On Wed, 25 Jun 2025 at 19:56, Jakub Jelinek <ja...@redhat.com> wrote:
>
> Hi!
>
> The following patch attempts to implement the C++26 P2927R3 - Inspecting
> exception_ptr
> paper (but not including P3748R0, I plan to play with it incrementally and
> it will really depend on the Constexpr exceptions patch).
>
> The function template is implemented using an out of line private method of
> exception_ptr, so that P3748R0 then can use if consteval and provide a
> constant evaluation variant of it.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2025-06-25 Jakub Jelinek <ja...@redhat.com>
>
> * include/bits/version.def (exception_ptr_cast): Add.
> * include/bits/version.h: Regenerate.
> * libsupc++/exception: Define __glibcxx_want_exception_ptr_cast before
> including bits/version.h.
> * libsupc++/exception_ptr.h (std::exception_ptr_cast): Define.
> (std::__exception_ptr::exception_ptr::_M_exception_ptr_cast): Declare.
> * libsupc++/eh_ptr.cc
> (std::__exception_ptr::exception_ptr::_M_exception_ptr_cast): Define.
> * config/abi/pre/gnu.ver: Export
>
> _ZNKSt15__exception_ptr13exception_ptr21_M_exception_ptr_castERKSt9type_info
> at CXXABI_1.3.17.
> * testsuite/util/testsuite_abi.cc (check_version): Allow
> CXXABI_1.3.17.
> * testsuite/18_support/exception_ptr/exception_ptr_cast.cc: New test.
>
> --- libstdc++-v3/include/bits/version.def.jj 2025-06-24 18:53:13.751807828
> +0200
> +++ libstdc++-v3/include/bits/version.def 2025-06-25 12:52:41.844921595
> +0200
> @@ -2012,6 +2012,14 @@ ftms = {
> };
> };
>
> +ftms = {
> + name = exception_ptr_cast;
> + values = {
> + v = 202506;
> + cxxmin = 26;
> + };
> +};
> +
> // Standard test specifications.
> stds[97] = ">= 199711L";
> stds[03] = ">= 199711L";
> --- libstdc++-v3/include/bits/version.h.jj 2025-06-24 18:53:13.751807828
> +0200
> +++ libstdc++-v3/include/bits/version.h 2025-06-25 12:52:47.754691329 +0200
> @@ -2253,4 +2253,14 @@
> #endif /* !defined(__cpp_lib_sstream_from_string_view) &&
> defined(__glibcxx_want_sstream_from_string_view) */
> #undef __glibcxx_want_sstream_from_string_view
>
> +#if !defined(__cpp_lib_exception_ptr_cast)
> +# if (__cplusplus > 202302L)
> +# define __glibcxx_exception_ptr_cast 202506L
> +# if defined(__glibcxx_want_all) ||
> defined(__glibcxx_want_exception_ptr_cast)
> +# define __cpp_lib_exception_ptr_cast 202506L
> +# endif
> +# endif
> +#endif /* !defined(__cpp_lib_exception_ptr_cast) &&
> defined(__glibcxx_want_exception_ptr_cast) */
> +#undef __glibcxx_want_exception_ptr_cast
> +
> #undef __glibcxx_want_all
> --- libstdc++-v3/libsupc++/exception.jj 2025-06-12 09:49:19.924910752 +0200
> +++ libstdc++-v3/libsupc++/exception 2025-06-25 12:53:09.924564775 +0200
> @@ -38,6 +38,7 @@
> #include <bits/exception.h>
>
> #define __glibcxx_want_uncaught_exceptions
> +#define __glibcxx_want_exception_ptr_cast
> #include <bits/version.h>
>
> extern "C++" {
> --- libstdc++-v3/libsupc++/exception_ptr.h.jj 2025-06-02 11:00:06.267523918
> +0200
> +++ libstdc++-v3/libsupc++/exception_ptr.h 2025-06-25 15:07:26.308301756
> +0200
> @@ -80,6 +80,13 @@ namespace std _GLIBCXX_VISIBILITY(defaul
> /// Throw the object pointed to by the exception_ptr.
