C++ ASTMangler::mangleConstructorVTableThunk方法代码示例

Optional<SILVTable::Entry>
SILGenModule::emitVTableMethod(ClassDecl *theClass,
                               SILDeclRef derived, SILDeclRef base) {
  assert(base.kind == derived.kind);

  auto *baseDecl = base.getDecl();
  auto *derivedDecl = derived.getDecl();

  // Note: We intentionally don't support extension members here.
  //
  // Once extensions can override or introduce new vtable entries, this will
  // all likely change anyway.
  auto *baseClass = cast<ClassDecl>(baseDecl->getDeclContext());
  auto *derivedClass = cast<ClassDecl>(derivedDecl->getDeclContext());

  // Figure out if the vtable entry comes from the superclass, in which
  // case we won't emit it if building a resilient module.
  SILVTable::Entry::Kind implKind;
  if (baseClass == theClass) {
    // This is a vtable entry for a method of the immediate class.
    implKind = SILVTable::Entry::Kind::Normal;
  } else if (derivedClass == theClass) {
    // This is a vtable entry for a method of a base class, but it is being
    // overridden in the immediate class.
    implKind = SILVTable::Entry::Kind::Override;
  } else {
    // This vtable entry is copied from the superclass.
    implKind = SILVTable::Entry::Kind::Inherited;

    // If the override is defined in a class from a different resilience
    // domain, don't emit the vtable entry.
    if (derivedClass->isResilient(M.getSwiftModule(),
                                  ResilienceExpansion::Maximal)) {
      return None;
    }
  }

  SILFunction *implFn;
  SILLinkage implLinkage;

  // If the member is dynamic, reference its dynamic dispatch thunk so that
  // it will be redispatched, funneling the method call through the runtime
  // hook point.
  if (derivedDecl->isDynamic()
      && derived.kind != SILDeclRef::Kind::Allocator) {
    implFn = getDynamicThunk(derived, Types.getConstantInfo(derived).SILFnType);
    implLinkage = SILLinkage::Public;
  } else {
    implFn = getFunction(derived, NotForDefinition);
    implLinkage = stripExternalFromLinkage(implFn->getLinkage());
  }

  // As a fast path, if there is no override, definitely no thunk is necessary.
  if (derived == base)
    return SILVTable::Entry(base, implFn, implKind, implLinkage);

  // Determine the derived thunk type by lowering the derived type against the
  // abstraction pattern of the base.
  auto baseInfo = Types.getConstantInfo(base);
  auto derivedInfo = Types.getConstantInfo(derived);
  auto basePattern = AbstractionPattern(baseInfo.LoweredType);
  
  auto overrideInfo = M.Types.getConstantOverrideInfo(derived, base);

  // The override member type is semantically a subtype of the base
  // member type. If the override is ABI compatible, we do not need
  // a thunk.
  if (M.Types.checkFunctionForABIDifferences(derivedInfo.SILFnType,
                                             overrideInfo.SILFnType)
      == TypeConverter::ABIDifference::Trivial)
    return SILVTable::Entry(base, implFn, implKind, implLinkage);

  // Generate the thunk name.
  std::string name;
  {
    Mangle::ASTMangler mangler;
    if (isa<FuncDecl>(baseDecl)) {
      name = mangler.mangleVTableThunk(
        cast<FuncDecl>(baseDecl),
        cast<FuncDecl>(derivedDecl));
    } else {
      name = mangler.mangleConstructorVTableThunk(
        cast<ConstructorDecl>(baseDecl),
        cast<ConstructorDecl>(derivedDecl),
        base.kind == SILDeclRef::Kind::Allocator);
    }
  }

  // If we already emitted this thunk, reuse it.
  if (auto existingThunk = M.lookUpFunction(name))
    return SILVTable::Entry(base, existingThunk, implKind, implLinkage);

  // Emit the thunk.
  SILLocation loc(derivedDecl);
  SILGenFunctionBuilder builder(*this);
  auto thunk = builder.createFunction(
      SILLinkage::Private, name, overrideInfo.SILFnType,
      cast<AbstractFunctionDecl>(derivedDecl)->getGenericEnvironment(), loc,
      IsBare, IsNotTransparent, IsNotSerialized);
  thunk->setDebugScope(new (M) SILDebugScope(loc, thunk));
//.........这里部分代码省略.........