C++ GlobalAlias::setVisibility方法代码示例

static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
  if (FnVec[i]->mayBeOverridden() && !FnVec[j]->mayBeOverridden())
    std::swap(FnVec[i], FnVec[j]);

  Function *F = FnVec[i];
  Function *G = FnVec[j];

  if (!F->mayBeOverridden()) {
    if (G->hasLocalLinkage()) {
      F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
      G->replaceAllUsesWith(F);
      G->eraseFromParent();
      ++NumFunctionsMerged;
      return true;
    }

    if (G->hasExternalLinkage() || G->hasWeakLinkage()) {
      GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "",
                                        F, G->getParent());
      F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
      GA->takeName(G);
      GA->setVisibility(G->getVisibility());
      G->replaceAllUsesWith(GA);
      G->eraseFromParent();
      ++NumFunctionsMerged;
      return true;
    }
  }

  if (F->hasWeakLinkage() && G->hasWeakLinkage()) {
    GlobalAlias *GA_F = new GlobalAlias(F->getType(), F->getLinkage(), "",
                                        0, F->getParent());
    GA_F->takeName(F);
    GA_F->setVisibility(F->getVisibility());
    F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
    F->replaceAllUsesWith(GA_F);
    F->setName("folded." + GA_F->getName());
    F->setLinkage(GlobalValue::ExternalLinkage);
    GA_F->setAliasee(F);

    GlobalAlias *GA_G = new GlobalAlias(G->getType(), G->getLinkage(), "",
                                        F, G->getParent());
    GA_G->takeName(G);
    GA_G->setVisibility(G->getVisibility());
    G->replaceAllUsesWith(GA_G);
    G->eraseFromParent();

    ++NumFunctionsMerged;
    return true;
  }

  DOUT << "Failed on " << F->getName() << " and " << G->getName() << "\n";

  ++NumMergeFails;
  return false;
}

static void AliasGToF(Function *F, Function *G) {
  if (!G->hasExternalLinkage() && !G->hasLocalLinkage() && !G->hasWeakLinkage())
    return ThunkGToF(F, G);

  GlobalAlias *GA = new GlobalAlias(
    G->getType(), G->getLinkage(), "",
    ConstantExpr::getBitCast(F, G->getType()), G->getParent());
  F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
  GA->takeName(G);
  GA->setVisibility(G->getVisibility());
  G->replaceAllUsesWith(GA);
  G->eraseFromParent();
}

// Replace G with an alias to F and delete G.
void MergeFunctions::writeAlias(Function *F, Function *G) {
  Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
  GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "",
                                    BitcastF, G->getParent());
  F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
  GA->takeName(G);
  GA->setVisibility(G->getVisibility());
  removeUsers(G);
  G->replaceAllUsesWith(GA);
  G->eraseFromParent();

  DEBUG(dbgs() << "writeAlias: " << GA->getName() << '\n');
  ++NumAliasesWritten;
}

/// LinkAliasProto - Set up prototypes for any aliases that come over from the
/// source module.
bool ModuleLinker::linkAliasProto(GlobalAlias *SGA) {
  GlobalValue *DGV = getLinkedToGlobal(SGA);
  llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;

  if (DGV) {
    GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
    GlobalValue::VisibilityTypes NV;
    bool LinkFromSrc = false;
    if (getLinkageResult(DGV, SGA, NewLinkage, NV, LinkFromSrc))
      return true;
    NewVisibility = NV;

    if (!LinkFromSrc) {
      // Set calculated linkage.
      DGV->setLinkage(NewLinkage);
      DGV->setVisibility(*NewVisibility);

      // Make sure to remember this mapping.
      ValueMap[SGA] = ConstantExpr::getBitCast(DGV,TypeMap.get(SGA->getType()));
      
      // Track the alias from the source module so we don't attempt to remap it.
      DoNotLinkFromSource.insert(SGA);
      
      return false;
    }
  }
  
  // If there is no linkage to be performed or we're linking from the source,
  // bring over SGA.
  GlobalAlias *NewDA = new GlobalAlias(TypeMap.get(SGA->getType()),
                                       SGA->getLinkage(), SGA->getName(),
                                       /*aliasee*/0, DstM);
  CopyGVAttributes(NewDA, SGA);
  if (NewVisibility)
    NewDA->setVisibility(*NewVisibility);

  if (DGV) {
    // Any uses of DGV need to change to NewDA, with cast.
    DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDA, DGV->getType()));
    DGV->eraseFromParent();
  }
  
  ValueMap[SGA] = NewDA;
  return false;
}

/// Given a disjoint set of bitsets and globals, layout the globals, build the
/// bit sets and lower the llvm.bitset.test calls.
void LowerBitSets::buildBitSetsFromGlobalVariables(
    ArrayRef<Metadata *> BitSets, ArrayRef<GlobalVariable *> Globals) {
  // Build a new global with the combined contents of the referenced globals.
  // This global is a struct whose even-indexed elements contain the original
  // contents of the referenced globals and whose odd-indexed elements contain
  // any padding required to align the next element to the next power of 2.
  std::vector<Constant *> GlobalInits;
  const DataLayout &DL = M->getDataLayout();
  for (GlobalVariable *G : Globals) {
    GlobalInits.push_back(G->getInitializer());
    uint64_t InitSize = DL.getTypeAllocSize(G->getValueType());

    // Compute the amount of padding required.
    uint64_t Padding = NextPowerOf2(InitSize - 1) - InitSize;

