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   setDLLStorageClass(Src->getDLLStorageClass());
  69   setDSOLocal(Src->isDSOLocal());
  70   setPartition(Src->getPartition());
  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 GlobalValue::getPartition() const {
 185   if (!hasPartition())
 186     return "";
 187   return getContext().pImpl->GlobalValuePartitions[this];
 188 }
 189
 190 void GlobalValue::setPartition(StringRef S) {
 191   // Do nothing if we're clearing the partition and it is already empty.
 192   if (!hasPartition() && S.empty())
 193     return;
 194
 195   // Get or create a stable partition name string and put it in the table in the
 196   // context.
 197   if (!S.empty())
 198     S = getContext().pImpl->Saver.save(S);
 199   getContext().pImpl->GlobalValuePartitions[this] = S;
 200
 201   // Update the HasPartition field. Setting the partition to the empty string
 202   // means this global no longer has a partition.
 203   HasPartition = !S.empty();
 204 }
 205
 206 StringRef GlobalObject::getSectionImpl() const {
 207   assert(hasSection());
 208   return getContext().pImpl->GlobalObjectSections[this];
 209 }
 210
 211 void GlobalObject::setSection(StringRef S) {
 212   // Do nothing if we're clearing the section and it is already empty.
 213   if (!hasSection() && S.empty())
 214     return;
 215
 216   // Get or create a stable section name string and put it in the table in the
 217   // context.
 218   if (!S.empty())
 219     S = getContext().pImpl->Saver.save(S);
 220   getContext().pImpl->GlobalObjectSections[this] = S;
 221
 222   // Update the HasSectionHashEntryBit. Setting the section to the empty string
 223   // means this global no longer has a section.
 224   setGlobalObjectFlag(HasSectionHashEntryBit, !S.empty());
 225 }
 226
 227 bool GlobalValue::isDeclaration() const {
 228   // Globals are definitions if they have an initializer.
 229   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(this))
 230     return GV->getNumOperands() == 0;
 231
 232   // Functions are definitions if they have a body.
 233   if (const Function *F = dyn_cast<Function>(this))
 234     return F->empty() && !F->isMaterializable();
 235
 236   // Aliases and ifuncs are always definitions.
 237   assert(isa<GlobalIndirectSymbol>(this));
 238   return false;
 239 }
 240
 241 bool GlobalValue::canIncreaseAlignment() const {
 242   // Firstly, can only increase the alignment of a global if it
 243   // is a strong definition.
 244   if (!isStrongDefinitionForLinker())
 245     return false;
 246
 247   // It also has to either not have a section defined, or, not have
 248   // alignment specified. (If it is assigned a section, the global
 249   // could be densely packed with other objects in the section, and
 250   // increasing the alignment could cause padding issues.)
 251   if (hasSection() && getAlignment() > 0)
 252     return false;
 253
 254   // On ELF platforms, we're further restricted in that we can't
 255   // increase the alignment of any variable which might be emitted
 256   // into a shared library, and which is exported. If the main
 257   // executable accesses a variable found in a shared-lib, the main
 258   // exe actually allocates memory for and exports the symbol ITSELF,
 259   // overriding the symbol found in the library. That is, at link
 260   // time, the observed alignment of the variable is copied into the
 261   // executable binary. (A COPY relocation is also generated, to copy
 262   // the initial data from the shadowed variable in the shared-lib
 263   // into the location in the main binary, before running code.)
 264   //
 265   // And thus, even though you might think you are defining the
 266   // global, and allocating the memory for the global in your object
 267   // file, and thus should be able to set the alignment arbitrarily,
 268   // that's not actually true. Doing so can cause an ABI breakage; an
 269   // executable might have already been built with the previous
 270   // alignment of the variable, and then assuming an increased
 271   // alignment will be incorrect.
 272
 273   // Conservatively assume ELF if there's no parent pointer.
 274   bool isELF =
 275       (!Parent || Triple(Parent->getTargetTriple()).isOSBinFormatELF());
 276   if (isELF && !isDSOLocal())
 277     return false;
 278
 279   return true;
 280 }
 281
 282 const GlobalObject *GlobalValue::getBaseObject() const {
 283   if (auto *GO = dyn_cast<GlobalObject>(this))
 284     return GO;
 285   if (auto *GA = dyn_cast<GlobalIndirectSymbol>(this))
 286     return GA->getBaseObject();
 287   return nullptr;
 288 }
 289
 290 bool GlobalValue::isAbsoluteSymbolRef() const {
 291   auto *GO = dyn_cast<GlobalObject>(this);
 292   if (!GO)
 293     return false;
 294
 295   return GO->getMetadata(LLVMContext::MD_absolute_symbol);
 296 }
 297
 298 Optional<ConstantRange> GlobalValue::getAbsoluteSymbolRange() const {
 299   auto *GO = dyn_cast<GlobalObject>(this);
 300   if (!GO)
 301     return None;
 302
 303   MDNode *MD = GO->getMetadata(LLVMContext::MD_absolute_symbol);
 304   if (!MD)
 305     return None;
 306
 307   return getConstantRangeFromMetadata(*MD);
 308 }
 309
 310 bool GlobalValue::canBeOmittedFromSymbolTable() const {
 311   if (!hasLinkOnceODRLinkage())
 312     return false;
 313
 314   // We assume that anyone who sets global unnamed_addr on a non-constant
 315   // knows what they're doing.
