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   setAlignment(MaybeAlign(Align));
 118 }
 119
 120 void GlobalObject::setAlignment(MaybeAlign Align) {
 121   assert((!Align || Align <= MaximumAlignment) &&
 122          "Alignment is greater than MaximumAlignment!");
 123   unsigned AlignmentData = encode(Align);
 124   unsigned OldData = getGlobalValueSubClassData();
 125   setGlobalValueSubClassData((OldData & ~AlignmentMask) | AlignmentData);
 126   assert(MaybeAlign(getAlignment()) == Align &&
 127          "Alignment representation error!");
 128 }
 129
 130 void GlobalObject::copyAttributesFrom(const GlobalObject *Src) {
 131   GlobalValue::copyAttributesFrom(Src);
 132   setAlignment(MaybeAlign(Src->getAlignment()));
 133   setSection(Src->getSection());
 134 }
 135
 136 std::string GlobalValue::getGlobalIdentifier(StringRef Name,
 137                                              GlobalValue::LinkageTypes Linkage,
 138                                              StringRef FileName) {
 139
 140   // Value names may be prefixed with a binary '1' to indicate
 141   // that the backend should not modify the symbols due to any platform
 142   // naming convention. Do not include that '1' in the PGO profile name.
 143   if (Name[0] == '\1')
 144     Name = Name.substr(1);
 145
 146   std::string NewName = Name;
 147   if (llvm::GlobalValue::isLocalLinkage(Linkage)) {
 148     // For local symbols, prepend the main file name to distinguish them.
 149     // Do not include the full path in the file name since there's no guarantee
 150     // that it will stay the same, e.g., if the files are checked out from
 151     // version control in different locations.
 152     if (FileName.empty())
 153       NewName = NewName.insert(0, "<unknown>:");
 154     else
 155       NewName = NewName.insert(0, FileName.str() + ":");
 156   }
 157   return NewName;
 158 }
 159
 160 std::string GlobalValue::getGlobalIdentifier() const {
 161   return getGlobalIdentifier(getName(), getLinkage(),
 162                              getParent()->getSourceFileName());
 163 }
 164
 165 StringRef GlobalValue::getSection() const {
 166   if (auto *GA = dyn_cast<GlobalAlias>(this)) {
 167     // In general we cannot compute this at the IR level, but we try.
 168     if (const GlobalObject *GO = GA->getBaseObject())
 169       return GO->getSection();
 170     return "";
 171   }
 172   return cast<GlobalObject>(this)->getSection();
 173 }
 174
 175 const Comdat *GlobalValue::getComdat() const {
 176   if (auto *GA = dyn_cast<GlobalAlias>(this)) {
 177     // In general we cannot compute this at the IR level, but we try.
 178     if (const GlobalObject *GO = GA->getBaseObject())
 179       return const_cast<GlobalObject *>(GO)->getComdat();
 180     return nullptr;
 181   }
 182   // ifunc and its resolver are separate things so don't use resolver comdat.
 183   if (isa<GlobalIFunc>(this))
 184     return nullptr;
 185   return cast<GlobalObject>(this)->getComdat();
 186 }
 187
 188 StringRef GlobalValue::getPartition() const {
 189   if (!hasPartition())
 190     return "";
 191   return getContext().pImpl->GlobalValuePartitions[this];
 192 }
 193
 194 void GlobalValue::setPartition(StringRef S) {
 195   // Do nothing if we're clearing the partition and it is already empty.
 196   if (!hasPartition() && S.empty())
 197     return;
 198
 199   // Get or create a stable partition name string and put it in the table in the
 200   // context.
 201   if (!S.empty())
 202     S = getContext().pImpl->Saver.save(S);
 203   getContext().pImpl->GlobalValuePartitions[this] = S;
 204
 205   // Update the HasPartition field. Setting the partition to the empty string
 206   // means this global no longer has a partition.
 207   HasPartition = !S.empty();
 208 }
 209
 210 StringRef GlobalObject::getSectionImpl() const {
 211   assert(hasSection());
 212   return getContext().pImpl->GlobalObjectSections[this];
 213 }
 214
 215 void GlobalObject::setSection(StringRef S) {
 216   // Do nothing if we're clearing the section and it is already empty.
 217   if (!hasSection() && S.empty())
 218     return;
 219
 220   // Get or create a stable section name string and put it in the table in the
 221   // context.
 222   if (!S.empty())
 223     S = getContext().pImpl->Saver.save(S);
 224   getContext().pImpl->GlobalObjectSections[this] = S;
 225
 226   // Update the HasSectionHashEntryBit. Setting the section to the empty string
 227   // means this global no longer has a section.
 228   setGlobalObjectFlag(HasSectionHashEntryBit, !S.empty());
 229 }
 230
 231 bool GlobalValue::isDeclaration() const {
 232   // Globals are definitions if they have an initializer.
 233   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(this))
 234     return GV->getNumOperands() == 0;
 235
 236   // Functions are definitions if they have a body.