    // Cap at 128 was found experimentally to have a good data/instruction
    // overhead tradeoff.
    if (Padding > 128)
      Padding = RoundUpToAlignment(InitSize, 128) - InitSize;

    GlobalInits.push_back(
        ConstantAggregateZero::get(ArrayType::get(Int8Ty, Padding)));
  }
  if (!GlobalInits.empty())
    GlobalInits.pop_back();
  Constant *NewInit = ConstantStruct::getAnon(M->getContext(), GlobalInits);
  auto *CombinedGlobal =
      new GlobalVariable(*M, NewInit->getType(), /*isConstant=*/true,
                         GlobalValue::PrivateLinkage, NewInit);

  StructType *NewTy = cast<StructType>(NewInit->getType());
  const StructLayout *CombinedGlobalLayout = DL.getStructLayout(NewTy);

  // Compute the offsets of the original globals within the new global.
  DenseMap<GlobalObject *, uint64_t> GlobalLayout;
  for (unsigned I = 0; I != Globals.size(); ++I)
    // Multiply by 2 to account for padding elements.
    GlobalLayout[Globals[I]] = CombinedGlobalLayout->getElementOffset(I * 2);

  lowerBitSetCalls(BitSets, CombinedGlobal, GlobalLayout);

  // Build aliases pointing to offsets into the combined global for each
  // global from which we built the combined global, and replace references
  // to the original globals with references to the aliases.
  for (unsigned I = 0; I != Globals.size(); ++I) {
    // Multiply by 2 to account for padding elements.
    Constant *CombinedGlobalIdxs[] = {ConstantInt::get(Int32Ty, 0),
                                      ConstantInt::get(Int32Ty, I * 2)};
    Constant *CombinedGlobalElemPtr = ConstantExpr::getGetElementPtr(
        NewInit->getType(), CombinedGlobal, CombinedGlobalIdxs);
    if (LinkerSubsectionsViaSymbols) {
      Globals[I]->replaceAllUsesWith(CombinedGlobalElemPtr);
    } else {
      assert(Globals[I]->getType()->getAddressSpace() == 0);
      GlobalAlias *GAlias = GlobalAlias::create(NewTy->getElementType(I * 2), 0,
                                                Globals[I]->getLinkage(), "",
                                                CombinedGlobalElemPtr, M);
      GAlias->setVisibility(Globals[I]->getVisibility());
      GAlias->takeName(Globals[I]);
      Globals[I]->replaceAllUsesWith(GAlias);
    }
    Globals[I]->eraseFromParent();
  }
}

// emit_alias_to_llvm - Given decl and target emit alias to target.
void emit_alias_to_llvm(tree decl, tree target, tree target_decl) {
  if (errorcount || sorrycount) return;

  timevar_push(TV_LLVM_GLOBALS);

  // Get or create LLVM global for our alias.
  GlobalValue *V = cast<GlobalValue>(DECL_LLVM(decl));
  
  GlobalValue *Aliasee = NULL;
  
  if (target_decl)
    Aliasee = cast<GlobalValue>(DECL_LLVM(target_decl));
  else {
    // This is something insane. Probably only LTHUNKs can be here
    // Try to grab decl from IDENTIFIER_NODE

    // Query SymTab for aliasee
    const char* AliaseeName = IDENTIFIER_POINTER(target);
    Aliasee =
      dyn_cast_or_null<GlobalValue>(TheModule->
                                    getValueSymbolTable().lookup(AliaseeName));

    // Last resort. Query for name set via __asm__
    if (!Aliasee) {
      std::string starred = std::string("\001") + AliaseeName;
      Aliasee =
        dyn_cast_or_null<GlobalValue>(TheModule->
                                      getValueSymbolTable().lookup(starred));
    }
    
    if (!Aliasee) {
      error ("%J%qD aliased to undefined symbol %qE",
             decl, decl, target);
      timevar_pop(TV_LLVM_GLOBALS);
      return;
    }
  }
  
  GlobalValue::LinkageTypes Linkage;

  // Check for external weak linkage
  if (DECL_EXTERNAL(decl) && DECL_WEAK(decl))
    Linkage = GlobalValue::WeakLinkage;
  else if (!TREE_PUBLIC(decl))
    Linkage = GlobalValue::InternalLinkage;
  else
    Linkage = GlobalValue::ExternalLinkage;

  GlobalAlias* GA = new GlobalAlias(Aliasee->getType(), Linkage, "",
                                    Aliasee, TheModule);
  // Handle visibility style
  if (TREE_PUBLIC(decl)) {
    if (DECL_VISIBILITY(decl) == VISIBILITY_HIDDEN)
      GA->setVisibility(GlobalValue::HiddenVisibility);
    else if (DECL_VISIBILITY(decl) == VISIBILITY_PROTECTED)
      GA->setVisibility(GlobalValue::ProtectedVisibility);
  }

  if (V->getType() == GA->getType())
    V->replaceAllUsesWith(GA);
  else if (!V->use_empty()) {
    error ("%J Alias %qD used with invalid type!", decl, decl);
    timevar_pop(TV_LLVM_GLOBALS);
    return;
  }
    
  changeLLVMValue(V, GA);
  GA->takeName(V);
  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
    GV->eraseFromParent();
  else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V))
    GA->eraseFromParent();
  else if (Function *F = dyn_cast<Function>(V))
    F->eraseFromParent();
  else
    assert(0 && "Unsuported global value");

  TREE_ASM_WRITTEN(decl) = 1;
  
  timevar_pop(TV_LLVM_GLOBALS);
  return;
}