 316   if (hasGlobalUnnamedAddr())
 317     return true;
 318
 319   // If it is a non constant variable, it needs to be uniqued across shared
 320   // objects.
 321   if (auto *Var = dyn_cast<GlobalVariable>(this))
 322     if (!Var->isConstant())
 323       return false;
 324
 325   return hasAtLeastLocalUnnamedAddr();
 326 }
 327
 328 //===----------------------------------------------------------------------===//
 329 // GlobalVariable Implementation
 330 //===----------------------------------------------------------------------===//
 331
 332 GlobalVariable::GlobalVariable(Type *Ty, bool constant, LinkageTypes Link,
 333                                Constant *InitVal, const Twine &Name,
 334                                ThreadLocalMode TLMode, unsigned AddressSpace,
 335                                bool isExternallyInitialized)
 336     : GlobalObject(Ty, Value::GlobalVariableVal,
 337                    OperandTraits<GlobalVariable>::op_begin(this),
 338                    InitVal != nullptr, Link, Name, AddressSpace),
 339       isConstantGlobal(constant),
 340       isExternallyInitializedConstant(isExternallyInitialized) {
 341   assert(!Ty->isFunctionTy() && PointerType::isValidElementType(Ty) &&
 342          "invalid type for global variable");
 343   setThreadLocalMode(TLMode);
 344   if (InitVal) {
 345     assert(InitVal->getType() == Ty &&
 346            "Initializer should be the same type as the GlobalVariable!");
 347     Op<0>() = InitVal;
 348   }
 349 }
 350
 351 GlobalVariable::GlobalVariable(Module &M, Type *Ty, bool constant,
 352                                LinkageTypes Link, Constant *InitVal,
 353                                const Twine &Name, GlobalVariable *Before,
 354                                ThreadLocalMode TLMode, unsigned AddressSpace,
 355                                bool isExternallyInitialized)
 356     : GlobalObject(Ty, Value::GlobalVariableVal,
 357                    OperandTraits<GlobalVariable>::op_begin(this),
 358                    InitVal != nullptr, Link, Name, AddressSpace),
 359       isConstantGlobal(constant),
 360       isExternallyInitializedConstant(isExternallyInitialized) {
 361   assert(!Ty->isFunctionTy() && PointerType::isValidElementType(Ty) &&
 362          "invalid type for global variable");
 363   setThreadLocalMode(TLMode);
 364   if (InitVal) {
 365     assert(InitVal->getType() == Ty &&
 366            "Initializer should be the same type as the GlobalVariable!");
 367     Op<0>() = InitVal;
 368   }
 369
 370   if (Before)
 371     Before->getParent()->getGlobalList().insert(Before->getIterator(), this);
 372   else
 373     M.getGlobalList().push_back(this);
 374 }
 375
 376 void GlobalVariable::removeFromParent() {
 377   getParent()->getGlobalList().remove(getIterator());
 378 }
 379
 380 void GlobalVariable::eraseFromParent() {
 381   getParent()->getGlobalList().erase(getIterator());
 382 }
 383
 384 void GlobalVariable::setInitializer(Constant *InitVal) {
 385   if (!InitVal) {
 386     if (hasInitializer()) {
 387       // Note, the num operands is used to compute the offset of the operand, so
 388       // the order here matters.  Clearing the operand then clearing the num
 389       // operands ensures we have the correct offset to the operand.
 390       Op<0>().set(nullptr);
 391       setGlobalVariableNumOperands(0);
 392     }
 393   } else {
 394     assert(InitVal->getType() == getValueType() &&
 395            "Initializer type must match GlobalVariable type");
 396     // Note, the num operands is used to compute the offset of the operand, so
 397     // the order here matters.  We need to set num operands to 1 first so that
 398     // we get the correct offset to the first operand when we set it.
 399     if (!hasInitializer())
 400       setGlobalVariableNumOperands(1);
 401     Op<0>().set(InitVal);
 402   }
 403 }
 404
 405 /// Copy all additional attributes (those not needed to create a GlobalVariable)
 406 /// from the GlobalVariable Src to this one.
