.
 164     if (const GlobalObject *GO = GA->getBaseObject())
 165       return GO->getSection();
 166     return "";
 167   }
 168   return cast<GlobalObject>(this)->getSection();
 169 }
 170
 171 const Comdat *GlobalValue::getComdat() const {
 172   if (auto *GA = dyn_cast<GlobalAlias>(this)) {
 173     // In general we cannot compute this at the IR level, but we try.
 174     if (const GlobalObject *GO = GA->getBaseObject())
 175       return const_cast<GlobalObject *>(GO)->getComdat();
 176     return nullptr;
 177   }
 178   // ifunc and its resolver are separate things so don't use resolver comdat.
 179   if (isa<GlobalIFunc>(this))
 180     return nullptr;
 181   return cast<GlobalObject>(this)->getComdat();
 182 }
 183
 184 StringRef GlobalObject::getSectionImpl() const {
 185   assert(hasSection());
 186   return getContext().pImpl->GlobalObjectSections[this];
 187 }
 188
 189 void GlobalObject::setSection(StringRef S) {
 190   // Do nothing if we're clearing the section and it is already empty.
 191   if (!hasSection() && S.empty())
 192     return;
 193
 194   // Get or create a stable section name string and put it in the table in the
 195   // context.
 196   if (!S.empty()) {
 197     S = getContext().pImpl->SectionStrings.insert(S).first->first();
 198   }
 199   getContext().pImpl->GlobalObjectSections[this] = S;
 200
 201   // Update the HasSectionHashEntryBit. Setting the section to the empty string
 202   // means this global no longer has a section.
 203   setGlobalObjectFlag(HasSectionHashEntryBit, !S.empty());
 204 }
 205
 206 bool GlobalValue::isDeclaration() const {
 207   // Globals are definitions if they have an initializer.
 208   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(this))
 209     return GV->getNumOperands() == 0;
 210
 211   // Functions are definitions if they have a body.
 212   if (const Function *F = dyn_cast<Function>(this))
 213     return F->empty() && !F->isMaterializable();
 214
 215   // Aliases and ifuncs are always definitions.
 216   assert(isa<GlobalIndirectSymbol>(this));
 217   return false;
 218 }
 219
 220 bool GlobalValue::canIncreaseAlignment() const {
 221   // Firstly, can only increase the alignment of a global if it
 222   // is a strong definition.
 223   if (!isStrongDefinitionForLinker())
 224     return false;
 225
 226   // It also has to either not have a section defined, or, not have
 227   // alignment specified. (If it is assigned a section, the global
 228   // could be densely packed with other objects in the section, and
 229   // increasing the alignment could cause padding issues.)
 230   if (hasSection() && getAlignment() > 0)
 231     return false;
 232
 233   // On ELF platforms, we're further restricted in that we can't
 234   // increase the alignment of any variable which might be emitted
 235   // into a shared library, and which is exported. If the main
 236   // executable accesses a variable found in a shared-lib, the main
 237   // exe actually allocates memory for and exports the symbol ITSELF,
 238   // overriding the symbol found in the library. That is, at link
 239   // time, the observed alignment of the variable is copied into the
 240   // executable binary. (A COPY relocation is also generated, to copy
 241   // the initial data from the shadowed variable in the shared-lib
 242   // into the location in the main binary, before running code.)
 243   //
 244   // And thus, even though you might think you are defining the
 245   // global, and allocating the memory for the global in your object
 246   // file, and thus should be able to set the alignment arbitrarily,
 247   // that's not actually true. Doing so can cause an ABI breakage; an
 248   // executable might have already been built with the previous
 249   // alignment of the variable, and then assuming an increased
 250   // alignment will be incorrect.
 251
 252   // Conservatively assume ELF if there's no parent pointer.
 253   bool isELF =
 254       (!Parent || Triple(Parent->getTargetTriple()).isOSBinFormatELF());
 255   if (isELF && hasDefaultVisibility() && !hasLocalLinkage())
 256     return false;
 257
 258   return true;
 259 }
 260
 261 const GlobalObject *GlobalValue::getBaseObject() const {
 262   if (auto *GO = dyn_cast<GlobalObject>(this))
 263     return GO;
 264   if (auto *GA = dyn_cast<GlobalIndirectSymbol>(this))
 265     return GA->getBaseObject();
 266   return nullptr;
 267 }
 268
 269 bool GlobalValue::isAbsoluteSymbolRef() const {
 270   auto *GO = dyn_cast<GlobalObject>(this);
 271   if (!GO)
 272     return false;
 273
 274   return GO->getMetadata(LLVMContext::MD_absolute_symbol);
 275 }
 276
 277 Optional<ConstantRange> GlobalValue::getAbsoluteSymbolRange() const {
 278   auto *GO = dyn_cast<GlobalObject>(this);
 279   if (!GO)
 280     return None;
 281
 282   MDNode *MD = GO->getMetadata(LLVMContext::MD_absolute_symbol);
 283   if (!MD)
 284     return None;
 285
 286   return getConstantRangeFromMetadata(*MD);
 287 }
 288
 289 bool GlobalValue::canBeOmittedFromSymbolTable() const {
 290   if (!hasLinkOnceODRLinkage())
 291     return false;
 292
 293   // We assume that anyone who sets global unnamed_addr on a non-constant
 294   // knows what they're doing.
