https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90679
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:0a37463758dabc9647fa3d675dffdf43a737035d commit r14-6715-g0a37463758dabc9647fa3d675dffdf43a737035d Author: Patrick Palka <ppa...@redhat.com> Date: Tue Dec 19 11:40:15 2023 -0500 c++: partial ordering and dep alias tmpl specs [PR90679] During partial ordering, we want to look through dependent alias template specializations within template arguments and otherwise treat them as opaque in other contexts (see e.g. r7-7116-g0c942f3edab108 and r11-7011-g6e0a231a4aa240). To that end template_args_equal was given a partial_order flag that controls this behavior. This flag does the right thing when a dependent alias template specialization appears as template argument of the partial specialization, e.g. in template<class T, class...> using first_t = T; template<class T> struct traits; template<class T> struct traits<first_t<T, T&>> { }; // #1 template<class T> struct traits<first_t<const T, T&>> { }; // #2 we correctly consider #2 to be more specialized than #1. But if the alias specialization appears as a nested template argument of another class template specialization, e.g. in template<class T> struct traits<A<first_t<T, T&>>> { }; // #1 template<class T> struct traits<A<first_t<const T, T&>>> { }; // #2 then we incorrectly consider #1 and #2 to be unordered. This is because 1. we don't propagate the flag to recursive template_args_equal calls 2. we don't use structural equality for class template specializations written in terms of dependent alias template specializations This patch fixes the first issue by turning the partial_order flag into a global. This patch fixes the second issue by making us propagate structural equality appropriately when building a class template specialization. In passing this patch also improves hashing of specializations that use structural equality. PR c++/90679 gcc/cp/ChangeLog: * cp-tree.h (comp_template_args): Remove partial_order parameter. (template_args_equal): Likewise. * pt.cc (comparing_for_partial_ordering): New global flag. (iterative_hash_template_arg) <case tcc_type>: Hash the template and arguments for specializations that use structural equality. (template_args_equal): Remove partial order parameter and use comparing_for_partial_ordering instead. (comp_template_args): Likewise. (comp_template_args_porder): Set comparing_for_partial_ordering instead. Make static. (any_template_arguments_need_structural_equality_p): Return true for an argument that's a dependent alias template specialization or a class template specialization that itself needs structural equality. * tree.cc (cp_tree_equal) <case TREE_VEC>: Adjust call to comp_template_args. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/alias-decl-75a.C: New test. * g++.dg/cpp0x/alias-decl-75b.C: New test.
