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From: "ppalka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/109277] [13 Regression] type_traits:1417:30: error: invalid use of incomplete type ‘class v8::internal::WasmArray’ Date: Sat, 25 Mar 2023 14:20:05 +0000 [thread overview] Message-ID: <bug-109277-4-uCJOhrRoZI@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-109277-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109277 Patrick Palka <ppalka at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |ppalka at gcc dot gnu.org --- Comment #9 from Patrick Palka <ppalka at gcc dot gnu.org> --- AFAICT the trait instantiation is legitimate, and this appears to be UB, here's a boiled down testcase: #include <tuple> #include <type_traits> struct Object; struct MaybeObject; struct WasmArray; template<class T, class U> struct is_subtype { static const bool value = std::is_base_of<U, T>::value || (std::is_same<U, MaybeObject>::value && std::is_convertible<T, Object>::value); }; template<class T> struct TNode { TNode(); template<class U, typename = std::enable_if_t<is_subtype<U, T>::value>> TNode(const TNode<U>&); // #1 TNode(const TNode&); // #2 }; std::tuple<TNode<WasmArray>> node; The instantiation of std::is_convertible<WasmArray, Object> happens when synthesizing tuple<TNode<WasmArray>> defaulted move constructor, for which we need to perform overload resolution of TNode's constructors with a TNode&& argument, and when considering the template candidate #1 we need to instantiate its default template argument which entails instantiation of is_convertible. In GCC 12 is_convertible for an incomplete type would silently return false. In GCC 13 the new built-in __is_convertible diagnoses this UB situation as a hard error. Clang's __is_convertible behaves like GCC 12's is_convertible it seems. One fix is to define a move constructor for TNode, which causes GCC's perfect candidate optimization (r11-7287-g187d0d5871b1fa) to kick in and avoid considering the template candidate #1. Another fix is to use std::conjunction/disjunction in is_subtype so that the condition properly short-circuits (is_base_of<T, T> is true even for incomplete T).
next prev parent reply other threads:[~2023-03-25 14:20 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-03-24 18:54 [Bug c++/109277] New: " marxin at gcc dot gnu.org 2023-03-24 18:54 ` [Bug c++/109277] " marxin at gcc dot gnu.org 2023-03-24 20:14 ` pinskia at gcc dot gnu.org 2023-03-24 20:20 ` [Bug libstdc++/109277] " pinskia at gcc dot gnu.org 2023-03-24 20:35 ` [Bug c++/109277] " pinskia at gcc dot gnu.org 2023-03-24 20:43 ` pinskia at gcc dot gnu.org 2023-03-24 20:47 ` pinskia at gcc dot gnu.org 2023-03-24 20:49 ` pinskia at gcc dot gnu.org 2023-03-24 20:53 ` pinskia at gcc dot gnu.org 2023-03-24 21:03 ` pinskia at gcc dot gnu.org 2023-03-24 21:07 ` redi at gcc dot gnu.org 2023-03-25 14:20 ` ppalka at gcc dot gnu.org [this message] 2023-03-25 14:30 ` ppalka at gcc dot gnu.org 2023-03-27 7:06 ` rguenth at gcc dot gnu.org 2023-04-04 3:33 ` jason at gcc dot gnu.org 2023-04-13 15:41 ` jason at gcc dot gnu.org 2023-04-13 18:59 ` cvs-commit at gcc dot gnu.org 2023-04-13 19:06 ` jason at gcc dot gnu.org
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