 407 void GlobalVariable::copyAttributesFrom(const GlobalVariable *Src) {
 408   GlobalObject::copyAttributesFrom(Src);
 409   setThreadLocalMode(Src->getThreadLocalMode());
 410   setExternallyInitialized(Src->isExternallyInitialized());
 411   setAttributes(Src->getAttributes());
 412 }
 413
 414 void GlobalVariable::dropAllReferences() {
 415   User::dropAllReferences();
 416   clearMetadata();
 417 }
 418
 419 //===----------------------------------------------------------------------===//
 420 // GlobalIndirectSymbol Implementation
 421 //===----------------------------------------------------------------------===//
 422
 423 GlobalIndirectSymbol::GlobalIndirectSymbol(Type *Ty, ValueTy VTy,
 424     unsigned AddressSpace, LinkageTypes Linkage, const Twine &Name,
 425     Constant *Symbol)
 426     : GlobalValue(Ty, VTy, &Op<0>(), 1, Linkage, Name, AddressSpace) {
 427     Op<0>() = Symbol;
 428 }
 429
 430
 431 //===----------------------------------------------------------------------===//
 432 // GlobalAlias Implementation
 433 //===----------------------------------------------------------------------===//
 434
 435 GlobalAlias::GlobalAlias(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
 436                          const Twine &Name, Constant *Aliasee,
 437                          Module *ParentModule)
 438     : GlobalIndirectSymbol(Ty, Value::GlobalAliasVal, AddressSpace, Link, Name,
 439                            Aliasee) {
 440   if (ParentModule)
 441     ParentModule->getAliasList().push_back(this);
 442 }
 443
 444 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 445                                  LinkageTypes Link, const Twine &Name,
 446                                  Constant *Aliasee, Module *ParentModule) {
 447   return new GlobalAlias(Ty, AddressSpace, Link, Name, Aliasee, ParentModule);
 448 }
 449
 450 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 451                                  LinkageTypes Linkage, const Twine &Name,
 452                                  Module *Parent) {
 453   return create(Ty, AddressSpace, Linkage, Name, nullptr, Parent);
 454 }
 455
 456 GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
 457                                  LinkageTypes Linkage, const Twine &Name,
 458                                  GlobalValue *Aliasee) {
 459   return create(Ty, AddressSpace, Linkage, Name, Aliasee, Aliasee->getParent());
 460 }
 461
 462 GlobalAlias *GlobalAlias::create(LinkageTypes Link, const Twine &Name,
 463                                  GlobalValue *Aliasee) {
 464   PointerType *PTy = Aliasee->getType();
 465   return create(PTy->getElementType(), PTy->getAddressSpace(), Link, Name,
 466                 Aliasee);
 467 }
 468
 469 GlobalAlias *GlobalAlias::create(const Twine &Name, GlobalValue *Aliasee) {
 470   return create(Aliasee->getLinkage(), Name, Aliasee);
 471 }
 472
 473 void GlobalAlias::removeFromParent() {
 474   getParent()->getAliasList().remove(getIterator());
 475 }
 476
 477 void GlobalAlias::eraseFromParent() {
 478   getParent()->getAliasList().erase(getIterator());
 479 }
 480
 481 void GlobalAlias::setAliasee(Constant *Aliasee) {
 482   assert((!Aliasee || Aliasee->getType() == getType()) &&
 483          "Alias and aliasee types should match!");
 484   setIndirectSymbol(Aliasee);
 485 }
 486
 487 //===----------------------------------------------------------------------===//
 488 // GlobalIFunc Implementation
 489 //===----------------------------------------------------------------------===//
 490
 491 GlobalIFunc::GlobalIFunc(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
 492                          const Twine &Name, Constant *Resolver,
 493                          Module *ParentModule)
 494     : GlobalIndirectSymbol(Ty, Value::GlobalIFuncVal, AddressSpace, Link, Name,
 495                            Resolver) {
 496   if (ParentModule)
 497     ParentModule->getIFuncList().push_back(this);
 498 }
 499
 500 GlobalIFunc *GlobalIFunc::create(Type *Ty, unsigned AddressSpace,
 501                                  LinkageTypes Link, const Twine &Name,
 502                                  Constant *Resolver, Module *ParentModule) {
 503   return new GlobalIFunc(Ty, AddressSpace, Link, Name, Resolver, ParentModule);
 504 }
 505
 506 void GlobalIFunc::removeFromParent() {
 507   getParent()->getIFuncList().remove(getIterator());
 508 }
 509
 510 void GlobalIFunc::eraseFromParent() {
 511   getParent()->getIFuncList().erase(getIterator());
 512 }