 237   if (const Function *F = dyn_cast<Function>(this))
 238     return F->empty() && !F->isMaterializable();
 239
 240   // Aliases and ifuncs are always definitions.
 241   assert(isa<GlobalIndirectSymbol>(this));
 242   return false;
 243 }
 244
 245 bool GlobalValue::canIncreaseAlignment() const {
 246   // Firstly, can only increase the alignment of a global if it
 247   // is a strong definition.
 248   if (!isStrongDefinitionForLinker())
 249     return false;
 250
 251   // It also has to either not have a section defined, or, not have
 252   // alignment specified. (If it is assigned a section, the global
 253   // could be densely packed with other objects in the section, and
 254   // increasing the alignment could cause padding issues.)
 255   if (hasSection() && getAlignment() > 0)
 256     return false;
 257
 258   // On ELF platforms, we're further restricted in that we can't
 259   // increase the alignment of any variable which might be emitted
 260   // into a shared library, and which is exported. If the main
 261   // executable accesses a variable found in a shared-lib, the main
 262   // exe actually allocates memory for and exports the symbol ITSELF,
 263   // overriding the symbol found in the library. That is, at link
 264   // time, the observed alignment of the variable is copied into the
 265   // executable binary. (A COPY relocation is also generated, to copy
 266   // the initial data from the shadowed variable in the shared-lib
 267   // into the location in the main binary, before running code.)
 268   //
 269   // And thus, even though you might think you are defining the
 270   // global, and allocating the memory for the global in your object
 271   // file, and thus should be able to set the alignment arbitrarily,
 272   // that's not actually true. Doing so can cause an ABI breakage; an
 273   // executable might have already been built with the previous
 274   // alignment of the variable, and then assuming an increased
 275   // alignment will be incorrect.
 276
 277   // Conservatively assume ELF if there's no parent pointer.
 278   bool isELF =
 279       (!Parent || Triple(Parent->getTargetTriple()).isOSBinFormatELF());
 280   if (isELF && !isDSOLocal())
 281     return false;
 282
 283   return true;
 284 }
 285
 286 const GlobalObject *GlobalValue::getBaseObject() const {
 287   if (auto *GO = dyn_cast<GlobalObject>(this))
 288     return GO;
 289   if (auto *GA = dyn_cast<GlobalIndirectSymbol>(this))
 290     return GA->getBaseObject();
 291   return nullptr;
 292 }
 293
 294 bool GlobalValue::isAbsoluteSymbolRef() const {
 295   auto *GO = dyn_cast<GlobalObject>(this);
 296   if (!GO)
 297     return false;
 298
 299   return GO->getMetadata(LLVMContext::MD_absolute_symbol);
 300 }
 301
 302 Optional<ConstantRange> GlobalValue::getAbsoluteSymbolRange() const {
 303   auto *GO = dyn_cast<GlobalObject>(this);
 304   if (!GO)
 305     return None;
 306
 307   MDNode *MD = GO->getMetadata(LLVMContext::MD_absolute_symbol);
 308   if (!MD)
 309     return None;
 310
 311   return getConstantRangeFromMetadata(*MD);
 312 }
 313
 314 bool GlobalValue::canBeOmittedFromSymbolTable() const {
 315   if (!hasLinkOnceODRLinkage())
 316     return false;
 317
 318   // We assume that anyone who sets global unnamed_addr on a non-constant
 319   // knows what they're doing.
 320   if (hasGlobalUnnamedAddr())
 321     return true;
 322
 323   // If it is a non constant variable, it needs to be uniqued across shared
 324   // objects.
