Re: [PATCH RFC] c++: lambda mangling alias issues [PR107897]

[Jan Hubicka <hubicka@ucw.cz>]

> Tested x86_64-pc-linux-gnu.  Does this look good, or do we want to factor the
> flag clearing into a symtab_node counterpart to cgraph_node::reset?
> 
> -- 8< --
> 
> In 107897, by the time we are looking at the mangling clash, the
> alias has already been removed from the symbol table by analyze_functions,
> so we can't look at n->cpp_implicit_alias.  So just assume that it's an
> alias if it's internal.
> 
> In 108887 the problem is that removing the mangling alias from the symbol
> table confuses analyze_functions, because it ended up as first_analyzed
> somehow, so it becomes a dangling pointer.  Fixed by clearing various flags
> to neutralize the alias.
> 
> 	PR c++/107897
> 	PR c++/108887
> 
> gcc/cp/ChangeLog:
> 
> 	* decl2.cc (record_mangling): Improve symbol table handling.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/concepts-lambda3.C: Use -flto if supported.
> 	* g++.dg/cpp0x/lambda/lambda-mangle7.C: New test.
> ---
>  gcc/cp/decl2.cc                               | 25 +++++--
>  .../g++.dg/cpp0x/lambda/lambda-mangle7.C      | 70 +++++++++++++++++++
>  gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C |  1 +
>  3 files changed, 91 insertions(+), 5 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-mangle7.C
> 
> diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
> index 387e24542cd..e6e58b08de4 100644
> --- a/gcc/cp/decl2.cc
> +++ b/gcc/cp/decl2.cc
> @@ -4742,15 +4742,30 @@ record_mangling (tree decl, bool need_warning)
>      = mangled_decls->find_slot_with_hash (id, IDENTIFIER_HASH_VALUE (id),
>  					  INSERT);
>  
> -  /* If this is already an alias, remove the alias, because the real
> +  /* If this is already an alias, cancel the alias, because the real
>       decl takes precedence.  */
>    if (*slot && DECL_ARTIFICIAL (*slot) && DECL_IGNORED_P (*slot))
> -    if (symtab_node *n = symtab_node::get (*slot))
> -      if (n->cpp_implicit_alias)
> +    {
> +      if (symtab_node *n = symtab_node::get (*slot))
>  	{
> -	  n->remove ();
> -	  *slot = NULL_TREE;
> +	  if (n->cpp_implicit_alias)
> +	    {
> +	      /* Actually removing the node isn't safe if other code is already
> +		 holding a pointer to it, so just neutralize it.  */
> +	      n->remove_from_same_comdat_group ();
> +	      n->analyzed = false;
> +	      n->definition = false;
> +	      n->alias = false;
> +	      n->cpp_implicit_alias = false;
We have n->reset () for that which is used in similar situation when
frontends overwrites extern inline function by its different offline
implementation.

reset doesn't call remove_from_same_comdat_group probably because it was
never used on anything in comdat group.  So I think it would make sense
to call n->reset() here and add remove_from_same_comdat_group into that.

OK with that change.
Honza
> +	    }
>  	}
> +      else
> +	/* analyze_functions might have already removed the alias from the
> +	   symbol table if it's internal.  */
> +	gcc_checking_assert (!TREE_PUBLIC (*slot));
> +
> +      *slot = NULL_TREE;
> +    }
>  
>    if (!*slot)
>      *slot = decl;
> diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-mangle7.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-mangle7.C
> new file mode 100644
> index 00000000000..c7946a2be08
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-mangle7.C
> @@ -0,0 +1,70 @@
> +// PR c++/108887
> +// { dg-do compile { target c++11 } }
> +
> +template <int __v> struct integral_constant {
> +  static constexpr int value = __v;
> +};
> +using false_type = integral_constant<false>;
> +template <bool, bool, typename...> struct __result_of_impl;
> +template <typename _Functor, typename... _ArgTypes>
> +struct __result_of_impl<false, false, _Functor, _ArgTypes...> {
> +  typedef decltype(0) type;
> +};
> +template <typename... _ArgTypes>
> +struct __invoke_result
> +    : __result_of_impl<false_type::value, false_type::value, _ArgTypes...> {};
> +template <typename, typename _Fn, typename... _Args>
> +void __invoke_impl(_Fn __f, _Args... __args) {
> +  __f(__args...);
> +}
> +template <typename, typename _Callable, typename... _Args>
> +void __invoke_r(_Callable __fn, _Args... __args) {
> +  using __result = __invoke_result<_Args...>;
> +  using __type = typename __result::type;
> +  __invoke_impl<__type>(__fn, __args...);
> +}
> +struct QString {
> +  QString(const char *);
> +};
> +template <typename> class function;
> +template <typename _Functor> struct _Base_manager {
> +  static _Functor _M_get_pointer(int) { __builtin_abort (); }
> +};
> +template <typename, typename> class _Function_handler;
> +template <typename _Res, typename _Functor, typename... _ArgTypes>
> +struct _Function_handler<_Res(_ArgTypes...), _Functor> {
> +  using _Base = _Base_manager<_Functor>;
> +  static _Res _M_invoke(const int &__functor, _ArgTypes &&...__args) {
> +    auto __trans_tmp_1 = _Base::_M_get_pointer(__functor);
> +    __invoke_r<_Res>(__trans_tmp_1, __args...);
> +  }
> +};
> +template <typename _Res, typename... _ArgTypes>
> +struct function<_Res(_ArgTypes...)> {
> +  template <typename _Functor>
> +  using _Handler = _Function_handler<_Res(_ArgTypes...), _Functor>;
> +  template <typename _Functor> function(_Functor) {
> +    using _My_handler = _Handler<_Functor>;
> +    _M_invoker = _My_handler::_M_invoke;
> +  }
> +  using _Invoker_type = _Res (*)(const int &, _ArgTypes &&...);
> +  _Invoker_type _M_invoker;
> +};
> +struct QRegularExpression {
> +  QRegularExpression(QString);
> +};
> +struct AbstractAccount {
> +  void get(function<void(AbstractAccount *)>,
> +           function<void(AbstractAccount *)>);
> +};
> +struct AbstractTimelineModel {
> +  AbstractAccount m_account;
> +};
> +struct LinkPaginationTimelineModel : AbstractTimelineModel {
> +  void fillTimeline();
> +};
> +void LinkPaginationTimelineModel::fillTimeline() {
> +  [] {};
> +  m_account.get([](AbstractAccount *) { static QRegularExpression re(""); },
> +                [](AbstractAccount *) {});
> +}
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C
> index 291e451ca1a..a7cb6c5dece 100644
> --- a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C
> @@ -1,4 +1,5 @@
>  // { dg-do run { target c++20 } }
> +// { dg-additional-options "-flto" { target lto } } (PR107897)
>  
>  template<typename T>
>  concept C1 = __is_same_as(T, int)
> 
> base-commit: 4f181f9c7ee3efc509d185fdfda33be9018f1611
> -- 
> 2.31.1
>