https://gcc.gnu.org/g:a0908b6723128799a68c9fdab65f65761f657488
commit r16-6247-ga0908b6723128799a68c9fdab65f65761f657488 Author: Egas Ribeiro <[email protected]> Date: Sat Dec 13 13:14:47 2025 +0000 c++: Fix ICE with type aliases in inherited CTAD [PR122070] When processing inherited CTAD in C++23, type_targs_deducible_from can be called with a synthetic alias template whose TREE_VALUE is a type alias. Since TYPE_TEMPLATE_INFO_MAYBE_ALIAS can return NULL for type aliases, we need to fall back to TYPE_TEMPLATE_INFO to get the template info of the underlying type before calling TI_TEMPLATE, which should always be non-NULL when called from inherited_ctad_tweaks. PR c++/122070 gcc/cp/ChangeLog: * pt.cc (type_targs_deducible_from): Fall back to TYPE_TEMPLATE_INFO when TYPE_TEMPLATE_INFO_MAYBE_ALIAS is NULL. gcc/testsuite/ChangeLog: * g++.dg/cpp23/class-deduction-inherited10.C: New test. * g++.dg/cpp23/class-deduction-inherited9.C: New test. Signed-off-by: Egas Ribeiro <[email protected]> Co-authored-by: Patrick Palka <[email protected]> Reviewed-by: Patrick Palka <[email protected]> Diff: --- gcc/cp/pt.cc | 6 ++++- .../g++.dg/cpp23/class-deduction-inherited10.C | 11 ++++++++ .../g++.dg/cpp23/class-deduction-inherited9.C | 31 ++++++++++++++++++++++ 3 files changed, 47 insertions(+), 1 deletion(-) diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index 20a1177ffab7..ccbc6eb5410a 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -31631,7 +31631,11 @@ type_targs_deducible_from (tree tmpl, tree type) per alias_ctad_tweaks. */ tparms = INNERMOST_TEMPLATE_PARMS (TREE_PURPOSE (tmpl)); ttype = TREE_VALUE (tmpl); - tmpl = TI_TEMPLATE (TYPE_TEMPLATE_INFO_MAYBE_ALIAS (ttype)); + tree ti = TYPE_TEMPLATE_INFO_MAYBE_ALIAS (ttype); + if (!ti) + /* TTYPE is a typedef to a template-id. */ + ti = TYPE_TEMPLATE_INFO (ttype); + tmpl = TI_TEMPLATE (ti); } int len = TREE_VEC_LENGTH (tparms); diff --git a/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited10.C b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited10.C new file mode 100644 index 000000000000..d3b1b18077d9 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited10.C @@ -0,0 +1,11 @@ +// PR c++/122070 +// { dg-do compile { target c++23 } } + +template<class T> struct A { A(T) {}; }; + +using B = A<int>; + +template<class T=void> +struct C : B { using B::B; }; + +C c = 0; diff --git a/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited9.C b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited9.C new file mode 100644 index 000000000000..c7d27202ccca --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited9.C @@ -0,0 +1,31 @@ +// PR c++/122070 +// { dg-do compile { target c++23 } } + +namespace std { + using size_t = decltype(sizeof(0)); + template<typename CharT> + struct basic_string_view { + const CharT* ptr; + size_t len; + constexpr basic_string_view(const CharT* p) : ptr(p), len(0) { while (p && p[len]) ++len; } + }; + using string_view = basic_string_view<char>; +} + +template<std::size_t N> +struct sized_string_view: std::string_view { + using std::string_view::string_view; +}; +template<std::size_t N> +sized_string_view(const char (&str)[N]) -> sized_string_view<N - 1>; + +constexpr auto string_builder(auto first, auto second, auto... trailing) { + constexpr auto is_last = sizeof...(trailing) == 0; + auto buffer = 1; + if constexpr (is_last) { + return buffer; + } else + return string_builder(buffer, trailing...); +} + +constexpr auto copyright = string_builder(sized_string_view("a"), sized_string_view("b"), sized_string_view("c"));