 325   if (auto *Var = dyn_cast<GlobalVariable>(this))
 326     if (!Var->isConstant())
 327       return false;
 328
 329   return hasAtLeastLocalUnnamedAddr();
 330 }
 331
 332 //===----------------------------------------------------------------------===//
 333 // GlobalVariable Implementation
 334 //===----------------------------------------------------------------------===//
 335
 336 GlobalVariable::GlobalVariable(Type *Ty, bool constant, LinkageTypes Link,
 337                                Constant *InitVal, const Twine &Name,
 338                                ThreadLocalMode TLMode, unsigned AddressSpace,
 339                                bool isExternallyInitialized)
 340     : GlobalObject(Ty, Value::GlobalVariableVal,
 341                    OperandTraits<GlobalVariable>::op_begin(this),
 342                    InitVal != nullptr, Link, Name, AddressSpace),
 343       isConstantGlobal(constant),
 344       isExternallyInitializedConstant(isExternallyInitialized) {
 345   assert(!Ty->isFunctionTy() && PointerType::isValidElementType(Ty) &&
 346          "invalid type for global variable");
 347   setThreadLocalMode(TLMode);
 348   if (InitVal) {
 349     assert(InitVal->getType() == Ty &&
 350            "Initializer should be the same type as the GlobalVariable!");
 351     Op<0>() = InitVal;
 352   }
 353 }
 354
 355 GlobalVariable::GlobalVariable(Module &M, Type *Ty, bool constant,
 356                                LinkageTypes Link, Constant *InitVal,
 357                                const Twine &Name, GlobalVariable *Before,
 358                                ThreadLocalMode TLMode, unsigned AddressSpace,
 359                                bool isExternallyInitialized)
 360     : GlobalObject(Ty, Value::GlobalVariableVal,
 361                    OperandTraits<GlobalVariable>::op_begin(this),
 362                    InitVal != nullptr, Link, Name, AddressSpace),
 363       isConstantGlobal(constant),
 364       isExternallyInitializedConstant(isExternallyInitialized) {
 365   assert(!Ty->isFunctionTy() && PointerType::isValidElementType(Ty) &&
 366          "invalid type for global variable");
 367   setThreadLocalMode(TLMode);
 368   if (InitVal) {
 369     assert(InitVal->getType() == Ty &&
 370            "Initializer should be the same type as the GlobalVariable!");
 371     Op<0>() = InitVal;
 372   }
 373
 374   if (Before)
 375     Before->getParent()->getGlobalList().insert(Before->getIterator(), this);
 376   else
 377     M.getGlobalList().push_back(this);
 378 }
 379
 380 void GlobalVariable::removeFromParent() {
 381   getParent()->getGlobalList().remove(getIterator());
 382 }
 383
 384 void GlobalVariable::eraseFromParent() {
 385   getParent()->getGlobalList().erase(getIterator());
 386 }
 387
 388 void GlobalVariable::setInitializer(Constant *InitVal) {
 389   if (!InitVal) {
 390     if (hasInitializer()) {
 391       // Note, the num operands is used to compute the offset of the operand, so
 392       // the order here matters.  Clearing the operand then clearing the num
 393       // operands ensures we have the correct offset to the operand.
 394       Op<0>().set(nullptr);
 395       setGlobalVariableNumOperands(0);
 396     }
 397   } else {
 398     assert(InitVal->getType() == getValueType() &&
 399            "Initializer type must match GlobalVariable type");
 400     // Note, the num operands is used to compute the offset of the operand, so
 401     // the order here matters.  We need to set num operands to 1 first so that
 402     // we get the correct offset to the first operand when we set it.
 403     if (!hasInitializer())
 404       setGlobalVariableNumOperands(1);
 405     Op<0>().set(InitVal);
 406   }
 407 }
 408
 409 /// Copy all additional attributes (those not needed to create a GlobalVariable)
 410 /// from the GlobalVariable Src to this one.
 411 void GlobalVariable::copyAttributesFrom(const GlobalVariable *Src) {
 412   GlobalObject::copyAttributesFrom(Src);
 413   setThreadLocalMode(Src->getThreadLocalMode());
 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   PointerType *PTy = Aliasee->getType();
 506   return create(PTy->getElementType(), PTy->getAddressSpace(), Link, Name,
 507                 Aliasee);
 508 }
 509
 510 GlobalAlias *GlobalAlias::create(const Twine &Name, GlobalValue *Aliasee) {
 511   return create(Aliasee->getLinkage(), Name, Aliasee);
 512 }
 513
 514 void GlobalAlias::removeFromParent() {
 515   getParent()->getAliasList().remove(getIterator());
 516 }
 517
 518 void GlobalAlias::eraseFromParent() {
 519   getParent()->getAliasList().erase(getIterator());
 520 }
 521
 522 void GlobalAlias::setAliasee(Constant *Aliasee) {
 523   assert((!Aliasee || Aliasee->getType() == getType()) &&
 524          "Alias and aliasee types should match!");
 525   setIndirectSymbol(Aliasee);
 526 }
 527
 528 //===----------------------------------------------------------------------===//
 529 // GlobalIFunc Implementation
 530 //===----------------------------------------------------------------------===//
 531
 532 GlobalIFunc::GlobalIFunc(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
 533                          const Twine &Name, Constant *Resolver,
 534                          Module *ParentModule)
 535     : GlobalIndirectSymbol(Ty, Value::GlobalIFuncVal, AddressSpace, Link, Name,
 536                            Resolver) {
 537   if (ParentModule)
 538     ParentModule->getIFuncList().push_back(this);
 539 }
 540
 541 GlobalIFunc *GlobalIFunc::create(Type *Ty, unsigned AddressSpace,
 542                                  LinkageTypes Link, const Twine &Name,
 543                                  Constant *Resolver, Module *ParentModule) {
 544   return new GlobalIFunc(Ty, AddressSpace, Link, Name, Resolver, ParentModule);
 545 }
 546
 547 void GlobalIFunc::removeFromParent() {
 548   getParent()->getIFuncList().remove(getIterator());
 549 }
 550
 551 void GlobalIFunc::eraseFromParent() {
 552   getParent()->getIFuncList().erase(getIterator());
 553 }