> void rethrow_exception(exception_ptr) __attribute__ ((__noreturn__));
>
> +#if __cpp_lib_exception_ptr_cast >= 202506L
> + template<typename _Ex>
> + const _Ex* exception_ptr_cast(const exception_ptr&) noexcept;
> + template<typename _Ex>
> + void exception_ptr_cast(const exception_ptr&&) = delete;
> +#endif
> +
> namespace __exception_ptr
> {
> using std::rethrow_exception; // So that ADL finds it.
> @@ -109,6 +116,13 @@ namespace std _GLIBCXX_VISIBILITY(defaul
> friend void std::rethrow_exception(exception_ptr);
> template<typename _Ex>
> friend exception_ptr std::make_exception_ptr(_Ex)
> _GLIBCXX_USE_NOEXCEPT;
> +#if __cpp_lib_exception_ptr_cast >= 202506L
> + template<typename _Ex>
> + friend const _Ex* std::exception_ptr_cast(const exception_ptr&)
> noexcept;
> +#endif
> +
> + const void* _M_exception_ptr_cast(const type_info&) const
> + _GLIBCXX_USE_NOEXCEPT;
>
> public:
> exception_ptr() _GLIBCXX_USE_NOEXCEPT;
> @@ -274,6 +288,16 @@ namespace std _GLIBCXX_VISIBILITY(defaul
> }
> #endif
> }
> +
> +#if __cpp_lib_exception_ptr_cast >= 202506L
> + template<typename _Ex>
> + [[__gnu__::__always_inline__]]
> + inline const _Ex* exception_ptr_cast(const exception_ptr& __p) noexcept
> + {
> + const type_info &__id = typeid(const _Ex&);
This won't work for -fno-rtti
Maybe we should just have one definition of exception_ptr_cast,
outside this #if group, like so:
#if __cpp_lib_exception_ptr_cast >= 202506L
template<typename _Ex>
[[__gnu__::__always_inline__]]
const _Ex* exception_ptr_cast(const exception_ptr& __p) noexcept
{
#ifdef __cpp_rtti
const type_info& __id = typeid(_Ex);
return static_cast<const _Ex*>(__p._M_exception_ptr_cast(__id));
#else
return nullptr;
#endif
}
#endif
> + return static_cast<const _Ex*>(__p._M_exception_ptr_cast(__id));
> + }
> +#endif
> #else // no RTTI and no exceptions
> // This is always_inline so the linker will never use this useless
> definition
> // instead of a working one compiled with RTTI and/or exceptions enabled.
> @@ -282,6 +306,15 @@ namespace std _GLIBCXX_VISIBILITY(defaul
> inline exception_ptr
> make_exception_ptr(_Ex) _GLIBCXX_USE_NOEXCEPT
> { return exception_ptr(); }
> +
> +#if __cpp_lib_exception_ptr_cast >= 202506L
> + template<typename _Ex>
> + [[__gnu__::__always_inline__]]
> + const _Ex* exception_ptr_cast(const exception_ptr& __p) noexcept
> + {
> + return nullptr;
> + }
> +#endif
> #endif
>
> #undef _GLIBCXX_EH_PTR_USED
> --- libstdc++-v3/libsupc++/eh_ptr.cc.jj 2025-04-08 14:10:30.518900025 +0200
> +++ libstdc++-v3/libsupc++/eh_ptr.cc 2025-06-25 15:29:17.416393720 +0200
> @@ -220,4 +220,20 @@ std::rethrow_exception(std::exception_pt
> std::terminate();
> }
>
> +const void*
> +std::__exception_ptr::exception_ptr::_M_exception_ptr_cast(const type_info&
> t)
> + const noexcept
> +{
> + void *ptr = _M_exception_object;
> + if (__builtin_expect(ptr == nullptr, false))
> + return nullptr;
> + __cxa_refcounted_exception *eh
> + = __get_refcounted_exception_header_from_obj (_M_exception_object);
> + const type_info* __thr_type = eh->exc.exceptionType;
> + if (t.__do_catch(__thr_type, &ptr, 1))
> + return ptr;
> + return nullptr;
> +}
> +
> +
> #undef _GLIBCXX_EH_PTR_COMPAT
> --- libstdc++-v3/config/abi/pre/gnu.ver.jj 2025-06-02 11:00:17.686375875
> +0200
> +++ libstdc++-v3/config/abi/pre/gnu.ver 2025-06-25 15:32:59.627528296 +0200
> @@ -2899,6 +2899,16 @@ CXXABI_1.3.16 {
> } CXXABI_1.3.15;
> #endif
>
> +CXXABI_1.3.17 {
> + # std::exception_ptr::_M_exception_ptr_cast
> +
> _ZNKSt15__exception_ptr13exception_ptr21_M_exception_ptr_castERKSt9type_info;
> +}
> +#ifdef __riscv
> +CXXABI_1.3.16;
> +#else
> +CXXABI_1.3.15;
> +#endif
> +
> # Symbols in the support library (libsupc++) supporting transactional memory.