 295   if (hasGlobalUnnamedAddr())
 296     return true;
 297
 298   // If it is a non constant variable, it needs to be uniqued across shared
 299   // objects.
 300   if (auto *Var = dyn_cast<GlobalVariable>(this))
 301     if (!Var->isConstant())
 302       return false;
 303
 304   return hasAtLeastLocalUnnamedAddr();
 305 }
 306
 307 //===----------------------------------------------------------------------===//
 308 // GlobalVariable Implementation
 309 //===----------------------------------------------------------------------===//
 310
 311 GlobalVariable::GlobalVariable(Type *Ty, bool constant, LinkageTypes Link,
 312                                Constant *InitVal, const Twine &Name,
 313                                ThreadLocalMode TLMode, unsigned AddressSpace,
 314                                bool isExternallyInitialized)
 315     : GlobalObject(Ty, Value::GlobalVariableVal,
 316                    OperandTraits<GlobalVariable>::op_begin(this),
 317                    InitVal != nullptr, Link, Name, AddressSpace),
 318       isConstantGlobal(constant),
 319       isExternallyInitializedConstant(isExternallyInitialized) {
 320   assert(!Ty->isFunctionTy() && PointerType::isValidElementType(Ty) &&
 321          "invalid type for global variable");
 322   setThreadLocalMode(TLMode);
 323   if (InitVal) {
 324     assert(InitVal->getType() == Ty &&
 325            "Initializer should be the same type as the GlobalVariable!");
 326     Op<0>() = InitVal;
 327   }
 328 }
 329
 330 GlobalVariable::GlobalVariable(Module &M, Type *Ty, bool constant,
 331                                LinkageTypes Link, Constant *InitVal,
 332                                const Twine &Name, GlobalVariable *Before,
 333                                ThreadLocalMode TLMode, unsigned AddressSpace,
 334                                bool isExternallyInitialized)
 335     : GlobalObject(Ty, Value::GlobalVariableVal,
 336                    OperandTraits<GlobalVariable>::op_begin(this),
 337                    InitVal != nullptr, Link, Name, AddressSpace),
 338       isConstantGlobal(constant),
 339       isExternallyInitializedConstant(isExternallyInitialized) {
 340   assert(!Ty->isFunctionTy() && PointerType::isValidElementType(Ty) &&
 341          "invalid type for global variable");
 342   setThreadLocalMode(TLMode);
 343   if (InitVal) {
 344     assert(InitVal->getType() == Ty &&
 345            "Initializer should be the same type as the GlobalVariable!");
 346     Op<0>() = InitVal;
 347   }
 348
 349   if (Before)
 350     Before->getParent()->getGlobalList().insert(Before->getIterator(), this);
 351   else
 352     M.getGlobalList().push_back(this);
 353 }
 354
 355 void GlobalVariable::removeFromParent() {
 356   getParent()->getGlobalList().remove(getIterator());
 357 }
 358
 359 void GlobalVariable::eraseFromParent() {
 360   getParent()->getGlobalList().erase(getIterator());
 361 }
 362
 363 void GlobalVariable::setInitializer(Constant *InitVal) {
 364   if (!InitVal) {
 365     if (hasInitializer()) {
 366       // Note, the num operands is used to compute the offset of the operand, so
 367       // the order here matters.  Clearing the operand then clearing the num
 368       // operands ensures we have the correct offset to the operand.
 369       Op<0>().set(nullptr);
 370       setGlobalVariableNumOperands(0);
 371     }
 372   } else {
 373     assert(InitVal->getType() == getValueType() &&
 374            "Initializer type must match GlobalVariable type");
 375     // Note, the num operands is used to compute the offset of the operand, so
 376     // the order here matters.  We need to set num operands to 1 first so that
 377     // we get the correct offset to the first operand when we set it.
 378     if (!hasInitializer())
 379       setGlobalVariableNumOperands(1);
 380     Op<0>().set(InitVal);
 381   }
 382 }
 383
 384 /// Copy all additional attributes (those not needed to create a GlobalVariable)
 385 /// from the GlobalVariable Src to this one.
