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"
27using 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.
36static_assert(sizeof(GlobalValue) ==
37                  sizeof(Constant) + 2 * sizeof(void *) + 2 * sizeof(unsigned),
38              "unexpected GlobalValue size growth");
39
40// GlobalObject adds a comdat.
41static_assert(sizeof(GlobalObject) == sizeof(GlobalValue) + sizeof(void *),
42              "unexpected GlobalObject size growth");
43
44bool GlobalValue::isMaterializable() const {
45  if (const Function *F = dyn_cast<Function>(this))
46    return F->isMaterializable();
47  return false;
48}
49Error 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.
55void GlobalValue::destroyConstantImpl() {
56  llvm_unreachable("You can't GV->destroyConstantImpl()!");
57}
58
59Value *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.
65void 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
73void 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
85void 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
97unsigned 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
111unsigned GlobalValue::getAddressSpace() const {
112  PointerType *PtrTy = getType();
113  return PtrTy->getAddressSpace();
114}
115
116void GlobalObject::setAlignment(unsigned Align) {
117  setAlignment(MaybeAlign(Align));
118}
119
120void 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
130void GlobalObject::copyAttributesFrom(const GlobalObject *Src) {
131  GlobalValue::copyAttributesFrom(Src);
132  setAlignment(MaybeAlign(Src->getAlignment()));
133  setSection(Src->getSection());
134}
135
136std::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
160std::string GlobalValue::getGlobalIdentifier() const {
161  return getGlobalIdentifier(getName(), getLinkage(),
162                             getParent()->getSourceFileName());
163}
164
165StringRef 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
175const 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
188StringRef GlobalValue::getPartition() const {
189  if (!hasPartition())
190    return "";
191  return getContext().pImpl->GlobalValuePartitions[this];
192}
193
194void 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
210StringRef GlobalObject::getSectionImpl() const {
211  assert(hasSection());
212  return getContext().pImpl->GlobalObjectSections[this];
213}
214
215void 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
231bool 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
245bool 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
286const 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
294bool 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
302Optional<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
314bool 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
336GlobalVariable::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
355GlobalVariable::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
380void GlobalVariable::removeFromParent() {
381  getParent()->getGlobalList().remove(getIterator());
382}
383
384void GlobalVariable::eraseFromParent() {
385  getParent()->getGlobalList().erase(getIterator());
386}
387
388void 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.
411void GlobalVariable::copyAttributesFrom(const GlobalVariable *Src) {
412  GlobalObject::copyAttributesFrom(Src);
413  setThreadLocalMode(Src->getThreadLocalMode());
414  setExternallyInitialized(Src->isExternallyInitialized());
415  setAttributes(Src->getAttributes());
416}
417
418void GlobalVariable::dropAllReferences() {
419  User::dropAllReferences();
420  clearMetadata();
421}
422
423//===----------------------------------------------------------------------===//
424// GlobalIndirectSymbol Implementation
425//===----------------------------------------------------------------------===//
426
427GlobalIndirectSymbol::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
434static const GlobalObject *
435findBaseObject(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
467const GlobalObject *GlobalIndirectSymbol::getBaseObject() const {
468  DenseSet<const GlobalAlias *> Aliases;
469  return findBaseObject(getOperand(0), Aliases);
470}
471
472//===----------------------------------------------------------------------===//
473// GlobalAlias Implementation
474//===----------------------------------------------------------------------===//
475
476GlobalAlias::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
485GlobalAlias *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
491GlobalAlias *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
497GlobalAlias *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
503GlobalAlias *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
510GlobalAlias *GlobalAlias::create(const Twine &Name, GlobalValue *Aliasee) {
511  return create(Aliasee->getLinkage(), Name, Aliasee);
512}
513
514void GlobalAlias::removeFromParent() {
515  getParent()->getAliasList().remove(getIterator());
516}
517
518void GlobalAlias::eraseFromParent() {
519  getParent()->getAliasList().erase(getIterator());
520}
521
522void 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
532GlobalIFunc::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
541GlobalIFunc *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
547void GlobalIFunc::removeFromParent() {
548  getParent()->getIFuncList().remove(getIterator());
549}
550
551void GlobalIFunc::eraseFromParent() {
552  getParent()->getIFuncList().erase(getIterator());
553}
554