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