 386 void GlobalVariable::copyAttributesFrom(const GlobalVariable *Src) {
 387   GlobalObject::copyAttributesFrom(Src);
 388   setThreadLocalMode(Src->getThreadLocalMode());
 389   setExternallyInitialized(Src->isExternallyInitialized());
 390   setAttributes(Src->getAttributes());
 391 }
 392
 393 void GlobalVariable::dropAllReferences() {
 394   User::dropAllReferences();
 395   clearMetadata();
 396 }
 397
 398 //===----------------------------------------------------------------------===//
 399 // GlobalIndirectSymbol Implementation
 400 //===----------------------------------------------------------------------===//
 401
 402 GlobalIndirectSymbol::GlobalIndirectSymbol(Type *Ty, ValueTy VTy,
 403     unsigned AddressSpace, LinkageTypes Linkage, const Twine &Name,
 404     Constant *Symbol)
 405     : GlobalValue(Ty, VTy, &Op<0>(), 1, Linkage, Name, AddressSpace) {
 406     Op<0>() = Symbol;
 407 }
 408
 409
 410 //===----------------------------------------------------------------------===//
 411 // GlobalAlias Implementation
 412 //===----------------------------------------------------------------------===//
 413
 414 GlobalAlias::GlobalAlias(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
 415                          const Twine &Name, Constant *Aliasee,
 416                          Module *ParentModule)
 417     : GlobalIndirectSymbol(Ty, Value::GlobalAliasVal, AddressSpace, Link, Name,
 418                            Aliasee) {
 419   if (ParentModule)
 420     ParentModule->getAliasList().push_back(this);
 421 }
 422
 423 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 424                                  LinkageTypes Link, const Twine &Name,
 425                                  Constant *Aliasee, Module *ParentModule) {
 426   return new GlobalAlias(Ty, AddressSpace, Link, Name, Aliasee, ParentModule);
 427 }
 428
 429 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 430                                  LinkageTypes Linkage, const Twine &Name,
 431                                  Module *Parent) {
 432   return create(Ty, AddressSpace, Linkage, Name, nullptr, Parent);
 433 }
 434
 435 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 436                                  LinkageTypes Linkage, const Twine &Name,
 437                                  GlobalValue *Aliasee) {
 438   return create(Ty, AddressSpace, Linkage, Name, Aliasee, Aliasee->getParent());
 439 }
 440
 441 GlobalAlias *GlobalAlias::create(LinkageTypes Link, const Twine &Name,
 442                                  GlobalValue *Aliasee) {
 443   PointerType *PTy = Aliasee->getType();
 444   return create(PTy->getElementType(), PTy->getAddressSpace(), Link, Name,
 445                 Aliasee);
 446 }
 447
 448 GlobalAlias *GlobalAlias::create(const Twine &Name, GlobalValue *Aliasee) {
 449   return create(Aliasee->getLinkage(), Name, Aliasee);
 450 }
 451
 452 void GlobalAlias::removeFromParent() {
 453   getParent()->getAliasList().remove(getIterator());
 454 }
 455
 456 void GlobalAlias::eraseFromParent() {
 457   getParent()->getAliasList().erase(getIterator());
 458 }
 459
 460 void GlobalAlias::setAliasee(Constant *Aliasee) {
 461   assert((!Aliasee || Aliasee->getType() == getType()) &&
 462          "Alias and aliasee types should match!");
 463   setIndirectSymbol(Aliasee);
 464 }
 465
 466 //===----------------------------------------------------------------------===//
 467 // GlobalIFunc Implementation
 468 //===----------------------------------------------------------------------===//
 469
 470 GlobalIFunc::GlobalIFunc(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
 471                          const Twine &Name, Constant *Resolver,
 472                          Module *ParentModule)
 473     : GlobalIndirectSymbol(Ty, Value::GlobalIFuncVal, AddressSpace, Link, Name,
 474                            Resolver) {
 475   if (ParentModule)
 476     ParentModule->getIFuncList().push_back(this);
 477 }
 478
 479 GlobalIFunc *GlobalIFunc::create(Type *Ty, unsigned AddressSpace,
 480                                  LinkageTypes Link, const Twine &Name,
 481                                  Constant *Resolver, Module *ParentModule) {
 482   return new GlobalIFunc(Ty, AddressSpace, Link, Name, Resolver, ParentModule);
 483 }
 484
 485 void GlobalIFunc::removeFromParent() {
 486   getParent()->getIFuncList().remove(getIterator());
 487 }
 488
 489 void GlobalIFunc::eraseFromParent() {
 490   getParent()->getIFuncList().erase(getIterator());
 491 }