C++ GlobalValue::use_empty方法代码示例

void ModuleLinker::dropReplacedComdat(
    GlobalValue &GV, const DenseSet<const Comdat *> &ReplacedDstComdats) {
  Comdat *C = GV.getComdat();
  if (!C)
    return;
  if (!ReplacedDstComdats.count(C))
    return;
  if (GV.use_empty()) {
    GV.eraseFromParent();
    return;
  }

  if (auto *F = dyn_cast<Function>(&GV)) {
    F->deleteBody();
  } else if (auto *Var = dyn_cast<GlobalVariable>(&GV)) {
    Var->setInitializer(nullptr);
  } else {
    auto &Alias = cast<GlobalAlias>(GV);
    Module &M = *Alias.getParent();
    PointerType &Ty = *cast<PointerType>(Alias.getType());
    GlobalValue *Declaration;
    if (auto *FTy = dyn_cast<FunctionType>(Alias.getValueType())) {
      Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage, "", &M);
    } else {
      Declaration =
          new GlobalVariable(M, Ty.getElementType(), /*isConstant*/ false,
                             GlobalValue::ExternalLinkage,
                             /*Initializer*/ nullptr);
    }
    Declaration->takeName(&Alias);
    Alias.replaceAllUsesWith(Declaration);
    Alias.eraseFromParent();
  }
}

/// Predicate for Internalize pass.
static bool mustPreserveGV(const GlobalValue &GV) {
  if (const Function *F = dyn_cast<Function>(&GV))
    return F->isDeclaration() || AMDGPU::isEntryFunctionCC(F->getCallingConv());

  return !GV.use_empty();
}

// RemoveUnusedGlobalValue - Loop over all of the uses of the specified
// GlobalValue, looking for the constant pointer ref that may be pointing to it.
// If found, check to see if the constant pointer ref is safe to destroy, and if
// so, nuke it.  This will reduce the reference count on the global value, which
// might make it deader.
//
bool GlobalDCE::RemoveUnusedGlobalValue(GlobalValue &GV) {
  if (GV.use_empty()) return false;
  GV.removeDeadConstantUsers();
  return GV.use_empty();
}

// 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;
}