> CXXABI_TM_1 {
>
> --- libstdc++-v3/testsuite/util/testsuite_abi.cc.jj 2025-06-02
> 11:00:18.007371713 +0200
> +++ libstdc++-v3/testsuite/util/testsuite_abi.cc 2025-06-25
> 15:51:56.745085075 +0200
> @@ -241,6 +241,7 @@ check_version(symbol& test, bool added)
> #ifdef __riscv
> known_versions.push_back("CXXABI_1.3.16");
> #endif
> + known_versions.push_back("CXXABI_1.3.17");
> known_versions.push_back("CXXABI_IEEE128_1.3.13");
> known_versions.push_back("CXXABI_TM_1");
> known_versions.push_back("CXXABI_FLOAT128");
> --- libstdc++-v3/testsuite/18_support/exception_ptr/exception_ptr_cast.cc.jj
> 2025-06-25 15:45:25.864969085 +0200
> +++ libstdc++-v3/testsuite/18_support/exception_ptr/exception_ptr_cast.cc
> 2025-06-25 15:47:11.156653475 +0200
> @@ -0,0 +1,81 @@
> +// { dg-do run { target c++26 } }
> +
> +// Copyright (C) 2025 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +
> +// You should have received a copy of the GNU General Public License along
> +// with this library; see the file COPYING3. If not see
> +// <http://www.gnu.org/licenses/>.
> +
> +// exception_ptr_cast.
> +
> +#include <exception>
> +#include <testsuite_hooks.h>
> +
> +#if __cpp_lib_exception_ptr_cast != 202506L
> +# error "__cpp_lib_exception_ptr_cast != 202506"
> +#endif
> +
> +struct A { int a; };
> +struct B : A {};
> +struct C : B {};
> +struct D {};
> +struct E : virtual C { int e; virtual ~E () {} };
> +struct F : virtual E, virtual C { int f; };
> +struct G : virtual F, virtual C, virtual E {
> + G () : g (4) { a = 1; e = 2; f = 3; } int g;
> +};
> +
> +void test01()
> +{
> + auto a = std::make_exception_ptr(C{ 42 });
> + auto b = std::exception_ptr_cast<C>(a);
> + VERIFY( b != nullptr );
> + VERIFY( b->a == 42 );
> + auto c = std::exception_ptr_cast<B>(a);
> + VERIFY( c == static_cast<const B*>(b) );
> + auto d = std::exception_ptr_cast<A>(a);
> + VERIFY( d == static_cast<const A*>(b) );
> + auto e = std::exception_ptr_cast<D>(a);
> + VERIFY( e == nullptr );
> + auto f = std::make_exception_ptr(42L);
> + auto g = std::exception_ptr_cast<long>(f);
> + VERIFY( g != nullptr );
> + VERIFY( *g == 42L );
> + try
> + {
> + throw G ();
> + }
> + catch (...)
> + {
> + auto h = std::current_exception();
> + auto i = std::exception_ptr_cast<G>(h);
> + VERIFY( i != nullptr );
> + VERIFY( i->a == 1 && i->e == 2 && i->f == 3 && i->g == 4 );
> + auto j = std::exception_ptr_cast<A>(h);
> + VERIFY( j == static_cast<const A*>(i) );
> + auto k = std::exception_ptr_cast<C>(h);
> + VERIFY( k == static_cast<const C*>(i) );
> + auto l = std::exception_ptr_cast<E>(h);
> + VERIFY( l == static_cast<const E*>(i) );
> + auto m = std::exception_ptr_cast<F>(h);
> + VERIFY( m == static_cast<const F*>(i) );
> + auto n = std::exception_ptr_cast<G>(a);
> + VERIFY( n == nullptr );
> + }
> +}
> +
> +int main()
> +{
> + test01();
> +}
>
> Jakub
>
